CONSERVATION
OF LEATHER
and related materials
Butterworth-Heinemann Series in Conservation and Museology
Series Editors: Andrew Oddy
British Museum, London
Consultants: Sir Bernard Feilden
Director Emeritus, ICCROM
Page Ayres Cowley
Conservation Architect, New York
David Bomford
National Gallery, London
John Fidler
English Heritage, London
C.V. Horie
Manchester Museum, University of Manchester
Sarah Staniforth
National Trust, London
Jeanne Marie Teutonico
The Getty Conservation Institute, Los Angeles
Published titles: Architectural Tiles: Conservation and Restoration (Durbin)
Chemical Principles of Textile Conservation (Timár-Balázsy, Eastop)
Conservation and Restoration of Ceramics (Buys, Oakley)
Conservation of Building and Decorative Stone (Ashurst, Dime)
Conservation of Furniture (Rivers, Umney)
Conservation of Historic Buildings (Feilden)
Conservation of Leather and Related Materials (Kite, Thomson)
A History of Architectural Conservation ( Jokilehto)
Lacquer: Technology and Conservation (Webb)
The Museum Environment, 2nd edition (Thomson)
Radiography of Cultural Materials, 2nd edition (Lang, Middleton)
Tapestry Conservation: Principles and Practice (Lennard, Hayward)
The Textile Conservator’s Manual, 2nd edition (Landi)
Upholstery Conservation: Principles and Practice (Gill, Eastop)
Related titles: Contemporary Theory of Conservation (Muñoz-Vinas)
Digital Collections (Keene)
Digital Heritage: Applying Digital Imaging to Cultural Heritage (MacDonald)
Fragments of the World: Uses of Museum Collections (Keene)
Historic Floors (Fawcett)
Managing Conservation in Museums (Keene)
Materials for Conservation (Horie)
The National Trust Manual of Housekeeping
Natural Materials: Sources, Properties and Uses (DeMouthe)
Organic Chemistry of Museum Objects (Mills, White)
Pigment Compendium: Dictionary (Eastaugh, Walsh, Siddall, Chaplin)
Pigment Compendium: Optical Microscopy (Eastaugh, Walsh, Siddall, Chaplin)
Pigment Compendium CD (Eastaugh, Walsh, Siddall, Chaplin)
Restoration of Motion Picture Film (Read, Meyer)
Risk Assessment for Object Conservation (Ashley-Smith)
Structural Aspects of Building Conservation (Beckman, Bowles)
CONSERVATION
OF LEATHER
and related materials
Marion Kite • Roy Thomson
Chairman, Former Chief Executive,
The Leather Conservation Centre The Leather Conservation Centre
AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD
PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO
Butterworth-Heinemann is an imprint of Elsevier
Butterworth-Heinemann is an imprint of Elsevier
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First published 2006
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Contents
v
Foreword xi
Dedications xiii
Acknowledgements xv
Contributors xvii
1 The nature and properties of leather 1
Roy Thomson
References 3
2 Collagen: the leathermaking protein 4
B.M. Haines
2.1 The collagen molecule 4
2.2 Bonding within the molecule 6
2.3 Bonding between molecules 6
2.3.1 Salt links 6
2.3.2 Covalent intermolecular
bonding 7
2.4 Fibril structure 8
2.5 Shrinkage temperature 9
References 10
3 The fibre structure of leather 11
B.M. Haines
3.1 The structure of mammalian skins 12
3.2 Variation of structure between
animal types 12
3.2.1 Mature cattle skins 12
3.2.2 Calfskins 14
3.2.3 Goatskins 14
3.2.4 Sheepskins 14
3.2.5 Deerskins 15
3.2.6 Pigskins 15
3.3 Grain surface patterns 17
3.4 Suede surfaces 17
3.5 Variation in structure with location
in the skin 17
3.6 Directional run of the fibres 19
3.7 The influence of fibre structure
on leather properties, structure
and tear strength 19
3.8 Structure and leather handle 20
3.9 Fibre weave and movement 20
References 21
4 The chemistry of tanning materials 22
A.D. Covington
4.1 Introduction 22
4.2 Vegetable tanning 23
4.3 Mineral tanning 27
4.3.1 Chromium(III) salts 27
4.3.2 Aluminium(III) salts 29
4.3.3 Titanium(IV) salts 29
4.3.4 Zirconium(IV) salts 30
4.4 Oil tanning 30
4.5 Aldehyde tanning 31
4.5.1 Formaldehyde tanning 31
4.5.2 Glutaraldehyde tanning 31
4.5.3 Oxazolidine tanning 31
4.6 Syntans 32
4.6.1 Auxiliary syntans 32
4.6.2 Combination or retanning
syntans 33
4.6.3 Replacement syntans 33
4.7 Overview 34
References 34
5 The mechanisms of deterioration in
leather 36
Mary-Lou E. Florian
5.1 Introduction 36
5.2 Agents of deterioration 37
5.2.1 Introduction 37
5.2.2 Acid hydrolysis 38
5.2.3 Oxidation 38
5.2.4 Metals and salts 40
5.2.5 Heat 41
5.2.6 Water 41
5.3 Collagen 43
5.3.1 Bonds in collagen: sites
of deterioration mechanisms 43
5.3.2 Peptides 43
5.3.3 Amino acids in collagen 44
5.4 Vegetable tannins 47
5.4.1 Introduction 47
5.4.2 Antioxidant ability of tannins 47
5.4.3 Analysis of tannins in aged
leather – deterioration
mechanisms 47
5.5 Other chemicals present due to
fabrication and use 50
5.5.1 Introduction 50
5.5.2 Fats, oils and waxes 51
5.5.3 Sulphur compounds and
their acids 51
5.5.4 Acids in leather due to
fabrication or use 52
5.5.5 Perspiration 52
5.6 Denaturation and shrinkage
temperatures as a method of
assessment for all tannages 52
5.7 Summary 53
Acknowledgements 54
References 54
6 Testing leathers and related materials 58
Roy Thomson
6.1 Introduction 58
6.2 Determination of raw material 58
6.3 Determination of tannage type 58
6.3.1 Ashing test 58
6.3.2 Spot test 59
6.3.3 Conclusion 59
6.4 Determination of degree of
deterioration 59
6.4.1 Organoleptic examination 59
6.4.2 Chemical tests 60
6.5 Conclusions 64
References 64
7 The manufacture of leather 66
Roy Thomson
7.1 Tanning in prehistoric and
classical times 66
7.2 Tanning in the medieval and
post-medieval periods 68
7.3 Tanning in the nineteenth century 73
7.4 Tanning in modern times 77
7.4.1 Pretanning 77
7.4.2 Tanning 80
7.4.3 Post-tanning 81
References 81
8 The social position of
leatherworkers 82
Robert D. Higham
References 87
9 Gilt leather 88
Roy Thomson
9.1 Production and art historical aspects 90
9.2 Conservation and restoration 91
10 Cuir bouilli 94
Laura Davies
10.1 The cuir bouilli technique 94
10.2 Leather moulding techniques 94
10.3 The origins of the cuir bouilli
technique 94
10.4 Changes undergone by the leather
in the cuir bouilli process 97
10.5 Conservation of cuir bouilli 97
10.5.1 Stability 97
10.5.2 Damage caused by old
treatments 98
10.5.3 Original treatments of
cuir bouilli leather 98
10.6 Case study of the conservation
of cuir bouilli leather 98
10.6.1 Analysis and use of noninvasive
xeroradiographic
imaging 99
10.6.2 Removal of inappropriate
surface coatings 99
Endnotes 101
References 101
11 The tools and techniques of
leatherworking: correct tools ϩ
skills ϭ quality 103
Caroline Darke
11.1 Leatherworking tools 103
11.1.1 The awl 103
11.1.2 The knife 103
11.1.3 The strop 104
11.1.4 The bone folder or crease 104
11.1.5 The steel rule 104
11.1.6 The dividers (compass) 104
11.1.7 The revolving hole punch 105
11.1.8 The hammer 105
11.1.9 The race 105
11.1.10 The clam 105
11.1.11 The edge shave 105
vi Contents
11.1.12 The crease iron 106
11.1.13 The stitch marker 106
11.1.14 The pricking iron 107
11.1.15 The needle 107
11.1.16 Thread 108
11.2 Adhesives 108
11.3 Reinforcements 108
11.4 Techniques 109
11.4.1 Skiving 109
11.4.2 Preparation 109
11.4.3 Sewing – stitch
formation 109
11.4.4 Decorative stitching 110
11.4.5 Machine stitching 110
11.4.6 Decorative machine
stitching 110
11.4.7 Seams and construction 111
Bibliography 112
12 General principles of care, storage
and display 113
Aline Angus, Marion Kite and
Theodore Sturge
12.1 Introduction 113
12.2 Objects in use 113
12.3 Display or storage 114
12.4 Levels of treatment 114
12.5 Handling by the public 114
12.6 The ‘finish’ 115
12.7 Preventive conservation 115
12.7.1 Environment 115
12.7.2 Pests 116
12.7.3 Storage and display 116
12.8 Shoes 117
12.9 Gloves 117
12.10 Leather garments 117
12.11 Luggage 117
12.12 Saddles 117
12.13 Harness 118
12.14 Screens, wall hangings and
sedan chairs 119
12.15 Carriages and cars 120
12.16 Conclusion 120
Reference 120
13 Materials and techniques: past and
present 121
Marion Kite, Roy Thomson and Aline Angus
13.1 Past conservation treatments 121
13.1.1 Introduction 121
13.1.2 1982 Jamieson survey 121
13.1.3 1995 survey 122
13.1.4 2000 list 123
13.1.5 2003 Canadian Conservation
Institute (CCI) survey 124
13.2 Notes on treatments in use in
2004 – additional information 124
13.2.1 Introduction 124
13.2.2 Dry cleaning 124
13.2.3 Wet cleaning and solvent
cleaning 125
13.2.4 Proprietary leather cleaners 125
13.2.5 Humidification 125
13.3 Repair materials 126
13.4 Adhesives 126
13.5 Surface infilling materials
and replacement techniques 127
13.6 Moulding and casting materials
and techniques 128
13.7 Consolidation techniques 128
13.8 Dressings and finishes 128
References 129
14 Taxidermy 130
J.A. Dickinson
14.1 A brief history 130
14.2 Taxidermy terms 131
14.3 Birds 131
14.3.1 Methods 131
14.3.2 Problems 132
14.4 Mammals 132
14.4.1 Methods 132
14.4.2 Problems 134
14.5 Fish 135
14.5.1 Methods 135
14.5.2 Problems 136
14.6 Care 137
14.6.1 Light 137
14.6.2 Temperature 137
14.6.3 Relative humidity 137
14.6.4 Storage 137
14.7 Preservatives 140
References 140
15 Furs and furriery: history, techniques
and conservation 141
Marion Kite
15.1 History of fur use 141
15.1.1 Introduction 141
15.1.2 Background and history 142
15.1.3 Husbandry and harvesting 145
15.1.4 Some fashionable furs
and dates 146
15.2 Structure, morphology,
dressing and making 148
15.2.1 Definitions and
terminology 148
Contents vii
15.2.2 Brief history of fur-skin
processing and dyeing 148
15.2.3 Hair and fur fibres 149
15.2.4 Keratin 149
15.2.5 Morphology of hair 150
15.2.6 Fur-skin dressing 151
15.2.7 Dyeing 153
15.2.8 Finishing 154
15.2.9 Pointing 154
15.2.10 Making up into garments
or accessories 154
15.2.11 Plates and crosses 157
15.3 Conservation and care 158
15.3.1 Introduction 158
15.3.2 Species identification 158
15.3.3 Damage 159
15.3.4 Conservation methods 159
15.3.5 Two case histories
illustrating methods 161
15.3.6 Freezing tests of adhesives 165
15.3.7 Care of furs 166
Endnotes 167
References 168
16 The tanning, dressing and
conservation of exotic, aquatic
and feathered skins 170
Rudi Graemer and Marion Kite
16.1 Exotic skins 170
16.1.1 Introduction 170
16.1.2 Origins and history of
exotic leathers 170
16.1.3 Uses of exotic leathers 170
16.1.4 Preparing the raw skins 171
16.1.5 Tanning and dressing 171
16.1.6 Conservation 172
16.1.7 Conclusion 172
16.2 Aquatic skins 173
16.2.1 Fish skin preparation 174
16.2.2 Structure and identification 174
16.2.3 Fish skin in ethnographic
objects 175
16.2.4 Conservation 178
16.3 Feathered skins and fashionable
dress 178
16.3.1 Processing 178
16.3.2 Conservation problems
with bird skins 181
Endnotes 182
References 182
17 Ethnographic leather and skin
products 184
Sherry Doyal and Marion Kite
17.1 Introduction 184
17.2 Ethics 184
17.3 Uses 184
17.4 Tanning methods 185
17.5 Construction techniques 185
17.6 Decoration 185
17.7 Conservation 186
17.7.1 Pre-treatment
examination 186
17.7.2 Poisons – health and
safety issues 186
17.7.3 Condition 187
17.7.4 Cleaning 187
17.7.5 Solvent cleaning 188
17.7.6 Reshaping 188
17.7.7 Mounts/internal supports 188
17.7.8 Mending 189
17.7.9 Repair supports 189
17.7.10 Sewing 189
17.7.11 Adhesives 189
17.7.12 Cosmetic repairs and
infills 190
17.7.13 Storage 190
17.7.14 Display 190
References 190
Bibliography 191
18 Collagen products: glues, gelatine,
gut membrane and sausage casings 192
Marion Kite
18.1 Animal glues and fish glues 192
18.2 Skin glues and hide glues 192
18.3 Parchment glue and parchment size 193
18.4 Rabbit skin glue 193
18.5 Bone glue 193
18.6 Gelatine 193
18.7 Fish glue 194
18.8 Gut membrane 194
18.9 Sausage casings 195
References 197
19 The manufacture of parchment 198
B.M. Haines
19.1 Temporary preservation 198
19.2 Soaking 198
19.3 Liming 198
19.4 Unhairing and fleshing 198
19.5 Drying 198
Bibliography 199
20 The conservation of parchment 200
Christopher S. Woods
20.1 Introduction 200
20.2 Parchment production and use 200
20.3 Chemical, physical and
deterioration characteristics 203
20.4 Display and storage 209
viii Contents
20.5 Conservation treatments 209
20.5.1 Mould and fumigation 210
20.5.2 Cleaning methods 210
20.5.3 Humidification and
softening 211
20.5.4 Consolidation of weak
parchment 215
20.5.5 Consolidation of inks
and pigments 216
20.5.6 Repairs and supports 217
20.6 Conclusion 220
Acknowledgements 220
Endnotes 220
References 221
21 Conservation of leather
bookbindings: a mosaic of
contemporary techniques 225
21.1 Introduction 225
Randy Silverman
21.2 Binding solutions to old
problems 225
Anthony Cains
21.2.1 Introduction 225
21.2.2 Klucel G 226
21.2.3 Application of Klucel G 227
21.2.4 Facing degraded leather 227
21.2.5 Technique 227
21.2.6 Treatment of the boards 228
21.2.7 Adhesives 228
21.2.8 Offsetting 228
21.2.9 Board attachment 228
21.2.10 Helical oversewing 228
21.2.11 The joint tacket 229
21.2.12 Drills 229
21.2.13 Making the needle
drill bit 229
21.3 Leather Conservation –
bookbinding leather consolidants 230
Glen Ruzicka, Paula Zyats,
Sarah Reidell and Olivia Primanis
21.3.1 Introduction 230
21.3.2 ENVIRONMENT
Leather Project 230
21.3.3 Consolidants 230
21.4 Solvent-set book repair tissue 232
Alan Puglia and Priscilla Anderson
21.4.1 Preparation of the repair
tissue 233
21.4.2 Leather consolidation 233
21.4.3 Repair technique 233
21.4.4 Reversing solvent-set tissue
repairs 233
21.4.5 Conclusion 233
21.5 Split joints on leather bindings 234
Don Etherington
21.6 A variation on the Japanese paper
hinge – adding a cloth inner hinge 235
Bill Minter
21.7 Split-hinge board reattachment 235
David Brock
21.8 Board slotting – a machinesupported
book conservation
method 236
Friederike Zimmern
21.8.1 Introduction 236
21.8.2 The method 237
21.8.3 Treatment of the text
block 237
21.8.4 Treatment of boards 237
21.8.5 Reattachment of text block
and boards 237
21.8.6 The board slotting
machine 238
21.8.7 Scientific analyses 238
21.8.8 Dyeing with reactive
dyes 239
21.8.9 Conclusions 241
21.8.10 Acknowledgements 241
21.9 A variation on the board
slotting machine 241
Bill Minter
References 242
22 The conservation of archaeological
leather 244
E. Cameron, J. Spriggs and B. Wills
22.1 Introduction 244
22.1.1 The archaeological context 244
22.1.2 Leather technology and
material culture 244
22.2 Wet leather 245
22.2.1 Condition 245
22.2.2 Preserving wet leather
before treatment 246
22.2.3 Past treatments 247
22.2.4 Present-day conservation
treatments 248
22.3 Dry leather 251
22.3.1 Condition 251
22.3.2 On-site retrieval 253
22.3.3 Recording procedures 254
22.3.4 Present-day treatments 256
22.4 Mineralized leather 257
22.4.1 Condition 257
22.4.2 On-site retrieval 259
22.4.3 Recording 259
22.4.4 Treatment 259
Contents ix
22.5 Long-term storage of
archaeological leather 260
22.5.1 Storage requirements 260
22.5.2 Condition assessments of
treated leather 260
22.5.3 Old collections/
retreatments 260
22.6 Purpose of treatment: a call
for clarity 260
22.7 Conclusion 261
References 261
23 Case histories of treatments 264
23.1 The Gold State Coach. 1762 265
23.1.1 Description 265
23.1.2 The problems and the
options 265
23.1.3 Treatment 265
23.2 Dog Whip – believed to be
eighteenth century 268
23.2.1 Description 268
23.2.2 Treatment 268
23.3 Fire Bucket 271
23.3.1 Description 271
23.3.2 Treatment 271
23.4 Fireman’s Helmet 274
23.4.1 Description 274
23.4.2 Treatment 274
23.5 Leather Lion 276
23.5.1 Description 276
23.5.2 Treatment 278
23.6 Sedan Chair 279
23.6.1 Description 279
23.6.2 Repairs 279
23.6.3 Cleaning 283
23.6.4 Gap filling and finishing 284
23.7 Jewellery Box 285
23.7.1 Description 285
23.7.2 Treatment 285
23.8 Dining Chairs 287
23.8.1 Description 287
23.8.2 The set of eight chairs
for reupholstering 287
23.8.3 The set of eight chairs
repaired without
removing the covers 287
23.8.4 The four chairs where
the covers were removed
and conserved 289
23.8.5 Overview 290
23.9 Alum Tawed Gloves, having
belonged to Oliver Cromwell 293
23.9.1 Description 293
23.9.2 Condition 293
23.9.3 Treatment 293
23.9.4 Future care 294
23.10 Court Gloves 296
23.10.1 Description 296
23.10.2 Treatment 296
23.11 Mounting of a Collection of
Flying Helmets 297
23.11.1 Description 297
23.11.2 Mount instructions 297
23.12 Leather Components from
Panhard et Levassor
Automobile. 1899 302
23.12.1 Description 302
23.12.2 Condition 303
23.12.3 Treatment 304
23.12.4 Future care 306
23.13 Altar Frontal. 1756 307
23.13.1 Description 307
23.13.2 Treatment 307
23.14 Gilt Leather Screen 313
23.14.1 Description 313
23.14.2 Treatment 313
23.15 Gilt Leather Wall Hangings,
Levens Hall 315
23.15.1 Description 315
23.15.2 Treatment 316
23.16 Phillip Webb Settle. 1860 – 65 325
23.16.1 Description 325
23.16.2 Treatment 325
23.17 Gilt Leather Wall Hangings at
Groote Schuur, Cape Town 329
23.17.1 Description 329
23.17.2 Condition 329
23.17.3 Conservation
treatment 331
23.17.4 Future care 333
Index 335
x Contents
xi
The first time I wished for a book like this was in
1957 when, as a member of the Victoria and Albert
Artwork Room, I was asked to conserve sixteenth and
seventeenth century gloves with beautiful embroidered
cuffs. I knew little about leather. It was essential
to learn about the methods of turning skins into
leather and how they could be recognized. Available
written information did not begin at the beginning.
It was then I met Dr Claude Spiers. Claude was
a senior lecturer at the Leathersellers’ Technical
College in Bermondsey and he invited me to visit.
There he showed me the vats in the floor where the
skins were held in suspension in the various processing
liquors and explained how tanning works. He
then arranged a meeting with John Waterer;
designer, antiquarian, author, historian and leather
craftsman. John guided me through the conservation
of the superfine tawed skins of the gloves and later
wrote the chapter on leather for Textile Conservation,
published by Butterworth in 1972. It was in the same
year that his Guide to the Conservation and Restoration of
Objects made Wholly or in Part of Leather was published
for the International Institution for Conservation.
These are still excellent introductions but The
Conservation of Leather and Related Materials widens the
scope to the benefit of collectors, conservators, curators
and anyone with responsibility for the care of
leather objects. It outlines the history and development
of the different types of tanning and what
makes each type of skin and each type of tanning
suitable for particular purposes. Most importantly, it
describes how to recognize skin patterns and treatments.
Finally the case studies indicate the range of
treatments available for the preservation of this often
overlooked segment of our cultural heritage.
Karen Finch OBE
Foreword
This page intentionally left blank
xiii
John W. Waterer R.D.I., F.S.A.,
F.I.I.C., 1892–1977
‘FITNESS FOR PURPOSE’
This book is dedicated to John Waterer. Although
John died in 1977, his lifelong involvement with
leather was such that, without the interest, influence
and enthusiasm he created it is doubtful whether
this book could have been written. Much loved and
respected, with an ever-ready smile, he epitomized
Chaucer’s words in the Canterbury Tales – ‘To any
kind of man he was indeed the very pattern of a
noble Knight.’
John was born in South London in 1892 and after
leaving school was invited in 1909 to join a wellknown
leathergoods company as an apprentice in
their luggage department. Although John had very
considerable career prospects as a talented musician,
this proved, almost by chance, to be the stepping
stone to his lifetime’s work. After a break in the Navy
during the Great War he rejoined his old company
and became increasingly involved in the design and
creation of the new ‘lightweight’ luggage, being
increasingly demanded by the travelling public due to
the evolution of the small inexpensive motor car and
the slow but steady growth in air travel.
With the knowledge thus gained, in 1936 John
joined S. Clarke & Co., a well-established but progressive
travel goods manufacturer, as managing director.
John was then able to fulfil his design flair but always
with ‘Fitness for Purpose’ in his mind – a guiding principle
throughout this life. After three exciting years
came the Second World War. By then John was 47
years of age, happily married with a daughter and at
the peak of his professional skill and ability.
The war years had a profound influence on John
Waterer’s life. With all its attendant problems, including
bomb damage, S. Clarke & Co. continued making
luggage but with part of its production given over
to war work. With his ever-enquiring mind, John
found time – possibly during the long hours of fire
watching – to begin his research into the history of
leather and its early uses. This led to a well-received
lecture to the Royal Society of Arts in 1942 for which
he subsequently received their Silver Medal. At the
same time both the government and trade association
set up committees to consider the best way forward in
the immediate post-war years, little realizing that the
years of difficulty and austerity would linger on until
well into the 1950s. Here John preached his gospel: a
vision of a better future where design and fitness for
purpose would be paramount, overcoming the innate
conservatism of manufacturers, by encouraging them
to embrace the benefits that good design would bring
to the manufacturing process.
All this led to the publication in 1946 of Leather in
Life, Art and Industry. Although in later years John
wrote many further well-researched books, this book
Dedications
set him up as an outstanding leather historian and
authority and can truly be regarded as his magnum
opus. If that was not enough, John was then instrumental
in setting up the Museum of Leathercraft to
enable others to see the use and evolution of leather
over the ages, thereby fostering design and craftsmanship
in the years to come.
John was by now conducting a worldwide correspondence
on leather-related matters. In 1953 his total
virtuosity resulted in his being elected to the faculty of
Royal Designers for Industry. This appointment is
considered the highest honour to be obtained in the
United Kingdom in the field of industrial design and
shows the high regard in which he was held by his
contemporaries. In the same year he was also admitted
to the Livery of the Worshipful Company of Saddlers,
with whom he had a long, friendly and supportive
association in the years that followed.
John remained as managing director of S. Clarke &
Co. until the early 1960s, producing modern looking
luggage designs which have stood the test of
time. It was then by a turn of fate that Clarke’s was
acquired by the company he had joined way back in
1909! John was then 71 years ‘young’ but with
undimmed enthusiasm and no concept of the meaning
of retirement – it seems to have slipped his mind –
which enabled him to give his increasing free time
to further his research into leather history. This led
to his realization that although there were many
beautiful and historic leather artefacts there was little
or no knowledge as to how they might be conserved
for the benefit of future generations. After
considerable research this led to his writing his
Guide to the Conservation and Restoration of Objects
made Wholly or in Part of Leather, first published in
1972, and his election as Fellow of the International
Institute for Conservation.
His vision also led to the creation of the Leather
Conservation Centre in 1978. The Centre is now
housed in purpose-built premises in Northampton,
through the generosity of the Worshipful Company
of Leathersellers. John did not live to see this, but
together with the Waterer/Spiers Collection, it is a
fitting memorial to a very special and dedicated man
whose like will not come again. The Waterer/Spiers
Collection was the inspired decision of the Council of
the Museum of Leathercraft, taken after John’s death,
to commission each year an article in leather to show
the best in contemporary design, skill and workmanship.
It was decided to conjoin his friend Claude
Spiers – a leather chemist – who had been instrumental
with John in setting up the museum during the
Second World War. This annually growing collection
now provides an outward and visible sign that leather
design, excellence and workmanship, which John
spent his life preaching and encouraging, still prosper.
Peter Salisbury
Betty M. Haines MBE, B.Sc., F.R.M.S.,
F.S.L.T.C., 1925–2003
Betty Haines, whose name is known throughout the
conservation world as a writer and teacher on all
aspects of collagen, skin and leather science, died
following a short illness while this book was being
brought together.
Betty graduated from Chelsea College of the
University of London in 1945 with a B.Sc. in Botany,
Chemistry and Zoology. She joined the British
Leather Manufacturers’ Research Association in 1946
becoming one of a line of eminent lady scientists
employed by them from its foundation in 1920 to the
present day. Working in the Biology Department she
applied her knowledge of protein science, bacteriology
and entomology in the fields of hide and skin
quality and the pretanning processes. In particular she
developed the field of leather microscopy first using
conventional light microscopes and later with the
new electron microscopes.
One application of this microscopical expertise
was with the identification of archaeological material
and Betty’s advice was sought by major museums
throughout the UK. This led to collaboration
with Dr Baines-Cope of the British Museum
Research Laboratory which culminated in the publication
of The Conservation of Bookbinding Leather
in 1984.
It was in 1978 while this work was being undertaken
that Betty was invited to join the Trustees of
the newly formed Leather Conservation Centre. She
was elected Chairman of the Technical Advisory
Panel in 1984, Chairman of Trustees in 1987 and
President from 1999.
During this period she contributed to summer
schools and wrote a series of monographs for the
Centre. She also lectured to students and gave papers
at professional conferences and seminars both in the
UK and abroad.
The chapters prepared by Betty for this volume
will, sadly, be her last written contributions in a
series of publications stretching over half a century.
Her deep knowledge of leather and its conservation
will, however, remain in the memories of those
who were privileged to know or work with her.
Roy Thomson
xiv Dedications
The editors wish to thank the many contributors to
this volume for their hard work and patience during
the editorial process. Particular appreciation is
expressed to the Victoria and Albert Museum and the
Leather Conservation Centre for permission to spend
time on the preparation and editing of this work and
to our respective colleagues there for their support.
We would like to thank Jodi Cusack and Stephani
Havard at Butterworth-Heinemann and also Neil
Warnock-Smith who was our first point of contact.
Thanks also must go to Carole Spring for her help
in the preparation of the texts and to Stephen Kirsch
for supplying an almost impossible to obtain image
of a sewing machine used to sew furs and gloves.
We would both like to thank our respective
spouses, John and Pat, for their unfailing help, encouragement
and tolerance throughout this project.
Marion Kite
Roy Thomson
Acknowledgements
This page intentionally left blank
xvii
Priscilla Anderson
Priscilla Anderson was awarded a Batchelor of Arts
cum laude majoring in the History of Art from Yale
University in 1990. She also holds a Master of
Library Science from the University of Maryland
and a Master of Science in Art Conservation from
the Winterthur/University of Delaware program.
Following internships at the Wilson Library,
University of North Carolina; the Walters Art
Museum, Baltimore and the University of Maryland
Libraries, she worked as a conservator/rare bookbinder
at the Library of Congress. She is now a
Special Collections Conservator at the Weissman
Preservation Centre of the University of Harvard
Library. She is a Professional Associate Member of
the American Institute for Conservation.
Aline Angus
Aline Angus was educated in Scotland and has an
honours degree in Ancient History and Archaeology
from the University of Durham. She gained a
Higher National Diploma in Conservation and
Restoration at Lincolnshire College of Art and
Design in 1992. She has worked on ethnographic
collections at the Horniman Museum in London
and the Royal Albert Museum in Exeter. She was at
the Royal Museum in Edinburgh for three years
preparing 18c and 19c objects for the new Museum
of Scotland. She has spent seven years at the Leather
Conservation Centre, Northampton.
David Brock
After studying at the University of Texas at Austin
and being awarded a degree majoring in Photographic
Studies at the Colombia College of Chicago,
David Brock received his first instruction in hand
bookbinding from Joan Flasch and Gary Frost at the
Art Institute of Chicago in 1977. In the following
year he began a six year apprenticeship with William
Anthony in hand bookbinding and conservation.
This was followed by five and a half years as a Rare
Book Conservator at the Library of Congress. In
1990 David became a conservator in private practice
and ran his own business for eight years, closing it in
1998 to assume his current position as Rare Book
Conservator for Stanford University.
Anthony Cains
Anthony Cains was indentured to a London trade
bookbinder in 1953. As part of his training he
attended the London School of Printing where he
received several prizes. During his National Service
he studied under William Matthews at Guildford
who recommended him to Douglas Cockerell and
Sons where the foundation of his career in book and
manuscript conservation was laid. He served both
the British and American funded rescue teams after
the Florence floods of 1966, being appointed
Technical Director of the programme set up in the
Biblioteca Nazionale Centrale Firenze. He was subsequently
invited to design and establish a workshop
in the Library of Trinity College Dublin which he
ran until his retirement in 2002. He is a founding
director and committee member of the Institute for
the Conservation of Historic and Artistic Works in
Ireland.
Esther Cameron
After reading Archaeology at Birmingham University,
Esther Cameron trained in Archaeological Conservation
at Durham University, gained a Masters
Contributors
degree and later went on to complete a doctorate at
Oxford University. She has worked for the Wiltshire
and Kent County Museums Services and for the
Institute of Archaeology at the University of Oxford.
She is now a freelance archaeological finds specialist
working on a range of materials including leather. She
is a Fellow of the Royal Society of Antiquaries of
London and has served on the executive committees
of the United Kingdom Institute for Conservation and
the Archaeological Leather Group. She is a Trustee of
the Leather Conservation Centre.
Anthony Covington
Tony Covington is Professor of Leather Science at
the British School of Leather Technology at
University College Northampton. He is also Visiting
Professor at Sichuan Union University, Chengdu,
China and Nayudamma-Wahid Professor at Anna
University, Chennai, India. He studied for
Graduateship of the Royal Institute of Chemistry at
Teesside Polytechnic and was awarded a doctorate at
Stirling University in Physical Organic Chemistry.
Before joining University College Northampton he
carried out research at BLC the Leather Technology
Centre for eighteen years. He is Past President of the
Society of Leather Technologists and Chemists and
of the International Union of Leather Technologists
and Chemists’ Societies. He is a Fellow of the Royal
Society of Chemistry and the Society of Leather
Technologists and Chemists.
Caroline Darke
Caroline Darke graduated from St Martins School of
Art with a National Diploma in Design (Fashion).
Running her own business SKIMP she produced
bags, belts, small leather goods and fashion accessories
for major shops and stores in UK, USA, Europe and
Japan. She has taught part time at Manchester College
of Art, Guildford School of Art, St. Martins School of
Art, Croydon College of Art and Brighton School
of Art. From 1965–94 she was Associate Lecturer
at London College of Fashion, from 1994–2000
Associate Lecturer and Accessories Co-ordinator at
Cordwainers College and from 1995 MA Accessories
course leader at Royal College of Art. In 2000
Caroline was appointed Course Director Professional
Development Unit-Cordwainers at London’s
University of Arts.
Laura Davies
Laura Davies graduated with a Fine Art Degree from
Staffordshire University specialising in Sculpture. She
then studied for a Masters degree at the Royal
College of Art/Victoria and Albert Museum joint
course in Conservation. During the three year duration
of the course she was placed in the Applied Arts
Conservation Department of the Museum of
London for the practical content of the course where
she gained experience with cuir bouilli objects. In
1999 she was awarded the Museums and Galleries
Commission Student Conservator of the Year Award.
After graduating she spent a year as an Objects
Conservator at London’s National Museum of
Science and Industry. She is now a Sculpture
Conservator at the Tate Gallery.
James Dickinson
In 1968 James Dickinson was awarded a Carnegie
UK/Museums Association bursary to study taxidermy.
This enabled him to train at various UK,
German and Swiss museums. In 1973 he was
appointed Senior Conservator Natural History at the
North West Museum Service, working on material
from museums all over north of England. In 2001 he
became the Conservation Officer Natural Sciences
for the Lancashire County Museum Service. He is a
Founder Member and former Chair of the Guild of
Taxidermists. In 1990 he was appointed a Member
of the Order of the British Empire for services to
taxidermy. In 1991 he became a Fellow of the
Museums Association.
Sherry Doyal
In 1981 Sherry Doyal was awarded a City and Guilds
Certificate with distinction in Conservation and
Restoration Studies from the Lincoln College
of Art. In 1984 she gained a post graduate Certificate
in Upholstery Conservation from the Textile
Conservation Centre and was subsequently engaged
as a conservator of furnishing textiles and upholstery
by the TCC, the Crown Suppliers, the Metropolitan
Museum of Art and the Victoria and Albert
Museum. From 1991–94 she was the National Trust
House and Collections Manager at Ham House.
From 1995 Sherry pursued her interest in ethnography
and natural history conservation, first at the
Horniman Museum and then Exeter City Museums.
xviii Contributors
From 1999 she combined a part time position as
Natural Trust Conservator and latterly Regional
Historic Properties Advisor with freelance enthnobotanical
conservation. In February 2005 Sherry
was appointed Deputy Head, Conservation and
Collections Care at the Horniman Museum and
Gardens, London. She is a Trustee of the Leather
Conservation Centre.
Don Etherington
Don Etherington began his career in conservation
and bookbinding in 1951 as an apprentice after
which he worked as a conservator for the British
Broadcasting Corporation and Roger Powell and
Peter Waters. Between 1967 and 1969 he was a training
consultant at the Biblioteca Nazionale in Florence
where he trained workers in book conservation practices
after the 1966 flood. Between 1960 and 1970 he
was a lecturer at Southampton College of Art in
England where he developed a four year programme
in bookbinding and design. From there he went to
the Library of Congress in Washington DC where he
served as a Training Officer and Assistant Restoration
Officer. In 1980 Mr Etherington became Assistant
Director and Chief Conservation Officer at the
Harry Ransom Humanities Research Center at the
University of Texas in Austin. In 1987 he joined
Information Conservation, Inc. located in Greensboro,
North Carolina where he created a new conservation
division for the preservation of library and archival
collections. He is now President of the Etherington
Conservation Center, Greensboro, North Carolina.
He is an Accredited Member of the Institute of Paper
Conservation and Fellow of both the American
Institute of Conservation and the International
Institute of Conservation.
Mary-Lou E. Florian
Mary-Lou Florian is Conservation Scientist Emerita
and Research Associate at the Royal British Columbia
Museum. She has a Bachelors and Masters degree in
biology specialising in fungi, insects and plant
anatomy. Her first introduction to conservation was
as a Biologist at the Conservation and Restoration
Research Laboratory at the National Gallery of
Canada in the early 1960s. She later worked as a
Senior Conservation Scientist in Environment
and Deterioration Services at the Canadian
Conservation Institute in Ottawa. In 1978 she went
to the Royal British Columbia Museum in Victoria,
British Columbia as a Conservation Scientist and
retired as Head of Conservation Services there in
1991. In her present capacity as Research Associate
at the Museum she is studying fungal stains and archaeological
wood identification. She is a Lifetime
Honorary Member of the American Institute of
Conservation and besides other professional excellence
awards has been awarded the 125th Commemorative
Medal from the Governor General of
Canada.
Rudi Graemer
Rudi Graemer received his early education in
Switzerland and in 1953 was awarded a First Class
Diploma from the National Leathersellers College
in London. His wide experience in technical management
in the leather trade includes work in the
UK, Switzerland, Australia and in the former
Belgian Congo. He returned to the UK to work
with the specialist reptile and exotic leather manufacturers,
T. Kinswood and Co. in 1960 from where
he retired as Managing Director in 1990.
Betty Haines
See dedication page xiii.
Robert D. Higham
Robert Higham qualified in leather technology at
the National Leathersellers College, London, in
1959 and served in tannery technical management
in Bolton, Galashiels and Edenbridge until 1969. In
that year he became Technical Editor of Leather, the
international journal for that industry, becoming
Editor a few years later. In addition he carried out
ad hoc consultancy work for several UN agencies.
He moved to Aberdeen in 1980 to study for the
Church of Scotland Ministry where he was awarded
the degree of Batchelor of Divinity. During this
period he continued as Consultant Editor of Leather
and with consultancy for UNIDO. He retired from
parish ministry in 2002 having served in
Berwickshire and latterly the Isle of Tiree.
Marion Kite
Marion Kite studied Textiles and Fashion at
Goldsmiths College School of Art where she was
Contributors xix
awarded a Batchelor of Arts specialising in goldwork
embroidery. She is a Senior Conservator in the
Textile Conservation Section of the Victoria and
Albert Museum having worked there since 1974
and where she developed a particular interest in the
conservation of animal products and other unusual
material incorporated into textiles and dress accessories.
She served on the Directory Board of the
International Council of Museum Committee for
Conservation between 1993 and 1999 and as
Treasurer between 1993 and 1996. She is a Fellow
of the International Institute of Conservation and
currently serves on the IIC Council. She is
Chairman of the Council of Trustees of the Leather
Conservation Centre and also sits on the Council of
the Museum of Leathercraft. She is a Trustee of
the Spence and Harborough collections of Gloves
administered by the Worshipful Company of
Glovers of London. She is an Accredited Conservator
Restorer and a Fellow of the Royal Society of Arts.
William Minter
Bill Minter was awarded a BSc in Industrial
Technology in 1970 from the Stout State University
in Menomonie. After completing seven years
apprenticeship with the book conservator and fine
bookbinder William Anthony, he set up his own
workshop specialising in the binding and conservation
of rare books and manuscripts which now
operates from Woodbury, Pennsylvania. Included
among his innovations for book conservation is the
development of an ultrasonic welder for polyester
fill encapsulation. He is a Professional Associate
Member of the American Institution for Conservation
and has served as President of both their Book and
Paper and Conservator in Private Practice Groups.
Olivia Primanis
After studying at the State University of New York
at Albany majoring in English Literature and being
awarded a Batchelor of Arts degree in 1973, Olivia
Primanis began her training through an apprenticeship
in hand book binding and book conservation at
the Hunt Institute of the Carnegie Mellon University
in Pittsburgh. Concurrently, she opened ‘The
Bookbinder’ which offered artists’ supplies and
bookbinding services for individuals and institutions.
In 1984 she moved to Los Angeles and continued her
private practice of conservation bookbinding and
teaching. Since 1990, Ms Primanis has held the
position of Senior Book Conservator at the Harry
Ransom Humanities Research Center at the
University of Texas at Austin where she undertakes
conservation treatments, teaches and participates in
departmental administration. She serves on the Book
and Paper Group Publication Committee of the
American Institute for Conservation.
Alan Puglia
Alan Puglia was awarded a Batchelor of Arts degree
from the University of New Hampshire in 1986.
Following studies in conservation at the George
Washington University in Washington and the
University of Texas at Austin, he was awarded the
degree of Master of Library and Information Science
and a Certificate of Advanced Study in Library and
Archives Conservation. Having worked for a number
of institutions in the field of book and archives conservation
for ten years he was appointed Conservator
for the Houghton Library Collections at Harvard
University in 1999.
Sarah Reidell
Sarah Reidell graduated from Bryn Mawr College
and then studied for a Masters degree in Library and
Information Science and a Certificate in Advanced
Studies at the University of Texas in Austin. Having
worked for a period as visiting conservator in
France and Spain she undertook internships at the
Center for American History in Austin, Harvard
University Library and as Mellon Advanced Intern
at the Conservation Center for Art and Historic
Artifacts in Philadelphia. In 2003 she was appointed
Conservator for Special Collections at the Harvard
University Library.
Glen Ruzicka
Glen Ruzicka was awarded the degree of BA at the
Emory University in Atlanta in 1971. He then
trained in rare book conservation at the Library of
Congress where he worked for over ten years. From
1986 to 1988 he served as Head of the Preservation
Department of the Milton S. Eisenhower Library,
John Hopkins University, Baltimore. In 1988 he was
appointed Chief Conservator of the Conservation
Center for Art and Historic Artifacts in Philadelphia
xx Contributors
where he is now Director of Conservation. He is a
Professional Associate Member of the American
Institute for Conservation where he served as Chair
of the Book and Paper Group. He is a member of the
Board of Directors of the Pennsylvania Preservation
Consortium and a member of the Historic Buildings
and Collections Committee of Girard College,
Philadelphia.
Randy Silverman
Randy Silverman has worked in the field of book
conservation since 1978 and was awarded a Masters
degree in Library Science from the Brigham Young
University in 1986. Having worked as conservator
and preservation librarian at the Brigham Young
University he was appointed as the Preservation
Librarian at the University of Utah’s Marriott Library
in 1993. Mr Silverman initiated the passage of Utah’s
permanent paper law in 1995. He is a Professional
Associate Member of the American Institute for
Conservation and has served as co-chair of their
Library Collections Conservation Discussion Group,
as a member of the Institute’s National Task Force on
Emergency Response, and as President of the Utah
Library Association. He is also an Adjunct Professor
with Emporia State University (Kansas), the University
of Arizona and the University of North Texas.
James Spriggs
Jim Spriggs studied conservation at the Institute
of Archaeology, University College London where
he was awarded a Diploma in Archaeological
Conservation. He is Head of Conservation at the
York Archaeological Trust. His department specialises
in the study and conservation of all types of
archaeological material from excavations in York
and elsewhere from both land based and marine
environments. He is an Accredited Conservator
Restorer, a Fellow of the Society of Antiquaries of
London and of the International Institute of
Conservation. He is a Founder Member of the York
Consortium for Conservation and Craftsmanship.
Theodore Sturge
Theo Sturge trained in conservation at the Institute
of Archaeology, University College London in
the 1970s. On leaving college he worked at
Leicester Museum as Assistant Keeper, Antiquities
Conservation, for 16 years. This was followed by six
years as Senior Keeper, Conservation and Restoration
at the Herbert Art Gallery and Museum in Coventry
and six years as Senior Conservator at the Leather
Conservation Centre, Northampton. In 2000 he set
up his own studio specialising in leather conservation.
He is an Accredited Member of the United
Kingdom Institute for Conservation and a Fellow of
the International Institute for Conservation.
Roy Thomson
Roy Thomson was awarded the degree of BSc with
Honours in the Chemistry of Leather Manufacture
from the University of Leeds in 1960. He worked in
research and technical services associated with the
leather trades until 1968 when he was appointed
Works Director responsible for technical and production
management at the largest lambskin clothing
leather tannery in the UK. In 1994 he was appointed
Chief Executive at the Leather Conservation Centre
from where he retired in 2004. He is an Accredited
Conservator, Fellow of the Royal Society of
Chemistry, a Fellow and Past President of the Society
of Leather Technologists and Chemists and Fellow of
the International Institute for Conservation. He is
Past Chairman of the Council of the Museum of
Leathercraft and Treasurer of the Archaeological
Leather Group.
Barbara Wills
Barbara Wills trained in conservation at Lincoln
College of Art. She joined the Department of
Conservation at the British Museum in 1979 and
completed a Museums Association Certificate in
Ethnographical Conservation in 1984. As Senior
Conservator in the Organic Artefacts Section, she
specialises in the treatment of leather, basketware and
Ancient Egyptian material. She is an Accredited
Member of the United Kingdom Institute for
Conservation and has served on the committee of the
Archaeological Leather Group for a number of years.
She is a Trustee of the Leather Conservation Centre.
Christopher S. Woods
Chris Woods gained a Post Graduate Diploma in
Library and Archive Conservation from Colchester
Institute following an Art History degree from
Contributors xxi
Sheffield Art College. He worked for fifteen years,
first as Conservator and then Head of the Preservation
Division for the Dorset Archives Services.
He was appointed as Head of Collection Care and
Conservation for Oxford University Library Service
at the Bodleian Library in 2002 responsible for the
care of the many and varied library and archive collections
in the 40 Oxford University Library Service
sites. He is an Accredited Conservator Restorer, a
Fellow of the International Institute for Conservation
and serves as Chairman of the United Kingdom
Institute for Conservation.
Friederike Zimmern
Following an apprenticeship in bookbinding in
Hamburg, Friederike Zimmern studied at the
Academy for Art and Design at Stuttgart and was
awarded her Diploma in the Restoration and
Conservation of Books, Paper and Archives in 1998.
After working for restoration companies in
Germany she obtained an advanced level internship
at the Straus Center for Conservation at Harvard
University Art Museums. In February 2002 she was
appointed as the Head of the paper conservation
workshop of the graphic art collection of the
Hessisches Landesmuseum in Darmstadt.
Paula Zyats
Paula Zyats studied at Temple University Tyler
School of Art in Rome and Philadelphia College of
Art and was awarded a Batchelor of Fine Art degree
specialising in illustration in 1987. Having become
involved with book conservation, she completed a
Master of Science degree with a Certificate in Art
Conservation from the Winterthur/University of
Delaware Art Conservation Program. This involved
internships served at Columbia University Libraries,
the Library of Congress and the Folger Shakespeare
Library with a Mellon Advanced Internship at the
Conservation Center for Art and Historic Artifacts
in Philadelphia. In 1998 she was appointed conservator
at the CCAHA and in 2004 became Assistant
Chief Conservator at the Yale University Library
Preservation Department.
xxii Contributors
Man and his early ancestors have exploited the unique
properties of skin and leather for millennia and almost
all human cultures have developed specialist techniques
to utilize this readily available raw material for
a wide variety of purposes. Indeed, tanning has been
described as man’s first manufacturing process. But
what are the properties which make these skin-based
products so special?
To begin with, leather is a sheet material with the
area of each piece ranging from tens of square centimetres
to six, seven or more square metres depending
on the animal from which it was obtained. Until
the development of woven textiles it was the only
material available in sheets of this size.
Then there is the complex physical structure of
skin and materials made from it. A close examination
of the make-up of a piece of skin shows that it consists
primarily of long thick fibres and fibre bundles
interweaving in three dimensions within a jelly-like
‘ground substance’. Other features such as hairs
and hair roots, muscles, blood vessels and fat cells are
present but it is this intricate, three-dimensional,
woven structure that predominates and gives skinbased
materials many of their unique physical qualities.
These properties include flexibility, a relatively
high tensile strength with particular resistance to
shock loads, resistance to tearing, puncturing and
abrasion, low bulk density, good heat insulation and
water vapour transmission. They also include
mouldability, resistance to wind and liquid water,
and an ability to be stretched and compressed without
distorting the surface.
Many of these characteristics are common to
both leather and other skin products but linguistic
studies suggest that the various materials such as raw
hide, oil-tanned pelt, alum-tawed skin and vegetabletanned
leather were differentiated from each other
from early times. It was not until the late eighteenth
century though that the actual nature of the tanning
process was examined and the question posed as to
how leather was different from these other materials.
A number of criteria have been put forward in an
attempt to define what is a true leather (Bienkiewicz,
1983; Covington, 2001; Lollar, 1958; Reich, 1999).
These will be considered.
A fundamental property of leather is that while a
raw skin is subject to rapid bacterial degradation due
in the main to the action of proteolytic enzymes,
leather is resistant to such microbiological attack even
if it is kept wet. There are, though, a number of techniques
such as salt curing, drying, solvent dehydration
and acid pickling which will impart temporary
preservation against bacterial attack. This resistance
to decay, however, is lost if the fibres are allowed to
become wet. Similarly the effects of the treatments
involved in the preparation of parchment or alumtawed
skins, both renowned for their longevity, are
reversed by repeated immersion in water.
Skin-based materials are prepared by many
indigenous peoples around the world by thoroughly
impregnating the raw hide with fatty materials and
then allowing it to dry out under carefully controlled
conditions. The fats coat the individual skin
fibres and fill the spaces between them. Even if the
treated hides are then immersed in water, the presence
of these water-repellent fats ensures that the
fibres remain too dry for bacterial attack to take
place. They therefore appear to satisfy the criteria
of resistance to microbiological degradation. These
products, which are found widely in ethnographic
collections, have been termed pseudo leathers.
These pseudo leathers should not be confused with
oil-tanned skins which are not treated with stable,
water-resistant fats but with reactive, oxidizible oils
1
1
The nature and properties of leather
Roy Thomson
often obtained from marine animals. These undergo
various chemical changes during processing to liberate
compounds with true tanning actions. Examples
of these oil-tanned products include chamois wash
leathers and the buff leather employed widely in the
sixteenth and seventeenth centuries to make protective
jerkins for the military.
Another characteristic attributed to leather is that
whereas if a raw skin is allowed to dry out it is
expected that it will become hard, horny, brittle and
translucent, a true leather is said to dry to give a soft,
flexible, opaque product.
It is true that if a raw skin is allowed to dry in an
uncontrolled manner it is likely to give a product with
the properties described. If, though, the rate of drying
is regulated as with the production of the pseudo
leathers described above, a soft opaque material
results. Similarly if a dehaired skin is dehydrated by
immersion in successive baths of a polar solvent such as
acetone or one of the lower alcohols and the residual
solvent evaporated, the resultant product will be
soft, white, opaque and flexible. This flexibility will
be enhanced by working the skin mechanically while
it is still only just damp with the solvent. It will
look and feel very similar to an alum-tawed or
formaldehyde-tanned leather. These characteristics
of solvent-dried skins are utilized in the solvent dehydration
methods employed to conserve waterlogged
archaeological leathers.
Parchment and vellum which are prepared by
drying unhaired pelts under tension also exhibit
many of the physical properties of a true leather.
The different properties of the various untanned
products made in the past depended on the amount
and type of oil used to treat the unhaired skin and the
rate of drying. These properties enabled these materials
to be used for such diverse purposes as mallet
heads, textile machinery parts and the protective corners
of basketwork skips. A modern successor to the
latter is the use of rawhide to protect the corners and
bottoms of baskets used by hot air balloonists. It is the
unique combination of impact and abrasion resistance
together with an elastic resilience which makes
this age old material ideal for its modern purpose.
While leathers produced for gloving and clothing
are soft and supple, those made for shoe soleing are
firm and resilient. In the period when the technique
of chrome tanning was being developed during the
last quarter of the nineteenth century it was found
that while a stable product could be made, this new
type of leather was liable to dry out to give a hard,
cracky, inflexible material, in many ways similar to
untanned skin. It was only with the introduction of
the fatliquoring process, which coated the tanned
fibres with oils, that a material could be manufactured
with the properties required for it to be recognized as
a true leather.
If a piece of wet skin, tanned or untanned, is heated
slowly it will reach a temperature at which it shrinks
dramatically to about one third of its original area.
This phenomenon has been likened to melting but is
fundamentally different. The hydrothermal shrinkage
of skin is irreversible and rather than being caused by
a single physicochemical change is the cumulative
result of a number of intermolecular processes.
The temperature at which this change takes place
is termed the shrinkage temperature and the
amount by which any process increases the shrinkage
temperature of a skin has often been considered
as a measure of its leathering ability.
The shrinkage temperature of a given sample of
skin will depend on a large number of factors. These
include the species and age of the animal from
which the skin is obtained, what pretanning and
tanning treatments the skin has undergone, the
moisture content of the sample and the exact procedures
employed in the determination. If, however,
care is taken to carry out the measurement in a standardized
manner, duplicate results within 1 or 2°C
can be obtained. Using methods described in international
standards, the following shrinkage temperatures
are exhibited by typical commercial products:
Raw mammalian skin 58– 64°C
Limed unhaired cattle hide 53–57°C
Parchment 55– 64°C
Oil-tanned leather 53–56°C
Alum-tawed skins 55– 60°C
Formaldehyde-tanned leather 65–70°C
Alum-tanned skins 70 –80°C
Vegetable-tanned leather (hydrolysable) 75–80°C
Vegetable-tanned leather (condensed) 80 –85°C
Chrome-tanned leather 100 –120°C
Most of these results confirm that tannage enhances
the shrinkage temperature. There is, however, an
anomaly with oil-tanned skins such as chamoistanned
wash leathers or the brain-tanned ‘elk skins’
produced by Native American and other cultures. In
these cases the stabilizing process does not increase
the shrinkage temperature. These products exhibit
all the characteristics of true leathers and what is
more they retain these after frequent washing and
drying in use. Oil-tanned leathers also exhibit another
significant difference in their hydrothermal properties.
When other skins and leathers shrink in hot water
they turn into a rubbery material which dries to a
2 Conservation of leather and related materials
hard, brittle, product. When oil-tanned materials
shrink they retain their leathery handle and when
dried retain their softness and flexibility to a significant
extent. In addition, if a wet oil-tanned leather is
heated above its shrinkage temperature and then
immersed in cold water it can be stretched back to
nearly its original size.
These exceptions to the various criteria proposed
to define what is and what is not a true tannage have
led to attempts to explain the conversion of skin
into leather according to the mechanisms involved.
For many years it has been accepted that the cohesion
of skin fibres is a result of the structure of the collagen
protein molecules from which these fibres are
formed. These have been shown to be held together
by a combination of a few, relatively strong, covalent
bonds and many weak hydrogen bonds. It has been
thought that hydrothermal shrinkage occurs when
the disruptive energy introduced by heating the sample
exceeds the cohesive strength of the bonding
within and between collagen molecules. Tannage has
been thought to introduce extra chemical crosslinking
bonds between adjacent collagen molecules
which are resistant to microbiochemical attack. The
nature and strength of these crosslinkages vary considerably
depending on the type of tanning material
employed. Vegetable tannage for instance is thought
to introduce many extra hydrogen bonds between
free amino side groups of the collagen protein and
hydroxyl groups from the polyphenolic tannin
molecules. Chrome tannage on the other hand is a
result of side chain carboxylic groups on the protein
molecule co-ordinating with the multinuclear
chromium complexes present in chrome tanning
liquors. The differences in the increase in shrinkage
temperature brought about by the different tanning
systems has been thought to be related to the combined
strength of these crosslinking bonds.
Recent work has shown that the energy associated
with the hydrothermal shrinkage is similar for all the
different tannages irrespective of the temperature at
which the shrinkage occurs. This has led to the concept
of the formation of a supramolecular matrix
around the collagen molecule during tanning and
that it is the size and complexity of this matrix which
determines shrinkage temperature. This mechanism
does not preclude the presence or importance of
crosslinking reactions occurring during tanning but
it does explain why oil tannage can be considered to
give a true leathering effect without increasing the
shrinkage temperature.
Although indicating the complexity of the problem,
the question of what exactly leather is has not
been fully answered by the above discussion. However,
a definition which appears to take into account
the points raised is as follows.
Leather is a material produced from the skin of a
vertebrate, be it mammal, reptile, bird, fish or amphibian,
by a process or series of processes which renders
it non-putrescible under warm moist conditions. A
true leather retains this property after repeated wetting
and drying. Leather usually dries out to give a
relatively pliable, opaque product but it can be hard
or soft, flexible or rigid, stiff or supple, thick or thin,
limp or springy, depending on the nature of the skin
used and the process employed.
It has been the aim of the tanner throughout the
ages to manufacture a product with just the combination
of properties demanded by the end user.
It should always be borne in mind that in a similar
way to ‘metal’ or ‘wood’, leather is not a single material
but a group of related products having many
characteristics in common but each varying in its
properties and reaction to conservation treatments.
References
Bienkiewicz, W. (1983) Physical Chemistry of Leather
Making. Malabar: Krieger, pp. 308–323.
Covington, A.D. (2001) Theory and Mechanism of
Tanning. J. Soc. Leather Technologists and Chemists, 85, 24.
Lollar, R.M. (1958) Criteria Which Define Tannage. In
Chemistry and Technology of Leather Vol. II (O’Flaherty, F.
et al., eds), pp. 1–27. New York: Reinhold.
Reich, G. (1999) The Structural Changes of Collagen
During the Leather Making Processes. J. Soc. Leather
Technologists and Chemists, 83, 63.
The nature and properties of leather 3
Collagen is the major protein from which skin is
formed and its unique structure is fundamental to the
leathermaking process. A knowledge of the nature of
this protein is therefore required if the properties of
leather are to be understood. The chemical and physical
nature of collagen have been reviewed, among
others, by Bailey (1992), Bailey and Paul (1998),
Kennady and Wess (2003), Reich (1995), Ward (1978),
and Woodhead-Galloway (1980).
2.1 The collagen molecule
The collagen molecule, like all proteins, is formed
by the linking together of naturally occurring smaller
units, amino acids.
All amino acids contain a carboxyl and an amino
group, with a side chain denoted as ‘R’ (Figure 2.1).
Amino acids differ only in the nature of their side
chains.
With the simplest amino acid, glycine, the side
chain is a single hydrogen atom (Figure 2.2). With
other amino acids the side chains may be short or
long, non-polar and therefore chemically inert, or
polar and chemically reactive.
Non-polar side chains contain only carbon and
hydrogen atoms. Polar side chains on the other hand
contain oxygen, present as hydroxyl or carboxyl end
4
2
Collagen: the leathermaking protein
B.M. Haines
R
/
H2N - C - COOH
\
H
Glycine
Acidic amino acids
Basic amino acids
Non-polar amino acids
Leucine
Lysine
Glutamic acid
H
C
NH3
ϩ
H COO–
H
C
O
O–
NH3
ϩ
CH2CH2 COO–
H
C
NH3
ϩ
H3Nϩ
CH2CH2CH2 CH2 COO–
H
C
NH3
ϩ
CH2
CH3
CH3
CH COO–
Figure 2.1 The structure of amino acids.
Figure 2.2 Structures of amino acids showing the different
sizes of common side chains.
Collagen: the leathermaking protein 5
groups and therefore acidic in nature, nitrogen, present
as amino or amide end groups and therefore basic
in nature, or sulphur, present as mercaptan groups.
The amino acids are linked by covalent peptide
bonding between the carboxyl group of one amino
acid and the amino group of an adjacent amino acid.
This formation of peptide bonds involves the loss of
water in a condensation reaction (Figure 2.3). In this
way numerous amino acids are linked to form a long
chain, or protein backbone.
All proteins have identical backbones: the distinctive
character of each protein lies in the particular
sequence of amino acids along the chain.
Collagen is composed of about 20 different amino
acids, linked to form a chain 300nm long containing
approximately 1000 units. Collagen is characterized
by a high proportion of glycine (30%) and by the
presence of the imino acids proline (10%) and
hydroxyproline (10%) (Figure 2.4). Hydroxyproline
is formed from proline after the backbone chain
has been synthesized. Hydroxyproline is found only
rarely in proteins other than collagen and so it is used
to identify the presence of collagen in a sample or to
determine the collagen content of a sample.
Many segments of the backbone chain of collagen
consist of simple tripeptide repeats of glycine, X, Y,
where X is frequently proline or hydroxyproline.
The spatial shape, the ring structure, of proline and
hydroxyproline twists the chain into a helical coil, a
left-handed helix with three amino acids per twist
with glycine occupying every third position along
the chain (Figure 2.5).
The collagen molecule is made up of three such
helical chains, which is the reason for the molecule
being termed the triple helix. These three chains twist
together to form a right-handed coil (Figure 2.6).
Water molecule eliminated
in condensation reaction
N
N
H
H
C C
C
C
O
O
OOH
R
H
H H
RЈ Side-chain
Side-chain
Single
polypeptide
chain of
tropocollagen
2.86 nm
Y
X
Gly
Figure 2.3 The reaction between two amino acids to
form a peptide.
H
H COOHC
NH2
CH2H2C
H2C
COOH
N
H
H
O
CH2
O
H2C
COOH
N
H
H
O
HO
Glycine Proline Hydroxyproline
Figure 2.4 The structures of the most common amino acids present in collagen.
Figure 2.5 Single helical polypeptide chain of
tropocollagen.
6 Conservation of leather and related materials
2.2 Bonding within the molecule
The coiling holds the three chains together but the
triple helix is further stabilized by chemical crosslinks
between the three backbone chains.
Hydrogen bonds form between the NH and the
CO groups of adjacent chains (Figure 2.7). Hydrogen
bonds are electrostatic and their stability depends
on the distance separating the reactive groups, the
greater the distance the weaker the bond. The three
chains need to be closely packed within the molecule
to allow hydrogen bonding to take place. Glycine has
the smallest side chain and is present at every third
position along the chain. The alignment of adjacent
chains needs to be such that the small side chain of
glycine projects into the centre of coiled molecule,
the larger side chains projecting out.
In order to bring glycine into the required
internal position in the helix, molecular models have
shown that to achieve the maximum number of
hydrogen bonds and to minimize the hindrance of
larger side chains, each chain of the triple helix needs
to be staggered by one amino acid with respect to its
neighbour.
2.3 Bonding between molecules
Many molecules pack together to form the fibril,
which is the smallest collagen unit seen under the
transmission electron microscope. The stability of
the fibril depends on crosslinks formed between
adjacent molecules, i.e. intermolecule bonding.
2.3.1 Salt links
Polar side chains project out from each molecule.
When acidic and basic end groups of these side
chains become aligned, electrostatic salt links can
form (Figure 2.8).
The sequence of amino acids along each chain of
the triple helix has been determined and this has
shown there to be distinct alternate grouping of
amino acids with either polar or non-polar side
chains giving rise to domains along the chain that
are either only polar or non-polar in reaction
(Figure 2.9). When the collagen fibril is immersed in
an electronoptically dense metallic stain for several
Left-hand
helix with 3
residues per
turn.
3
2
1
C C
C
O
O
CC
C
N
N
N
N
H
H
Side-chain
Hydrogen
bond
Side-chainRЈ
R
Figure 2.6 Three tropocollagen helices coiled together
to form the collagen molecule.
Figure 2.7 Hydrogen bonding between adjacent
peptides.
Backbone Backbone
ϩ Ϫ
C – (CH2 )n – NH2 O2 C – (CH2 )n – C
l l
Ï Ï
Figure 2.8 Salt links between adjacent peptides.
Collagen: the leathermaking protein 7
minutes (positive staining) the charged end groups
of the polar side chains react with the metal. This
enables their location to be revealed under the transmission
electron microscope. Fibrils stained in this
way exhibit a series of fine striations (Figure 2.10)
which indicate that in fibril formation molecules are
so aligned as to bring together those regions where
polar side chains predominate. This allows the maximum
salt links between adjacent molecules.
2.3.2 Covalent intermolecular bonding
If collagen fibrils are immersed in the metallic
stain for only a few seconds (negative staining) this
allows the stain to merely outline the surface features
of the collagen such as cavities. A fibril stained
in this way exhibits a regular dark banding at
intervals of 67nm (Figure 2.11). The collagen molecules
are 300nm long, that is 4.4 times that of the
banding.
Since the sum of the band spacing does not coincide
with the length of the molecule, a gap must
therefore exist between the end of one molecule and
the beginning of the next. Such gaps are accessible to
the stain, hence the dark banding.
This banding has also led to the theory that
adjacent molecules are displaced relative to one
another by one quarter of their length, as shown
Rich in polar
residues
Rich in polar
residues
Rich in imino acid
and non-polar residues
Figure 2.9 Idealized scheme showing domains rich in polar or non-polar amino acids.
67 nm ϭ D period
Figure 2.10 Positively stained collagen fibril revealing reactive polar domains.
8 Conservation of leather and related materials
diagrammatically in (Figure 2.12). This alignment
has been described as the ‘quarter stagger’ of the
molecules, with overlaps of 27nm.
It is at these overlaps that another form of crosslinking
occurs. At each end of the triple helix there
is a short non-helical region called the telopeptide.
Covalent bonds form between the telopeptide
region of one molecule and the helical region of an
adjacent molecule (Figure 2.13). Such an array leaves
no weak point along the fibril which could give way
under stress.
2.4 Fibril structure
There have been various theories as to the spatial
arrangement of the aligned molecules within the
fibril. Some indication of the internal structure of
Figure 2.11 Negatively stained collagen fibril showing characteristic dark banding.
70 nm
280 nm
Tropocollagen
molecules
Collagen
fibril
Figure 2.12 Diagram showing ‘quarter stagger’ alignment
of adjacent collagen molecules.
Figure 2.13 Diagram showing covalent bonding in the
telopeptide region.
Collagen: the leathermaking protein 9
the fibril has been seen when collagen fibrils, highly
swollen with alkali, were examined under the transmission
electron microscope. The swollen fibril
exhibited longitudinal striations with a helical twist
(Figure 2.14). Therefore the fibril would appear to
be made up of a series of helical coils, alternating
in direction, beginning with the backbone chain of
the molecule, then the triple helix and finally the
grouping of molecules within the fibril. Such
repeated coiling imparts strength to the fibril.
The collagen fibrils are remarkably consistent in
diameter, irrespective of animal type or location
within the skin. It is only at the extreme grain surface
where fibrils smaller in diameter have been found.
Under the transmission electron microscope
there appears to be a distinct grouping of fibrils into
larger units or elementary fibres. The fibrils are held
in these groups by helical coiling of the fibril.
The elementary fibres are in turn grouped into
fibre bundles which then interweave through the
skin in the manner already described.
2.5 Shrinkage temperature
One property of collagen is that it exhibits a sudden
shrinkage in length when heated in water. Mammalian
skin collagen that has received no chemical processing
shrinks at about 65°C. There is little variation in
this temperature with different mammalian species
or different regions of the skin.
The reason for this shrinkage is that the backbone
chains of the molecule exist in an extended form,
held in this form by hydrogen bonding. When
collagen is heated a point is reached at which the
energy input exceeds that of the hydrogen bonding.
There is then a sudden release from the extended
form and the fibre shrinks to a rubber-like consistency.
Only the remaining covalent and salt links
hold the collagen molecules together and prevent
the shrunken collagen from immediately going into
solution.
Prolonged exposure to alkali, such as in the liming
process, causes changes to certain amino acids;
these changes in turn reduce the degree of hydrogen
bonding within the collagen molecule. As a consequence,
the shrinkage temperature of skins that have
been limed falls to 60°C or even 55°C.
Ageing conditions that bring about hydrolytic
or oxidative degradation of the collagen cause
breaks in the backbone chain of the molecule and
changes to the chemical composition of the side
chains. These both lead to a reduction in shrinkage
temperature.
Figure 2.14 Swollen fibril showing subfibrillar helical structure.
10 Conservation of leather and related materials
Chemical cross-links introduced into the collagen
by tanning agents raise the shrinking temperature
depending on the type of tanning material and the
nature of the process employed.
References
Bailey, A.J. (1992) Collagen – Nature’s Framework in the
Medical, Food and Leather Industries. J. Soc. Leather
Technologists and Chemists, 76, 111.
Bailey, A.J. and Paul, R.G. (1998) Collagen: A Not So
Simple Protein. J. Soc. Leather Technologists and Chemists,
82, 104.
Kennady, C.J. and Wess, T.J. (2003) The Structure of Collagen
within Parchment – A Review. Restorator, 24, 61.
Reich, G. (1995) Collagen: A Review of the Present
Position. Leder, 46, 195.
Ward, A.G. (1978) Collagen 1891–1977: Retrospect and
Prospect. J. Soc. Leather Technologists and Chemists, 62, 1.
Woodhead-Galloway, J. (1980) Collagen: The Anatomy of a
Protein. London: Edward Arnold.
Figure 2.15 Grouping of elementary fibres into fibre bundles.
In making leather a raw, putrescible animal skin is
converted into a dry, non-putrescible material with
the handle and degree of flexibility required for its
specific end use.
The skin of any vertebrate animal can be made
into leather, and the one common characteristic of
these skins is that they are primarily composed of the
protein collagen. The molecules of collagen are
extremely long in relation to their cross-section, and
during their formation they become naturally orientated
into fibrils and bundles of fibrils (Figure 3.1),
which interweave in a three-dimensional manner
through the skin.
This natural fibrous weave is preserved in the final
leather and it is this fibrous structure that gives its
unique physical properties of handle and ability to
accommodate to the stresses and movement imposed
during its use.
However, this fibrous skin structure varies considerably
between skins of different species and types
within species, thus giving the leather industry a
wide variety in raw materials from which a careful
11
3
The fibre structure of leather
B.M. Haines
Figure 3.1 Fibrils and fibril bundles of collagen.
selection has to be made in order to achieve the
combination of mechanical and aesthetic properties
required for specific end uses.
The diverse structures of skins and the effects on
the properties of leathers made from them have been
described by British Leather Manufacturers’ Research
Association (1957), Haines (1981, 1984, 1999) and
Tancous (1986).
3.1 The structure of mammalian skins
Although the skin of any vertebrate animal, be it fish,
reptile, bird or mammal, can be made into leather.
The most commonly used skins have been, and are
at the present time, those from cattle, calf, goats, sheep
and to a lesser extent pig and deer. These being
mammalian in origin they are covered by hair.
The mammalian skin has distinct layers (Figure 3.2):
the layer which extends from the outer surface to
the base of the hair roots is termed the grain layer
and contains the hairs, sebaceous and sweat glands
and numerous blood vessels. The collagen fibres
become increasingly fine as they pass through this
grain layer to the outer surface, which in life is
covered by the epidermis.
In the underlying corium the fibre bundles are
considerably larger and interweave at a higher angle
relative to the skin surface. Towards the inner or flesh
surface the fibres become finer and run in a horizontal
plane to form a limiting or flesh layer, separating
the skin from the underlying muscles.
In the early stages of leather processing the epidermis,
together with the hair, is removed chemically.
This exposes at the surface the compact interweaving
of extremely fine fibrils that create the smooth, aesthetically
pleasing grain surface of the leather.
3.2 Variation of structure between
animal types
Each species has a distinctive skin structure: the skins
vary in total thickness, dimensions of the corium fibre
bundles and in the proportion of the total thickness
occupied by the grain layer.
3.2.1 Mature cattle skins
The skins of mature cattle are generally between
4 and 6mm thick with a proportion reaching 8mm
in thickness, and measuring 3.3 to 4.2m2
in area.
12 Conservation of leather and related materials
CORIUM
JUNCTION OF
GRAIN & CORIUM
GRAIN
Hair RootHair Shaft
Sebaceous
Gland
Epidermis
Erector Pili
Muscle
Sweat Glands
Artery
Vein
FLESHFat
Figure 3.2 Diagrammatic representation of structure of a typical mammalian skin.
The grain layer occupies about one sixth the total
thickness (Figure 3.3). The hairs are straight, relatively
coarse and spaced equidistant through the grain layer.
The corium fibre bundles are relatively large
(0.1mm in diameter) and interweave at a fairly high
angle relative to the surface.
Such a skin is highly suited for sole leather, harness,
saddlery, or mechanical belting leather but it is far
too thick for shoe uppers or upholstery unless it is
split into two layers. The upper or outer layer consisting
of the grain layer and part of the underlying
corium, the grain split, is used for shoe uppers or
upholstery or case leather. This outer layer can be
split to 1mm thick for upholstery leather or from
1.3 to 2mm for shoe uppers. Due to the coarseness
of the corium fibres and the compactness of their
weave, the leather tends to have a heavy handle and
to lack drape. Consequently cattle skin is rarely used
for clothing leather.
After splitting, the remainder of the corium forming
the flesh split is used in various ways. Some splits
are taken in the untanned state for the production of
sausage casings, but most are used for making coarse
suede leather, the split surface being abraded to form
the suede nap. Due to the large size of the corium
fibres the nap raised is coarse and less suited to fashion
footwear or clothing. Generally flesh splits are made
into coarse suede shoes and boots or industrial gloves.
The fibre structure of leather 13
Figure 3.3 Cross-section of leather made from mature cattle hide.
3.2.2 Calfskins
A calfskin is a miniature version of the adult cattle
skin. The proportion of grain layer to total thickness
is similar (approximately one sixth) but the skin
thickness and fibre bundle size are dependent on the
age of the animal, both increasing with age.
The skin of a young calf aged 1 month (Figure 3.4)
is about 1mm thick and 0.5 to 0.7m2
in area. The
corium fibre bundles are fine and interweave compactly
at a medium angle.
The skin of an animal aged 6 months is about
1.3mm thick and 1m2
in area, the corium fibre
bundles are thicker and interweave at a higher angle
than in the younger animal.
At 12 months, when the calf is almost fully grown,
the skin will be about 3mm thick and with an area
of 2.7m2
. At this stage the fibre structure closely
resembles that of the mature animal.
A young calfskin yields a leather which although
only 1mm thick, is strong due to the compact interweaving
of the fine corium fibre bundles and the
grain surface is extremely fine. This makes the
leather ideally suited to fashion footwear, handbag,
bookbinding and fine case leathers. Calf leather is
unsuitable for clothing as the weave is too compact for
the softness and drape required from clothing leather.
3.2.3 Goatskins
These skins range between 1 and 3mm in thickness
and measure 0.5 to 0.7m2
in area. The grain layer
occupies about one third the total thickness (Figure
3.5). The hairs are a mixture of coarse and fine
straight hairs widely spaced through the grain layer.
This spacing allows for the smooth interweaving of
the corium fibres into the grain layer and there is no
discontinuity between the two layers. The corium
fibre bundles are relatively fine and interweave compactly
at a medium angle. This structure makes
goat leather highly suitable for shoe uppers and particularly
for bookbinding. The compactness of the
fibre structure makes the leather less suitable for
clothing leather as it lacks softness and drape. It is
only with very young kid skins that the fibre structure
is sufficiently open for the leather to be used in
gloving.
3.2.4 Sheepskins
There are several types of sheep, each with a different
skin structure.
The hair sheep, indigenous to tropical countries,
is a relatively small animal, yielding thin skins
(0.8mm) of 0.4 to 0.5m2
in area. The fine corium
14 Conservation of leather and related materials
Figure 3.4 Cross-section of leather made from young calfskin.
fibres interweave fairly compactly with no looseness
between the grain and corium layers. Such skins are
ideally suited for gloving.
In woolbearing sheep, native to Britain, the skins
are thicker (2 to 3mm) and 0.5 to 0.6m2
in area. To
accommodate the density of the wool fibres the
grain layer occupies at least half the total skin thickness
(Figure 3.6).
The density and curl of the wool fibres within
the grain layer limits the space through which the
corium fibres can interweave into the grain layer
and there is a tendency to looseness at the junction
between the two layers. In addition, natural fat tends
to be stored in a layer of fat cells at the junction
between grain and corium. These fat cells interrupt
the fibre weave still further and after the fat has been
removed during leather processing, the collapsed fat
cells add to the looseness in this region.
The corium fibres are fine and less compactly
interwoven than in the goat or calf skin. This allows
the leather to be softer and drapeable; qualities
required of clothing leather.
The coarse-woolled domestic hill sheep has a lower
wool density with less tendency to looseness at the
junction of grain and corium. These skins are primarily
used for grain or nappa clothing leather.
The fine-woolled sheep is best suited to the production
of woolskin clothing where the wool is
retained and the flesh surface of the skin is sueded.
For the production of chamois leather the grain
layer is split off and only the underlying corium layer
is used.
3.2.5 Deerskins
These skins range between 2 and 3mm in thickness
and measure 0.9 to 1.3m2
. The shallow grain
layer occupies one sixth the total thickness. The
corium fibre bundles are somewhat coarse and
rather loosely interwoven, yielding a leather that
tends to be stretchy. This property was well suited
to the production by oil tannage of buff clothing
leather.
3.2.6 Pigskins
Pigskins differ in structure from the other skins
described in that there is no distinct grain layer, the
hair penetrating the full thickness of the skin
(Figure 3.7). Throughout the skin the fibres interweave
in a particularly compact and distinctive basket
weave type of pattern, yielding a tight-structured
leather best suited for case leather and bookbinding.
The fibre structure of leather 15
Figure 3.5 Cross-section of leather made from goatskin.
16 Conservation of leather and related materials
Figure 3.7 Cross-section of leather made from pigskin.
Figure 3.6 Cross-section of leather made from woolled sheepskin.
The fibre structure of leather 17
The rather coarse grain surface pattern makes pig
leather less suitable for fashion footwear.
3.3 Grain surface patterns
When in processing the hairs are removed chemically
from the skin, the empty hair follicles at the grain surface
can be seen to be arranged in distinctive patterns,
characteristic of each animal type. For example, in
calfskin the follicles are of equal size and arranged in
regular rows (Figure 3.8). As the animal matures, while
the sizes of the follicles and the distances between them
increase, the overall pattern is maintained (Figure 3.9).
In goatskin there are regular alternating rows of
large and fine follicles (Figure 3.10) whereas in
woolled sheepskins the fine follicles are arranged in
groups (Figure 3.11).
Such follicle patterns can be used to identify the
animal origin of leather artefacts.
3.4 Suede surfaces
The fineness of nap that can be raised is determined
by the size of the constituent fibre bundles of the
skin. If the grain surface is sueded then the fine
fibrils of the grain surface yield a particularly fine
nubuck nap. Where the nap is raised on the split
corium surface of cattle skin the large corium fibre
bundles give rise to a coarse open nap. The naturally
finer corium fibre bundles of a goat or sheep permit
a finer nap to be raised at the flesh surface.
3.5 Variation in structure with location
in the skin
As the skin develops and has to adapt to meet the
demands of the animal in life, so the natural fibre
weave changes with location on the original animal.
Along the line of the backbone the skin is thickest
and the weave most compact and dense. These
backbone features are particularly marked in animals
with a mane such as goats.
In the central butt region which originally covered
the back of the animal, the fibre weave is particularly
compact with the fibres interweaving at a high angle.
In the belly region, the weave is looser with fibre
bundles running at a far lower angle of weave. These
structural differences result in the leather in the belly
region being weaker, softer and more stretchy. Due
to the looser weave in the belly the grain surface has
Figure 3.8 Hair follicle pattern of calfskin leather.
18 Conservation of leather and related materials
Figure 3.10 Hair follicle pattern of goatskin leather.
Figure 3.9 Hair follicle pattern of mature cattle hide leather.
a greater tendency to form coarse wrinkles when the
leather is flexed. The loosest weave is found in the
axillae regions.
These location differences in fibre structure are
common to most animal types.
3.6 Directional run of the fibres
The three-dimensional weave of the fibre bundles is
not random throughout the skin. There is, parallel
to the grain surface, a predominating direction in
which the majority of the fibres run (Figure 3.12).
This arises when the collagen fibrils are being laid
down in the developing foetus. The fibrils tend to
become aligned along the main lines of tension as
when the backbone lengthens and the legs extend.
The hairs’ growth follows the same lines.
This directional run profoundly affects the physical
properties of the skin and of the final leather. For
example, the strength of the leather is greater and the
extensibility less in the direction parallel with the
main run of the fibres. The reason for this is that
when measuring the strength of leather or skin, it is
standard practice to take the mean of two tests, one
made in the direction parallel to the backbone, the
other at right angles.
If the backbone line is not known then two tests
can be made: one parallel with the run of the hairs,
the other across the run of the hairs.
The directional run governs the way in which
leather is cut in use. Shoe uppers are cut, toe to heel,
in line with the backbone, the direction of greater
stretch. Similarly the bindings of books are cut with
the greater stretch along the spine of the book.
3.7 The influence of fibre structure on
leather properties, structure and tear
strength
The strength of a leather is dependent not only on
its total thickness but on the proportion that is
corium tissue and the frequency with which the
corium fibres interweave and cross over each other,
a prerequisite for strength.
To illustrate this point three leathers of lmm substance
are compared:
(a) A 1mm leather prepared from a young calfskin
where the full thickness of the original skin is
retained will have a grain layer of about 0.16mm
deep and the fineness of the corium fibres permits
frequent interweaving through the corium.
Such a leather will tear at about 8kg.
The fibre structure of leather 19
Figure 3.11 Hair follicle pattern of sheepskin leather.
(b) A 1mm leather produced from a woolled sheepskin
will have a grain layer of 0.5mm depth and
the corium fibres although fine will be more
loosely interwoven than in the calfskin. This
leather can be expected to tear at about 4kg.
(c) When an upper leather is prepared by splitting a
layer from a mature cattle skin the natural weave
is disturbed and the tear strength is highly
dependent on the depth of corium present. A
lmm leather split from a mature cattle skin may
have a grain layer as deep as 0.6mm. The large
size of the corium fibres restricts the frequency
with which they can interweave in the remaining
0.4mm of corium tissue. Such a leather will
have a tear strength of 3kg.
It is common practice in, for example, bookbinding
to reduce the substance of leather by paring away
corium tissue from the flesh side. In so doing the
reduction in leather strength will be far greater than
the reduction in substance. For example, a goat
binding leather that before paring measures 1.4mm
and tears at 7.5kg: after paring to 0.6mm the leather
would tear at about 1.2kg. The paring removes
almost all of the corium tissue but whereas the thickness
had been reduced by about a half, the strength
was reduced by five sixths.
3.8 Structure and leather handle
Although the tanner is bound by the natural structure
of the skin, his skill lies in bringing about, by
chemical and mechanical processing, limited
changes to the structure in order to produce a range
of leathers with differing properties.
For example, if in the final dry leather the processing
allows fine spaces to remain between the
fibrils and between fibre bundles, then the leather
will have a full, soft and flexible handle. Conversely
if the processing causes the fibrils and fibres to
adhere on drying, then the leather will be firmer
and far less flexible.
3.9 Fibre weave and movement
When fine spaces remain between fibrils and fibres
they are free to move over each other within the
20 Conservation of leather and related materials
Figure 3.12 Direction of fibre run through a skin.
fibre bundle and within the fibre weave as a whole.
This permits the leather to accommodate to stretching,
compression or creasing.
When a leather is stretched the angle of weave
falls and the structure becomes more compact.
Similarly if the leather is compressed the angle of
weave falls and the weave becomes more compact as
spaces within the structure are reduced.
If the leather processing has not allowed sufficient
spaces to remain within the fibre weave then on
stretching the leather, unable to accommodate to
the stress, will break and on compression the leather
will be cut.
One of the attractive features of leather is the fine
creasing of the outer grain surface that occurs when
leather is curved grain inwards. The folds in the
grain surface are formed by the underlying weave
being able to open out and extend into the fold or
to compress in the adjoining crease line.
The fineness of the surface folds also depends on
uniformity of structure throughout the leather. Any
change to a firmer or looser layer will create coarser
and unattractive surface folds. This is all important
when laminating leather. The backing material
needs to be equally flexible as the leather and the
method of bonding should not restrict movement
of the leather fibres, particularly the extension of
the flesh fibres. Failing in this can cause an unattractive
coarse wrinkling of the grain surface.
References
British Leather Manufacturers’ Research Association
(1957) Hides, Skins and Leather Under the Microscope.
Egham: BLMRA.
Haines, B.M. (1981) The Fibre Structure of Leather.
Northampton: The Leather Conservation Centre.
Haines, B.M. (1984) The Skin Before Tannage – Procter’s
View and Now. J. Soc. Leather Technologists and
Chemists, 68, 57.
Haines, B.M. (1999) Parchment. Northampton: The
Leather Conservation Centre.
Tancous, J.J. (1986) Skin, Hide and Leather Defects.
Cincinnati: Leather Industries of America.
The fibre structure of leather 21
4.1 Introduction
The chemical nature of collagen allows it to react
with a variety of agents, often resulting in its conversion
to leather (Covington, 1997), when the
putrescible material becomes resistant to microorganisms
– the definition of tanning. Untanned skin
can be very stable; witness the longevity of parchment.
However, when wetted and redried untanned
skin, even parchment, becomes hard and horny,
useless for most purposes. Part of the benefit of tanning
and lubricating leather is the ability to resist
fibre sticking upon drying. Of the changes in
appearance and properties that are a consequence of
tanning, one of the more important is the increase
in hydrothermal stability. This can be measured by
the conventionally measured shrinkage temperature,
Ts. Shrinking is a kinetic process and, as such,
can be treated thermodynamically. Such thermodynamic
studies indicate that breakdown of the tanning
interaction is not the cause of shrinking;
indeed 27
Al NMR studies demonstrate that even the
weak, hydrolysable aluminium tannage is not
reversed during shrinking (Covington et al., 1989).
22
4
The chemistry of tanning materials
A.D. Covington
G ϭ
O
HO
HO
HO
C
GO
GO
OG
OG
OG
O
G
G
G
O
HO
OH
OH
C
O
HO
HO
O
C
G G ϭ
Figure 4.1 The structure of Chinese gallotannin (tannic acid).
The chemistry of tanning materials 23
The reaction which is manifested as heat shrinking
is a breakdown of the hydrogen bonding in collagen
or leather; that is, regardless of the tanning process,
the shrinking reaction is the same.
This begs the question: where does hydrothermal
stability come from? That is, if the tanning process
only modifies the shrinkage temperature, without
changing the shrinking mechanism, what causes the
Ts to rise? The answer may have something to
do with the size of the co-operating unit in the
shrinking process: the larger the unit, the slower are
the kinetics and the higher is the shrinkage temperature
(Covington, 1998). It has been found that the
size of the co-operating unit in raw collagen, with
shrinkage temperature 60°C, is 20 residues, but
aluminium- and chromium-tanned collagens with
shrinkage temperatures of 73 and 107°C have
co-operating units containing 71 and 206 amino
acid residues respectively.
The nature of these co-operating units is not clear;
they may function through the natural covalent
crosslinks and additional hydrogen bonding structure
elements in collagen, supplemented or modified by
the tanning effects of hydrogen bonding or covalent
reaction at polar groups on the amino acid side chains
or through multiple interactions at the peptide link
itself. It has universally been assumed that the stabilizing
effects of tanning reactions are founded in the creation
of new crosslinks, giving rise to new structure
within the collagen triple helix. However, recently
it has been proposed that stabilization is based on
modifying the structure around the triple helix
(Covington, 2001a). In raw collagen, this supramolecular
structure is bound water, nucleated at the
hydroxyproline moieties in the amino acid sequence
(Berman et al., 1995). Tanning reactions change the
water matrix, causing it to confer different degrees of
stability, which depend on the nature of the interactions
between the matrix and the triple helix
(Covington and Song, 2003). It is the ability of tanning
agents to fit into or displace the water structure
and bind the matrix covalently to collagen that
affects the magnitude of the change in the shrinkage
temperature of the collagen. Thus, tanning reactions
may be highly complex on the molecular level.
Current tanning technology is dominated by
chromium; it was introduced about 130 years ago
and by the turn of the nineteenth century had begun
to replace the traditional tannages, which were based
on plant polyphenols (so-called vegetable tannins).
Today, about 90% of the world’s leather production
is chrome tanned, the remainder is tanned with vegetable
tannins, mostly for leathergoods or shoe soles.
The range of options available to the modern tanner
will now be considered.
4.2 Vegetable tanning
Many plant materials contain polyphenols which
can be used in tanning. To be effective, the molecular
mass must be in the range 500 –3000; lower
molecular mass fractions in the tannin are referred
to as non-tans and higher molecular mass species are
gums, which are sugar complexes with polyphenols.
The properties that vegetable tannins confer to the
leather are as varied as the many sources from which
they are obtained. Tannins are classified as follows:
hydrolysable or pyrogallol tannins, subclassified as
gallotannins (examples are Chinese gallotannin or
tannic acid, sumac, tara) or ellagitannins (examples are
myrabolam, chestnut, oak) and condensed or catechol
tannins (examples are mimosa, quebracho, gambier).
Hydrolysable tannins are sugar derivatives, based
on glucose, but may contain larger polysaccharides.
Gallotannins are characterized by glucose esterified
by gallic acid (Figure 4.1), where esterification may
occur directly with the glucose ring or as depside
esterification of bound gallic acid.
Ellagitannins have sugar cores, esterified not only
with gallic acid, but also with ellagic acid (Figure
4.2) and chebulic acid (Figure 4.3).
O
O
O
O
C
C OH
HO
HO OH HO
HOHOOC
COOHHO OH
OH
OH
Figure 4.2 The structure of ellagic acid.
Examples of the structures of hydrolysable tannins
are chebulinic acid (Figure 4.4), chebulagic acid
(Figure 4.5) from myrabolam or vescalagin and castalagin
(Figure 4.6) from chestnut.
The presence of the trihydroxyphenyl moiety
gives this group its name, the pyrogallol tannins.
Hydrolysable tannins typically raise the shrinkage
temperature of collagen to 75–80°C. The presence
of the trihydroxy group allows complexation with
metal ions, to make so-called semi-metal tannage.
The remarkable property of the reaction is that the
shrinkage temperature is raised as high as 120°C.
Many metals exhibit this effect, but the preferred
salts are aluminium(III), see below.
As the name suggests, these tannins tend to break
down by hydrolysis, depositing the esterifying acids in
the fibre structure of the leather; this is called ‘bloom’.
Because of the presence of so many hydroxy groups in
the hydrolysable tannins, they are highly reactive
(astringent) as tanning agents. Advantages of this class
of polyphenols are that they can be pale coloured, e.g.
24 Conservation of leather and related materials
HOOC
HOOC COOH
OH
O
OH
OH
O
Figure 4.3 The structure of chebulic acid.
HO
HO
HO
HO
HO
HO
HO
HO
HO
COO
COO
COOH
CO
O
OOC
OOC
OH
OH
OH
CH
CH
HC
HC
HC
COO CH2
O
Figure 4.4 The structure of chebulinic acid.
HO
HO
HO
HO
HO
HO
HO
HO
HO
COO
COO
COOH
CO
O
OOC
OOC
OH
OH
OH
CH
CH
HC
HC
HC
COO CH2
O
Figure 4.5 The structure of chebulagic acid.
The chemistry of tanning materials 25
tara, and they are typically lightfast, i.e. they do not
readily darken on exposure to light.
Condensed tannins are based on the flavonoid ring
system (Figure 4.7).
The A ring usually contains phenolic hydroxy
groups and the presence of the C ring makes both
rings reactive to forming carbon-carbon bonds, to
create flavonoid polymers: the B ring does not
exhibit the same reactivity, it often contains the
dihydroxyphenyl moiety, hence the alternative
name for this group of compounds is the catechol
tannins. The flavonoid structure can be hydroxylated
in different ways, giving rise to different types
of polyphenols: the more common patterns are
shown in Figure 4.8.
In nature, the commonest classes are the procyanidins
and the profisetinidins. The dihydroxy
group in the B ring is not reactive towards metal
salts, so these tannins do not undergo the semimetal
process. The very much less common prodelphinidins
and prorobinetinidins can form semi-metal
complexes and consequently produce high shrinkage
temperature.
The condensed tannins are illustrated in the structures
of mimosa (Figure 4.9) and quebracho (Figure
4.10) tannins.
The condensed tannins do not undergo hydrolysis,
instead they may deposit a precipitate, an aggregate
of polyphenol molecules, called ‘reds’ or
phlobaphenes. Unlike the hydrolysable tannins, the
HO OH
C C
O OO
H2C
R2
R1
O
O
O
OC CC
HO OH
HO OH HO OH
OH
HO OH
R1 ϭ H, R2 ϭ OH, castalagin
R1 ϭ OH, R2 ϭ H, vescalagin
O
O O
HO OH
HO OH
Figure 4.6 The structures of chestnut tannins.
A C
O
B
Figure 4.7 The flavonoid ring system of condensed
polyphenols.
Procyanidin
OHO
HO
OH
OH
OH
Profisetinidin
OHO
OH
OH
OH
Prodelphinidin
OHO
HO
OH
OH
OH
OH
Prorobinetinidin
OHO
OH
OH
OH
OH
Figure 4.8 Hydroxylation patterns for classes of condensed tannins.
26 Conservation of leather and related materials
condensed tannins redden markedly upon exposure
to light; this is understandable in terms of their
linked ring structure, conferring the ability to
undergo oxidative crosslinking. Condensed tannins
typically raise the shrinkage temperature of collagen
to 80 –85°C.
All vegetable tannins react with collagen primarily
via hydrogen bonding at the collagen peptide
links (Figure 4.11), but it is known that polyphenols
also fix to amino and carboxylic acid groups on side
chains (depending on pH).
Condensed tannins have an additional mechanism
for reaction: it has been suggested that this additional
interaction is a covalent reaction between the protein
and aromatic carbon in the tannin molecules via
quinoid structures and this more stable interaction
with collagen would account for the higher shrinkage
temperatures achievable by these vegetable tannins.
The presence of hydroxyl groups in the flavonoid ring
system makes the A ring susceptible to reaction with
aldehydic agents (see below). This means they can be
crosslinked in a way analogous to metals crosslinking
hydrolysable polyphenols and similarly the combination
tannage produces the same high shrinkage temperature.
The catechol B ring plays no part in the
reaction, but a pyrogallol structure in the B ring is
reactive like the A ring and contributes to the effectiveness
of the reaction.
HO
HO
R
HO
OHO
OH
OH
HO
O
OH
OH
OH
R
OH
OHHO
OH
R
R O
O
HO
OH
HO
n
OH
R O
HO
OH
Figure 4.9 The structure of mimosa tannin, a commercial tannin, with an uncommon prorobinetinidin structure.
The chemistry of tanning materials 27
4.3 Mineral tanning
A review across the Periodic Table of the tanning
effects of simple inorganic compounds reveals that
many elements are capable of being used to make
leather. But, if the practical criteria of effectiveness,
availability, toxicity and cost are applied, the number
of useful options is much reduced. In all cases,
the benchmark for comparison is tannage with
chromium(III), when Ts Ͼ 100°C is easily achieved,
it is readily available, it is relatively cheap and there
are minimum associated health hazards or environmental
impact.
From the Periodic Table: Groups 1, 2, 6, 7, 8 do
not tan, in Groups 3, 4, 5 elements of the first
period do not tan. The remainder have weak tanning
powers, but only elements of the second period
are of practical interest: of those, aluminium has the
best effect, silicates and polyphosphates have auxiliary
functions in tanning. From the transition elements
only titanium(III) or (IV), zirconium(IV),
chromium(III) and iron(III) have practical possibilities.
The lanthanides, as individual elements or
mixtures, have moderate tanning properties, but no
greater than any alternative in the transition periods.
The actinides are ruled out.
So, in the whole Periodic Table there are only
five elements plus the lanthanides that might find
application in tanning, but only four of those play a
significant role in the modern industry.
4.3.1 Chromium(III) salts
There is a fortuitous coincidence of reactivities in
chrome tanning. The reaction between the tanning
material and the collagen molecule occurs at ionized
carboxy groups: aspartic and glutamic acid side
chain carboxys have pKa values of 3.8 and 4.2 respectively,
providing a reaction range at pH 2–6.
Chromium(III) forms basic salts in the range pH 2–5,
although in practice the useful range is pH 2.7–4.2.
OHO
HO
OH
OH
OH
R
OHO
HO
OH
OH
OH
R
n
OHO
HO
OH
OH
OH
R
Figure 4.10 The structure of quebracho, a typical
profisetinidin tannin.
HO
O O
O
H H
H
H
N
H
C
O
␦Ϫ
O
␦Ϫ
␦ϩ␦ϩ ␦ϩ ␦ϩ
O
␦Ϫ
O
N C CH N C CH N C CHCH
OH
H H HR1 R2 R3 R4
H
O
␦Ϫ
O
OH
Figure 4.11 Model of hydrogen bonding between polyphenols and peptide link in protein.
28 Conservation of leather and related materials
Cr
H2O
H2O
H2O
SO4
OH2
OH2
Cr
H2O
H2O
H2O
SO4
OH2
OH
Hϩ
4ϩ
Cr
H2O
H2O
H2O
H2O H2OOH2 OH2
OH2
OH2
H
O
O
H
Cr
OH2 OH2H
O
O
H
Cr
H2O
H
O
O
H
Cr
ϩ
ϩ
hydrolysis or
olation
basification
basification
50% basic chromium(III)
OH2
OH2
2ϩ
Cr
H2O
H2O
H2O
O
H
O
O
H
S
Cr
OH2
O
OO
hexaquo-µ-dihydroxy-µ-sulphato
dichromium (III)
Figure 4.12 The changes in chromium(III) species during basification.
In that useful range, the number of chromium atoms
in the molecular ion increases from 2 to 4 and the
availability of ionized collagen carboxyls increases
from 6 to 47% of the total number. Chrome tanning
is usually initiated at pH 2.5–3.0 using 33% basic
chromium(III) sulphate. During the course of the
tanning process, the pH is raised to 3.5–4.0, causing
both the number of reaction sites on collagen to
increase and the chrome species to increase in size.
Starting the process under conditions of low reactivity
of both collagen and chrome favours fast penetration
of chrome into the substrate, but slow
reaction; increasing the pH increases the reactivity
of the collagen, although not the reactivity of the
chrome (Covington, 2001a), resulting in reduced
penetration rate. Chrome fixation is accelerated by
elevated temperature and pH: in general the higher
the chrome content of the leather, the higher the
shrinkage temperature, although the industrial
requirement is to achieve the highest shrinkage
temperature from the least amount of chrome. To
obtain a continuing balance between reaction rate
and penetration rate is part of the tanner’s art: this is
not simple, especially if the skin is thick.
The chemistry of chrome tanning is essentially
based on the formation of co-ordination compounds
and the changes that occur in chrome species are
complex. The formation of olated species was first
suggested by Bjerrum. Co-ordinated sulphate is
present in the solid tanning salt, but it is rapidly
hydrolysed in solution: it plays no part in the bound
complex, but it is an important component in stabilizing
the tanning matrix (Figure 4.12) (Covington
2001b; Covington et al., 2001).
It has been generally assumed in leather science
that the reaction which determines the powerful
tanning effect and high hydrothermal stability
conferred by chromium(III) is through crosslinking
at the carboxylate side chains. Indeed, Gustavson
(1953) claimed to calculate that about 10% of bound
The chemistry of tanning materials 29
chrome is reacted in this way. However, the argument
has been shown to be flawed and incorrect. Recent
research has indicated that crosslinking does not
need to be invoked as the mechanism of chrome
tanning (Covington and Song, 2003).
The co-ordination of ligands to chromium(III) to
modify the properties of the salt is routinely exploited
as ‘masking’. Monodentate ligands, especially formate,
may be applied at different ligand-to-metal ratios, taking
up co-ordination sites and hence reducing the
reactivity, increasing the ability to penetrate hide. In
addition, such masking can increase the pH at which
the salt precipitates; in these circumstances the final
pH of the tannage may be elevated beyond that of
unmasked tannage, thereby enhancing the reactivity
of the collagen. In this way, the reaction rate can be
accelerated, but without the same effect of increasing
the size of the chrome species, which hinders penetration.
Masking with bidentate ligands, capable of
crosslinking chromium ions, causes an increase in
molecular size and changes the hydrophilic–lipophilic
balance of the complex. Dicarboxylates containing
two or more methylene groups perform this function:
phthalate is the salt of choice, when the mechanism of
enhanced fixation depends on making the complex
more hydrophobic, weakening the hydrating effect of
the solvent, therefore driving the complex onto the
collagen. Whichever masking salts are used, they are
usually added to the tanning bath: this means the
masking reaction proceeds at the same rate as the tanning
reaction, and because the reactions are identical,
both are the formation of carboxy complexes with
chromium(III).
Chrome-tanned leather is highly versatile, largely
due to the low level of tanning agent needed to
achieve the desired stability. This means that the variety
of retanning materials which might be applied to
the part-processed leather can produce a wide range
of final products. Indeed, from any one chrometanned
cattle hide, it is possible (at a pinch) to produce
a sole leather or combat boot upper leather or
softee shoe upper leather or upholstery leather or
garment leather, all as full grain or suede.
4.3.2 Aluminium(III) salts
The use of potash alum in leathermaking is almost as
old as leathermaking itself; it occurs in nature and it
is known that the Egyptians used it 4000 years ago,
because written recipes survive. Throughout tanning
history, alum was often used in conjunction
with vegetable tannins, typically to enhance the
colouring reactions, in which the natural dyes would
form intensely coloured lakes with the basified metal
species.
Used by itself, alum interacts only weakly with
collagen, scarcely raising the shrinkage temperature
and having little leathering effect. However, in a mixture
of water, salt, flour (to mask the aluminium ion
and fill the fibre structure) and egg yolk (the lecithin
content is an effective lubricant), skin can be turned
into a soft, white, leathery product, traditionally used
in the past for gloving. But, even in this case, the
shrinkage temperature is not raised (hence, it is possible
to discriminate between leathering and tanning)
and the aluminium salt can be washed out of the
leather if it gets wet; for these reasons, this process is
called ‘tawing’, to distinguish it from tanning.
The reaction sites for aluminium(III) are the collagen
carboxyls, but unlike chromium(III) to which
it bears a superficial resemblance in a tanning
context, aluminium(III) does not form defined basic
species nor does it form stable covalent complexes
with carboxy groups; that interaction is predominantly
electrovalent, accounting for the ease of
hydrolysis. The reaction can be optimized for tanning
by modifying aluminium sulphate with masking
salts, such as formate or citrate, and basifying the tannage
to pH 4, close to the precipitation point. In this
way, reversibility of tannage is minimized and shrinkage
temperatures as high as 90°C can be achieved.
Basic aluminium(III) chlorides are also well known in
leathermaking and several commercial tanning formulations
are available. As solo tanning agents, they
are slightly superior to salts based on the sulphate.
However, the leathering effect of aluminium(III) is
inadequate, producing firm leather, which may dry
translucent due to the fibre structure resticking.
Therefore, as tanning agents, aluminium(III) salts
have limited value.
4.3.3 Titanium(IV) salts
In tanning terms, titanium(IV) salts are slightly superior
to Al(III). Empirically, the chemistry is dominated
by the titanyl ion TiO2ϩ
but the actual species
are chains of titanium ions bridged by oxygen atoms.
However, the co-ordinating power is weak with
respect to carboxy complexation, so the interaction
is more electrostatic than covalent.
The traditional use for titanium(IV) in tanning
was in the form of potassium titanyl oxalate, to retan
vegetable-tanned leather for hatbanding, a product
for which demand fell away in the latter half of the
twentieth century. Titanium solo tanning is only
moderately effective, because large quantities are
30 Conservation of leather and related materials
required to achieve the highest shrinkage temperatures,
ϳ90°C, and this causes the leather to be overfilled,
although remaining soft. An advantage of
tanning with titanium(IV) is that it is a colourless
tannage and therefore makes white leather. Hence,
it has found application in tanning sheepskins with
the wool on for rugs.
4.3.4 Zirconium(IV) salts
The development of zirconium tannage is relatively
recent but it soon gained industrial acceptance.
From its position in the Periodic Table, Zr(IV)
might be expected to display similar tanning properties
to Ti(IV). The tanning power exceeds that of
Al(III) and Ti(IV), but in no way matches Cr(III).
While the tanning effects of Zr(IV) and Ti(IV) are
similar, the chemistries of their salts are different.
Zirconium(IV) salts are characterized by eight coordination
and high affinity for oxygen, resulting in
a tetrameric core structure (Figure 4.13); the basic
unit of structure is four Zr ions at the corners of a
square, linked by diol bridges, above and below the
plane of the square.
By hydrolysis or basification, the tetrameric units
can polymerize, by forming more diol or sulphato
bridges. In this way, zirconium species may be
cationic, neutral or anionic and large ions can
form. So, tanning may involve all the polar side
chains of collagen, those bearing carboxy, amino or
hydroxy groups. Hydrogen bonding via the
hydroxy groups in the Zr(IV) species is an important
feature of the tanning reaction; together with
the filling effect by the big molecules, the overall
tanning effect is somewhat similar to tanning with
plant polyphenols, hence zirconium tanning has
been referred to as the inorganic equivalent of vegetable
tanning.
4.4 Oil tanning
The familiar wash leather (chamois or ‘chammy’) is
tanned with unsaturated oil and the preferred agent
is cod liver oil. Useful tanning oils contain fatty
acids, either free or as glyceride derivatives, which
are polyunsaturated. The degree of unsaturation is
critical, because if there is too little unsaturation the
oil will not oxidize readily and therefore function
only as a lubricant, if there is too much unsaturation
the oil will crosslink itself and harden with oxidation,
like linseed oil.
In this tannage, dewoolled (fellmongered) sheepskins
are processed in the normal way to the pickled
state, when they are then swollen by the osmotic
effect in water, so they can be split more easily. The
flesh splits are then treated with the cod oil in rotating
drums. Blowing warm air into the vessel serves
two functions; the skins are dried a little, to aid oil
penetration, and autoxidation of the oil is initiated,
which is the basis of the process.
The actual nature of the tannage is not known,
except for the following observations (Sharphouse,
1985):
1. The unsaturation of the oil decreases as the
process progresses.
2. Peroxy derivatives are formed.
3. Hydroxy function appears.
4. Acrolein, CH2¨CH.CHO, is produced.
It is thought that the tannage may be due in part to
an aldehydic reaction and to polymerization of the
oil; the presence of the latter effect could account for
the difference between the characteristics of oil- and
aldehyde-tanned leathers. The situation is further
complicated by the observation that oil tanning
hardly raises the shrinkage temperature of collagen;
so oil tanning is a leathering process rather than a typical
tanning process, based on the accepted criteria of
tanning. This is an extreme form of a stabilizing
matrix, relying for its effect on physical rather than
chemical interaction with the triple helix. It also has
unusual consequences.
The most remarkable feature of oil-tanned leather
is its hydrophilicity, surprising considering the
chemical nature of the tanning agent. A well-tanned
chamois leather is expected to take up at least 600%
water on its dry mass and to be hand wrung to 180%.
Also this must be repeatable after drying. In use, no
grease must be exuded to cause smearing. The
hydrophilicity probably arises from the effect of the
matrix, holding the hydrophilic protein structure
apart, allowing it to absorb a lot of water. Another
4ϩ
Zr
HO
HO OH
(H2O)3
H
O
O
H
Zr
OH
HO OH
(H2O)3
Zr
HO
(H2O)3
H
O
O
H
Zr
OH
(H2O)3
Figure 4.13 The structural unit of basic zirconium(IV).
strange property is the Ewald effect, in which heat
shrunk leather will regain about 80% of its dimensions
if plunged into cold water. This presumably
can happen because the matrix allows the separated
chains to reregister. The phenomenon has been
exploited to mould oil-tanned leather into required
shapes, sometimes called tucking.
A synthetic version of oil tanning is to use a
sulphonyl chloride which reacts predominantly
with the amino groups on collagen:
Collagen¶NH2 ϩ C16H33SO2Cl →
Collagen¶NH¶SO2C16H33 ϩ HCl
Clearly this cannot be a crosslinking reaction, so
it is not surprising that the shrinkage temperature is
not raised by this tannage, but there is a powerful
leathering effect and the product exhibits similar
properties to oil-tanned leather.
It was pointed out that acrolein is produced during
the oil tanning reaction: indeed, acrolein itself can be
used to make a product similar to oil-tanned leather.
But, although it is not used itself for this purpose (for
toxicity reasons) it is used indirectly, as a component
of wood smoke. The traditional method of preserving
hides and skins used by the plains dwellers, such as the
Native Americans and the Mongols, is to use brains
tanning. In this process, the animal brain is partly
cooked in water, so it can be mashed into a paste,
which can be worked into the pelt. The leathering
effect turns the skin to a soft, open-structured leather,
buckskin, largely due to the lubricating power of the
phospholipids of the brain. The Sioux Indians have a
saying, ‘every animal has enough brains to tan its own
hide’. The leathering effect is serviceable, as long as
the pelt is not rewetted, because then it will harden on
drying due to the fibres resticking. To make the
leather resistant to wetting, the solution is to smoke it
over a wood fire; the multiplicity of free radical and
other reactions does not adversely affect the handling
qualities and the tannage is made permanent.
4.5 Aldehyde tanning
4.5.1 Formaldehyde tanning
The archetypal aldehyde tannage is with formaldehyde,
probably most familiar in preserving biological
specimens or in embalming. Reaction occurs primarily
at amino groups, shown empirically as follows:
Collagen¶NH2 ϩ HCHO →
Collagen¶NH¶CH2OH
The N-hydroxymethyl group is highly reactive
and crosslinking can occur at a second amino group:
Collagen¶NH¶CH2OH ϩ H2N¶Collagen →
Collagen¶NH¶CH2¶HN¶Collagen
In this way, the shrinkage temperature can typically
be raised to 80 –85°C. However, the crosslinking is
relatively inefficient, probably because the formaldehyde
species are not monomeric, as shown in the
equations. Among the species formed in solution is
paraformaldehyde, HOCH2(CHOH)nCHO. The
presence of polyhydroxy species and their reaction
with skin produces a white, spongy, hydrophilic
leather, although the absorptive property of oil-tanned
leather is not matched.
4.5.2 Glutaraldehyde tanning
Of the many mono- and multifunctional aldehydes
which might be used for tanning (and all can be made
to work), only glutaraldehyde and its derivatives
have found commercial acceptance, with the possible
exception of the more expensive starch dialdehyde.
There would appear to be a number of possible
tanning reactions of glutaraldehyde: the crosslinking
options seem wider than for simple aldehydes, but the
result is the same, a maximum shrinkage temperature
of 85°C, because in the same way that formaldehyde
is not a simple species in solution, glutaraldehyde can
form polymerized species (Figure 4.14).
The terminal hydroxy groups of the polymer are
active and capable of reacting with amino groups.
The polymer itself can interact with the collagen
peptide links by hydrogen bonding via the alicyclic
oxygens and so the leather is given its spongy,
hydrophilic character.
Tanning with glutaraldehyde itself confers a
yellow–orange colour to the leather, which is undesirable.
Several attempts have been made to modify the
chemistry, to prevent colour development, including
making the monobisulphite addition compound or
hemiacetals, but none has been totally successful.
4.5.3 Oxazolidine tanning
An alternative to aldehyde tanning, but which retains
the essential reactions, is to use oxazolidines, reported
about 20 years ago. These compounds are alicyclic
derivatives of an amino alcohol and formaldehyde.
Under hydrolytic conditions, the rings can open, to
form an N-hydroxymethyl compound which can
react with one or more amino sites, in an effective
though acridly odiferous tannage (Figure 4.15).
The chemistry of tanning materials 31
32 Conservation of leather and related materials
4.6 Syntans
The term syntan means synthetic tanning agent. This
class of tanning agents was introduced early in the last
century, with the purpose of aiding vegetable tanning,
although the range of reactivities currently available
means that they may serve several different functions.
They are classified into three types, according to their
primary properties. This can be expressed diagrammatically,
as relative trends in properties (Figure 4.16).
4.6.1 Auxiliary syntans
These compounds are frequently based on naphthalene
and are synthesized by the ‘Nerodol’ method,
i.e. the base material is sulphonated to a high degree
and then polymerized, typically by formaldehyde
(Figure 4.17); the products are usually relatively
simple chemical compounds.
The presence of the sulphonate groups means
that these compounds can interact strongly with the
amino side chains of collagen at pH Ͻ 6:
Collagen¶NH3
ϩ
---Ϫ
O3S¶Syntan
In this way, reaction sites for vegetable tannins can be
blocked (see vegetable tanning) promoting penetration
through the hide cross-section. At the same time,
they serve to solubilize the aggregated phlobaphenes
H2C CH2
CH2
C C
H HO O HO OHO
H2C CH2
CH2
CH CH
HO OO
H2C CH2
CH2
CH CH
OHO
H2C CH2
CH2
CH CH
O
n
O
H2C CH2
CH2
CH CH
Figure 4.14 The reactivity of glutaraldehyde.
4,4-dimethyl-1,3-
oxazolidine
5-(ethyl or hydroxyethyl)-
1-azo-3, 7-dioxabicyclo
(3,3,0) octane
1,3-dihydroxy-2-(ethyl or
hydroxyethyl)-2-N, N-di
(hydroxymethyl) propane
CH3
CH2
CCH3 CH2
HN O
R
CH2
CH2C
H2C
CH2
N OO
R
CH2OH
CH2C
HOH2C
CH2
N OHHO
Figure 4.15 The structures of oxazolidines.
The chemistry of tanning materials 33
of condensed tannins, thereby reducing reaction with
the hide surfaces.
4.6.2 Combination or retanning syntans
These syntans are usually based on simple phenolic
compounds, they are synthesized by the ‘Novolac’
method, i.e. the base material is polymerized, typically
with formaldehyde, and then the product may
be partially sulphonated (Figure 4.18).
The products are more complex than the auxiliary
syntans, having higher molecular masses, and may
be crosslinked in two dimensions. Their enhanced
tanning functionality means that they can confer
hydrothermal stability and their larger molecular size
means that they can have a filling effect. Because they
are relatively small polymers, with consequently weak
tanning power, these syntans work best as retanning
agents; they are applied after main chrome tannage, to
modify the handling properties of the leather.
4.6.3 Replacement syntans
By increasing the tanning power of syntans, the
agents may be classified as replacement syntans, by
which it is meant that they could replace vegetable
tannins. These syntans can be used for solo tanning,
because their properties of tanning are comparable
with plant polyphenols. Again, there is no clear
distinction between the retanning syntans and
the replacement syntans, the difference lies in the
degree of the effects. Base materials for syntans can
range from the simple to the relative complicated
(Figure 4.19).
Nerodol synthesis
auxiliary syntans
Novolac synthesis
replacement syntans
Spectrum of syntan structure
increasing astringency
increasing molecular weight
increasing phenolic hydroxyl content
increasing [hydroxyl] to [sulphonate] ratio
increasing sulphonate content
retans
Figure 4.16 Classification of syntans.
SO3H
SO3H
SO3H
H2SO4
CH2
HCHO
Figure 4.17 The Nerodol synthesis of syntans.
34 Conservation of leather and related materials
In addition, the bridging groups may be more
diverse, including dimethyl methylene, ether, and
urea. They rely less on sulphonate groups for their
reactivity, but synthesis by the Novolac method may
incorporate some sulphonic acid functionality.
The replacement syntans vary in their effects on
leather, but can produce properties similar to vegetable
tannins, including raising the shrinkage temperature
to 80 –85°C. They are still used to prepare
hide to receive vegetable tannins, though they can
be used in their own right, to make leather that is
more lightfast than vegetable-tanned leather; a
common use is for making white leather.
4.7 Overview
Leathermaking has traditionally been viewed as a
craft, often as a dark art. That has changed. Since the
early part of the twentieth century, leather science
has had an increasing impact on the understanding of
the processes involved in the preparation of hides
and skins for leather and the subsequent tanning
reactions, followed by retanning, dyeing, lubricating,
drying and finishing the leather.
It is clear that the deeper our understanding is
of the scientific principles that underpin the
technologies involved in leathermaking, the better
will be our potential to conserve leathers and to
improve leathers of the future. Improvements in the
environmental impact of tannery operations and in
the performance of the products will ensure the
continued place of leather in the range of modern
materials.
References
Berman, H.M., Bella, J. and Brodsky, B. (1995) Hydration
Structure of a Collagen Peptide. Structure, 3(9), 893.
CH2
H2SO4
SO3H
n
HCHO
OH OH OH
CH2
OH
CH2
n
OH
SO3H
OH
CH2
OH
Figure 4.18 The Novolac synthesis of syntans.
OH
2-naphthol 4,4Ј-dihydroxy diphenyl sulphoneresorcinol
OH
OHHO
OH
S
O
O
Figure 4.19 Examples of base materials for replacement syntans.
The chemistry of tanning materials 35
Covington, A.D. (1997) Modern Tanning Chemistry.
Chem. Soc. Rev., 26(2), 111.
Covington, A.D., Hancock, R.A. and Ioannidis, I.A. (1989)
Novel Studies on the Mechanism of the Aluminium
Tanning Reaction. Proc. IULTCS Congress, Philadelphia,
USA.
Covington, A.D. (1998) New Tannages for the New
Millennium. Amer. Leather Chem. Assoc., 93(6), 168.
Covington, A.D. (2001a) Theory and Mechanisms of
Tanning: Current Thinking and Future Implications.
J. Soc. Leather Technol. Chem., 85(1), 24.
Covington, A.D. (2001b) Chrome Tanning Science.
J. Amer. Leather Chem. Assoc., 96(12), 467.
Covington, A.D. and Song, L. (2003) Crosslinking? What
Crosslinking? Proc. IULTCS Congress, Cancun, Mexico.
Covington, A.D. et al. (2001) Leather Tanning Studies
Using Extended X-ray Absorption Fine Structure.
Polyhedron, 20, 461.
Gustavson, K.H. (1953) Uni- and Multipart Binding of
Chromium Complexes by Collagen and the Problem of
Crosslinking. J. Amer. Leather Chem. Assoc., 48(9), 559.
Sharphouse, J.H. (1985) Theory and Practice of Modern
Chamois Leather Production. J. Soc. Leather Technol.
Chem., 69(2), 29.
5.1 Introduction
This chapter describes the mechanisms of leather
deterioration. Not just the changes in the material
and the causes of deterioration but how and where,
in the chemical make-up of the leather, the deterioration
occurs. To understand the mechanisms of
deterioration two components must be known: first,
the agents of deterioration and their environmental
parameters for reactivity and, second, the bonds in
the material where the deterioration occurs. This still
is not enough, as it only illustrates the potential reactions.
For the final analysis the deteriorated leathers
must speak for themselves.
Thus this chapter will start with a review of the
deteriorating agents. This will be followed by a discussion
of the reactivity of some of the various
chemical constituents within the leather structure,
and finally a review of the analyses of old, artificially
aged, and new leathers to determine what deteriorating
mechanisms have actually occurred.
Skin has survived under special conditions for centuries,
e.g. the ice man, the bog man, the Dead Sea
scrolls, and Egyptian mummies. What is common
in their environments that has allowed the skin to
survive is that all have been held in conditions that
have prevented deterioration, by either reduced
moisture, reduced temperature or astringent environments
and all without significant environmental
fluctuations. In all, the rates of reactions were
reduced either by too little or too much water or by
reduced temperature. It is important to note that all
were without light. As we proceed we will see the
significance of these environments to the deterioration
of leathers.
Leathers have a very complex mixture of chemical
structures. They vary according to the chemicals
used in hide pretreatment, the chemicals that occur
naturally in the tannin extracts that are used in the
tanning process and the chemicals used for the various
finishing operations. They also vary in the chemicals
they come into contact with in use and the
chemicals they absorb from their varying environments.
Basically what conservators have to deal with
is an active chemical reaction. Thus each type of
leather may have some specific mechanism of deterioration
because of its own particular make-up. But
because of the common denominator present in all
leathers, the collagen protein – the component that
gives it integrity – there must be many deterioration
mechanisms in common with all leathers. To make a
logical presentation, vegetable-tanned leather will
mainly be discussed because it presents the major
problems of leather deterioration and is the commonest
leather in heritage collections. Also the greatest
amount of research has been conducted on these.
Many of the same mechanisms of deterioration that
occur in vegetable-tanned leather also occur in
leathers of other tannages.
Over the past 20 years the major research into
the deterioration of leathers has been conducted by
the British Leather Confederation formerly the
British Leather Manufacturers’ Research Association
(BLMRA) in Northampton, UK; the Canadian
Conservation Institute in Ottawa, Canada; the
Leather Conservation Centre in Northampton, UK;
and by the co-operative work of the STEP Leather
Project Group in the European Community. The
published results of this co-operative work will be
discussed in this chapter. Much of the co-operative
work was carried out on the historical leather samples
from the British Long Term Storage Trials
(BLTST) started in 1935 as a source of naturally aged
vegetable-tanned leather (Haines, 1991a). These
36
5
The mechanisms of deterioration in leather
Mary-Lou E. Florian
The mechanisms of deterioration in leather 37
trials were undertaken using over 300 volumes
which were bound in leathers prepared in various
ways. Pairs of books bound with these leathers were
deposited for natural ageing, one in the British
Library in London, the other in the National Library
of Wales in Aberystwyth. The goal was to determine
if the sulphur dioxide present in the polluted air in
London, but not in Wales, was the cause of leather
deterioration. These samples are still being studied
with new scientific instrumentation in hopes of
understanding the causes and mechanisms of deterioration
on a physical and molecular level. These are
not the only naturally aged leathers used for research,
but they are still an excellent reference collection
because of the detailed documentation of the materials
and their environmental history. For more
information on the British Long Term Storage Trials
see BLMRA (1932, 1945, 1954, 1962, 1977).
At the Leather Conservation Centre in
Northampton, UK, much of the recent research on
leather deterioration, started in 1986, was done to
determine the effect of controlled environmental
conditions on artificially aged leathers of different
tannages (Calnan, 1991). The purposes were to find a
suitable leather for conservation treatments, define a
suitable environment for storage, evaluate conservation
treatments, and study the mechanisms involved
in ageing. Haines (1991b) and Chahine (1991)
extended the work to examine the role of the acidic
environmental pollutants, sulphur dioxide and nitrogen
dioxide, in the ageing of new leathers, by using
artificial ageing chambers at BLMRA and in France
respectively, which also allowed adsorption and desorption
studies to be undertaken (Chahine and
Rottier, 1997a).
The STEP project, which was started in 1991,
involved conservation and research laboratories in
Denmark, France, England, Holland, and Belgium.
The goals of the project were to identify and quantify
the chemical and physical changes which occurred
in historic and BLTST naturally aged vegetabletanned
leathers caused by environmental factors
including air pollution; to establish the parameters and
conditions of an artificial ageing method which will
bring about the same changes in new leathers as in
these naturally aged leathers and to establish a standard
test method to determine the resistance of new
leathers to artificial ageing and the effects of leather
conservation methods on this resistance.
Having the three sources of leather (naturally
aged historical samples, the BLTST leathers and
artificially aged leathers) the STEP Project, with the
expertise, knowledge and state of the art equipment
of the European participant institutions, was able to
do a comparative, comprehensive and detailed analysis
of the causes and mechanisms of deterioration of,
mainly, vegetable-tanned leathers.
It is difficult to know how to proceed without
putting the cart before the horse. Should the mechanisms
of deterioration be discussed before the
structure of leather or vice versa? In this chapter a
general overview of the agents and mechanisms of
deterioration will be considered first, followed by
an examination of the chemical structure of leather
and the relevant details that assist in the interpretation
of the actual analytical data from aged leathers.
5.2 Agents of deterioration
5.2.1 Introduction
For the past 150 years, leather chemists have been
speculating on the cause of leather deterioration.
The history of the interpretation of the deterioration
of vegetable-tanned leathers is reviewed in the literature
(Larsen, 1995; Haines, 1991a; Calnan, 1991).
From 1900 to the 1990s, many components of the
tannin/collagen complex and aspects of the environment
were considered as factors of deterioration.
In reviewing the literature on all aspects of the
deterioration of the tannin/collagen complex it is
apparent that there are two main causes, hydrolysis
and oxidation. These reactions are both influenced
by the environment within the leather, e.g. water,
heat, light, pH, gases, etc. Both may act in the
leather on the tanning materials and other chemicals
used in its fabrication, as well as on the amino acids
and peptides of the collagen protein. The two main
causes are, however, quite different in their mechanisms
and results. Recent studies have suggested
that the hydrolytic breakdown in vegetable-tanned
leather is chiefly due to the actions of sulphur dioxide
and nitrogen dioxides present in acidic air pollution
and that oxidative breakdown is due to the
effects of high energy radicals from light, oxygen,
oils, and the self-perpetuating reactions within the
altered internal chemical structure. It has been shown
that acid hydrolysis from acidic air pollution has an
inhibitory action on the oxidative decomposition of
collagen (Larsen, 1995).
Tanning agents themselves break down under
oxidative and acid hydrolytic conditions and the
breakdown products formed can promote both the
oxidative and hydrolytic breakdown of collagen.
Thus there are interactions on many levels.
The reactions of various deteriorating agents on
synthetic polymers are described by Reich and
Stivala (1971). Many of the reactions are similar for
protein polymers such as collagen.
5.2.2 Acid hydrolysis
Water in the liquid form contains a few molecules
that have formed positive hydronium (H3Oϩ
) and
negative hydroxyl (OHϪ
) ions. The hydronium ions
both act as hydrogen bond breakers and cause the
breaking of bonds within ionic structures. The
breakage of bonds by hydronium ions is termed
hydrolysis.
When an acid, e.g. hydrochloric acid (HCl), is
dissolved in water it dissociates to form hydrogen
ions (Hϩ
) and chloride ions (ClϪ
). The hydrogen
ions react with water molecules to form hydronium
ions (H3Oϩ
) which cause hydrolysis. When an
acid is involved in hydrolysis in this way it is called
acid hydrolysis.
Sulphuric acid in leather, originating from the
adsorption of sulphur dioxide from industrial air
pollution, is commonly considered as the primary
agent of acidic hydrolysis in historical leathers. In
sunlight, sulphur dioxide is transformed to sulphur
trioxide. The sulphur trioxide is adsorbed by tannins
in the leather. There it is hydrated into sulphuric
acid, which dissolves in the moisture present in
the leather producing active hydronium ions. These
hydronium ions, in turn, break the links between the
amino acids in the collagen polymer chain. It should
be noted that sulphuric acid is only one part of the
internal acidic environment in the leather. There are
organic acids and acidic breakdown products from
tannins and amino acids inherently present within
the structure which add to the hydrogen ion concentration
and acid hydrolysis potential.
The collagen protein is colloidal in that it does
not ionize in water but swells. A concentration of
hydronium ions in the water can break bonds selectively
within the polymeric structure leading to loss
of structural integrity. Ultimately this results in the
breakdown of the protein into a gelatin colloidal
solution. Heat, moisture and low pH increase the
rate of these hydrolytic reactions.
In synthetic poly films the rate of hydrolysis for a
given film thickness is dependent on the relative
humidity. This must also apply to leather. The water
in leather which is involved in chemical reactions is
the multilayer or free water (see section 5.2.6) which
moves in and out of the fibre structure as water
vapour with changes in relative humidity.
Although the most common form of hydrolytic
deterioration is acid hydrolysis, different hydrolytic
reactions can occur under acidic, basic or neutral
conditions.
5.2.3 Oxidation
5.2.3.1 Introduction
Oxidation involves the loss of electrons from, and an
increase in positive valence of, a chemical compound.
Often oxidation is described as a reaction in which
oxygen combines chemically with another molecule,
but there are many oxidation reactions where the loss
of an electron occurs in which oxygen itself is not
involved. When oxygen combines with other elements
it is the oxidizing agent, but when two compounds
react to cause a loss of an electron by one, the
substance which loses the electron is called an oxidizing
agent. Oxidation and reduction occur simultaneously
(redox reactions) with the transfer of electrons
between substances. The substance oxidized, the one
which gains in positive valence, loses electrons: the
substance reduced, the one which decreases in positive
valence, gains electrons.
Oxidation, the loss of electrons, can occur due to
the effects of oxygen, light, heat or the presence of
high energy free radicals.
5.2.3.2 Free radicals
(For details see Bernatek et al., 1961; Scott, 1965;
Eisenhauer, 1968; Reich and Stivala, 1971.)
5.2.3.2.1 Introduction
In most oxidative reactions free radicals are involved.
Radicals are highly reactive groups of atoms containing
unpaired electrons such as N., NO. or O2. (the
subscript point notates the odd electron). They may
be positively charged, negatively charged or neutral.
Their reactivity is influenced by temperature and by
chemical concentration.
The main reactions that produce free radicals
which are associated with leather deterioration are
caused by: radiation, which includes some visible
light as well as UV; air pollutants such as ozone,
nitrogen oxides, and sulphur dioxide; peroxides
from oxidizing agents; products of autoxidation of
lipids and charged amino acids and tannins and their
breakdown products. Heckly (1976) states that free
radicals are produced by a reaction between oxygen
and a variety of freeze-dried biological materials
including tissues and microorganisms. This has
38 Conservation of leather and related materials
relevance to leathers which have been freeze-dried.
He also reports that although heat denaturation
destroys the protein structure, the cofactors of biooxidation
remain undamaged, and they could still
react with molecular oxygen. This suggests that oxidation
can also occur in dry materials.
The great array of sources of radicals suggests that
they are possibly the most common cause of the
deterioration of organic materials and Pryor (1976)
considers that all oxidation of organic molecules
involves free radicals and intermediates. Examples
of each source will follow.
5.2.3.2.2 Light – photolysis, photoxidation
As mentioned in the introduction, the skin of the
bog man and mummies, etc. were in environments
without light. What is the importance of this?
The optical radiation spectrum extends from the
far ultraviolet through the visible region into the
near infrared, from the wavelengths of 200 nanometers
(nm) to about 1400nm (McNeill, 1992). The
bonds in macromolecules have energies between
300 and 500kJ moleϪ1
. Visible and infrared light have
energies too low to break these bonds, but ultraviolet
light with wavelengths lower than 400nm are sufficiently
strong to break them. In order for ultraviolet
light to cause photolysis, it must first be absorbed, this
requires a chromophore. Chromophores are present,
for example, in the red anthocyanins in condensed
tannins and in amino acids with aromatic side chains,
such as phenylalanine, tyrosine and tryptophane.
Ionizing radiation produces cationic radicals and
electrons as primary species and these decay and react
further to yield a host of charged and neutral reactive
free radicals. These radicals can undergo various electron
transfer reactions without oxygen, i.e. they can
transfer the energy to another molecule or dissipate
the energy by breaking the bonds or producing heat.
Usually the energy from visible light photons that
is absorbed by chemical compounds is reflected as
light energy or converted to heat energy. In light
sensitive materials, such as dyes, the energy causes
molecular changes, expressed as loss of colour. Most
polymers which are light sensitive at room temperature
will be below their glass transition temperature
(Tg). This is often equated with the shrinkage temperature
of collagen (Ts) (see section 5.6). In other
words, the shrinkage temperature of visible lightsensitive,
strongly deteriorated, hydrated collagen
can be as low as 20°C, whereas for normal undamaged
collagen it is around 65°C.
With polymers, photolysis is capable of cleaving
the C–C bonds in the backbone of the polymer
chain, and causing chain scission, crosslinking, and
the production of small molecular weight fractions,
including momomers (Reich and Stivala, 1971).
If oxygen is involved, the light reaction is called
photoxidation. This occurs when a photon which is
absorbed into a material reacts with an oxygen molecule
forming an activated oxygen free radical
which in turn reacts with water to form a peroxide
which is a strong oxidizing agent.
Photoxidation does extensive damage to polymers,
for example resulting in loss of mechanical strength,
embrittlement, cracking, crazing, solubility changes,
lowering of pH, and colour change. The causes
of this damage are chain scission, changes in the
amorphous/crystalline ratio, crosslinkage, density
change and the production of new functional groups
and acidic products. Analogous reactions occur to the
collagen protein chain.
5.2.3.2.3 Autoxidation of lipids
The oxidation of organic materials by self-perpetuated
radicals is called autoxidation.
In the process of manufacturing leather, a lubricant
is essential. In addition, during use, leathers are
commonly surface treated with dressings that contain
fats or oils. The most common fats and oils are
triglycerides, which are molecules made up of a
combination of one glycerol molecule to which are
attached three fatty acids. The fatty acids are either
saturated or unsaturated.
In saturated fatty acids each carbon atom is linked
to adjacent carbon atoms by a single bond and the
remaining two bonds are reacted with hydrogen
atoms. The saturated fatty acids commonly do not
combine with oxygen but will react under severe
conditions at a much slower rate than unsaturated
fatty acids.
In unsaturated fatty acids some of the carbon atoms
are linked by double bonds and each carbon atom is
attached to only one hydrogen atom. All unsaturated
fatty acids are particularly susceptible to oxidation.
The conversion of the unsaturated oils to a gummy or
hard surface is the result of autoxidation by a free radical
chain reaction (Mills and White, 1987). The free
radicals and peroxides formed in these reactions can
also oxidize adjacent proteins. This is a major problem
in the food industry where the reactions occur at
room temperatures and in materials with low moisture
content (Karel and Yong, 1981). They certainly
must be a source of free radicals in leather.
This reaction between lipids and molecular
oxygen increases with degree of unsaturation and
The mechanisms of deterioration in leather 39
in lipid autoxidation there are many complex reactions
involved and chain reactions may occur which
make them self-perpetuating. Oxygen, ozone, nitrogen
dioxide, sulphur dioxide and metals are potent
catalysts of autoxidation of unsaturated fatty acids.
5.2.3.2.4 Atmospheric pollutants – ozone, sulphur
dioxide, nitrogen dioxide and carbon dioxide
Ozone is a strong oxidizing agent. It is the most
reactive component of air pollutants. It can cause
main-chain scission in polymers. The concentration
of ozone in air, 0.01–0.02ppm, is sufficient to initiate
autoxidation of unsaturated fatty acids. Ozone
can react with many types of organic molecule to
yield radicals.
Unsaturated fatty acids or oils are particularly
sensitive to oxidation by ozone. They produce intermediary
ozonides which, in turn, produce aldehydes
and hydrogen peroxide, which interact to form acids.
In living systems, ozonides can bring about disulphide
crosslinkage with sulphur containing amino
acids. In collagen the amino acid methionine contains
sulphur and theoretically could be subject to
similar oxidative changes.
As has been described previously, sulphur dioxide,
in the presence of sunlight, is converted to
sulphur trioxide on the surface of leather. In the
presence of oxygen, sulphur trioxide may form sulphur
dioxide and ozone, a strong oxidizing agent.
Tannins in leather act as sinks for sulphur dioxide.
Wouters (1994) showed that, under similar conditions,
leathers tanned with condensed tannins
adsorbed twice as much sulphur dioxide as those prepared
with hydrolysable tannins. Unlike hydrolysable
tannins, the condensed tannins because of their
polymerized–condensed state, form an impermeable
surface in which sulphur dioxide can concentrate.
Absorption of sulphur dioxide depends on ambient
concentration of the gas and the velocity of deposition
onto the leather surface. Reich and Stivala (1971) discuss
some aspects of the interaction between sulphur
dioxide and polymer films. The mechanism of the
reactions of sulphur dioxide with polymers in the
presence of ultraviolet radiation is difficult to ascertain
because of the many side reactions which they can
undergo. Thus in the presence of oxygen, ozone may
form along with sulphur trioxide. Sulphur trioxide
reacts with water to produce sulphuric acid which
dissociates to form the damaging hydronium ion.
Electron spin resonance spectroscopy experiments
(Rasmussen et al., 1999) show that sulphur dioxide
combined with oxygen causes oxidation of nitrogen
atoms resulting in nitroxide radicals and possibly –CO.
radicals which cause hydrolysis of the free peptide
bond.
Nitrogen dioxide is a potent catalyst of the peroxidation
of polyunsaturated fatty acids. Nitrogen
dioxide reactions are complicated. In sunlight and
water it produces nitrogen trioxide and oxygen radicals.
This activated oxygen reacts rapidly with
organic molecules to produce further radicals which
cause chain scission. The ethylene group present in
unsaturated fatty acids is readily attacked by nitrogen
dioxide, generating further free radical species.
Carbon dioxide is the most common of air pollutants
and is present in the largest amount. With sunlight
and moisture it accelerates the production of
the hydroxyl radical HO. from nitrogen dioxide.
There is little reference to the role of carbon dioxide
in deterioration of leather.
5.2.4 Metals and salts
Ash analysis of tannin extracts (Okell, 1945) show the
presence of copper, iron, aluminium, manganese,
zinc, calcium, magnesium, sodium, and potassium.
Electron dense X-ray (EDX) analysis of samples of
12 contemporary leathers shows the presence of iron
in all 12 samples along with the same variety of the
above metals (Florian, 1984). In leather processing
metal salts are used for a wide range of reasons – from
biocides to whitening. We often consider generally
that metals act as catalysts for oxidizing reactions, but
the role of metals is complex. Magnesium and iron
increase the rate of photolysis whereas zinc and aluminium
slow it down and at the same time iron and
aluminium can act as antioxidants. As deteriorating
agents it is those metals which act as catalysts of oxidation
which are the main concern.
Several metals such as cobalt, copper, and iron,
which undergo univalent redox reactions, can participate
as catalysts in the promotion of autoxidation
and peroxidation of polyunsaturated fatty acids.
Iron is the most active promoter of lipid peroxidation
and is common as a contaminant in the fabrication
of leather and in vegetable tannin extracts and
is readily chelated by organic compounds.
The role of iron in causing hydrolysis of collagen
is discussed by Stambolov (1996). Under aerobic
conditions the iron acts as a catalyst to cause oxidation
of the air pollutant sulphur dioxide to form
sulphuric acid which, through hydrolysis, causes
solubility of the collagen. Florian (1987) has
reviewed the literature on the effects of metal ions
on collagen in reference to archaeological objects
excavated from a marine environment.
40 Conservation of leather and related materials
Ciferri (1971) discusses the role of different metal
salts and salt concentrations on the shrinkage temperature
of collagen crosslinked with aldehydes.
The following ions are listed in decreasing order of
activity: ClϪ
N3
Ϫ
BrϪ
SCNϪ
Kϩ
Mg2ϩ
Naϩ
Csϩ
Liϩ
Ca2ϩ
, with Ca2ϩ
causing the lowest shrinkage
temperature. Common salt used in the tanning
industry often contains calcium chloride, CaCl2.
Thampuran et al. (1981) suggest that protein degradation
observed with long storage of salted hides
was probably caused by calcium and magnesium
chloride salts.
The reason for the varied effects of the different
salts on shrinkage temperature is due to the different
degree of adsorption or ionic bonding of each salt
to the protein molecules; the greater the adsorption,
the greater the effect. Some of these salts may be
present in leather in high concentrations as a result
of the reduction in moisture content due to ageing.
5.2.5 Heat
Supplying external heat to a chemical compound is
simply transferring kinetic energy to it. This externally
applied energy causes an increase in molecular
movement which increases the rate of collision
between adjacent molecules and thus increases the
rate of reaction. In a polymer it increases the molecular
movement until it is so extreme that the bonds
holding the chain together can no longer resist the
movement and break. Thermal degradation can lead
to separation of the three protein chains in a triple
helix, such as is found in collagen. An example is
the denaturing of proteins using heat to determine
the shrinkage temperature. It is a sudden reaction
and can be compared to a zipper breaking all at once.
External heat and the moisture content of materials
and the air around them are interconnected. The
long-term effects of moderate heat fluctuations cause
loss of the ability of the leather to adsorb water
vapour from the air. After many fluctuations the
leather loses its regain ability and becomes hard and
brittle. The internal chemical compounds become
concentrated because of the reduced amounts of
water present. When leather loses or gains moisture a
rapid change in the internal temperature of the
leather will occur due to the latent heat of vaporization
or condensation (Florian, 1984).
In general a leather which is highly degraded,
not hard but fibrous and porous, will lose or gain
moisture more rapidly than one which is not
degraded. The reasons for this are the changed
physical and chemical state such as losses in degree
of tannage and coherence, the increase in permeability
of the fibre structure, and an increase in
the presence of hygroscopic chemicals (Calnan and
Thornton, 1997).
5.2.6 Water
5.2.6.1 Types of water in leather
At normal temperatures and relative humidities
there are two types of water present in permeable
organic materials such as leather: multilayer water
(also called free water) and molecularly bound
water.
Multilayer free water is located between the network
of interwoven collagen bundles. It is present as
monolayers bound to strong and weak binding sites
on the protein and as multilayers in the interfibrillar
spaces. It is weakly bonded by hydrogen bonds and
van der Waals bonds between and on the surfaces of
the fibrils, and to themselves, pushing the polymers
apart and increasing their mobility. The amount
of multilayer free water varies between 0.07g and
0.25g water/g of dry collagen depending on relative
humidity (Horie, 1992). Free water moves in and out
of the fibre structure with changes in relative humidity
whereas bound water is retained attached to the
protein molecules. This free, multilayer water can
enter into, and increase the rate of, chemical reactions
such as hydrolysis and oxidation. Its loss will
cause stiffness but it is reversible with increases in
relative humidity as long as the physical structure, the
regain ability, of the leather has not been destroyed.
The amount of free water varies with the physical
state of the leather, such as porosity and chemicals
present.
In describing the water relationship in food in
systems containing chelating agents and other antioxidants
Karel and Yong (1981) suggest that free
water, at the monolayer and bilayer, is required to
permit solubilization and activity of these agents,
which are used to lower the rate of oxidation.
Bound water is present in the form of an integral
part of the collagen structure and affects its physical
and chemical properties. Bound water is considered
to be that water which is not available to dissolve
electrolytes because it does not move by diffusion
or according to the osmotic gradient. In the case of
collagen, the amount of bound water is about two
molecules per tripeptide, i.e. up to 0.07g water/g
of dry collagen, at an equilibrium relative humidity
of around 10% (Nomura et al., 1977). Removal of
bound water alters the intra- and intermolecular
The mechanisms of deterioration in leather 41
42 Conservation of leather and related materials
bond arrangement and causes irreversible stiffness.
Freeze-drying can cause removal of the bound
water and it is also reported to cause denaturation of
the interfibrillar proteins.
5.2.6.2 Water activity
Certainly, one aspect of the deterioration of
vegetable-tanned leather, which is often overlooked,
is due to the water in the leather itself.
Water in food is always characterized by its vapour
pressure ratio relative to the vapour pressure of pure
water and is expressed as water activity, aw. This
means that if a solute is dissolved in the water its
vapour pressure is changed as well as properties such
as rate of evaporation and availability to microorganisms.
Water activity at aw ϭ 0.5–0.6 accelerates
oxidation by introducing swelling of macromolecules
and exposing additional catalytic sites. At
higher water activity (aw ϭ 0.75–0.85), oxidation
will be retarded by dilution.
Another aspect of water relationships deals with
deliquescence of specific compounds. Some salts in
leathers can deliquesce and form condensed water to
enhance deterioration. This is called sweating and has
nothing to do with temperature and relative humidity
relationships. Water content will also dictate the
pH of the complex system. With natural loss of water
as a result of ageing, the pH may drop due to an
increase in concentration of any acids present.
5.2.6.3 Hysteresis
Stiffness or brittleness in leather is commonly caused
by fluctuations in moisture content as a result of temperature
and relative humidity changes. As material
goes through these fluctuations the moisture gain and
loss can be graphed into two curves, adsorption and
desorption, collectively called the hysteresis curve
(Figure 5.1) or isotherms (Florian, 1998). The curves
show that the amount of adsorption of water is lower
than desorption. Over many cycles the two curves
become one straight line because of a decrease in the
ability of the material to adsorb water, which reflects
the relative accessibility of hydrophilic groups within
the collagen. This results in the leather becoming
stiff. This may be due to the realigning of the polymers
and their hydrogen bonding to each other using
sites that were originally used to bond water.
5.2.6.4 Colloidal nature of collagen
Another aspect of water is its role in the colloidal
nature of collagen (see Florian, 1987 for details).
This will be discussed under the description of collagen
reactivity. There is a link between moisture
content, shrinkage temperature and the chemical
state (Odlyha et al., 1999a). We often forget that loss
of moisture in materials means concentration of
solutes which can increase the rate of and initiate
chemical reactions.
5.2.6.5 Relative humidity changes
Relative humidity is the amount of water vapour in a
specific volume of air, at a specific temperature and
pressure, relative to the full amount that that volume
of air could hold at saturation. Relative humidity
changes mean varying amounts of water vapour
becoming available for diffusion into or out of
organic materials. The moisture present in materials
moves according to a diffusion gradient but is also
controlled by the water bonding in the material.
In materials treated with humectants, these hygroscopic
materials chemically bind water molecules
into the material taking them out of the diffusion
process. This allows more water to enter until all the
hygroscopic bonds are satisfied and diffusion has
reached an equilibrium between the material and the
environment. The movement of water in and out of
material is an exothermal and endothermal reaction.
Thus the fluctuations over a long-term scale enhance
Adsorption
Desorption
25
20
15
10
5
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
%H2O
Water activity
Figure 5.1 Schematic representation of moisture sorption
hysteresis loop. Water activity can be converted to
RH for ease of interpretation. The graph shows that the
rate of water vapour adsorption is faster than the rate of
desorption. Thus at 0.5 water activity or 50% RH there is
more water in materials on the desorptive curve (from
Florian, 1998).
heat damage. Also, the presence of water often
enhances the rate of, or is required for, chemical
reactions. Water also plays a role in the formation of
high energy radicals in photolysis, enhancing light
damage.
In summary, the role of free and multilayer water is
to act as a solvent for hydrolytic chemical reactions
and its presence often increases the rate of reaction.
Decreases in water content may increase the concentration
and thus increase the rate of reaction of other
chemical compounds present. In some cases, such as
autoxidation of fats, water slows the reaction. With
biological systems the vapour pressure or water activity
is the limiting feature for growth. Even if there is a
large amount of water present, it may have a low
vapour pressure or water activity because of the
solutes in it and is not available for fungal growth. This
must also play a role in chemical activity in materials.
Water bound to molecules such as humectants and
salts may not be available for chemical reactions.
5.3 Collagen
(See also Chapter 2.)
5.3.1 Bonds in collagen: sites of
deterioration mechanisms
Hydrolysis of the polypeptide chains in collagen
involves the breaking of the peptide (C–N) linkages
forming smaller polymers or releasing free amino
acids. Oxidative breakdown of the collagen on the
other hand is restricted to specific amino acid residues
and to certain tripeptide segments situated in charged
areas of the collagen peptide chains. Oxidation of
the amino acid involves altering the side chains with
the formation of breakdown products and finally
ammonia. Collagen derives its strength from the
higher structures of superhelices. Crystalline structures
give a stability, and the tight packing prevents
access to deteriorating chemicals. Loss of crystallinity
therefore makes it vulnerable to chemical
attack. Young (1999) researched the use of loss of
crystallinity as a measure of deterioration.
It is important to realize that deterioration can
occur at any one of the levels of organization of the
collagen molecule independent of each other and
may result in changes in the physical–chemical
characteristics of the material. At every level of
organization there are both hydrogen and covalent
bonds holding the complex structure together. It is
the breaking of these bonds which causes the
denaturation and ultimately dissolving of the collagen.
The bonds have different strengths, and it takes
equal or greater energy (strength) to break them.
This energy comes from the agents of deterioration
discussed in the previous section, e.g. the electrical
charge of chemical ions such as the hydronium ions
of water in acids hydrolyses, and the high energy
radicals from light, peroxides or oxidizing agent
reactions and from heat. Where and how are these
bonds broken?
5.3.2 Peptides
5.3.2.1 Introduction, polypeptides to peptides
In proteins, all the bonds between the amino acids
in the main chain are called peptide linkages. If
these bonds are broken it results in fragments of the
protein polypeptide called peptides, i.e. amides
formed from two or more amino acids.
In the peptide, by convention, the amino acid
with the free amino group is called the N-terminal
amino acid or residue and the amino acid with the
free carboxyl group is called the C-terminal residue.
Degradation of a polypeptide will increase the number
of peptides which in turn increases the number
of N and C terminal amino acids. The increase in
number of N-terminals in aged leather has been
used as a measure of the production of peptides
which itself is a measure of deterioration.
5.3.2.2 Peptide formation in deteriorated leather
Larsen (1995) reviewed the literature on peptide
formation in deteriorated leather. He reports that
both hydrolysis and oxidation produce peptides and
that the rate of hydrolysis increases as the reaction
proceeds, probably due to autocatalysis by the carboxyl
end groups. Bowes (1963) suggests that during
deterioration only partial hydrolysis of the
collagen occurs and, thus, free amino acids are not
present, only peptides. Larsen (1995) also reports
that splitting occurs at the telopeptide regions and
that in 9 out of 10 peptides produced by the breakdown
of the collagen molecule, arginine is in the
second position, either before or after the splitting
point. Arginine is a hydrophobic residue with a
basic amino group in its side chain. It is more sensitive
to heat oxidation after short-term exposure to
hydrolysis, suggesting that the arginine becomes
more exposed for oxidation. The opposite occurs
after prolonged hydrolysis, suggesting that acid pollution
inhibits oxidation.
The mechanisms of deterioration in leather 43
44 Conservation of leather and related materials
In the STEP Project Vilmont (1992, 1993) and
Juchauld and Chahine (1997) have analysed aged
leathers for the presence of N-terminals. Larsen
(1995) reviews the literature on N-terminal analysis
and states that in all essentials the STEP results are in
accordance with those reported in the literature
reviewed for leathers of different tannage (Bowes,
1963; Bowes and Raistrick, 1964; and Deasy and
Michele, 1965). Vilmont (1993) found an increase
in N-terminal residues in artificially aged samples
but not a significant increase in historic leathers,
suggesting that hydrolysis is not the predominant
agent in natural ageing.
Larsen (1995) compared the results of the Vilmont
(1993) report to those of Bowes (1963) on
N-terminals and states that even a few chain breaks
may lead to severe damage of the collagen structure
and the formation of the N-terminal peptides with
molecular weights down to 10000. This size is in
agreement with those found in gelatine and hydrolysis
of collagen and leather.
Larsen (1995) concludes that the preliminary
results of the Vilmont (1992, 1993) research show
that there is a fine agreement between leathers containing
2% or more of sulphate and the number of
N-terminal residues formed by acidic cleavage of the
collagen chain and that both the qualitative identification
of the N-terminal amino acids formed and
the quantitative determination of N-terminals are
important for a complete clarification of the extent
of leather deterioration.
5.3.3 Amino acids in collagen
(See Chapter 2, Hey, 1973 and Munro and Allison,
1964 for details.)
5.3.3.1 General characteristics of amino acids
In understanding the potential deterioration mechanisms
in leather, a knowledge of the various amino
acids present is important, not only because of their
loss, but also the presence of their breakdown products
such as ammonia and organic acids. Also, as will
be shown, the presence of a specific ratio of basic to
acidic amino acids in deteriorated leather is an indicator
of the degree of deterioration.
Figure 5.2 shows the relative amounts of amino
acids in calf collagen, untanned goatskin and calfskin
leather. The high amount of glycine, hydroxyproline
and proline is characteristic of collagen.
Because amino acids are amphoteric, the predominant
form of the amino acid present in a solution
5
0
hyp
asp
thr
glu
ser
pro
gly
ala
val
m
et
lie
leu
try
phe
his
hyl
lys
arg
10
15
20
25
30
35
% amino acids/mol in calf collagen and leather, and goatskin
calf collagen goatskin calf leather
Figure 5.2 % amino acids in new calf collagen and leather and goatskin. The three sources of collagen show similar
amounts of the different amino acids. The high amount of glycine naturally occurs because glycine is in every third
position on the polypeptide chain. Raw data from Larsen et al. (1994).
The mechanisms of deterioration in leather 45
depends on the nature of the amino acid and the
pH. In a strong acid solution all amino acids are
present primarily as cations; in strong basic solutions
they are present as anions. At some intermediate
pH, called the isoelectric point (pI), the concentration
of the dipolar ion is at maximum and the concentration
of the anions and cations are equal. Thus
the isoelectric point is the pH at which an amino
acid carries no net ion charge.
In solutions they are electrolytes with the ability
to form acidic and basic salts and thus act as buffers
over at least two ranges of pH.
5.3.3.2 Side chains of amino acids (Mills and
White, 1986)
Each amino acid has its own properties because of
its side chain. According to the nature of the side
chain (R-group), the amino acids can be classified
into neutral, acidic and basic groups The isoelectric
points of the amino acids reflect the neutral, acidic
or basic nature of the side chains. Because of the
hydroxyl group in the side chain, the amino acids
serine, threonine and tyrosine are significant hydrogen
binders as is hydroxyproline.
The reactive groups on the side chains of amino
acids are capable of a wide range of chemical alterations
leading to a large variety of degradation, synthetic
and transformation products.
5.3.3.3 Amino acid changes
5.3.3.3.1 Deterioration mechanisms
The common reactions of amino acids are deamination
(loss of amine group), and decarboxylation (loss
of carboxyl group). There is also the conversion of
one amino acid to another called transamination.
All three types of reactions result in changes in the
amino acids and the formation of products which
suggest specific types of deterioration, e.g. amines,
ammonia, organic acids, ␥-aminobutyric acid,
␣-amino adipic acid, ␤-alanine.
In oxidative decarboxylation, the carboxylic acid
group is lost and the amino acid converted to an
amine, e.g. glutamic acid is converted to the amine
glutamine. As the word deamination suggests, there
is a loss of the amine group and the formation of the
corresponding ␣-keto acid, such as ␣-ketoglutaric
acid. The fate of the amino acid damaged by oxidative
deamination and non-oxidative decarboxylation
is the same, that is the conversion of the amino acid
to the ␣-keto acid, and then to ammonia. When
analysing the amino acid profile in old and aged
leathers Larsen et al. (1994) observed an increase in
aspartic acid compared with the reference, new
leathers. This increase could be due to transamination.
Another example is the transformation of glutamic
acid to alanine.
In ageing studies of living skin it has been
observed that the degradation of histidine, arginine,
proline and hydroxyproline by a series of reactions,
transamination, dehydrogenation, oxidation etc., all
result in the formation of glutamic acid. This could
also occur in ageing of leather producing an increase
in the relative amount of glutamic acid in old
leathers.
Thus changes in the kinds and relative amounts of
amino acids and the presence of the deterioration
products mentioned above, suggest deterioration of
the free amino acids or the amino acids at the ends
of peptides in leather.
As leather deteriorates the ammonia derived from
breakdown of amino acids is thought to react with
any sulphuric acid present and form ammonium
sulphate, thus the presence of sulphates has also been
used as an indicator of hydrolytic deterioration.
The greater the oxidative breakdown of the amino
acids to ammonia, the greater is the buffering power
against sulphuric acid. Thus oxidation can reduce
hydrolytic activity.
Other characteristics of amino acids, important in
leather deterioration mechanisms, are their ability
to bind metals of many kinds and to act as adsorbers
of ultraviolet and infrared radiation. Both these
characteristics can enhance deterioration of other
components of the leather such as fats and tannins.
The effect of ultraviolet damage depends on the
structure of the amino acids. Methionine, histidine,
tryptophane, tyrosine, and cysteine are the principal
amino acids affected, both as free amino acids or
in peptides. No breaking of peptide or disulphide
bonds occurs. Methionine is oxidized at all pH
values (Foote, 1976).
When amino acids are irradiated in air in the dry
solid state, the following reactions occur: decarboxylation,
with the formation of the corresponding
amine; deamination and formation of the corresponding
␣-keto acid; the formation by dehydrogenation
of amino acids with ␤,␥-, or ␥,␦-unsaturated bonds
(␥-butyric acid). The end product is ammonia.
The products of photolysis of glycine, the commonest
amino acid in collagen, may be ammonia,
acetic acid, glyoxylic acid and formaldehyde.
Photolytic products of the amino acids can be
obtained at room temperature (Greenstein and Winitz,
1961). The rate of their production is significantly
46 Conservation of leather and related materials
increased by the addition of divalent metals such as
magnesium or iron, but slowed down by the addition
of zinc or aluminium ions (Lewis, 1991).
In the decarboxylation and deamination processes,
leucine, glutamic acid and phenylalanine yield radicals.
Figure 5.3 shows variable vulnerability of some
amino acids to the breakdown to ammonia by ultraviolet
light.
The above information is necessary to understand
the significances of the changes in amino acid types
and amounts in aged leather.
5.3.3.3.2 Amino acid changes in deteriorated leather
Larsen et al. (1997a) has shown that after the natural
or artificial ageing of vegetable-tanned leathers, there
are changes in the relative amount of some amino
acids. Figure 5.4 shows the increases and decreases in
amounts of the specific amino acids in aged leather
compared to new leather. They found lower values
for the basic amino acids: lysine, arginine and hydroxylysine,
accompanied by an increase in the acidic
amino acids; aspartic and glutamic acid as well as
changes in neutral amino acids and the formation of
several breakdown products such as ␥-aminobutyric
acid and ␤-amino acids.
Changes in the ratio of the basic and acidic amino
acids present were expressed calculated as changes in
the B/A ratio. The B/A ratio is the sum in mol% of
basic (B) amino acids to the sum in mol% of acidic
(A) amino acids. The B/A ratio (Arg ϩ Hyl ϩ Lys)/
(Asp ϩ Glu) was shown (Larsen, 1995; Larsen et al.,
1997) to be a good measure for the average degree
his
0
20
40
60
80
100
% total ammonia on deamination by photolysis of amino acids
cst lys try ala gly arg asp try
NH3
Figure 5.3 % total ␣-NH3 formed on deamination
of some amino acids after ultraviolet exposure (2 hours
under a mercury lamp) (after Greenstein and Winitz,
1961).
Changes in amounts of amino acids in old leather compared to new leather
2
1.5
1
0.5
0
hyp asp thre ser glu alagly val met lsol leu phetry his hyl lys argpro
Ϫ0.5
Ϫ1
ve1600 ve1850 al1569 al1633
Figure 5.4 The amounts of change, positive or negative, as compared to new leather, in the relative amounts of the
amino acids in naturally aged, vegetable-tanned (ve) and alum-tawed (al) historic leathers. 0 ϭ the baseline for new
leather. Those amounts of the specific amino acids above 0 show an increase in amount, and those below 0 a decrease
from the new leather due to natural ageing. Raw data from Larsen et al. (1994).
The mechanisms of deterioration in leather 47
of oxidation. The isoelectric points of these amino
acids are shown in Figure 5.5. In new leather the
B/A value is around 0.69 whereas in old leather and
artificially aged leather it is below 0.50. This ratio
was used to determine the best methods of fabrication
of leather to be used in conservation.
The following is an excerpt from Larsen and Vest
(1999) which gives the mechanisms and reasons for
the amino acids changes.
Lysine, arginine, hydroxyproline and proline are sensitive
to oxidation. In the oxidation of these amino and
imino acids, breakdown products are formed in the form
of amino acids, Lysine to Glu, Arg to Glu, Pro to
␤-ala and Arg to ␤-ala. The formation of ␤-ala is only
possible by the oxidation of the ␣-carbon atom in Pro
and Arg which leads to cleaving of peptide chains.
Many of the breakdown products are amino acids with
acidic side chains. This means that the balance of charge
between the collagen side chains is altered and the isoelectric
point of the collagen is shifted further towards the
acidic area, whereby the stability of the leather is weakened.
This oxidative breakdown can be measured by
amino acid analysis, since the form of deterioration
opposite to the hydrolytic breakdown involves the modification
of the amino acids in the collagen. This causes a
change in the relative amounts of different amino acids
in old leather or collagen relative to intact leather and
collagen. The different tannages do not significantly
change the relative amounts of amino acids on analysis.
5.4 Vegetable tannins
5.4.1 Introduction
(General references for the tannins include: Bickley,
1991; Harborne, 1989; Haslam, 1989; Porter, 1989a,
b; Porter and Hemingway, 1989; Hemingway, 1989;
Haslam, 1979; Roux et al., 1975; Ishak, 1974;
Ribéreau-Gayon, 1972; White, 1958.)
5.4.2 Antioxidant ability of tannins
( Jurd and Geissman, 1956; Lentan, 1966)
Tannins have strong antioxidant activity. The strength
of this activity depends on the number and position
of phenolic hydroxyl groups (Greenhow and Shafi,
1975). The hydrolysable tannins appear to have greater
antioxidant ability than the condensed tannins. Antioxidants
work in several ways: in the removal of free
radicals, as metal ion deactivators (sequestering,
chelation), as UV light deactivators, and as peroxide
decomposers.
The antioxidant ability of tannins can be significantly
reduced by oxidizing agents, such as UV light,
hydrogen peroxide and ozone. In the analysis of
metals in water, ozonation under acid conditions
below pH 2 is used to release all metal ions sequestered
by tannins. This conceivably would occur in deteriorated
(pH 2) vegetable-tanned leather, releasing the
metal ions to catalyse autoxidation processes of tannins,
collagen and oils. In the history of the technology
of the tanning process, citrate, oxalate and tartrate
salts and sodium pyrophosphate have been used to
sequester any iron contamination. The antioxidant
ability of tannins may also be reduced by methylation.
Tannins could conceivably become methylated during
fumigation with a methylating agent such as
methyl bromide (Florian, 1985).
5.4.3 Analysis of tannins in aged
leather – deterioration mechanisms
Wouters (1994) undertook analysis of extracts from
new, naturally aged and artificially aged leathers using
HPLC (high power liquid chromatography). The
amount of tannin and monomers of the phenolic acids
present in the extracts was measured by optical density
OD/100mg. The HPLC profiles show the typical
changes on ageing of the extracts from leathers tanned
arg
0
2
4
6
8
10
12
Isoelectric point in pH of B/A amino acids
lys hyl asp glu
pl ϭ pH of lsoelectric point
pl
Figure 5.5 The isoelectric point in pH of the amino
acids that were used to calculate the Basic/Acidic (B/A)
amino acid ratio B (Arg ϩ Hyl ϩ Lys)/A (Asp ϩ Glu).
Raw data from Larsen (1995) and Larsen et al. (1996).
48 Conservation of leather and related materials
with hydrolysable and condensed tannins. Figure 5.6
shows the changes in the chromatographic profiles
of the extracts from hydrolysable-tanned leather
before and after ageing. It shows the presence of
new monomers in the extract from aged leathers and
an increase in gallic and ellagic acid monomers. The
change in extracts from leathers made with condensed
tannins (not shown) was a chemical shift of the main
peaks towards more hydrophobic compounds. Both
showed increases in ellagic acid. Gallic acid can
be copolymerized to ellagic acid by mineral acids such
as sulphuric acid. This may explain the increased
presence of ellagic acid in deteriorated leathers with a
low pH.
Figure 5.7 shows the optical density of the extractable
tannin, its total monomer content and the
amount of the monomers, gallic and ellagic acid present
in the extracts from the different leathers.
Figure 5.7A indicates that with all the naturally
and artificially aged leathers produced with hydrolysable
tannins there is less tannin extracted after
ageing than with the new leather. This suggests loss
of tannins due to their breakdown into end products
such as organic acids and sugar. The condensed tannins
do not show a specific pattern of change. This
could be explained by differences in the original
tannin extracts because of methods of fabrication; it
is difficult to work with such heterogeneous materials.
Because of the above, Wouters and Claeys (1997) state
that a measurement of the total amount of tannin
extracted cannot be used to determine deterioration
of leather.
Figure 5.7B shows that ageing causes an increase
in the amount of monomers extracted from all
samples compared with new leather as a result of oxidation
of the tannins. Extracts from aged samples of
leathers prepared with condensed tannin contained a
greater percentage of monomers than those tanned
with hydrolysable tannin, suggesting greater deterioration
due to oxidative and hydrolytic reactions.
In Figure 5.7C, gallic acid is naturally present in
both tannin types. While the relative amounts of gallic
acid are not significant, the presence of the gallic
acid monomers is. The figure shows a comparable
increase of these acids present in extracts prepared
from aged leathers made from both types of tannin as
compared to the amount present in new leather.
Figure 5.7D shows the amount of ellagic acid in
the tannin extract. Gallic acid can be dimerised by
mineral acids, such as sulphuric acid to ellagic acid.
This is a possible reason for the large amount of
ellagic acid in the naturally aged leathers produced
with condensed tannins.
As expected, Figures 5.7A–D show, increases
in monomer contents due to both oxidation and
hydrolysis of the tannin.
0
0
0.1
0.2
0.3
0.4
0.5
0
0.1
0.2
0.3
0.4
0.5
5 10 15 20
2015100 5
(min)
HPLC tannin profile from untreated sumactanned
experimental leather
HPLC tannin profile from a typical hydrolysable
tannin from historical leather 4;
(x): monomers; ga: gallic acid; ea: ellagic acid
Ϫ.05–––.05^U
280nm
0 5 10 15 20
2015100 5
0
0.02
ga
ea
x x
0.04
0.06
0.08
0.1
0
0.02
0.04
0.06
0.08
0.1
(min)280nm
Figure 5.6 HPLC hydrolysable tannin profile from untreated and a historical leather (from Wouters, 1994).
The mechanisms of deterioration in leather 49
In summary (Wouters and Claeys, 1997), it can
be concluded that the absolute or relative amounts
of monomer products which are produced during
natural and artificial ageing can be used as a measure
of deterioration.
Gallic acid and ellagic acids are both monomers
but were considered separately. The amount of gallic
acid present increased during ageing in acid environments
in both condensed-and hydrolysabletanned
leathers. The authors suggested their analysis
is useful to determine deterioration. The presence
of ellagic acid in condensed tannins suggests its
formation from gallic acid due to the presence of
strong acids such as sulphuric acid. The data is also
significant in that it shows that the changes that
occur in naturally aged leather also occur in the artificially
aged leathers.
The variations in the amount of monomers present
in extracts from BLTST-aged leathers due to plant
species used as the source of the tannin extract and
methods of fabrication are illustrated in Figure 5.8.
The figure shows similarities in the results from several
samples of leathers made using the same species, i.e.
oak and quebracho, but significant differences in the
10
8
6
4
2
0
bh wh nh a1 a2 a3
C. Gallic acid % tannin
wc nc a6a5a4bc
bh wh n a2 a3a1
0
0.5
1.5
2.5
1
2
3
B. Monomers % in tannin
a6a5a4wc nbc
bh wh nh a2 a3a1
0
0.5
1.5
2.5
1
2
3
D. Ellagic acid % in tannin
a6a5a4wc ncbc
2000
1500
1000
500
0
bh wh wcn na1 a2 a3 a6a5a4bc
A. Tannin optical density/100 mg
Figure 5.7 The tannin analysis and their breakdown products in naturally aged leather long-term trial and new and
artificially aged leather. Raw data from Wouters (1994). The amounts of extractable tannin and monomers were
analysed by HPLC and their amounts determined by optical density. The group on the left in each chart is hydrolysable
tannins and the group on the right is condensed tannins.
h ϭ hydrolysable tannin; c ϭ condensed tannin; b ϭ naturally aged leather from bindings of books placed in the
British Library in 1932; w ϭ as b, except books placed in Wales Library, 1932; n ϭ new leather; a ϭ leather artificially
aged (6th ageing trial); 1 and 4 ϭ 2 weeks’ ageing with O3, plus 2 weeks with SO2 (45 ppm), NO2 (10 ppm), NO (10
ppm), 40°C, 35% RH; 2 and 5 ϭ 4 weeks’ ageing with O3, plus 4 weeks with SO2, NO2, 40°C, 35% RH;
3 and 6 ϭ 1–2 days at 120°C plus 4 weeks SO2, NO2, 40°C, 35% RH.
50 Conservation of leather and related materials
samples prepared from sumac. The results suggest differences
are due to the species used but there are also
differences from one leather to another as well due to
different methods of fabrication. Overall both groups
show significant changes with aged leather compared
to the new leather, but the two groups of tannins show
different deterioration patterns. The condensedtanned
leathers show a higher amount of monomers in
the tannin extracted than that obtained from the
hydrolysable-tanned leathers. The average and range
of amount of monomers extracted from aged leathers
tanned with hydrolysable tannins, 2.4% (1.9–3.9), and
from those tanned with condensed tannins, 5.25%
(3.5–6.8), show, despite the species differences, that a
trend is present. This illustrates the greater deterioration
of the condensed tannin.
5.5 Other chemicals present due to
fabrication and use
5.5.1 Introduction
Leather is not just a product of collagen and tannins,
it is a complex mixture made up of collagen, tannin
extracts which themselves contain a complex mixture
of different types of polyphenolic tannins, nontannins
(sugars, low molecular weight phenols, etc.),
metal ions, organic and mineral acids, salts and sulphur
compounds. Besides these two major mixtures
there are other materials used in its fabrication.
Tanned leather may be subjected to a variety of
chemical and mechanical processes or finishing operations
such as fat liquoring, staining, dyeing, graining
or embossing, plating, boarding, enamelling or
abrading, etc. (Thomson, 1991a, b).
Products employed during use to increase its
serviceability, such as saddle soap, oils and phenolic
biocides, and adsorbed gases (sulphur dioxide,
nitrous oxide) may also be present. These products
may prevent or enhance deterioration. The presence
of some of these materials may give misleading
information in analyses of old leathers, for example
the phenols from biocides may be mistaken as coming
from the tannins, and sulphur compounds from
fat liquors and dyes as coming from air pollution.
Contaminants arising from use, such as perspiration,
are also a source of deteriorating chemicals.
Only the relevant common chemicals involved in
deterioration will be discussed.
0
sf s1 s2 s3 s4
hydrolysable tannin
% m
condensed tannin
a1 a2 s0 o1 o2 o3 m c q qs g mo
0.5
1
1.5
2
2.5
3
3.5
4
% monomers from naturally aged leather book bindings
Figure 5.8 Comparison of analysis of % monomers in extracted tannins from different species used in the British
long-term tests in book bindings from books placed in the British Library in 1932. The ageing environments were the
same for all tannins. Raw data from Larsen (2000). sf ϭ sulphited sumac; s ϭ sumac; a ϭ acacia; n ϭ new; o ϭ oak;
m ϭ mimosa; q ϭ quebracho; g ϭ gambier; %m ϭ % monomers in extractable tannin.
The mechanisms of deterioration in leather 51
5.5.2 Fats, oils and waxes
The role of fats and oils as agents of deterioration is
in producing high energy radicals which catalyse
oxidation of proteins (see section 5.2.3.2.3).
Fats, oils and waxes are introduced after tannage,
to lubricate the leather fibres and prevent them from
sticking together as the leather dries.
Sulphated (incorrectly called sulphonated) oils
are oils treated with sulphuric acid to make them
miscible in water (Tuck, 1983). These oils have an
ester-type bond between the oil and the combined
sulphur trioxide which is not stable and is easily
hydrolysed releasing sulphuric acid. Sulphited oils
made by treating unsaturated fatty acids esters with
sodium bisulphite form the true sulphonated oil with
carbon–sulphur linkage. These are very stable, especially
in the presence of electrolytes such as salts.
Analysis of the amounts of fat in vegetable-tanned
leathers has been done by Wouters and Claeys
(1997), and Wouters et al. (1997), but their implication
in deterioration was not pursued.
5.5.3 Sulphur compounds and their acids
5.5.3.1 Introduction
The topic of sulphur compounds (sulphites, sulphides,
sulphates, sulphuric and sulphurous acids) in
the tannin liquors and extracts is indeed complex.
Again the information is simplified and presented as a
first step in studying the deterioration of the tannin/
leather complex.
The sulphur compounds come from various
sources. Sulphuric acid and sulphide may come in
with pretreated hides. Organic sulphonated materials
and inorganic chemicals may be added to the tanning
liquor to maintain the necessary acidic pH for tanning,
solubility of components and control of viscosity.
It should be noted that hydrolysable tannins are
not usually sulphonated in the final tanning process,
and that most of the inorganic water soluble sulphur
compounds will be washed out. But the organic
sulphonated materials (the sulphonated condensed
tannins and ligno-sulphonates and syntans) may
remain as bound sulphur. On degradation of these
sulphonated organic materials in the leather, the sulphur
must be released.
In deteriorated leather at pH 2, there is a possible
sulphurous acid content along with sulphuric acid
from sulphur dioxide pollution, which could cause
hydrolysis of protein and tannins. Sulphur dioxide
as an agent of deterioration is discussed in section
5.2.3.2.4.
5.5.3.2 Changes in sulphates and pH in
deteriorated leather
In leathers the presence of sulphates has been
considered as an indication of the presence of sulphuric
acid. Wouters and Claeys (1997) showed
that with aqueous extracts from artificially aged
vegetable-tanned leathers, as the pH becomes more
acidic the sulphate content increases. On the other
hand they observed that some badly degraded historical
leathers (see Figure 5.9, 1715 and eighteenth
century), with low shrinkage temperature, which
had not been exposed to industrial sulphur dioxide,
had a normal pH, but a high sulphate content.
Because of this they stated that the pH measurement
alone cannot be a good measure for deterioration,
and suggested that the total concentration of sulphate
is also needed.
Wouters (1994) described how the amounts of sulphate
and nitrate present in a leather can be used to
calculate the quantity of nitric acid or sulphuric acid
which would be required to give these amounts.
Using these quantities, a theoretical pH was calculated
assuming that no other relevant material was
present pH(c). If this pH(c) was different from the
measured pH (pH(m)), the difference is considered to
be due to sulphate present as ammonium sulphate.
High levels of ammonium sulphate are considered to
be indicative of severe deterioration in the past. The
amount of sulphate present in hydrolysable-tanned
6
4
2
0
1838 1715 1730 189019th 18th
Historical leathers, pH and % sulphates
%S Ts (ϫ0.1) pH
Figure 5.9 Historic leathers: %S ϭ percent sulphate in
2200 –1000g of leather; Ts ϭ shrinkage temperature
expressed as ϫ0.1 for ease of comparison. Raw data from
Larsen (2000).
52 Conservation of leather and related materials
and condensed-tanned leather inherently varies
because the condensed tannins act as a sulphur dioxide
sink. Sulphur dioxide is deposited at twice the rate in
condensed- than hydrolysable-tanned leathers.
Figure 5.9, besides showing that badly degraded historical
leathers can have a normal pH, shows the
inverse relationship between pH and sulphate, that is
as the pH decreases the sulphates increase. This confirms
the work of Wouters (1997) who suggested that
pH alone is not a parameter to assess deterioration.
5.5.4 Acids in leather due to
fabrication or use
Okell (1945) lists acids that are likely to be met in
tannery practice. These include hydrochloric, sulphuric,
sulphonic, oxalic, sulphurous, formic, lactic,
acetic, ellagic, gallic, and carbonic. Burton (1948)
reports that the acidity of a tan liquor was considered
to be the result of free hydroxyl groups of the pyrogallol
(hydrolysable) tannins and possibly from catechol
(condensed) tannins; phenolic hydroxyl groups
of the pyrogallol and catechol tannins and lignins;
natural acidity due to gallic, lactic, acetic, carbonic,
oxalic, citric, tartaric, and phosphoric acids present in
natural tanning materials; uronic acid and pectins;
added formic, boric, sulphurous and sulphuric acid.
How many of these end up in the leather is an
unknown. Their role in deterioration mechanisms
is their involvement in acid hydrolysis and as a part
of the acidic environment of the leather. pH
changes in leathers is discussed in section 5.5.3.2.
5.5.5 Perspiration
Perspiration is considered as an important deteriorating
agent of leathers in use. Bowes (1963) reports
on extensive research on its effects on different types
of tannage. It is the combination of moisture, heat
and perspiration that cause the problem in, for
example, shoes. The chief constituents of perspiration
are sodium chloride (0.3–0.5%), lactic acid
(0.1–0.3%), amino acids (0.05%) and urea (0.05%).
The sodium lactate formed under moist conditions
causes losses of chromium crosslinkage and
reduces the shrinkage temperature (Haines, 1991c).
In vegetable-tanned leather, tests using synthetic
perspiration showed that these tannins reduced the
effects of the perspiration as compared to chrometanned
leather. The main change in the vegetabletanned
leather was the darkening caused by released
phenols, due to the increase in pH.
5.6 Denaturation and shrinkage
temperatures as a method of assessment
for all tannages
(For details see Chahine and Rottier, 1997b; Larsen
et al., 1993, 1997b; Larsen, 1995; Young, 1990, 1998,
1999.)
Denaturation is simply a term which implies the
physical change of the hydrated collagen complex.
It is commonly defined as the transition from the
triple helix to a randomly coiled form that has been
caused by any one of the many deterioration agents
that could affect leather. These include alcohols,
acids, heat, radiation, oxidizing and reducing agents,
detergents, etc. Boghosian et al. (1999) using Raman
spectroscopy did not observe random coiling, which
suggests more research is necessary.
Our present understanding is that denaturation is
the result of the loss of collagen’s higher structural
features due to disruption of the hydrogen bonding
and other secondary forces that hold the molecule
together. The temperature at which fully hydrated
collagen or leather shrinks under defined conditions
is called the shrinkage temperature (Ts).
The Ts of undeteriorated mature collagen is
around 65°C but it can be as low as 30°C in deteriorated
collagen. The Ts for new vegetable-tanned
leather is from 70 to 90°C depending on the tannin
type. Again with severely deteriorated leathers this
can be as low as 30°C. In chrome-tanned leather the
weak hydrogen bonds keeping the collagen polypeptides
together are replaced by strong covalent
chromium chemical bonds, thus the shrinkage temperature
is around 100°C.
(For details of the methods used for determining
Ts see Young, 1990, 1998, 1999; Larsen, 1995, Larsen
et al., 1997b; Larsen and Vest, 1999; Chahine and
Rottier, 1999; Bowden, 1999; Odlyha et al., 1999b.)
Ts is used as a measure of deterioration of collagen
or leathers. It is apparent from the information already
presented that hydrolytic and oxidative mechanisms
occur in the deterioration of both tannins and collagen
and that these are influenced by environmental
parameters. As vegetable-tanned leathers deteriorate,
the extractable vegetable tannins show a decrease
and the amount of monomers present increases. The
hydrolytic breakdown is measured by an increase in
sulphate content, by a reduction in the B/A ratio of
amino acids and by changes in hydrogen ion concentration
(Figure 5.10). The total effect of oxidation and
hydrolysis is reflected in the shrinkage temperatures.
Using data for monomers and sulphate contents,
B/A and [Hϩ
], Larsen (1995) has shown by common
The mechanisms of deterioration in leather 53
multiple regression based on classical least-squares
method, that it is possible to predict the shrinkage
temperature of a deteriorated vegetable-tanned
leather. This shows clearly that shrinkage temperature
changes are effected by the interaction of all
four factors.
Figure 5.10 compares the observed Ts (O/Ts) and
predicted Ts (P/Ts).
As mentioned in the introduction, the emphasis
in this chapter has been on vegetable tanned leather,
but the deterioration mechanisms are similar in
leathers of different tannages. Assessment of deterioration
of parchment by Ts has been demonstrated by
Odlyha et al. (1999), Chahine and Rottier (1999),
Bowden (1999) and Rasmussen et al. (1999). In addition,
Bowes (1963), Haines (1991a) and Larsen
(1995) show that oxidation and hydrolytic activity
are the causes of deterioration in mineral-and alumtanned
leather and Ciferri (1971) discusses the role
of salts on shrinkage temperature of aldehyde-tanned
collagen. There are, of course, differences of degree
of deterioration, chrome tannage is vulnerable to
detannage because of perspiration and alum-tanned
leather has the most resistance to deterioration provided
it is kept dry.
5.7 Summary
It is now possible by using as little as 50mg of leather
to determine its composition and deterioration
(Wouters and Claeys, 1997). The analytic procedure
determines the denaturation of collagen polymer or
shrinkage temperature, the amount, type, and ratio
of degradation products of extractable tannins, the
amount and composition of protein materials, the
concentration of anions such as sulphate and nitrate,
the pH of the aqueous extract, the relative amount
of volatile materials and amounts and composition of
lubricants and mineral ashes.
The results of these analyses have made it possible
to determine the deteriorating mechanisms. Oxidation
and hydrolysis are the main deteriorating agents.
Sulphur dioxide is considered the main source of
the acidic environment that causes hydrolysis. High
energy free radicals from light, ozone, sulphur dioxide
and specific chemical reactions must be important
in initiating oxidation. Other aspects of the environment
such as heat, moisture and the presence
of acidic gases are also part of the group of agents of
deterioration or play a role in increasing the rates of
oxidation and hydrolysis. The presence of chemicals
O/Ts P/Ts B/A % T/monomers % sulphate (Hϩ
)ϫ104
pH
Historical leathers
32.9 31.2 0.50 5.85 3.60 11.04 2.96
43.8 47.3 0.54 6.18 3.46 14.75 2.83
52.4 54.2 0.58 5.92 2.18 12.61 2.90
61.4 61.6 0.60 3.88 1.84 10.05 3.00
70.0 67.7 0.61 3.50 5.60 26.30 2.58
81.9 81.8 0.60 1.63 0.45 0.89 4.05
Unaged leathers S = hydrolysable tannage, M = condensed tannage
76.0S 74.9 0.69 0.6 0.1 6.92 3.16
79.0M 78.2 0.69 0.0 0.2 5.50 3.26
Figure 5.10 The observed Ts (O/Ts/°C) and predicted Ts (P/Ts/°C) and the variable used for the prediction of the
Ts. The values are the mean values of 44 (only half the original data (Larsen, 1995, table 1, p. 124) is included in the
table) historical leather samples. The means are calculated by grouping and averaging the values within overlapping
intervals of 5°C. The pH values are calculated from the average hydrogen ion concentration (after Larsen, 1995).
O/Ts/°C ϭ observed shrinkage temperature, the temperature at which hydrated corium fibres shrink, according to
Larsen (2000).
P/Ts/°C ϭ predicted shrinkage temperature. The prediction of Ts is preformed as a common multiple regression
based on the statistical classical least-squares method (see Larsen, 2000).
B/A value ϭ the ratio of the amounts of basic (B) and acidic (A) amino acids.
% sulphate ϭ sulphate as dry mass/%.
%T/monomers ϭ tannin monomers%.
pH ϭ the acid/alkaline nature of the aqueous extract of soluble components.
[H؉
] ϭ [Hϩ
] Ϫ 104
calculated from the pH value.
Measurements of pH, sulphate and tannin were analysed according to procedures of Wouters and Clayes (1997).
54 Conservation of leather and related materials
such as sulphur compounds and metals within the
leather and which make up a part of the internal
chemical environment may alter the hydrogen ion
concentration and rates of reactions.
Analysis has shown that the effect of these agents on
tannins cause them to become insoluble or to break
down into their monomers and to finally degrade into
products such as sugar and phenols. The latter may be
broken down by further oxidation into organic acids.
Equivalent effects occur with the collagen protein. It
may be hydrolysed into peptides and these into amino
acids. The amino acids can be broken down by oxidation
into other amino acids through transamination,
oxidative decarboxylation or deamination. Finally the
amino acids may be oxidized into organic acids or
ammonia. Knowing this and being aware of the variability
in leather due to environmental and use history
as well as differences in fabrication, it seems overwhelming
and almost impossible to be able to fully
assess the deterioration state of a particular piece of
leather. However, through the research efforts of
the Leather Conservation Centre and the STEP and
ENVIRONMENT Leather Project groups, it has
been shown that it is possible to make a logical assessment
of leather deterioration and to determine some
of the mechanisms of deterioration.
As was already mentioned, leather chemists have
been speculating on the deterioration process of
leathers for the past 150 years, it is probable that
they will still be speculating in another 150 years.
There are many new approaches today with new
instrumentation and non-destructive analyses
(Boghosian et al., 1999; Odlyha et al., 1999a, b;
Rasmussen et al., 1999; Young, 1999 and others) still
in initial stages of work. They are promising as they
give a more detailed analysis without disruption of
the complex product of a series of complicated
chemical reactions. This seems logical because in
such a complex chemical reaction as deteriorating
leather, any chemical analytical intervention can
alter the products of deterioration present.
The new unintrusive methods of analysis may help
determine the role of radicals in oxidation, which
must be a major cause of deterioration. The water
relationships between the chemical environment in
the leather and its reactivity on the tannins and collagen
are important. How much internal water is
necessary for reactions to occur? The sulphur complexes
present in the leather are also confusing.
Certainly sulphur dioxide has been shown to cause
hydrolytic activity in leather in a polluted environment,
but what is the role of the other sulphur compounds
inherently in the complex chemical mixture?
More recently there have been critical reviews
(Larsen and Chahine, 2003; Thomson, 2001, 2002,
2003a, b) on the appropriate artificial ageing protocol
that should be used for research. The STEP
group goal was to determine the processes of
deterioration and devise an artificial ageing protocol
which would give similar chemical changes to
proteins, vegetable tannins and leather to those
observed in historical, naturally aged leathers. They
proposed that this protocol could be used to standardize
research. The ENVIRONMENT Group
devised a similar protocol but using a lower temperature
for a longer period of time than the STEP protocol
for assessing tannages appropriate for archival
use (Larsen et al., 1997). The CRAFT Group, a
consortium of specialist bookbinders and leather
chemists, used yet another protocol for assessing
bookbinding leathers which omitted the oxidizing
heating stage (Thomson 2001, 2002, 2003a, b). It
may be that these differences in test procedures
express the need for different protocols reflecting
the tremendous variation in leather and the environments
in which they are held over the years. All
this suggests that more intensive research is needed.
But without the goal of the ‘Golden Egg’ as
Larsen (1995) termed it, there would not be the
incentive to continue to strive to find it.
Acknowledgements
I want to thank Dr René Larsen, Scientific
Co-ordinator of the STEP Project, and Rector of
the School of Conservation, Royal Danish Academy
of Fine Arts, Copenhagen, for his generous assistance
in supplying the STEP literature and help in
the interpretation of research details as well as his
encouragement. I also want to thank Dr Gerry
Poulton, Professor of Organic Chemistry at the
University of Victoria, for his kind assistance in
reviewing chemical aspects of this chapter.
Any remaining inaccuracies or inadequate expression
of fact or concepts are of course wholly my
responsibility. I know well that the risk of error is
high when generalizing from so many and such varied
studies by so many different researchers.
References
Bernatek, E., Moskeland, J. and Valen, K. (1961)
Ozonolysis of Phenols II. Catechol, Resorcinol and
Quinol. Acta Chemica Scandinavica, 15, 471– 476.
Bickley, J.C. (1991) Vegetable Tannins. In Leather, its
Composition and Changes with Time (C. Calnan and
B. Haines, eds), pp. 16–23. Northampton: The
Leather Conservation Centre.
Boghosian, S., Garp, T. and Nielsen, K. (1999) Study of
the chemical breakdown of collagen and parchment by
Raman spectroscopy. In Preprints of the Advanced Study
Course 1999, pp. 73–88. Copenhagen: Royal Danish
Academy of Fine Arts.
Bowden, D. (1999) Studies in the Thermophysical
Behaviour of Parchment Using Surface Sensing
Techniques. In Preprints of the Advanced Study Course
1999, pp. 161–168. Copenhagen: School of Royal
Academy of Fine Arts.
Bowes, J.H. (1963) Deterioration of Leather Fibres. Final
Technical Report to US Dept of Agriculture,
Agricultural Research Services Project UR-E29-(60)-2,
July 1958–June 1963, p. 63.
Bowes, J.H. and Raistrick, A.S. (1964) The Action of
Heat and Moisture on Leather. V. Chemical Changes
in Collagen and Tanned Collagen. Journal of the
American Leather Chemists Association, 29, 201–215.
British Leather Manufacturers’ Research Association
(1932–77) Laboratory Reports, 1977, 58; 1962, 41;
157; 1954, 33, 208; 1945, 24, 104; 1932, 11, 276.
Burton, D. (1948) Vegetable Tanning – I. The Determination
of the Different Kinds of Acids and Salts in Tan
Liquors. Journal of the Society of Leather Trades’ Chemists,
32, 362–376.
Calnan, C.N. (1991) Ageing of Vegetable Tanned Leather
in Response to Variations in Climatic Conditions. In
Leather, its Composition and Changes with Time (C. Calnan
and B. Haines, eds), pp. 41–50. Northampton: The
Leather Conservation Centre.
Calnan, C.N. and Thornton, C. (1997) Determination of
Moisture Loss and Regain. In Environment Leather Project
(R. Larsen, ed.), pp. 17–22. Copenhagen: Royal Danish
Academy of Fine Arts.
Chahine, C. (1991) Acidic Deterioration of Vegetable
Tanned Leather. In Leather, its Composition and Changes
with Time (C. Calnan and B. Haines, eds), pp. 75–79.
Northampton: The Leather Conservation Centre.
Chahine, C. and Rottier, C. (1997a) Artificial Ageing.
In Environment Leather Project (R. Larsen, ed.),
pp. 33–38. Copenhagen: Royal Danish Academy of
Fine Arts.
Chahine, C. and Rottier, C. (1997b) DSC Measurement. In
Environment Leather Project (R. Larsen, ed.), pp. 129–144.
Copenhagen: Royal Danish Academy of Fine Arts.
Chahine, C. and Rottier, C. (1999) Studies of Change in
the Denaturation of Leather and Parchment Collagen
by Differential Scanning Calorimetry. In Preprints of the
Advanced Study Course 1999, pp. 151–158. Copenhagen:
Royal Danish Academy of Fine Arts.
Ciferri, A. (1971) Swelling and Phase Transition of
Insoluble Collagen. In Biophysics of the Skin, I
(H.R. Eldon, ed.), pp. 101–151. Chichester: Wiley-
International.
Deasy, C. and Michele, Sr. S.C. (1965) A Study of
Oxidative Degradation of Gelatine and Collagen by
Aqueous Hydrogen Peroxide Solutions. Journal of
American Leather Chemists Association, 60, 665– 674.
Eisenhauer, H.R. (1968) The Ozonization of Phenolic
Wastes. Water Pollution Control Fed. Journal, 1887–1899.
Florian, M.-L.E. (1984) Conservation Implications of
the Structure, Reactivity, Deterioration and Modification
of Proteinaceous Artifact Material. In Protein
Chemistry for Conservators (C.L. Rose and D.W. von
Endt, eds), pp. 61–88. American Institute of
Conservation.
Florian, M.-L.E. (1985) A Holistic Interpretation of the
Deterioration of Vegetable Tanned Leather. Leather
Conservation News, 2(1), 1–5.
Florian, M.-L.E. (1987) Deterioration of Organic
Materials Other Than Wood. In Conservation of Marine
Archaeological Objects (Colin Pearson, ed.), pp. 21–54.
London: Butterworths.
Florian, M.-L.E. (1998) Heritage Eaters; Insects and Fungi
in Heritage Collections. London: James & James.
Foote, C.S. (1976) Photosensitized Oxidation and Singlet
Oxygen: Consequences in Biological Systems. In Free
Radicals in Biology, II (W.A. Pryor, ed.), pp. 85–133.
New York: Academic Press.
Greenhow, E.J. and Shafi, A.A. (1975) The Determination
of Polyfunctional Carboxylic Acids and
Phenols, Including Vegetable Tannins by Catalytic
Thermometric Titrimetry. Proc. Anal. Div. Chem. Soc.,
12(11), 286 –288.
Greenstein, J.P and Winitz, M. (1961) Chemistry of the
Amino Acids, 1. New York: John Wiley and Sons.
Haines, B. (1991a) Natural ageing of leather in
Libraries. In Leather, its Composition and Changes with
Time (C. Calnan and B. Haines, eds), pp. 66–74.
Northampton: The Leather Conservation Centre.
Haines, B. (1991b). Deterioration Under Accelerated
Acidic Ageing Conditions. In Leather, its Composition and
Changes with Time (C. Calnan and B. Haines, eds), pp.
80–87. Northampton: The Leather Conservation Centre.
Haines, B. (1991c) The Structure of Collagen. In Leather,
its Composition and Changes with Time (C. Calnan and
B. Haines, eds), pp. 5–9. Northampton: The Leather
Conservation Centre.
Harborne, J.B. (1989) Plant Phenolics, Methods in Plant
Biochemistry, 1 (P.M. Dey and J.B. Harborne, eds),
New York: Academic Press.
Haslam, E. (1979) Vegetable Tannins. In Recent Advances
in Phytochemistry, 12. Biochemistry of Plant Phenolics
(T. Swain, J.B. Harborne and C.F. Van Sumere, eds),
pp. 475–523. New York: Plenum Press.
Haslam, E. (1989) Gallic Acid Derivatives and Hydrolysable
Tannins. In Natural Products of Woody Plants, 1
( J.W. Rowe, ed.), pp. 399–438. New York: Springer-
Verlag.
Heckly, R.J. (1976) Free Radicals in Dry Biological
Systems. In Free Radicals in Biology, II (W.A. Pryor,
ed.), pp. 135–158. New York: Academic Press.
The mechanisms of deterioration in leather 55
Hemingway, R.W. (1989) Biflavonoids and Proanthocyanidins.
In Natural Products of Woody Plants, II:
Chemicals Extraneous to Lignocellulosic Cell Wall
( J.W. Rowe, ed.), pp. 571– 651. New York: Springer-
Verlag.
Hey, D.H. (1973) Amino Acids, Peptides and Related
Compounds. Organic Chemistry Series 1, 6. London:
Butterworths.
Horie, C.V. (1992) Preservation of Natural Macromolecules.
In Polymers in Conservation (N.S. Allen,
M. Edge and C.V. Horie, eds), pp. 32–36. Cambridge:
The Royal Society of Chemistry.
Ishak, M.S. (1974) Some Aspects on the Chemistry of
Phlobaphenes from Acacia Nilotica Bark. Egypt. J. Chem.,
17(5), 699–703.
Juchauld, F. and Chahine, C. (1997) The Analysis of
N-terminal Residues in Hide Collagen. In Environment
Leather Project (R. Larsen, ed.), pp. 75–85. Copenhagen:
Royal Danish Academy of Fine Arts.
Jurd, L. and Geissman, T.A. (1956) Absorption of Spectra
of Metal Complexes of Flavonoid Compounds. Journal
of Organic Chem., 21, 1395–1401.
Karel, M. and Yong, S. (1981) Auto-oxidation B Initiated
Reactions in Foods. In Water Activity: Influence on Food
Quality (L.B. Rockland and G.R. Steward, eds),
pp. 511–529. New York: Academic Press.
Larsen, R. (1994) Summary Discussion and Conclusion.
In STEP Leather Project (R. Larsen, ed.), pp. 165–180.
Copenhagen: Royal Danish Academy of Fine Arts.
Larsen, R. (1995) Fundamental Aspects of the Deterioration
of Vegetable Tanned Leathers. Unpublished Ph.D. thesis.
The Royal Danish Academy of Fine Arts, Copenhagen,
p. 35.
Larsen, R. (2000) Experiments and Observations in
the Study of Environmental Impact on Historical
Vegetable Tanned Leathers. Thermochimica Acta, 365,
85–99.
Larsen, R. and Vest, M. (1999) The Study of Oxidative
Breakdown and Identification of Collagen Materials
by Amino Acid Analysis. In Preprints of the Advanced
Study Course 1999, pp. 11–20. Copenhagen: School of
Royal Academy of Fine Arts.
Larsen, R., Vest, M. and Nielsen, K. (1993) Determination
of Hydrothermal Stability (Shrinkage Temperature) of
Historical Leather by the Micro Hot Table Technique.
Journal of the Society of Leather Technologists and Chemists,
77, 151–156.
Larsen, R., Vest, M., Nielsen, K. and Jensen, A.L. (1994)
Amino Acid Analysis. In STEP Leather Project
(R. Larsen, ed.), pp. 39–58. Copenhagen: Royal
Danish Academy of Fine Arts.
Larsen, R., Vest, M., Poulsen, D.V., Kejser, U.B. and
Jensen, A.L. (1997a) Amino Acid Analysis. In Environment
Leather Project (R. Larsen, ed.), pp. 39– 68.
Copenhagen: Royal Danish Academy of Fine Arts.
Larsen, R., Vest, M., Poulsen, D.V. and Kejser, U.B.
(1997b) Determination of Hydrothermal Stability by
Micro Hot Table Method. In Environment Leather
Project (R. Larsen, ed.), pp. 145–166. Copenhagen:
Royal Danish Academy of Fine Arts.
Larsen, R. and Chahine, C. (2003), Comments on John
Arthur Wilson Lecture. Journal of the American Leather
Chemists Association, 98, 360 –363.
Letan, A. (1966) The Relation of Structure to Antioxidant
Activity of Quercetin and Some of its Derivatives. II.
Secondary Metal-complexing Activity. Journal of Food
Science, 3, 395–399.
Lewis, D.M. (1991) Some Aspects of the Photochemistry
of Fibrous Proteins. In Leather, its Composition and
Changes with Time (C. Calnan and B. Haines, eds),
pp. 60 – 65. Northampton: The Leather Conservation
Centre.
McNeill, I.C. (1992) Fundamental Aspects of Polymer
Degradation. In Polymers in Conservation (N.S. Allen,
M. Edge and C.V. Horie, eds), pp. 14–31. Cambridge:
Royal Society of Chemistry.
Mills, J.S. and White, R. (1987) The Organic Chemistry of
Museum Objects. London: Butterworths.
Munro, H.N. and Allison, J.B. (1964) Mammalian Protein
Metabolism, 1. New York: Academic Press.
Nomura, S., Hiltner, A., Lando, J.B. and Baer, E. (1977)
Interaction of Water with Native Collagen. Biopolymers,
16, 231 pp.
Odlyha, M., Foster, E.M., Cohen, N.S. and Caupana, R.
(1999a) Studies of the Changes in Thermophysical
Behavior of Leather and Parchment Samples Using
Thermomechanical (TMA and DMTA), Non-invasive
Dielectric and Thermogravimetric (TGA) Techniques.
In Preprints of the Advanced Study Course 1999,
pp. 169–194. Copenhagen: Royal Danish Academy of
Fine Arts.
Odlyha, M., Cohen, N.S., Campana, R. and Aliev, A.
(1999b) Study of Chemical Changes in Leather and
Parchment by Solid Phase Nuclear Magnetic Resonance
Spectroscopy (NMR). In Preprints of the Advanced Study
Course 1999, pp. 103–117. Copenhagen: Royal Danish
Academy of Fine Arts.
Okell, R.L. (1945) Acids and Salts as a Control Factor in
Tannery Practice. Journal of the Society of Leather Trades’
Chemists, 29(56), 56 –74.
Porter, L.J. and Hemingway, R.W. (1989) Significance of
the Condensed Tannins. In Natural Products of Woody
Plants, I, Chemicals Extraneous to Lignocellulosic Cell Wall
( J.W. Rowe, ed.), pp. 988–1027. New York: Springer-
Verlag.
Porter, L.J. (1989a) Condensed Tannins. In Natural
Products of Woody Plants, II ( J.W. Rowe, ed.),
pp. 651– 690. New York: Springer-Verlag.
Porter, L.J. (1989b) Tannins. In Plant Phenolics, Methods in
Plant Biochemistry, 1 (P.M. Dey and J.B. Harborne,
eds), pp. 389– 420. New York: Academic Press.
Pryor, W.A. (1976) Free Radicals in Biology, vols 1–5. New
York: Academic Press.
Rasmussen, S.B., Hansen, D.B. and Nielsen, K. (1999)
Detection of Radicals in Collagen and Parchment
Produced by Natural and Artificial Deterioration,
56 Conservation of leather and related materials
The mechanisms of deterioration in leather 57
Electron Spin Resonance Spectroscopy (ESR) and its
Implications for Artificial Ageing and Test of
Conservation. In Preprints of the Advanced Study Course
1999, pp. 89–101. Copenhagen: Royal Academy of
Fine Arts.
Reich, L. and Stivala, S.S. (1971) Elements of Polymer
Degradation. New York: McGraw-Hill.
Ribéreau-Gayon, P. (1972) Plant Phenolics. New York:
Hafner.
Roux, D.G., Ferreira, D., Hundt, H.K.L. and Mahan, E.
(1975) Structure, Stereochemistry and Reactivity of
Natural Condensed Tannins as Basis for Their Extended
Industrial Application. App. Polymer Symposium, 28,
335–553.
Scott, G. (1965) Atmospheric Oxidation and Anti-oxidants.
New York: Elsevier.
Stambolov, T. (1996) Manufacture, Deterioration, and
Preservation of Leather. A Literature Survey of Theoretical
Aspects and Ancient Techniques. ICOM.
Thampuran, K.R.V., Vijayaramayya, T., Ghosh, D.
et al. (1981) The Use of Lyotropic Salts in the Rapid
Tanning of Heavy Leather. Leather Science, 28(12),
442–443.
Thomson, R.S. (1991a) A History of Leather Processing
from the Medieval to the Present Time. In Leather, its
Composition and Changes with Time (C. Calnan and
B. Haines, eds), pp. 12–15. Northampton: The Leather
Conservation Centre.
Thomson, R.S. (1991b) Surface Coatings and Finishes. In
Leather, its Composition and Changes with Time
(C. Calnan and B. Haines, eds), pp. 34 –38.
Northampton: The Leather Conservation Centre.
Thomson, R.S. (2001) Bookbinding Leather; Yesterday,
Today and, Perhaps, Tomorrow. Wolstenholme
Memorial Lecture 2000. Journal of the Society of Leather
Technologists and Chemists, 85, 66 –71.
Thomson, R. (2002). Conserving Historical Leathers:
Saving our Past for the Future. Journal of American
Leather Chemists Association, 97, 307–320.
Thomson, R. (2003a) Towards a Longer Lasting Leather:
A Summary of the CRAFT Leather Project. Leather
Conservation News, 17(1), 1–9.
Thomson, R. (2003b) Letter to the Editor. Journal of the
American Leather Chemists Association, 98, 363–365.
Traub, W. and Piez, K.A. (1971) The Chemistry and
Structure of Collagen. In Advancements in Protein
Chemistry, 25, 243–352.
Tuck, D.H. (1983) Oils and Lubricants Used on Leather.
Northampton: The Leather Conservation Centre.
Vest, M. and Larsen, R. (1999) Studies in Shrinkage
Activities of Leather and Parchment by Micro Hot
Table Method (MHT). In Preprints of the Advanced
Study Course 1999, pp. 143–150. Copenhagen: Royal
Danish Academy of Fine Arts.
Vilmont, L. (1992) Determination of the N-terminal
Groups in Vegetable Tanned Leathers by HPLCDerivation
Procedure and Preliminary Qualitative
Analysis. In ICOM Committee for Conservation Leathercraft
Working Group Interim Symposium, London, pp. 10 –15.
London: ICOM.
Vilmont, L. (1993) N-terminal Group Analysis. In The
STEP Leather Project, Second Progress Report (R. Larsen,
ed.), pp. 105–114.
White, T. (1958) Chemistry of Vegetable Tannins.
In Chemistry and Technology of Leather. (F. O’Flaherty,
W.T. Roddy and R.M. Lollar, eds), pp. 98–160.
New York: Reinhold.
Wouters, J. (1994) Tannin and Ion Analysis of Naturally
and Actinically Aged Leathers. STEP Leather Project
(R. Larsen, ed.), pp. 91–106. Copenhagen: Royal
Danish Academy of Fine Arts.
Wouters, J. and Claeys, J. (1997) Analysis of Tannins,
Sulphate, Fat, Moisture and Ash: Evolution and a
Significance of Parameters to be Followed for Measuring
the Degradation of Vegetable Tanned Leather. In
Environment Leather Project (R. Larsen, ed.), pp. 87–94.
Copenhagen: Royal Danish Academy of Fine Arts.
Wouters, J., van Bos, M., Poulsen, D.V., Claeys, J. and
Oostvogels, A. (1997) Analysis of Tannins, Sulphate,
Fat, Moisture and Ash of Leather, Treated or Produced
for Conservation. In Environment Leather Project
(R. Larsen, ed.), pp. 103–112. Copenhagen: Royal
Danish Academy of Fine Arts.
Young, G.S. (1990) Microscopical Hydrothermal Stability
Measurements of Skin and Semi-tanned Leather.
Preprints of the ICOM Committee for Conservation
9th Triennial Meeting, Dresden, 1990, II, pp. 626–630.
Los Angeles: ICOM.
Young, G.S. (1992). Loss of Infrared Linear Dichroism in
Collagen Fibers as a Measure of Deterioration in
Artifacts of Skin and Semi-tanned Leather. In Materials
Issues in Art and Archaeology, III (P.B. Vandiver,
J. Druzik and G.S. Wheeler, eds), pp. 859–867.
Pittsburgh: Materials Research Society.
Young, G.S. (1998) Thermodynamic Characterization of
Skin, Hide and Similar Materials Composed of Fibrous
Collagen. Studies in Conservation, 43 (2), 65–79.
Young, G.S. (1999) The Application of Thermal Microscopy,
Differential Scanning Calorimetry and Fourier Transform
Infrared Microspectroscopy to Characterize Deterioration and
Physicochemical Change in Fibrous Type I Collagen.
Unpublished Ph.D. Thesis, University of London.
6.1 Introduction
Leather is not a single substance but rather a group of
related materials with many characteristics in common.
Other skin-based products such as rawhide,
parchment and the so-called pseudo leathers also share
many of these properties. In this manner, the term
‘leather’ is analogous to the word ‘metal’ which covers
a wide range of related materials. Just as different metals
vary widely in their properties, each type of leather
will have its own unique range of characteristics. This
will depend on the raw material employed and the
processes used in its manufacture. The properties of a
particular piece of leather will also be affected by the
type and degree of deterioration which has taken
place over its lifetime. These properties will determine
which methods can and, more importantly,
should not be used during conservation. The application,
for instance, of aluminium alkoxide in non-polar
solvents, a technique developed for the chemical stabilization
of red rotted leathers, to ethnographic
pseudo leathers will cause irretrievable damage. It is
necessary, therefore, to determine its exact nature
before embarking on any treatment programme.
The examination of leathers and related materials
falls into three main groups:
(a) The determination of the type of raw material.
(b) The determination of the tanning process
employed.
(c) An assessment of the type and degree of deterioration
that has occurred.
6.2 Determination of raw material
The determination of the species of animal used
by a microscopical examination of hair follicle
patterns and the fibre structure has been described
in Chapter 3. Work is being undertaken to analyse
DNA extracted from skin-based objects. It might well
be possible to develop such procedures for untanned
materials and successful results have been reported
with oil-tanned chamois leathers (Langridge, 2004). It
is less likely, however, that successful methods will be
found for use with vegetable- or mineral-tanned
leathers as the crosslinking mechanisms involved in
the tanning processes will probably interfere with the
extraction procedure.
6.3 Determination of tannage type
Determination of the type of tannage is relatively
straightforward. An initial visual and manual examination
is often enough to give the required information
and has the advantage of being non-destructive.
With experience, the colour and structure of a skin
will reveal whether it is untanned or whether it has
been treated by a vegetable, alum or chrome process.
6.3.1 Ashing test
The type of tannage can sometimes be determined by
burning a small sample. Chrome-tanned leather will
give a green ash, alum-tanned materials a white ash
and vegetable, oil and untanned samples will combust
completely. Many untanned products, however, contain
appreciable quantities of common salt or calcium
compounds which give white residues that can be
confused with those of aluminium salts. In any case,
it is necessary to burn the carbon completely from
the charred leather before it is possible to examine
the ash fully. This requires surprisingly high temperatures
and long times if valid conclusions are to be
58
6
Testing leathers and related materials
Roy Thomson
Testing leathers and related materials 59
reached. It is for this reason that a range of spot tests
or more complex instrumental analytical techniques
have been developed (Reed, 1972).
6.3.2 Spot test
Originally spot tests were carried out on the objects
themselves, ideally in an inconspicuous area, but this
left a contaminated, coloured mark. This might once
have been thought of as an advantage as the spot is a
permanent record that the test has been carried out
and results obtained. However, any permanent contamination
of an object can never be considered good
practice. Spot tests have therefore been modified for
application to single fibres or small groups of fibres
taken from the leather. These include tests to determine
the presence of vegetable tannins and whether
these are of the condensed or hydrolysable type, as
well as the presence of aluminium compounds. Details
of these are as follows.
6.3.2.1 Detection of vegetable tannins
Place two samples, each consisting of fibres from the
material under examination, one at each end of a
microscope slide. Moisten each sample with a drop
of distilled water. Add one drop of a 1% aqueous
solution of ferric chloride to one sample. The presence
of vegetable tannins is indicated by the development
of a blue–black or green–black colouration.
6.3.2.2 Detection of aluminium
Place two samples, each consisting of several fibres
from the material under examination, one at each
end of a microscope slide. Moisten each sample
with a drop of 2M aqueous ammonium hydroxide
solution. Add one drop of a 0.1% solution of sodium
alizarin sulphonate solution in 90% ethyl alcohol to
one sample. After five minutes, remove excess reagent
using filter paper and add several drops of 2M aqueous
acetic acid solution. The presence of aluminium
compounds is indicated by a red colouration which
does not turn yellow on acidification.
6.3.2.3 Detection of condensed tannins
Place two samples, each consisting of several fibres
from the material under examination, one at each
end of a microscope slide. Moisten one sample with
a 1% solution of vanillin in 90% ethanol. Remove
excess reagent with a filter paper and add one drop
of concentrated hydrochloric acid to both samples.
The development of a deep red colour indicates the
presence of condensed tannins.
6.3.2.4 Detection of hydrolysable tannins
Place two samples, each consisting of several fibres
from the material under examination, one at each end
of a microscope slide. Add one drop of 2M aqueous
sulphuric acid to one sample. Wait three minutes.
Remove excess acid with filter paper. To the same
sample, add one drop of a 0.7% solution of
rhodomine in 99% ethanol. Wait five minutes.
Remove excess reagent with a filter paper. Add one
drop of a 2M aqueous potassium hydroxide solution
to both samples. The development of a red colouration
indicates the presence of gallic acid derived
from the acid hydrolysis of hydrolysable tannins.
6.3.3 Conclusion
Of these, the most widely used has been the test for
the presence of vegetable tannins (Driel Murray,
2002). Care must be taken in the interpretation of
results. This is particularly relevant with leather
recovered from archaeological sites as vegetable tannins
and aluminium salts are commonly found in
soils, leading to false positive results.
More complex techniques requiring specialist analytical
instruments include atomic adsorption or X-ray
fluorescence spectroscopy for the detection of aluminium
and potassium associated with the use of alum,
calcium possibly arising from the pretanning liming
process or chromium. They also include the use of
high performance liquid chromatography on extracts
from the leather to determine the presence and type of
vegetable tanning materials (Wouters, 1992).
6.4 Determination of degree of
deterioration
As with the determination of the type of tannage, an
organoleptic examination of a leather object will
yield a considerable amount of information on the
amount of deterioration it has suffered. Different
senses can be involved independently or, often subconsciously,
in combination.
6.4.1 Organoleptic examination
Simply looking at an object, with or without magnification,
will reveal whether the leather surface
is coherent or friable. This immediately gives a
reasonable indication as to whether the material is
in a good, fair or poor condition. The colour of a
leather, particularly a vegetable-tanned leather, will
indicate whether it has been affected by the form
60 Conservation of leather and related materials
of acidic degradation known as red rot. As the
name suggests, this manifests itself as an orange–red
discolouration.
Handling the leather and gently rubbing the surface
will confirm whether it is breaking up. It will
also give an indication as to whether the leather
is flexible or stiff. Larsen and his co-workers have
developed this subjective type of handling assessment
into a more systematic, objective method capable of
giving numerical values which can then be replicated
by different testers (Larsen et al., 1994, 1996).
The smell of vegetable-tanned leather can also
give an indication as to its state of deterioration.
Red-rotted leather has a characteristic acrid odour
which pervades the stacks of many major libraries.
It is difficult to describe but once it has been experienced,
it is instantly recognizable.
The taste of acidic leather is also characteristic
but this method of testing leather is not to be
recommended.
6.4.2 Chemical tests
In addition to these non-invasive, organoleptic
examination methods to determine the condition of
leather objects, chemical tests have been developed.
Hendricus van Soest and his colleagues from the
then Central Research Laboratory in Amsterdam
have described a series of tests they considered necessary
to undertake before deciding on a conservation
programme. These include the determination
of pH and the sulphate, fat and moisture contents
(Soest et al., 1984). They suggest samples should be
taken from at least three different places on an object
to obtain a representative set of results. This, they
state, can require up to 30g of material. Wouters
(1992) pointed out that limitations exist on the
amount of sample that can be taken from an historic
object. He describes an analytical scheme for the
determination of volatile matter (primarily moisture
content), shrinkage temperature, pH and pH
difference figure, the contents of anions such as sulphate
chloride, nitrate and phosphate, tannin type
and content, fat content and the amount of such
cations as aluminium, chromium and iron present,
all using a sample as small as 200mg. Due to the
heterogeneity of leather, particularly aged leather,
he admits that large deviations between the results
given by different samples from the same object
might be expected. He states, however, that this
lack of absolute accuracy is preferable to obtaining
more reproducible figures which can be produced
from larger samples. It should be noted that this
analytical scheme requires access to specialist equipment
such as anion and reverse phase, high performance
liquid chromatographs and atomic absorption
spectroscopes, together with experience in using
such instruments on a regular basis.
It may be useful to concentrate on the most
important tests that can be carried out on historic
leathers by bench conservators and on how the
results obtained should be interpreted.
6.4.2.1 Shrinkage temperature
If a piece of leather or other collagen-based material
is thoroughly wetted, placed in water and gradually
heated, a temperature will be reached at which the
sample will suddenly and irreversibly shrink to
about one third of its original area. This temperature
is called the shrinkage temperature and will
depend on the raw material, the methods of
tannage, the amount and type of deterioration
the leather has undergone during its lifetime and
details of how the shrinkage temperature was determined
(Balfe and Humphreys, 1948; Nayndamma,
1958).The difference between the shrinkage temperature
of an historical skin product when it was
new and the figure obtained now is considered to
be an indication of the various chemical changes
which have occurred to the collagen/tanning material
complex during its lifetime. These chemical
changes are together responsible for the physical
changes which take place such as losses in strength
and flexibility. Measurement of the shrinkage temperature,
together with a knowledge of the probable
initial shrinkage temperature of the product will
therefore give an understanding of the level of deterioration
it has undergone.
Details of the standard method for the determination
of shrinkage temperature have been standardized
as Test IUP 16 of the International Union of
Leather Technologists and Chemists Societies
(Williams, 2000). This method requires a sample of
50mm ϫ 3mm. It is unlikely that such a sample
could be cut from any historic artefact. Conservators
have therefore used smaller samples and procedures
using single fibres under the microscope have been
developed (Young, 1990; Larsen et al., 1993) based
on earlier work by leather chemists (Nageotte and
Guyon, 1930; Salcedo and Highberger, 1941;
Nutting and Borasky, 1948, 1949).
The hydrothermal shrinkage of leather has been
likened to melting, except that it is irreversible.
As with melting, the shrinkage phenomenon is a
transition from one phase to another and, as with
Testing leathers and related materials 61
other phase transitions, this shrinkage is associated
with energy transfer. These energy changes can be
measured using techniques such as differential scanning
colorimetry, also known as differential thermal
analysis. This technique was first used to examine
the shrinkage of collagen in the 1960s (Witnauer
and Wisnewski, 1964) and had been applied to the
examination of the effects of natural and artificial
ageing of leathers in particular by Chahine and her
co-workers (1991, 1992).
Differential scanning colorimetry studies indicate
that the temperature at which the phase transition
occurs is close to the shrinkage temperature measured
by conventional means. They also show that
the transition associated with hydrothermal shrinkage
is endothermic, that is there is an overall absorption
of energy by the sample. Ageing, whether
natural or artificial, causes a reduction in the shrinkage
temperature. It also results in a reduction of the
amount of energy required to shrink the leather.
This has practical implications. Not only will wet,
partially degraded leathers shrink irreversibly at relatively
low temperatures, that is at ambient summer
temperatures in temperate climates, but the amount
of heat required to cause damage is much less. It
must be remembered, however, that the shrinkage is
hydrothermal, not just thermal. The amount of
water present is critical to the transition. An undegraded
vegetable-tanned leather, for instance, will
contain about 15% moisture when equilibrated at
65% relative humidity. Although it would shrink at
about 80°C when wet, it will withstand temperatures
well in excess of 100°C in this equilibrated
condition (Bienkiewicz, 1983). It is therefore possible
to use treatments involving heat on new or partially
degraded leather objects provided that they are
relatively dry. These procedures include the use of
hot melt adhesives or fillers (see Chapter 22) and pest
eradication systems such as the Thermo Lignum
process (Thomson, 2002).
6.4.2.2 pH
In 1923, Brønsted and Lowry proposed their theory
regarding the nature of acids and bases. This
included the concept of strong and weak acids and
bases. This proposes that when they are dissolved in
water, strong compounds, such as hydrochloric and
or sodium hydroxide dissociate completely into
their constituent ions:
HCl : Hϩ
ϩ ClϪ
NaOH : Naϩ
ϩ OHϪ
Weak compounds, on the other hand, such as acetic
acid or ammonia only dissociate partially on solution:
CH3COOH 4 Hϩ
ϩ CH3COOϪ
NH3 ϩ H2O 4 NH4
ϩ
ϩ OHϪ
It has been shown that the degree of dissociation for
any compound is constant at a given temperature.
The concentration of hydrogen or hydroxyl ions
in a solution is therefore determined not only by the
amount of acid or alkaline compound present, but
also by the degree to which the particular compound
has dissociated. By convention, this concentration
of hydrogen or hydroxyl ions is expressed as
the pH value. This has been defined as the negative
logarithm to the base of 10 of the concentration of
hydrogen ions present in a solution:
pH ϭ Ϫlog10 [Hϩ
]
Because water dissociates only very weakly to give
equal quantities of hydrogen and hydroxyl ions, it
can be calculated that the pH value of pure water at
ambient temperatures is 7.0. It can also be shown
that adding acid reduces this figure to a minimum of
0 and adding alkali increases it to a maximum of 14
(Phillips, 1999).
It will be noted that the dissociation of a compound
and the formation of ions is a solution effect.
The measurement of a pH of a solid such as leather
is therefore problematical. As a result it is usual to
measure the pH of an aqueous extract. It will also be
noted that the result obtained depends on the concentration
of the ions in the extract which itself is
determined by the amount of water used to extract
a given quantity of solid. In order to obtain reproducible
results, it is therefore necessary to fix the ratio
of sample to water. This has been defined internationally
as 5g of leather to 100ml of water
(Standard Test IUC 11). It is rarely possible to
obtain samples this large from historic objects but
similar results can be obtained from smaller samples
provided this ratio is maintained. Using standard
glass electrodes, it is possible to reduce the sample
size to 0.25g extracted with 5ml water and ‘one
drop’ electrodes are now obtainable which can
measure solutions prepared from samples as small as
0.025g extracted in 0.5ml water.
In the scheme for leather analysis described by
Wouters (1992) 1g of leather is extracted with 50ml
of water. As he points out, results given using this
procedure would be expected to be up to 0.4 units
higher than those obtained with the standard method.
The form of deterioration known as red rot is
considered to be caused by the action of strong acids
62 Conservation of leather and related materials
on vegetable-tanned leathers especially on those
processed with condensed tannins. These strong
acids, particularly sulphuric acid, could have been
added to the leather during processing or to have been
formed in situ from sulphur dioxide absorbed from
polluted atmospheres. A number of analytical methods
have been developed to determine the amount
of strong acid present in a leather. However, it has
been found empirically that if a standard extract
from a vegetable-tanned leather has a pH in excess
of 3.2 it was unlikely to contain damaging quantities
of strong acids and to develop red rot.
Conversely, a leather having a pH of 2.8 or less
is likely to be suffering actively from this kind of
deterioration.
By extension, it has sometimes been thought that
any leather having a pH of 3.2 or more is unlikely to
be in a deteriorated condition. This is not the case.
As was pointed out in the 1930s, leathers which are
strongly degraded by the ‘conjoint effects of oxidation
and acidity’ can break down to liberate ammonia
(Atkin and Thompson, 1937). This reacts with
any strong acid present with a resultant formation of
ammonium sulphate and increases in pH. Wouters
has noted that a number of historic leathers, which
despite having a low shrinkage temperature indicating
deterioration, have a relatively high pH. These,
though, have a relatively high sulphate content. He
suggests that at one stage in their lifetime, these
leathers had a low pH due to the presence of sulphuric
acid but at a later stage, the acid was neutralized.
He has developed a procedure for determining
a calculated pH assuming that all the sulphate present
in the leather at one time existed as free sulphuric
acid (Wouters and Claeys, 1966).
While there is no doubt that the pH of a leather
will be a major factor as to whether it will deteriorate
rapidly or not, it is not the only or even the predominant
one. In 1975, Raistrick surveyed leather from
the Long Term Deterioration Trials undertaken by
the British Leather Manufacturers’ Research Association
(Raistrick, 1977). He showed that the initial
pH values measured in the 1930s bore no relationship
to the amount of deterioration observed in the
1970s. Indeed the leather with the lowest pH of 2.6
in 1931 had not deteriorated to any extent whereas
that with the highest initial pH of 6.5 had decayed
severely.
6.4.2.3 pH difference
If a solution of a strong acid is titrated against a solution
of a strong alkali (that is small, equal aliquots of
the alkali solution are added to a given quantity of the
acid solution) and the changes in pH are noted, the
following will be observed. Initially, there will be
little change from the original low value. This will be
followed by a sudden increase. The pH will then
level off at a high value. This is shown in Figure 6.1.
If a similar solution of weak acid is titrated against
the solution of a strong alkali, a different situation
emerges. Initially the titration curve will increase
gradually. Then, the rate of increase jumps suddenly.
The titration curve then follows that observed with
the strong acid. The point at which this change occurs
is related to the degree of dissociation of the weak
acid. This is shown in Figure 6.2.
As has been defined above, the pH is related logarithmically
to the base 10 to the concentration of
14
12
10
8
6
4
2
pH
Amount of alkali added →
Figure 6.1 Strong acid–strong alkali.
14
12
10
8
6
4
2
pH
Amount of alkali added →
Figure 6.2 Weak acid–strong alkali.
hydrogen ions present. Therefore if a given quantity
of a solution of a strong acid having a pH value of
3–5 is diluted tenfold, by definition its pH value
will increase by one unit. On the other hand, if a
solution with a similar pH value contains only a
weak acid, it will be seen that the reduction will be
less. This phenomenon has been utilized to determine
whether a leather contains appreciable quantities
of strong acid. An aliquot of the aqueous extract
used to determine the pH of the leather is diluted
tenfold, the new pH is determined and the difference
between the two figures calculated. If this difference
is greater than 0.7 it is considered that
dangerous quantities of strong acid are present. If it
is less than 0.6 harmful acids are absent (Innes, 1948).
It must be noted that as with the initial pH figure,
the absence of strong acids in a sample of historic
leather at the time of examination does not indicate
that they have never been present. Nor does the
presence of strong acids mean that the leather will
inevitably deteriorate. As Innes put it, ‘vegetable
tanned leathers which contain sulphuric acid after
storage are not always rotted’ and this is confirmed
by Raistrick (1977) who showed that the amount of
deterioration of a leather over 40 years was independent
of its initial difference figure.
6.4.2.4 Sulphate content
The sulphate content of a leather has generally been
determined gravimetrically by adding barium chloride
to an aqueous extract and weighing the amount
of barium sulphate precipitated (Rowley, 1999).
Many leathers only contain small quantities of sulphate
so to obtain meaningful results large samples
are required. Alternative methods have therefore
been suggested which employ much smaller samples.
These include titrimetry with the aid of ion
selective lead electrodes (Hallebeek, 1992) and
anion chromatography (Wouters, 1992).
The presence of sulphate in vegetable-tanned
leathers has been linked to the presence, now or
in the past, of sulphuric acid. Indeed, as has been
described above, sulphate contents have been used to
determine the ‘calculated pH’ of historic leathers. It
should be noted, however, that this calculation
assumes that all the sulphate in the leather has derived
from sulphuric acid. It also assumes that all strong
acid in the leather has arisen from sulphuric acid.
A wide variety of sulphur compounds, which
may or may not be converted to sulphuric acid,
have been employed increasingly in the manufacture
of leather from the mid-nineteenth century.
These include sodium sulphide for unhairing,
sodium sulphite and related compounds as bleaches
and stabilizing agents in the vegetable tanning
process, sodium sulphate associated with chrome
tanning compounds or added to many dyestuffs as a
diluent, sulphated and sulphonated oils used for
fatliquoring and a wide range of sulphonated aromatic
compounds employed as synthetic tanning
agents, the syntans. Care should therefore be taken
before assuming that sulphate present in a leather is
necessarily deleterious. Indeed the presence of large
quantities of neutral sulphate in vegetable-tanned
leather added in the form of the sodium salt has
been reported to give ‘considerable protective
power’ against the effects of acidic atmospheric pollution
(Innes, 1948).
6.4.2.5 Fat content
Oils and fats are added to leather during its manufacture
to prevent the fibres from sticking together
as it dries thereby imparting the desired degree of
softness and flexibility. These can be applied as a
paste to the warm, wet leather and allowed to impregnate
the fibre structure over an extended period of
time in the currying process. Alternatively, they are
applied in the form of an emulsion in the fatliquoring
process which was introduced at the end of the
nineteenth century.
As leathers age they can become firm, hard and
cracky. At the same time, the amount of material that
can be extracted using organic solvents is reduced. It
has therefore been assumed that the fatty materials
added during processing have been lost. This concept
of ‘feeding’ the leather with new oil and fat
mixtures to replace this lost material and restore the
original properties has therefore grown up
(Waterer, 1972). It was noted early on that adding
too much new fatty material could result in an even
greater amount of damage. Methods were therefore
developed to determine the amount of fatty materials
still present in the leather with a view to calculating
how much new oil and fat needed to be applied
to achieve a desired final oil content. Initially,
methods involved extracting samples of the leather
with organic solvents such as petroleum ether
(Soest et al., 1984), n-methane (Wouters, 1992) or
dichloromethane (Wouters, 1994) in a Soxhlet
apparatus. As with the other determinations, the
size of sample required is rather large. An alternative
method has therefore been investigated using gas
chromatography/mass spectrometry techniques.
These, potentially, could give some idea of the type
Testing leathers and related materials 63
64 Conservation of leather and related materials
of oil present in the leather, the type and degree of
deterioration which it has undergone as well as the
quantity of fatty material still free to be extracted
(Bos et al., 1996).
6.4.2.6 Moisture content
This is determined by equilibrating a sample of the
leather in an environment of 20°C and 65% RH,
weighing it, drying it for 24 hours at 102°C, cooling
it in a desiccator and weighing it again. The material
lost is presumed to be moisture.
New leathers would be expected to contain about
14% moisture under these conditions. Old, deteriorated
leather usually contains less, down to 10%. In
addition, it is generally considered that deteriorated
leathers absorb and desorb moisture to a smaller
extent and at a slower rate than new leathers. Recent
studies (Hallebeek, 1994) have shown that this is not
necessarily true particularly if the degraded leathers
contain hygroscopic breakdown products.
6.5 Conclusions
As with other materials, it is generally accepted that
historic leather objects presented for conservation
should be examined thoroughly before treatment
proposals are drawn up and any practical work undertaken.
Questions to be answered include:
(a) What was the leather made from?
(b) How was it manufactured?
(c) How much and what type of deterioration has
it suffered?
In addition, conservators, because of their specialist
experience and knowledge, are often asked their
opinion on historical technological and other aspects
regarding the object.
Any study of an object can include a non-invasive,
organoleptic examination and/or a more intrusive
series of chemical or physical tests. In principle,
providing the necessary information can be gained
without changing or damaging the object this is the
route to follow.
If, for instance, the object is a pair of ladies’ white
gloves from the mid-nineteenth century, the leather is
likely to be alum tawed and should be treated as such.
If it comes from the early twentieth century, it might
have been tanned using formaldehyde or one of the
early syntans. An experienced conservator with a
knowledge of the changes in the tanning processes
that took place over this period would realize that the
methods employed for treatment would be exactly the
same for all three types of leather. It would not therefore
be necessary or ethically valid to take samples to
carry out tests.
Equally, if a leather bookbinding exhibits the
colour, surface texture and smell of a red-rotted
vegetable-tanned leather, is it necessary to take samples
to determine the pH and difference figure?
These are the type of questions a practising conservator
needs to consider on a daily basis. Nevertheless,
any conservator considering a leather object should be
aware of the test methods available so that they can
apply them when required.
References
Atkin, W.R. and Thompson, F.C. (1937) Proctor’s Leather
Chemists’ Pocket Book, 3rd edition, p. 273. London: E. &
E.N. Spon.
Balfe, M.P. and Humphreys, F.E. (1948) The Shrinkage
Temperature of Leather and the Effects of Heat and
Moisture on Leather. In Progress in Leather Science
1920 –1945, pp. 415– 425. London: British Leather
Manufacturers’ Research Association.
Bienkiewicz, K. (1983) Physical Chemistry of Leather Making
pp. 243–252. Malabar, Fl.: Krieger.
Bos, M. van (1996) Quantitative and Qualitative Determination
of Extractable Fat from Vegetable Tanned
Leather by GC-MS. In ENVIRONMENT Leather Project
(R. Larsen, ed.), pp. 95–102. Copenhagen: Royal Danish
Academy of Fine Arts.
Chahine, C. (1991) Acid Deterioration of Vegetable
Tanned Leather. In Leather, its Composition and Changes
with Time (C. Calnan and B. Haines, eds), pp. 75–87.
Northampton: Leather Conservation Centre.
Chahine, C. and Rottier, C. (1992) Changes in Thermal
Stability During Artificial Ageing with Pollutants: A
DSC Study. In Postprints of the ICOM Committee for
Conservation Leathercraft Group Interim Symposium.
pp. 6 –10, London: ICOM.
Driel Murray, C. van (2002) Practical Evaluation of a Field
Test for the Identification of Ancient Vegetable Tanned
Leathers. Journal of Archaeological Science, 29, 17–21.
Hallebeek, P.B. (1992) Moisture Uptake/Release and
Chemical Analysis. In Postprints of the ICOM Committee
Leathercraft Group Symposium, London 1992, pp. 19–21.
ICOM.
Hallebeek, P.B. (1994) Moisture Uptake/Release and
Chemical Analysis. In STEP Leather Project (R. Larsen,
ed.), pp. 107–116. Copenhagen: Royal Danish Academy
of Fine Arts.
Innes, R.F. (1948) The Preservation of Vegetable Tanned
Leathers Against Deterioration. In Progress in Leather
Science 1920 –1945, pp. 426 – 450. London: British
Leather Manufacturers’ Research Association.
Langridge, D. (2004) A Goat in Sheep’s Clothing? BLC
Journal, September, 3–5.
Testing leathers and related materials 65
Larsen, R. et al. (1993) Determination of Hydrothermal
Stability (Shrinkage Temperature) of Historical Leather
by the Micro Hot Table Technique. Journal of the Society
of Leather Technologists and Chemists, 77, 151–156.
Larsen, R. et al. (1994) Materials. In STEP Leather Project
(R. Larsen, ed.), pp. 11–30. Copenhagen: Royal Danish
Academy of Fine Arts.
Larsen, R. et al. (1996) Fibre Assessment. In ENVIRONMENT
Leather Project (R. Larsen, ed.), pp. 113–120.
Copenhagen: Royal Danish Academy of Fine Arts.
Nageotte, J. and Guyonne, L. (1930) American Journal of
Pathology, 6, 631– 638.
Nayndamma, Y. (1958) Shrinkage Phenomena. In The
Chemistry and Technology of Leather (F. O’Flaherty et al.,
eds), 28– 65. New York: Reinhold.
Nutting, G.C. and Borasky, R. (1948) Journal of the
American Leather Chemists’ Association, 43, 96 –101.
Nutting, G.C. and Borasky, R. (1949) Journal of the
American Leather Chemists’ Association, 44, 831–838.
Phillips, P. (1999) Acids, Bases and Salts. In Leather
Technologists’ Pocket Book (M. Leafe, ed.), pp. 353–369.
Withernsea: Society of Leather Technologists and
Chemists.
Raistrick, A. (1977) Long Term Evaluation of Bookbinding
Leathers with a Critique of the Peroxide Test. British
Leather Manufacturers’ Research Association Laboratory
Report LR58. Egham: BLMRA.
Reed, R. (1972) Ancient Skins, Parchments and Leathers, pp.
265–287. London: Seminar Press.
Rowley, G. (1999) The Analysis of Leather. In Leather
Technologists’ Pocket Book (M. Leafe, ed.), p. 261.
Withernsea: Society of Leather Technologists and
Chemists.
Salcedo, I.S. and Highberger, J.H. (1941) Journal of the
American Leather Chemists’ Association, 36, 271–283.
Soest, H.A.B. van et al. (1984) Conservation of Leather.
Studies in Conservation, 29(1), 21–31.
Thomson, R.S. (1995) The Effects of the Thermo
Lignum Pest Eradication Treatment on Leather and
Other Skin Products. Leather Conservation News, 11,
11–12.
Thomson, R.S. (2002) Conserving Historical Leathers:
Saving Our Past for the Future. Journal of the American
Leather Chemists’ Association, 97, 307–320.
Waterer, J. (1972) A Guide to the Conservation and
Restoration of Objects Made Wholly or in Part of Leather.
London: G. Bell.
Williams, J.M.V. (2000) IULTCS (IUP) Test Methods.
Journal of the Society of Leather Technologists and Chemists,
84, 359–362.
Witnauer, L.P. and Wisnewski, A.J. (1964) Absolute
Measurement of Shrinkage Temperature by
Differential Thermal Analysis. Journal of the American
Leather Chemists’ Association, 59, 598– 612.
Wouters, J. (1992) Evaluation of Small Leather Samples
Following Successive Analytical Steps. In Postprints of
the ICOM Committee for Conservation Leathercraft Group
Interim Symposium, London. ICOM.
Wouters, J. and Claeys, J. (1996) Analysis of Tannins,
Sulphate, Fat, Moisture and Ash: Evolution and
Significance of Parameters to be Followed for Measuring
the Degradation of Vegetable Tanned Leather. In
ENVIRONMENT Leather Project (R. Larsen, ed.),
pp. 87–94. Copenhagen: Royal Danish Academy of
Fine Arts.
Young, G.S. (1990) Microscopical Hydrothermal
Stability Measurements of Skin and Semi-tanned
Leather. In Preprints of the ICOM Committee for
Conservation 9th Triennial Meeting, Dresden 1990, II,
pp. 626 – 630. Los Angeles: ICOM.
7.1 Tanning in prehistoric and
classical times
The hides and skins of animals killed for food appear
to have been used for clothing, shelter and other
purposes long before the evolution of modern man.
The earliest creature which appears to have made a
systematic use of animal skins was Australopithecus
habilis who roamed East Africa some two million years
ago and seems to have developed a diet in which meat
played an increasingly significant part. Unlike other
carnivores, the Australopithicines were not equipped
with specialized teeth or claws to penetrate the tough,
fibrous, outer protective layer – the skin – but artefacts
indicate that they discovered that the serrated edge of
a chipped stone was capable of cutting through the
thickest hide. This fundamental technological discovery
led to a wider use of edged stone tools – an essential
factor in the evolution of man. The presence of
accumulations of specific bones at Australopithecine
sites suggests that the more succulent joints of larger
animals were butchered from the carcass and possibly
dragged back to the living quarters on the skin of the
animal itself. Once back at the living site the skins, relatively
large sheets of a tough, flexible material, could
have been used for a wide range of purposes.
The next stage in the development of the use of
hides and skins is associated with the Pithecanthropoid
group of hominids. These creatures were systematic
and successful hunters. They had learned to control
fire and cooked their meat. They had also developed a
wider range of tools including the typical Acheulean
coup-de-point which has been shown to have been used
for both butchering and skinning. Some bands of these
Pithecanthropoids lived in large, tent-like shelters constructed
by spreading skins over wooden frameworks,
supported by rows of upright poles. Skins also appear
to have been used to make rough bundles running
along the sides of the shelters. These dwellings were
warmed by a fire in a central hearth. With such a
structure, the curing effect produced by drying the
skins out slowly would have been demonstrated. More
importantly, the mild tanning action of wood smoke
would also have manifested itself. The suggestion that
Pithecanthropus erectus observed and exploited these
changes is supported by the fact that they devised special
stone implements for scraping away the unwanted
fat and flesh. This scraping would also have distributed
the fats throughout skins giving a more supple product.
Flexing the pelt while it was drying would also
have given a softer product. It is very possible that a
crude form of leather was being produced by these
hominids over a million years ago (Schwerz, 1958).
The next major stage in human development was
the evolution of Neanderthal Man about one hundred
thousand years ago. This close relative of modern
man is typically associated with a wider range of specialized
stone implements including a higher proportion
specifically made for working the hides and skins.
The Neanderthals were skilful hunters preying on animals
such as deer, horses, bears, rhinoceros or even
mammoth, and had access to large quantities of hides
and skins. Neanderthal Man is associated with the last
great ice age when they flourished despite the intense
cold, living in skin-covered tents. The fact that they
expanded their territory into the bleak tundra regions
supposes the production of warm, protective clothing
had been perfected. Neanderthal Man employed
stone, horn, antler and bone for skin-working tools.
The bone implements included lower leg bones
sharpened along the concave edge to give fleshing
knives. A similar range of stone and bone tools were
used in an analogous manner by Native American
peoples until the end of the nineteenth century. The
earliest skin remains also date from this period.
Between thirty-five and forty thousand years ago,
Cro Magnon Man, Homo sapiens, appeared in Europe.
Their tools included many specialized skin-working
66
7
The manufacture of leather
Roy Thomson
The manufacture of leather 67
implements including different stone and bone
scrapers, burnishers, knives and awls each designed
for a specific and slightly different purpose. By twenty
thousand years ago, delicate skin-working implements
including fine needles, awls and knives were being
made from bone and flint. These were of such fragile
construction that it can only be surmised that the art
of preparing soft flexible leathers had been completely
mastered. The works of the prehistoric
artists have given us the first direct evidence of the
use of leather for clothing. Rock paintings dating
from thirty-five thousand years ago show males
wearing leather loin cloths and a female wearing a
skirt. Similar pictures ranging over the next twentyfive
thousand years depict people wearing trousers
and dresses presumably made from leather (Figure
7.1). In the colder, more northerly regions, warmer
garments were necessary and stone statuettes have
been excavated in Central Asia showing people
wearing fur clothing closely resembling the anorak
and trousers of modern Inuit. Cave paintings also
show the use of leather for bags, belts and rope, and
leather bindings were used to attach stone blades
and axe heads to wooden, bone and antler shafts. It
must therefore be concluded that by the time Homo
sapiens evolved, the art of leathermaking had been
fully developed and that tanning was probably man’s
first manufacturing process (Forbes, 1957).
Excavations in Egypt have given us the first pictures
of tanning operations in the form of wall paintings
from tombs, ranging from the fifth to the twentysixth
dynasties. A scene from the tomb of Rekhmire,
dating from about 1500 BC, depicts skins being
fleshed, steeped in large jars containing an unknown
liquor and staked or softened by pulling it over an
implement similar to a lawn edging tool (Figure 7.2).
The finest gloving leathers are still softened in this
Figure 7.1 Upper paleolithic depiction of men and
women wearing skin garments.
Figure 7.2 Leather manufacturing processes from fifteenth century BC Egyptian tomb.
68 Conservation of leather and related materials
manner using an identical implement. The first
recipes giving details of the tanning processes also date
from about the same period. A series of Sumerian ritual
magical texts describe the preparation of bullock
and goatskin leathers to be used in the manufacture of
drums employed in religious festivals (Levey, 1959).
The texts themselves date from about 1000 BC but
probably reflect techniques dating back to the third
millennium or earlier. One reads:
You will steep the skin of a young goat with milk of a
yellow goat and with flour. You grease it with fine oil,
ordinary oil and the fat of a pure cow. You will soak
alum in grape juice and cover the surface of the skin
with gall nuts of the tree growers of the Hittite country.
The rise of the city-state and the move towards
urban living led to an increased demand for leather
for civilian and, particularly, military purposes.
Tanning developed from a small-scale craft activity
to an important occupation organized on an industrial
basis. Early Sumerian and Egyptian texts indicate
that a complex trade in raw and cured hides and
skins, tanning materials, finished leather and madeup
goods flourished throughout the Near East over
5000 years ago. This trade continued and expanded
until, by the period of Classical Greece, tanners were
a prosperous and influential section of the community
and a single factory at Piraeus, specializing in
manufacturing leather shields, employed 120 slaves.
The development of leathermaking was not, however,
restricted to the urban civilizations. Remains of
high quality leathers have been found from Late
Neolithic, Bronze and Iron Age sites as diverse as the
Frozen Tombs of Central Asia, the Hallstatt salt mines
of Upper Austria and the bog burials of Denmark.
The Romans, too, recognized the vital importance
of leather to their military forces. Hides and skins
were demanded as a tribute by the legions and it has
been suggested that cattle were bred for their hides
rather than for their meat. Rather than rely on local
supplies, the Roman Army organized its own tanneries
and leather workshops.
Some idea of the tanning techniques used at the
time of the Romans can be deduced from the remains
of the civilian tannery excavated at Pompeii (Faber,
1938). It housed 15 tanning pits, each 1.5m in diameter
and about 1.2m deep. There were also a series
of smaller vats in which the tanning materials were
prepared. A separate area was for the mechanical
working of the hides. Here, two-handed scrapers, a
currier’s knife, sharpening steel and half-moon
knives were found. The layout of the plant and the
tools found suggest that a Roman tanner would have
felt completely at home in the tanneries depicted
by the eighteenth-century French encyclopaedists.
Indeed, there appear to have been few fundamental
advances in the technology of leather manufacture
between the classical Greco-Roman period and the
Industrial Revolution of the nineteenth century.
7.2 Tanning in the medieval and
post-medieval periods
Leather and leathergoods manufacture were crafts
widely practised throughout Europe and from the
early medieval period until the mid-eighteenth century
were second only in importance to the wool
textile industries (Cameron, 1998).
The first job of the tanner was to wash the hides
free from blood, dung and curing salts and to rehydrate
them. This was often done by immersion in
the local river or stream (Figure 7.3). The rehydration
of dried hides could be accelerated by pounding
them with hammers or by treading them underfoot.
It was then necessary to treat the hides in various
ways to loosen the hair and enable it to be scraped off
without damaging the grain surface. The most primitive
method was to fold the hides and pile them until
putrefaction set in just enough to loosen the hair
roots. This putrefaction action was often speeded up
by sprinkling the hair side with biologically active
liquors prepared from such materials as stale beer,
urine, dung, fermenting barley or mulberry and bryony
leaves. An alternative method was to soak the
skins in alkaline liquors prepared from wood ash or,
more commonly, lime. A third method can be considered
as a combination of the first two. In this, the
hides were immersed in lime liquors which had been
‘mellowed’ by repeated use. These liquors would
have contained large concentrations of organic breakdown
products which would have accelerated the
depilatory action. The hide was then spread over a
wooden beam and both sides scraped with tanners’
two handled knives (Figure 7.4). The hair side was
scraped with a blunt, single-edged unhairing knife
and the flesh with a sharper, two-edged fleshing knife.
The hide was then put back into the liquors to open
up the skin structure further, prior to another scraping
with a blunt scudding knife.
The pelts were then washed and given a further
cleansing and opening-up treatment using the alkaline
bating, puering or mastering process or the
acidic raising or drenching process.
In the alkaline processes, the pelts were immersed
in a warm infusion of bird droppings or dog dung.
The manufacture of leather 69
This removed excess lime and biochemically altered
the hide structure to give a softer leather with a
finer, more flexible grain. In the first decade of the
twentieth century the active ingredients in the dung
were found to be proteolytic enzymes secreted in
the pancreas and activated by ammonium salts. The
raising or drenching process involved treating the
hides in liquors prepared by fermenting barley, rye
and other vegetable matter (Thomson, 1981). The
fermentation was often promoted by the addition of
materials such as stale beer, urine or rotting pieces
of hide. The action of the fermentation was to produce
a complex mixture of organic acids and enzymes
which again dissolved the non-fibrous protein of
the skin and removed excess lime. Once the pelts
were judged to be in the correct condition, the
hides were again washed and worked over the beam
to remove the slime that had been liberated.
The majority of hides were vegetable tanned and
this technique will be considered first (Thomson
and Beswick, 1983).
The preliminary stage of the tanning operation
itself was to immerse the hides in weak, almost spent
tanning liquors, moving them around almost continuously
(Figure 7.5). Once the colour of the grain
was judged to be satisfactory, the hides were transferred
to a further set of pits. To prepare these, a
layer of ground vegetable tanning material was
tipped into the bottom of the pit and a hide laid flat
Figure 7.3 Washing hides in stream.
Figure 7.4 Removing hair with two-handled knife.
70 Conservation of leather and related materials
over it. The vegetable tanning material employed
depended on what was available locally. Birch,
willow, spruce and larch were used in northern
Europe and Russia; various species of oak in Britain
and central Europe; sumac, valonia, oak galls and
various acacias around the eastern Mediterranean.
A second layer of ground tanning material was strewn
over the first hide and a second hide spread out.
In this manner alternate layers of tanning material
and hides were added until the pit was nearly full
(Figure 7.6). A final layer of tanning material was
piled on top and the whole pit filled either with
water or an infusion prepared by extracting tanning
materials with cold water. The hides were generally
kept in these pits for at least a year. When the tanner
had judged the hides to be fully tanned, they were
rinsed off and smoothed out using a two-handled
setting pin. The leather was then dried out slowly
in a dark shed. This was often fitted with louvered
panels to control the rate of drying.
The dried rough leather was sold to a currier
whose first operation was to dampen it and then
soften it by pummelling with heavy wooden mallets
or by trampling under foot. This was followed by the
scouring operation in which the leather surfaces were
scrubbed clean using stone blocks or stiff brushes and
smoothed out using stone or metal-bladed slickers.
The next operation was to pare the skin down to
the required thickness using the currier’s shaving
knife (Figure 7.7). This had a rectangular, doublededged
blade fitted with two handles, one in line
with the blade and one at right angles to it. Both
edges of the knife were sharpened and turned by
pressing along them with a steel pin until the keen
edge was bent almost perpendicularly to the face of
the blade. The dampened leather was placed over a
near vertical currier’s beam and, holding the blade
of the shaving knife almost at right angles to the
leather, thin shavings were pared from the flesh surface
until the desired thickness was achieved.
The shaved hides were worked on a bench with
various stones, slickers and brushes to flatten the
leather, remove loose tanning materials and stretch
it. They were then partially dried and impregnated
with a warm mixture of tallow and fish oils. After
piling the skins to allow the fats to penetrate evenly,
they were hung in a warm room. Once dry, the surplus
grease was removed. On the grain side this was
done using smooth burnishing stones or leather
pads. The flesh side was often cleaned by removing
the surface layer completely using a sharpened steel.
If the leather was to be used where a firm product
was required, the hides were simply hung to dry
before selling them to the various leather working
Figure 7.5 Handling hides in weak tan liquors.
The manufacture of leather 71
craftsmen. If a softer, finer product was required, further
mechanical operations such as boarding or staking
were carried out (Figure 7.8). In the boarding
operation, the hide was folded grain side in, and
rolled firmly up and down using boarding arms.
Boarding emphasized the natural grain of the skin
and a wide range of surface effects could be obtained.
In the staking or perching operations the leather was
softened by rubbing the flesh side over the convex
edge of various blunt, curved blades in a manner similar
to that shown in Egyptian tomb paintings.
If required, the leather was coloured, using natural
dyestuffs or pigments. Finally, after swabbing
the surface with such materials as weak animal glue,
waxes, milk and blood, the leather was polished
using a range of slickers, brushes and pads. It was
only after all these operations had been carried out
that the leather was ready to be sold to the various
craftsmen who made it up into finished articles.
The above operations were employed by the tanner
and the currier who generally worked on the larger
cattle hides. Sheep, goat, deer and dog skins were
processed by the fellmonger, the whittawyer, or the
glover. Smaller, fur bearing pelts, on the other hand,
were prepared by the skinners (Thomson, 1981–82).
The trade of fellmongering was to take sheepskins
from the butcher or the farmer, remove the
wool from the skin, sell the wool to the textile trade
Figure 7.6 Laying skins away in pits.
Figure 7.7 Shaving leather to uniform thickness.
72 Conservation of leather and related materials
and the pelt to the whittawyer or the glover. The
process employed was to hang the skin in a warm
room and allow it to sweat until the wool root
structure just started to rot. The wool was then
pulled from the skin and sorted into various grades.
The skin was washed thoroughly and salted to preserve
it. An alternative method was to paint the flesh
side with a paste of slaked lime and water. The alkali
penetrated through the skin loosening the wool
roots allowing the wool to be pulled out.
The pretanning processes used by the whittawyer
were similar to those used by the tanner. Once the
skins had been limed, unhaired, fleshed and given a
thorough bating they were put into large wooden
tubs. There they were kneaded with a mixture of
materials such as alum, salt, egg yolks, butter, oatmeal,
olive oil and flour. Traditionally the tawyer
worked the mixture into the skins by trampling it in
with his bare feet (Figure 7.9). Once the required
amount of the tawing paste had been taken up by
the skins, they were stretched out flat and piled
overnight. The next day, they were mechanically
worked again, often by twisting them into a rope
and pulling this over an uneven surface such as a
ram’s horn set into a wooden upright. The skins
were flattened and smoothed and hung to dry. The
leather was then softened by staking or perching.
Figure 7.8 Working leather mechanically to obtain desired softness and appearance.
Figure 7.9 Working the tawing mixture into the skins
mechanically in the foot-tubbing process.
Widely used alternatives to the alum-based tawing
pastes were the various oxidizable marine oils
that were applied in the production of the chamois
and buff leathers. The oils were trampled into the
skins in a similar manner to that used in tawing.
The skins were then hung in warm, airy stoves for
the oxidation process to take place. After the oiling
and stoving sequence had been repeated, three or
four times, the leather was washed off in alkaline
liquors to remove excess oil.
The whittawyer also used vegetable tanning materials
to produce bazils, vegetable-tanned sheepskins,
and as this trade increased, the more general term
leatherdresser was introduced to describe the craftsmen
who undertook these operations.
Originally glovers made up leather purchased
from whittawyers. By medieval times, however,
they not only produced their own leathers but also
dealt in raw sheepskins and wool. They used the
same methods of tanning as the whittawyers.
Skinners processed pelts from a wide variety of fur
bearing animals ranging from rabbits and cats to
wolves and bears (Veale, 1966). The skins were usually
obtained in a dried condition and required careful
wetting back before excess flesh could be removed
and the pretanning operations undertaken. Great skill
was required to ensure that the structure of the pelt
was opened up sufficiently, while at the same time the
hair remained firmly attached. Skinners employed
the alum and oil tanning processes similar to those
used by whittawyers. Alternatively, fur skins were
treated in baths of fermenting grains similar to those
described in the raising or drenching processes used
by tanners. The organic acids and enzymes helped to
remove the non-collagenous interfibrillary materials
and give a softer product. These drenches did not tan
the pelts but made them acidic enough to prevent
bacterial attack.
7.3 Tanning in the nineteenth century
The nineteenth century in Europe was a period of
rapid expansion and tanners were forced to keep
pace with the general economic climate. The rapidly
increasing population and the gradually improving
standard of living during the nineteenth century
added their own demands on the leather trade.
The tanning process was based on the application
of the by-product of the forester, to the by-products
of the farmer. It is not surprising, therefore, that the
profound changes that took place in agricultural
practices throughout the nineteenth century had
their repercussions on the tanning trades. In particular
they led to a shortage of both indigenous tanning
materials and hides with a resultant increase in prices.
The hides and skins themselves were also affected.
Breeding experiments resulted in larger animals
being produced and larger and thicker hides coming
on the market. But larger size and artificial feeding
generally leads to poorer quality skins. With sheepskins,
the introduction of Merino strains to improve
wool yields also led to a deterioration in skin quality.
This resulted in shortages of both suitable quality
hides and of tanning materials that could only
be made up by importing, first, raw materials and
then finished leathers from the expanding European
empires and elsewhere.
The shortage of indigenous tanning materials also
stimulated a search for alternatives. In addition, it
encouraged attempts to use these materials more
effectively. It was recognized that the traditional
methods of layering and preparing oozes by leaching
with cold water failed to extract all of the tanning
materials. It was hoped that by employing more
efficient extraction techniques, larger amounts of
purer forms of tannin would be produced. These
improved methods worked to some extent but
despite this, there was just not enough European
material available to tan all the leather required and
the newly discovered imported materials had to be
made to work. Tanners had always known that hides
had to be fully penetrated with weak, almost spent,
tanning materials before they could be subjected to
the action of stronger, fresher extracts. The tanners
learnt that this principle was even more important
when dealing with these newer, more astringent
products. They also learnt how to blend the new
materials to obtain the required properties and to
apply gentle mechanical action to get more uniform
results (Thomson, 1991).
In parallel with the slow development of the vegetable
tanning process, improvements were gradually
introduced into the methods of pretanning. Traditionally,
only lime was used as a depilating agent,
although the beneficial effects of the repeated use of
the same lime liquor had been known for centuries.
To speed the process, alternative alkalis had been
suggested, either as additives or as alternatives. The
use of a mixture of orpiment and lime was introduced
which unhaired in less than 36 hours instead
of the usual three to four weeks and the modern sulphide
unhairing system was born. Later, further
improvements were introduced including the use of
cheap, waste lime liquors from gas works, where
lime was employed to scour hydrogen sulphide from
The manufacture of leather 73
the coal gas. Mixtures of lime and sodium sulphide
are still used today in most tanneries to remove the
hair prior to tanning.
In the 1830s Robert Warington patented the use
of potassium dichromate and chromic acid for preserving
the tanning skins but no use appears to have
been made of the discovery (Thomson, 1985). Over
the next 20 years, a number of chemists studied the
tanning action of various chromium salts. It was not,
however, until the 1870s, with the Heinzerling
process, that the leather was tanned on a commercial
scale using chromium chemicals. In the early 1880s
Augustus Schultz was asked to devise a process for
the production of leathers used to cover corset steels.
Schultz used his experience in the textile industry
and developed a system based on the processes
employed for mordanting cotton. The skins were
immersed in an acidified solution of sodium bichromate
and then in a solution of sodium thiosulphate.
This two-bath method of chrome tanning was
examined by a number of tanners in the USA who
found that excellent leather could be produced in a
matter of hours rather than weeks. In 1893 Martin
Dennis patented the use of trivalent chromium compounds
for tanning and the so-called one-bath
method of chrome tanning spread rapidly throughout
the world. Today, 80% or more of leather is
manufactured using variants of this process.
The first introduction of mechanization to the
working of hides appears to have been the use of
various types of fulling stocks used to assist in the
chamois tanning process and to speed up the rehydration
of the dried hides. A wide range of other
methods for applying mechanical action to speed
up the pretanning and tanning processes was also
devised. Of these, the most widely accepted was the
tanning drum which appears to have been developed
in northern Italy in the late seventeenth century
and is still the tanners’ main wet processing vessel
(Figure 7.10).
While leather manufacturers showed a reluctance
in accepting many of the early mechanical aids, the
one exception was the splitting machine. This split
the hide into two layers, a top split equivalent to a
shaved hide, and an extra, bottom split which had
all the properties of leather except for the grain
pattern. With the incentive of obtaining two hides
for the price of one, the tanners were prepared to
undertake development work and a number of different
types of splitting machine were developed
throughout the century.
A further development vital to the mechanization
of the leather industries was the invention of spiralbladed
cylinder knives. These were originally
developed for shearing furskins and were similar
to those used today in the blades of a lawn mower.
The use of two sets of these blades, opposing
each other at an oblique angle, enable soft, irregularly
shaped skins to be smoothed and stretched
out, thus preventing creases, while the blade carried
74 Conservation of leather and related materials
Figure 7.10 Water-driven tanning drum.
out its function (Figure 7.11). A considerable number
of machines for unhairing, fleshing, scudding,
setting, scouring, striking, staking and shaving were
designed over the next hundred years based on this
idea (Watt, 1855). Many leather working machines
used today throughout the trade are based on late
nineteenth century designs.
By the beginning of the twentieth century, the
majority of tanneries were using improved tanning
processes and were mechanized. A wide range of
machines was employed, supplied by specialist tanning
machinery manufacturers.
While many of the changes that took place in
processing during the nineteenth century were
improvements on previous techniques or produced
a less expensive, more uniform, product, some had
deleterious effects which only became apparent
decades after they were introduced. This was particularly
significant in the case of leathers for bookbinding,
which, unlike those for other purposes, are
expected to last a lifetime.
The first major change which was to lead to problems
was the introduction of a wider range of tanning
materials. As has been said, alternative products
were imported including many species not previously
employed in Europe. Although most of the
new imported tannins were used for the production
of heavy leathers, it is likely that some were tried for
bookbinding leathers.
Vegetable tannins can be divided into two main
classes depending on their chemical composition; the
hydrolysable tannins, such as sumac and Turkish galls,
and the condensed tannins, such as mimosa and mangrove.
We now know that leathers prepared using
condensed tannins decay more rapidly than those
manufactured using hydrolysable tannins. It is fortuitous
therefore that the new imported materials which
gave the best quality light leathers such as divi divi,
myrabolams, algarobilla, tara and bulbool are of the
hydrolysable type. It is quite possible, however, that
materials such as mimosa, mangrove or gambier were
employed by some tanners, particularly towards the
end of the nineteenth century. The gradually increasing
introduction of these newer materials throughout
the century resulted in more and more bookbinding
leathers with poor ageing properties (Thomson,
2001).
A potentially more damaging improvement was
the introduction of synthetic dyestuffs from the middle
of the century onwards. Initially, these were
developed for colouring textiles, but soon they were
being used on a wide range of leathers. The replacement
of the traditional methods with these new
products adversely affected the ageing properties of
the leathers in two ways. First, the natural dyestuffs
previously employed were almost invariably applied
in conjunction with alum. The beneficial effect of
aluminium compounds on vegetable-tanned leathers
The manufacture of leather 75
Figure 7.11 Spiral-bladed fleshing machine.
76 Conservation of leather and related materials
is well known and is the basis of the British Standard
for Archival Leathers. The new dyestuffs were either
used alone or together with mordants such as potassium
bichromate or iron sulphate which, unlike alum,
actually have a damaging effect. Second, in order to
‘fix’ the dyestuff to the leather and ‘clear’ the dyebath
it was necessary to increase its acidity. Sulphuric acid
was generally used with extremely deleterious results.
It is now known that sulphuric acid derived from
atmospheric pollution is the major cause of the deterioration
of bookbinding leathers and that the presence
of strong acids is particularly damaging.
Just as the demand for leather outstripped the supply
of vegetable tanning materials, as the century
progressed, there was an increasingly serious shortage
of skins for the tanners to process. This problem
was overcome by the importation of crust EI leathers
originally from East India, hence the name, but later
from throughout the Middle East, the Indian subcontinent
and Africa. These leathers were tanned in
their country of origin either using local, traditional
methods or local variations of ‘European’ systems.
In all cases local indigenous tanning materials were
employed. The skins were prepared on a very small
scale and gathered together from over a wide area to
a centralized trading centre. Here they were sorted,
mainly into size and quality, and exported. Once in
Europe, they were often sorted again before selling
on to a tanner or leather dresser. Crust skins were
sold by weight and often contained adulterants such
as excess tannins, oils, earthy materials and soluble
salts. In addition, the dresser was purchasing a very
mixed lot of skins from a wide range of sources having
very different processing histories. It was his job
to minimize these differences and produce as uniform
a batch of leather as possible.
In order to achieve this, he first washed the skins
thoroughly to remove as much of the unwanted
weighting material as possible. He often added alkalis
to the wash water in what is known as the stripping
process. This was designed to remove excess
tannins but, unfortunately, it also removed nontans.
These are various organic salts which are present
in the leather but do not actually contribute to
the tanning reaction. They are, however, effective
buffers and have a protective action against the
action of acidic atmospheric pollutants.
Next, the skins were shaved to the required thickness.
By the last quarter of the nineteenth century
various shaving machines had been developed which
replaced the laborious skilled hand operations (Figure
7.12). With these machines it was possible to cut skins
down to the required thickness, cheaply and accurately.
One feature of these machines, though, was that
in order to ensure a clean cut, their blades had to be
sharpened continuously. This resulted in a shower of
sparks and small specks of iron dropping onto the
leather. These caused a pattern of blue–black iron
stains which had to be removed in the clearing
process. In this, the skin was immersed in a solution
Figure 7.12 Shaving machine.
The manufacture of leather 77
of sulphuric acid which not only dissolved the iron
salts but changed the colour of the leather from a reddish
brown to a pale yellowish buff. However, once
again, dangerous sulphuric acid was introduced into
the leather. In order to produce a more uniform substrate
for the dyeing process, the leathers were then
retanned either using sumac or one of the newly
available tanning materials. They were then dyed,
possibly with synthetic colours, acidified, again with
sulphuric acid, dried out and finished.
As the century progressed, more and more
machinery was introduced into the tanneries. This
included a range of embossing presses or rolling
machines which produced artificial grain patterns.
In this way, for instance, it was possible to make
sheepskins look like goat, pig or seal skins (Lamb,
1905). They were also employed to disguise scuffs,
scratches and other damaged areas. These artificial
patterns were formed using a combination of heat
and pressure which, at best, distorted the natural
fibre structure and, at worst, caused heat damage.
By the last decade of the century the effects of
these changes had become only too apparent and
work was carried out to determine the causes of the
problems and eliminate them. Conservators are,
however, working today on leathers manufactured
during the period when the long-term effects of
these ‘improvements’ had not been appreciated.
During the nineteenth century, then, leathermaking
developed from a traditional craft into a sciencebased
technological industry. The skills of the
chemist and the engineer were being allied to the age
old sense of craftsmanship of the practical tanner to
produce an ever-widening range of materials, at the
same time both utilitarian and aesthetically pleasing.
7.4 Tanning in modern times
A brief outline of the stages involved in converting
raw skins into the most important types of leather
today is indicated in the flow diagrams in Figures
7.13 and 7.14. These should, however, only be
used as a rough guide to tannery practice as individual
tanners may depart considerably from these
schemes (O’Flaherty et al., 1956; Sharphouse, 1995;
Thorstensen, 1992). The various tannery operations
are still generally divided into three main groups:
(a) The beamhouse or pretanning operations in
which the non-leathermaking constituents of
the skin, such as hair, fat cells, non-fibrous proteins
and flesh are removed and the collagen
fibres converted into a chemical and physical
state suitable for tanning.
(b) The actual tanning processes where the skin is
turned into leather by the formation of chemical
crosslinks and supramolecular matrices
between adjacent collagen molecules.
(c) The post-tanning operations where the skins are
treated to give the required properties such as
handle, colour and appearance.
The various chemical operations generally take
place in dilute aqueous solution. The hides or skins
are usually placed, together with the appropriate
liquor, into large wooden drums fitted with internal
shelves. As the drums revolve, the skins are lifted up
on the shelves and then allowed to fall back under
their own weight, thus receiving a vigorous kneading
and pummelling action which accelerates the
penetration of the various chemicals into the skin.
7.4.1 Pretanning
Hides and skins are generally received by the tanner
in the cured condition, that is, with the effective
moisture content of the fibres reduced to such an
extent that bacterial decay can no longer take place.
This reduction is normally done at the point of
slaughter by physically drying the skins under more
or less carefully controlled conditions or by saturating
the pelt with a concentrated brine solution containing
a small amount of a bacteriostat. The cured
skins are passed to the beamhouse where the following
pretanning processes are carried out:
Washing and soaking in dilute solutions of alkalis and
wetting agents in order to remove blood, dirt and
excess salt.
Liming in a suspension of calcium hydroxide, usually
containing sharpening agents such as sodium sulphide
or sodium hydrosulphide which accelerate
the unhairing process. In this treatment the hair and
epidermal layer are attacked and loosened to such
an extent that they are completely pulped away.
The liming process also breaks down various
non-collagenous constituents of the skins, opens up
the skin structure and chemically modifies the collagen
in preparation for tannage.
Fleshing in which any loose pieces of membrane, fat
or meat still adhering to the underside of the skin
are cut away.
Splitting by machine to give the desired thickness.
Deliming using various weak acids or buffer salts to
reduce the alkalinity of the skins.
78 Conservation of leather and related materials
SALTED HIDES
AND SKINS
WASHING AND
SOAKING
DELIMING
to pH 8
PICKLING
to pH 2.5
LIMING
with Ca(OH)2 + Na2S
UNHAIRING, SCUDDING,
FLESHING AND SPLITTING
by machine
BATING
with pancreatic enzymes
WASHING AND
SOAKING
EI SKINS
roughly
vegetable
tanned
SHAVING
by machine
STRIPPING
with alkalis
BLEACHING
CLEARING
to pH 2.5
DEPICKLING
to pH 2.5
To retannage with
chromium salts,
syntans or vegetable
tanning materials
To chrome
tannage
To vegetable
tannage
To chrome
tannage
To vegetable
tannage
DEGREASING
with paraffin
DEGREASING
with paraffin
FRESH HIDES
AND SKINS
PICKLED
SKINS
DRIED HIDES
AND SKINS
Figure 7.13 Pre-tanning treatment of hides.
The manufacture of leather 79
DELIMED HIDES
VEGETABLE TANNAGECHROME TANNAGE
HEAVY LEATHER LIGHT LEATHER
BATED OR DEPICKLED
SKINS, OR DEGREASED
EI SKINS
TANNING
with vegetable or synthetic
tanning extractsTANNING
with basic chromic
sulphate liquors
FINISHING
with pigmented surface
coating systems
Shoe uppers, gloves,
clothing, etc.
Shoe soles
Shoe linings, book
binding, handbags,
wallets, etc.
RETANNING
with vegetable,
synthetic or other
tanning materials
WASHING
BLEACHING
DYEING
DRYING
FATLIQUORING
with oil emulsions
STAKING
by machine
FINISHING
with pigmented
surface coating
systems
HOT PITTING
at 40°C
BASIFYING
to pH 3.5
CLEARED
EI SKINS
PICKLED
HIDES
AND
SKINS
AGEING
for 24 hours
NEUTRALIZING
to pH 6
FATLIQUORING
with oil emulsions
STAKING
by machine
SHAVING OR SPLITTING
by machine
BLEACHING
DYEING
DRYING
FILLING AND
OILING
DRYING to
25% moisture content
DRYING to
18% moisture content
DRYING to
14% moisture content
OILING AND
POLISHING
ROLLING OFF
at 8 tons/in2
ROLLING ON
at 3 tons/in2
TANNING
in a series of
liquors containing
increasing amounts
of vegetable
tanning materials
Figure 7.14 Tanning and post-tanning operations.
Bating is a term given to the whole process of treating
delimed pelts with enzymes to give the required
flexibility and appearance to the finished leather. As
has been said, dog and pigeon dung were once the
source of the proteolytic enzymes which attack specific
types of protein, but standardized products
consisting of mixtures of deliming salts and enzymes
have now completely replaced the traditional materials.
The action of the enzymes is to clean up the
skin structure even further by making soluble
various non-collagenous proteins already partially
degraded during the liming process.
Pickling in which the pH of the skins is reduced to
between 2.0 and 2.5 by the action of sulphuric or
hydrochloric acid. Salts such as sodium chloride or
sodium sulphate are added to the pickle liquor to
prevent osmotic swelling. Skins are often preserved
in the pickled state and large quantities of sheepskins
are transported around the world in this condition.
Another method widely used for preserving skins
was to tan them lightly with vegetable tanning
materials after the soaking, liming and unhairing
processes: the dressing of such vegetable-tanned
East Indian stock was an important section of the
European leather industry. Large quantities of kips,
small ‘rough-tanned’ cattle hides, were imported
from the Madras area of India and goat and sheep
skins were imported in the same crust condition
from India, Pakistan, the Near East and West Africa.
The skins were treated first by removing any excess
vegetable tanning materials or adulterants and then
by retanning them as required. The skins were ‘wet
back’, shaved to the required thickness and the following
processes carried out:
Stripping the excess vegetable tanning materials and
adulterants from the grain by the action of dilute
solutions of weak alkalis.
Bleaching using dilute solutions of oxalic acid or
acidified solutions of sodium metabisulphite or
sodium hydrosulphite.
Clearing in which the pH of the skins was reduced
to about 2.5 at which point they have the palest
colour and are in a suitable state for retannage with
chromium chemicals.
7.4.2 Tanning
An increasing number of tanning materials became
available to the tanner since the beginning of the
twentieth century to enable him to produce leathers
having exactly the required characteristics, but the
three groups most widely used are the various vegetable
tanning extracts, basic chromic sulphates and
syntans.
Vegetable-tanned leathers are generally firm and
dense and have a high dimensional stability. They are,
therefore, widely used for the soles and linings of
shoes, bags, belting, etc. They can also be embossed
satisfactorily and are, therefore, chosen for bookbinding
and for the manufacture of fancy leathergoods.
Chrome-tanned leathers on the other hand are
relatively loose and soft and are more stretchy. The
also tend to have a smoother, more supple grain
which is resistant to scuffing and flexing. Leathers
for shoe uppers, gloving, clothing, etc. are therefore
usually chrome tanned.
The various syntans are normally used only in
conjunction with other tanning materials, e.g. to
improve the handle of chrome-tanned leathers or to
speed up the vegetable tanning process for light leathers.
However, some of these materials are used
on their own when very pale, light-fast leathers are
required. In general, such leathers resemble vegetabletanned
rather than chrome-tanned skins.
Most leathers are now produced using a combination
of tanning materials chosen to give the blend of
chemical, physical and aesthetic properties demanded
by the customer.
Vegetable-tanned leathers to be used for shoe soles
were normally tanned in a series of ten or more pits
using the countercurrent principle. At one end of
this system of pits, washed, delimed hide was
immersed in an almost completely exhausted tanning
liquor, while at the other end a strong, freshly
prepared solution of tanning extract met the almost
completely tanned leather. Thus over a period
which may have extended up to ten weeks, the hide
was immersed in a series of liquors containing an
increasing concentration of tanning materials. When
tanning was judged to be complete, the hides were
rinsed to remove excess tanning material from the
grain surface and drummed in a mixture of glucose,
magnesium sulphate and china clay. The leather was
dried out very slowly, during which time it was
compressed under hydraulic rollers to give a compact,
abrasion-resistant product. After conditioning,
it was lightly oiled on the grain and given a final polishing
treatment. Today drum tanning systems are
more frequently found.
The vegetable tannage of light leathers, where
solidity and firmness are less important, for example
for the linings of shoes, is a more rapid process. The
skins are drummed in dilute solutions of vegetable
tanning materials, often containing additions of
80 Conservation of leather and related materials
The manufacture of leather 81
syntans. Once the grain surface is ‘fixed’, the concentration
is gradually increased over a period of ten
hours or more by the addition of more vegetable or
synthetic tanning extract. The skins are then washed
to remove excess tannin from the grain surface,
drummed in a solution of oxalic acid to improve the
colour and then dyed, fatliquored, dried, staked and
finished.
The chrome tanning process usually consists of
drumming the pickled skin in a solution of basic
chromic sulphate until the tanning salt has penetrated
through to the centre of the skin and then
gradually increasing the alkalinity. This basification
process renders the chrome tanning materials more
astringent and accelerates the tanning reaction. The
skins are then piled in a damp state for one or two
days to complete the tanning reaction. In this state
the tanned hides are termed ‘wet blue’. Today many
hides and skins are processed to this wet blue stage
in the country of origin and traded throughout the
world in this condition. Sales of wet blue hides and
skins have almost completely replaced the traditional
trade in EI crust stock.
7.4.3 Post-tanning
After tanning some or all of the following posttanning
operations take place:
Shaving or splitting by machine to give the required
thickness.
Neutralizing using dilute solutions of mild alkalis.
Retanning with vegetable or synthetic tanning materials
to give the required handle to the leather and to
modify the dyeing characteristics as required.
Dyeing with selected acid and direct dyestuffs.
A very wide range of dyeing auxiliaries, syntans or
surface active agents, is used to give the required
levelness and depth of shade.
Fatliquoring by drumming the skins in an emulsion
of various animal, marine, vegetable or mineral oils.
These oils were generally emulsified with the aid of
the anionic sulphated oils, which were prepared by
the action of sulphuric acid on oils of animal,
marine or vegetable origin. A wide range of other
cationic, nonionic or anionic wetting agents are,
however, now widely used. These oils penetrate
into the skin structure and prevent the fibres from
sticking together, producing a hard, brittle material
when the skins are dried out.
Drying under very carefully controlled conditions.
Staking in which the slightly damp skins are flexed
and stretched.
Finishing using a pigmented surface coating system.
Casein and nitrocellulose finishes were widely
employed in the trade but the majority of leathers are
now finished using coating systems similar to emulsion
paints. These ‘resin finishes’ are now generally
based on acrylic or polyurethane polymer systems.
References
Cameron, E., ed. (1998) Leather and Fur: Aspects of Early
Medieval Trade and Technology. London: Archetype.
Clarkson, L.A. (1960) The English Leather Industry in
the Sixteenth and Seventeenth Centuries (1563–1700).
Unpublished thesis, University of Nottingham.
Faber, G.A. (1938) Greek and Roman Tanners. Ciba
Review, 9, 303.
Forbes, R.J. (1957) Leather in Antiquity. In Studies in
Ancient Technology, 5. Leiden: Brill.
Lamb, M.C. (1905) Leather Dressing including Dyeing, Staining
and Finishing. London: Anglo American Technical Co.
Levey, M. (1959) Chemistry and Chemical Technology in
Ancient Mesopotamia. Amsterdam: Elsevier.
O’Flaherty, F. et al., eds (1956) The Chemistry and
Technology of Leather, 4 volumes. New York: Reinhold
(reprinted Krieger, 1995).
Schwerz, F. (1938) Leather Dressing in the Stone Age.
Ciba Review, 8, 259.
Sharphouse, J.H. (1995) Leather Technicians’ Handbook,
75th Anniversary edition. Northampton: Leather
Producers Assn.
Thomson, R.S. (1981) Leather Manufacture in the Post
Medieval Period. Post Medieval Archaeology, 15, 161.
Thomson, R.S. (1981–82) Tanning – Man’s First
Manufacturing Industry? Trans. Newcomen Soc., 53, 139.
Thomson, R.S. (1985) Chrome Tanning in the
Nineteenth Century. J. Soc. Leather Technologists and
Chemists, 69, 93.
Thomson, R.S. (1991) The English Leather Industry
1790 –1900: The Case of Bevingtons of Bermondsey.
J. Soc. Leather Technologists and Chemists, 75, 85.
Thomson, R.S. (2001) Bookbinding Leather: Yesterday,
Today and Perhaps Tomorrow. J. Soc. Leather
Technologists and Chemists, 85, 66.
Thomson, R.S. and Beswick, J.A., eds (1983) Leather
Manufacture Through the Ages, Proceedings of the 27th
East Midlands Industrial Archaeology Society Conference,
October 1983, Northampton.
Thorstensen, T.C. (1992) Practical Leather Technology, 4th
ed. Melbourne: Krieger.
Veale, E.M. (1966) The English Fur Trade in the Later
Middle Ages. Oxford: Oxford University Press.
Watt, A. (1885) The Art of Leather Manufacture. London:
Crosby Lockwood & Co.
With demand for leather by a wide range of manufacturing
trades having been fairly consistent over
many centuries, one would imagine that the social
status of those who have worked in leather production
to be high. However, this has not always been
the case, despite the importance of the tanning
industry to most national economies. For example,
in 1783, leather was second to woollen textiles in
value of production in Britain (MacPherson, 1805)
and in 1830 leather and leather product manufacture
accounted for 8% of the country’s Gross National
Product (Thomas, 1983).
Most towns in the Middle Ages had a tannery
and in market towns there could be as many as five.
In cities this could rise to 20 and in London and its
suburbs there were nearly 200. Between 10 and
20% of adult males in many towns in Tudor times
worked in the industry (Thomas, 1983). Tanning
had also been a part-time craft pursued by farmers.
With an abundance of native oak trees whose bark
yielded the tannin and with availability of lime for
unhairing and plumping hides and skins before tanning,
farmers could lay away the hides and skins
from their slaughtered beasts for the year or so necessary
to complete the process in their own tan pits.
In many parts of the countryside one can find such
names as ‘Tan Pits Lane’ as the lingering evidence of
rural tanning.
The problem for tanners ensued from the development
of trade guilds. In reality these trade associations
became a necessity. In medieval times there
was no recognition of voluntary associations that
protected trades. They began in feudal times as
Christian brotherhoods formed for mutual protection
before there was any state protection of individuals
and their property. The Church was exempted
from the feudal hierarchical system and as trade
became increasingly important, businessmen managed
to secure exemption from the feudal duty of
military service for the local liege lords by paying
fees to the Crown. These agreements were set out as
borough charters and often included rights to control
local markets by borough councils elected by
‘freemen’ who usually belonged to the craft guilds.
They determined who could trade and the terms of
trade so that oversupply did not cause price reductions.
They also controlled raw material prices and
thereby ensured reasonable profitability to the various
trades (Thomson, 2002).
Several trades were involved in the production of
leather; tanners, whittawyers, fellmongers, skinners (furriers)
and curriers. These were formalized throughout
Europe during medieval times under guild control
into heavy and light leather manufacturing. Heavy
leather production involved the tanning and currying
of hides (currying is the transformation of roughtanned
leather into finished leathers for a variety of
purposes through the use of oils and mechanical
processes). Light leather production involved fellmongers
(producers of pelts and wool from sheepskins),
whittawyers (who applied alum and oil in making soft
leathers from sheep, goat, deer, horse and dog skins)
and leather and fur dressers. The trades which
utilized leather were more numerous: cordwainers
(shoemakers), girdlers, loriners (bit and stirrup manufacturers),
saddlers, harness-makers, pouch-makers,
cofferers, glovers, bottle-makers, male- makers (who
made leather trunks) and leathersellers (traders in
raw material and leathers).
Craft guilds ensured that one craft could never
monopolize and control the whole leathermaking
and leather using sequence of operations. The tanner
was required to take rough dried leather to the local
market for examination, certification and sale to a
82
8
The social position of leatherworkers
Robert D. Higham
The social position of leatherworkers 83
currier. A tanner could not be a currier or a butcher,
a currier could not be a tanner and a shoemaker
could not be a currier. In London, where there was
a proliferation of trades, the demarcation between
them was more strictly enforced than in the English
towns where single guilds incorporated several crafts.
The severe disadvantage for tanners was their subjugation
to suppliers of raw material and to the leather
finishing and utilizing guilds. Indeed, despite the close
association between tanners and curriers, only the
curriers became a chartered body during the time
when guilds had effective power. In 1410, the court of
Aldermen of London issued an ordinance for assaying
and proving tanned hides. The appointed examiners
were from the cordwainers, girdlers, male-makers,
bottle-makers and curriers guilds. The absence of tanners
among the appointees is evidence of their subservience.
Although they were listed in 1376 as being
among ‘the 47 misteries’ (crafts) in London, they did
not attain the dignity of a London livery company
until guild authority had declined. While whittawyers
were incorporated in 1346 (later to be absorbed in the
Leathersellers Company in 1479), it was not until
1703 that Queen Anne granted a charter of incorporation
to the ‘Masters, Warden and Commonalty
of the Art and Mistery of Tanners in the Parish of
St Mary Magdalene, Bermondsey’ (Waterer, 1944).
Because of the lengthy tanning process, tanners
were often suspected of cheating by taking hides out
of their pits too early. The Parliament of 1548 and
1562 attempted to enact measures to prevent such
practices by stipulating various parameters for leather
production. Unfortunately the legislators knew little
about tanning and if a tanner abided by these rules he
produced unsaleable leather. Consequently tanners
broke the rules and were often fined.
In 1575 a compromise measure allowed a court
official, Sir Edward Dyer, to licence tanners to produce
unlawful leather for fees paid by tanners to
Dyer’s agents. Dyer’s patent expired in 1596 and was
not renewed because it had been seen as an extortionate
abuse of the tanners (Thomson, 2002). The
ludicrous situation was partially resolved in 1604
with the ‘Great Statute of Leather’ which defined
leather and controlled its preparation and sale. All
artificers were allowed to buy any kind of leather to
Figure 8.1 Sarkis are Nepal’s traditional leatherworking caste. This hide, which has been tanned in a crude pit sunk
in the ground, is being cut into sides before further simple processing. The stigma attached to this low-caste occupation
caused a decline in rural tanning and leather product manufacture until the United Mission to Nepal established
the Village Leather Training Association to encourage its revival. These simple methods reflect today what rural tanning
and shoemaking would have been like in Europe in medieval times.
84 Conservation of leather and related materials
convert into manufactured goods. Several companies
were still involved in quality inspection and
seizure of faulty goods (Waterer, 1944), so tanners
remained a suspect breed.
The companies had long since become monopolized
in their memberships by capitalists and
traders. In 1445 only one actual skinner was left in
the skinners company. Consequently artisans were
often oppressed in their wages and conditions and
‘rich traders sold rubbish at high prices’ (Waterer,
1944). Nevertheless the livery companies, despite
the ills of self-interest and exclusivity of membership,
administered a control upon undesirable trade
practices.
The nature of certain parts of leather processing
ensured that those involved could be at a disadvantage
in the social order. Before the chemistry of
leather production was understood, there was a
reliance upon noxious processes. Unhairing was by
partial putrefaction, often accelerated by soaking
hides and skins in urine, dung and stale beer. Prior
to tanning, skins would be puered or mastered in
dog dung to render them very soft. An alternative
process was bating, which employed pigeon dung
for the same purpose. Tanneries were obliged to be
outside any centre of population and downstream
so that effluent could not pollute drinking water. In
London’s archives there is a reference to ‘Tanners
without Crepelgate’ and ‘Tanners without Neugate’.
Bermondsey became the centre for tanning in the
London area because it was across the Thames from
the City. Chaucer made reference to the ‘tan yeardes
of Bermondsie’ in the Canterbury Tales.
This separation of the tanning trade from the rest
of society is reflected in the Jewish Mishnaic regulations
that date from pre-Christian times. They
required that deposits of dead bodies and carrion,
burial grounds and tanneries be at least 50 cubits
downwind of all centres of population (Mishnah
Tractate Baba Bathra, ii.9). The separation even
invaded personal relationships. All claims for divorce
in Jewish marriages were the privilege of dissatisfied
husbands, except where a husband had leprosy or
polypus or was a tanner or dung collector. In these
cases a wife could sue for divorce even though she
had known she was marrying such a person. She
could plead that she thought she could endure it, but
now she could no longer do so (Mishnah Tractate
Ketuboth, vii.11 270 and vii.10).
At Jerusalem tanneries were located outside the
Dung Gate which borders on the Hinnom Valley
where the city rubbish dump smouldered perpetually.
Figure 8.2 Shoemakers’ simple tools.
The social position of leatherworkers 85
Ge Hinnom in Hebrew became Gehenna in Greek and
became the source of the Biblical description of Hell.
In crusader times, plans of Jerusalem show a cattle
market and skinners’ premises inside the city, near the
Dung Gate. But by this date the gate had become
known as the ‘Postern of the Tannery’, indicating that
tanneries were outside the city’s back gate (Higham,
1999).
The pattern is similar in many parts of the world.
For example, the former tannery suburb of Istanbul,
Kaslicesme, lies outside the city’s ancient Byzantine
walls. In India, tannery zones can be found near but
outside the main centres of population such as
Chennai (formerly Madras), Bombay, Kanpur and
Calcutta. Today advances in process technology have
reduced the noxious nature of the industry and in
most societies tanners no longer suffer serious social
disadvantage. The grouping nowadays of tanneries
in specific industrial zones is for the purpose of
sharing common effluent treatment facilities and has
nothing to do with any social obloquy. It would be a
mistake to assume from the disadvantages that tanners
endured through the noxious nature of some of
their processes and the suspicions of the craftsmen
and traders in other guilds that they were social pariahs.
Many tanners became wealthy and influential.
John Tatam, a tanner, was mayor of Leicester three
times at the end of the sixteenth century. William
House of Buckinghamshire was described in 1575 as
‘a man both of great wealth, very wise and most skilful
in his art and such a one as made the best leather
in the land’ (Clarkson, 1960). Many York dignitaries
were tanners. However, economies of scale were
essential to profitability. Leather production could
be undertaken with little capital, but this would have
to be combined with another occupation, such as
farming, in order to attain a reasonable standard of
living. Tanning required capital to be tied up in
process for over a year. This required regular input to
produce regular output and the pit capacity to wait
until the best leather prices could be achieved. Less
capital was required in light leather production, in
currying and in shoemaking because of lower processing
times and less space requirements, but their
labour costs were higher than in hide tanning. Heavy
leather crafts were generally located where hides,
oak bark and water were available. In this respect
Bermondsey was an ideal situation being next to
England’s largest centre of meat consumption and
taking advantage of the many streams that flowed
into the Thames and the oak woods of northern
Kent. Shoemakers were scattered throughout London
Figure 8.3 The finished products. Village leatherworkers also produce simple leathergoods such as shoes. (Figures 8.1–8.3
by courtesy of Anthony Tilly, TEAR Fund)
so that they were near their bespoke customers.
In the early seventeenth century there was said to be
about 3000 of them in the city and an equal number
of light leather workers.
Curriers, the intermediate trade, were located near
the shoemakers rather than the tanners simply because
it was cheaper to transport rough leather from the
leather market than it would be to deliver the heavier
curried leather to their customers. While tanners had
to be outside the city, curriers could work within the
city provided that their windows did not open onto the
street and that they ceased work at midday on Saturday
so that the workmen could clean themselves and their
homes before Sunday dawned (Clarkson, 1983).
Light leather crafts also tended to be nearer the
sources of their inputs; but, with less bespoke work in
gloves, belts, bags, purses, etc., manufacturers did not
need to be near their customers so they stayed close
to the leather dressers. Their products were also relatively
light to transport. These crafts were also more
suited to ‘putting out’ than the heavy leather crafts
because of the ease of transport of leather and goods,
and the availability of cheap labour. Light leather
crafts were often integrated through one central
merchant and producer who subcontracted out the
leather dressing and goods manufacture.
Oak bark was the cornerstone of the tanning industry
until the late nineteenth century. In early times the
term tanner was synonymous with the term barker. A
tanner collected his own bark and barkery was a term
often used for a tan house. No other tanning material
would be envisaged and the law demanded that hides
lie in pits layered with oak bark for a year. The use of
heat to extract tannin from oak bark was said to produce
dark, cracky leather that was undertanned in the
centre. The law of 1604 forbade them from setting
their pits in old tan hills where fermentation of waste
tanning materials could generate heat to warm the tanning
liquors. Being proscribed by law from developing
more efficient processing conditioned tanners to be
suspicious of new theoretical technologies. They preferred
the tried and tested methods.
Between 1780 and 1850 a boom in leather demand
coincided with a boom in shipping, the former emanating
from the spread of the industrial revolution and
the latter with the growth in naval and merchant shipping
that came with the expansion of the British
Empire. Demand for oak bark for tannery and oak
wood for ship building escalated but it was said that
the tanyards were greater consumers of oak trees than
the naval and merchant shipyards (Rackham, 1986).
Eventually the shortage of native oak bark forced
the import of oak bark. In the 1850s tanners in
England used 200,000 tons of native oak bark and
imported 30,000 tons. In the 1890s the figures were
respectively 100,000 tons and 700,000 tons. Chrome
tanning technology had been discovered in the
1830s but it was not widely taken up until the 1890s.
Such was the culture of resistance to change. Indeed
there had been few radical changes in leather processing
from the Greco-Roman period until the late
nineteenth century, as can be witnessed from the
layout and artefacts discovered in a tannery at
Pompeii (Thomson, 1983).
The industrial revolution powered by coal and
steam made greater economies of scale possible in
many industries including the leather and its downstream
industries. Workers were drawn from their
rural and small town communities into the expanding
towns where they were forced into very poor,
unhealthy living conditions. Women and children
worked alongside their men for long hours. Rural
craft industries were turned into forms of drudgery
and work became a necessary evil. Machines made
economies of scale even more realizable and they
were often better cared for than the factory workers.
The former were more expensive and difficult to
acquire whereas the latter could easily be replaced
when worn out (Brown, 1954). However, this dark
picture can be lightened to some degree by the
enterprise of industrial entrepreneurs who had
strong Christian beliefs and principles and practised
a paternalistic benevolence towards their workforces.
In the leather industry the industrial revolution
did not initially alleviate the noxious nature of some
of the processing. Puering continued and boys,
indeed anyone desperate for work, were sent out
with buckets and shovels to collect dog excrement.
In health terms, anthrax remained a minor but fatal
health hazard and dangers from the use of chemicals,
as their favourable properties in leather processing
were discovered, were added. Respiratory
problems from hydrogen sulphide and sulphur dioxide
gases, lime burns, chrome ulcers and the discovery
that some dyestuffs and finishing materials
contained carcinogens ensured that the tannery
environment was not the healthiest.
It is ironic that the old natural tanning process was
a source of good health. Tannery workers were
renowned for being the healthiest people in a community.
Nobody knew why this was so. In the Great
Plague in London (1665) many people crossed the
Thames to Bermondsey because of the belief that the
tan pit odours had medicinal virtue (Waterer, 1944).
This was, in fact, true because surface crusts of mould
formed on the pits during the long tanning process.
86 Conservation of leather and related materials
The social position of leatherworkers 87
The mould was penicillium glaucum and, when this
was disturbed, spores were released into the air thus
ensuring that tannery workers had regular inhalations
of penicillin.
The widespread perception of the tanning industry
as offensive in Victorian times is amply illustrated
in the novel John Halifax Gentlemen by
Mrs Craik. Being a tanner is depicted as being a definite
bar to his advancement in local polite society.
By changing to being exclusively a flour miller he
finds acceptance. Today such a situation would not
arise as modern processing technologies have replaced
the former noxious elements. But where concepts
of personal defilement through contact with dead or
decaying material are enshrined in theology, those
who handle hides, skins and leather find themselves
in situations of hereditary social disadvantage.
This is particularly the case in India, Nepal and
Japan where there is sensitivity to imparted impurity
that stems from Hindu and Buddhist religious beliefs.
In India and Nepal tanners and shoemakers are drawn
from the scheduled castes, the term that officially
replaced ‘the untouchables’ in 1935. They live outside
the caste system and often outside society altogether,
being confined to ‘no caste’ villages and ghettoes.
They are forbidden to enter temples because of their
ritual impurity. Sensitivity to pollution by contagion
is greatest among the Brahmins, the highest caste
group. The sensitivity decreases with lower rank.
Brahmin attitudes to contact with lower caste groups
were evaluated in socio-anthropological research in
Uttar Pradesh in the late 1950s. The shoemaker, tanner
and sweeper were untouchable in all respects.
Nevertheless, they had rank according to source of
pollution. The shoemaker who utilized leather
ranked lower than a washerman who was in contact
with the grime of humans. The tanner was closer to
dead organism than the shoemaker so he ranked lower
still. While the sweeper who was in contact with animal
waste ranked the lowest of the three.
In Japan, the Burakumin, meaning ghetto dwellers,
are a people who derive from the stratified Japanese
society of centuries ago with its warrior administrators
at the peak (Samurai) followed by merchants and
landowners. Beneath them were two despised classes,
the ‘hinin’ or non-people who included beggars, prostitutes,
mediums, itinerant entertainers and criminals
and the ‘eta’ meaning filthy, who undertook polluting
work such as animal slaughter and disposal of the dead.
The despised groups are now the Burakumin and constitute
2% of Japan’s population. The governments of
India and Japan have striven to eradicate concepts of
caste. As more and more people live in cities, they can
become more anonymous and so caste awareness
diminishes. But with sensitivities being rooted in theology
it will be difficult to remove the old prejudices
(Higham, 1999). In A Suitable Boy, a novel by Vikram
Seth, an Indian mother seeks a suitable husband for
her daughter. The young man who seems destined to
marry her is a shoemaker in a factory that owns a tannery.
A saving feature is that it processes only hides
from fallen animals and not hides from animals slaughtered
in Muslim abattoirs. The inferred loss of caste
integrity by the young lady through associating with a
person who works with leather is portrayed as an outdated
prejudice (Seth, 1993).
References
Brown, J.A.C. (1954) The Social Psychology of Industry,
pp. 31–32. London: Pelican.
Clarkson, L.A. (1960) The Organisation of the English
Leather Industry in the Late 16th and 17th Centuries.
Economic History Review, 13(2), 245–256.
Clarkson, L.A. (1983) Developments in Tanning Methods
During the Post Medieval Period, 1500 –1850. In Leather
Manufacture Through the Ages. (R. Thomson and J.A.
Berwick, eds) Proceedings of the 27th East Midlands
Industrial Archaeology Conference, Northampton.
Higham, R.D. (1999) The Tanner’s Privilege, a Historical
Review of the Tanner’s Status in Different Societies.
Journal of the Society of Leather Technologists and Chemists,
83, 25–31.
MacPherson, D. (1805) Annals of Commerce, 4, 15.
Mishnah Tractate Baba Bathra, ii.9.
Mishnah Tractate Ketuboth, vii.11 270 and vii.10.
Rackham, O. (1986) The History of the Countryside, p. 92.
London: J.M. Dent.
Seth, V. (1993) A Suitable Boy, pp. 623– 626. London:
Orion Books.
Thomas, S. (1983) Leathermaking in the Middle Ages.
In Leather Manufacture Through the Ages (R. Thomson,
and J.A. Beswick, eds). Proceedings of the 27th
East Midlands Industrial Archaeology Conference,
Northampton.
Thomson, R. (1983) The 19th Century Revolution in
the Leather Industries. In Leather Manufacture Through
the Ages (R. Thomson, and J.A. Beswick, eds). Proceedings
of the 27th East Midlands Industrial Archaeology
Conference, Northampton.
Thomson, R. (2002) Post Medieval Tanning and the
Problems Caused by 16th and 17th Century Bureaucrats.
In Le Travail du Cuir de la Préhistoire à Nos Jours
(F. Audoin-Rouzeau and S. Beyriers, eds), pp. 465–472.
Antibes: Editions APDCA.
Waterer, J.W. (1944) Leather in Life, Art and Industry.
London: Faber and Faber.
Leather has been employed for a range of utilitarian
purposes throughout time. Its properties also allow
it to be decorated using a wide variety of techniques.
Among these is the production of what has
been called Spanish leather, cordovan, guadameci
or, most correctly, gilt leather.
The production of gilt leather seems to have
developed in Moorish Spain in medieval times and
there is evidence of this material being made into
wall hangings from the fourteenth and fifteenth centuries.
Spain remained the centre for its manufacture
until the late sixteenth century when a combination
of factors including the persecution of the Moors
and an incident of bubonic plague in Cordoba led to
an exodus of skilled craftsmen either to Italy, particularly
Venice, or to the Low Countries which were at
the time under the rule of Spain. Two distinct
schools of design and production methods developed
in these new centres and it was from these that
the techniques of gilt leather manufacture were
disseminated throughout Europe in the seventeenth
and eighteenth centuries, the decorative patterns
88
9
Gilt leather
Roy Thomson
Figure 9.1 Late seventeenth century Dutch gilt leather in dining room at Levens Hall, Cumbria.
Gilt leather 89
changing to suit the varying fashions of place
and time.
Briefly, gilt leather was produced as follows:
uniform-sized pieces of leather, usually vegetable
tanned, were cut out and covered with leaves of
silver foil using a proteinacious adhesive such as egg
white or parchment glue. After the silver had been
cleaned and burnished, two or more coats of orange
or yellow varnish were applied giving a rich, golden
appearance. A three-dimensional design was then
produced using hand stamps and/or embossing
moulds. This was then coloured using a range of oilor
natural resin-based paints or glazes. Occasionally,
with the Italian school, clear varnish was used as part
of the design, enhancing areas of silver. In this way
panels of leather, sumptuously decorated with threedimensional
motifs were produced which could be
joined together to give sheets large enough to cover
whole walls. One can imagine the effect of these with
their bright, often fairground colours and golden
stamp marks glittering in the candlelight, contrasting
with the then more usual two-dimensional tapestries
and other textile-based wall coverings.
While the main use for gilt leather throughout
this period was for wall hangings, it was also
employed widely for upholstering chairs, covering
trunks, etc. Gilt leather also appears to have been a
preferred material for covering screens. Sometimes
newly produced leather was utilized but often
leather from wall hangings which had gone out of
fashion or parts of which had deteriorated were
recycled for this purpose. Many country houses still
have one or more gilt leather screens standing in
corners of their main reception rooms.
Because of the importance of this material in the
field of interior decoration and the specific problems
associated with the combination of a deteriorated
vegetable-tanned leather substrate and a decorative
top surface, the conservation of gilt leather has been
studied in some depth. These problems include damage
associated with its use, either as part of a piece of
furniture or as a wall covering in an often damp or
otherwise unsuitable environment. They also include
complications associated with past conservation
treatments which may have included overoiling or
the application of inappropriate surface coatings. A
number of case histories giving practical examples of
the treatment of gilt leather are included in Chapter
23 which will serve as an introduction to the conservation
of this material. There are, in addition, a large
number of publications dealing directly with all
aspects of gilt leather: its history, its conservation,
Figure 9.2 Levens Hall gilt leather showing nineteenth century remounting.
90 Conservation of leather and related materials
and the rehanging of large panels in historic interiors.
The reader is directed to consult these for further
information. Important papers include those
which follow. It should be noted that the majority
of these references have been taken from the bibliography
on gilt leather prepared by Dr Eloy Koldeweij
and distributed by him freely at the ICOM Committee
for Conservation Leathercraft Group Interim
Meeting in Brussels in 1998.
9.1 Production and art historical
aspects
Bergmans, A. and Koldeweij, E.F. (1992) Inventaris van
het 17de en 18de-eeuwse goudleder in Vlaanderen.
Monumenten en Landschappen, 11(6), 33– 46.
Bonnot-Diconne, C., Couroal, C.N. and Koldeweij, E.
(2002) Meeting between Solomon and the Queen of
Sheba: History, Technology and Dating of Gilt Leather
Wall-hangings. In Preprints of ICOM Committee for
Conservation 13th Triennial Meeting Rio de Janeiro, II,
pp. 764 –769. London: James & James.
Clouzot, Henri (1925) Cuirs decorés. Paris.
Colomer Munmany, A., Ainaud de Lasarte, J. and Soler, A.
(1992) L’art en pell. Cordovans i guadamassils de la colIecció
ColomerMunmany. Vic: Colomar Munmany.
Diderot, D. and Rond d’Alembert, J. le (1751–1772).
L’Encyclopédie. Paris.
Doorman, G. (1953) Techniek en octrooiwezen in hum aanvang.
Geschiedkumdige aanvulingen. Gravenhage.
Dossie, R. (1763) The Handmaid to the Arts, 2nd edition.
London: J. Nourse.
Ferrandis Torres, J. (1955) Cordobanes y Guadamecies.
Catalogo ilustrado de la exposición. Madrid.
Fougeroux de Bondaroy, A.D. (1762) Art de Travailler les
Cuirs Dorés ou Argentés, Paris. (Déscription des Arts et
Métiers).
Gall, G. (1965) Leder im Europäischen Kunsthandwerk.
Braunschweig.
Glass, H. (1991) Ledertapete. Essen: Galerie Glass.
Glass, H. (1998) Bedeutende Ledertapeten. Essen: Kunsthandel
Glass.
Huth, H. (1937) English Chinoiserie Gilt Leather.
Burlington Magazine, 71 ( July), 25–35.
Johannsen, O. (1941) Peder Månssons Schriften über Chemie
und Hüttenwesen, Eine Quelle zur Geschichte der Technik
des Mittelalters, 16. Berlin.
Koldeweij, E. (1992) How Spanish is Spanish Leather? In
Conservation of the Iberian and Latin American Cultural
Heritage. Preprints of the Contributions to the Madrid
Congress 1992 (H.W.M. Hodges, J.S. Mills and P. Smith,
eds), pp. 84 –88. London: IIC.
Koldeweij, E. (1992) Het Gouden Leer. Monumenten en
Landschappen, 11(6), 8–32.
Figure 9.3 Levens Hall gilt leather detail.
Koldeweij, E. (1996) The Marketing of Gilt Leather in
Seventeenth Century Holland. Print Quarterly,
XIII(2), 136 –148.
Koldelweij, E. (1997) Leather. In Encyclopaedia of Interior
Design ( J. Banham, ed.), pp. 705–707. London/
Chicago.
Koldeweij, E. (2000) Gilt Leather Hangings in Chinoiserie
and Other Styles: An English Speciality. Furniture
History, 36, 61–101.
Leiss, J. (1969–70) Leder Tapeten. In Tapeten, Ihre
Geschichte his zur Gegenwart. (H. Olligs, ed.) I, pp.
45–98, II, pp. 191–194. Braunschweig.
Madurell Marimon, J.-M. (1972) Guadamacilers i
Guadamaccils. Barcelona.
Madurell Marimon, J.-M. (1973) El Antiguo arte del
Guadameci y sus artifices. Vic: Colomar Munmany.
Mühlbacher, E. (1988) Europäische Lederarbeiten vom 14.
bis 19.jahrhundert aus dem Sammlungen des Berliner
Kunstgewerbemuseums. Berlin: Staatliche Museen zu
Berlin.
Paz Aguilo, M. (1982) Cordobanes y Guadamecies. In
Historia de las artes aplicades e industriales en España,
pp. 325–336. Madrid.
Scholten, F. and Koldeweij, E., eds (1989) Goudleer
Kinkarakawa. De geschiedenis van het Nederlands goudleer
en zijn invloed in Japan. Zwolle: Uitgeverij Waanders.
Soest, H.A.B. van (1989) The Manufacture of Gilded
Leather-tapestry. In Postprints of the ICOM Committee
for Conservation Leathercraft Working Group Symposium,
p. 185. Offenbach am Main: ICOM.
Waterer, J.W. (1971) Spanish Leather, A History of its Use
from 800 to 1800 for Mural Hangings, Screens, Upholstery,
Altar Frontals, Ecclesiastical Vestments, Footwear, Gloves,
Pouches, and Caskets. London: Faber.
Wormser, Jac. Ph. (1913) Het Goudleder. Bouwkunst, 5,
45–87.
9.2 Conservation and restoration
Amoore, J., Bergeon, S. and. Erlande-Brandenburg, A.
(1980) La restauration des tentures en cuir peint du
Musée d’Ecouen. L’Estampille, 127, 39– 46.
Bansa, H. and. Mair, H. (1981) Bemerkungen und
Betrachtungen zur Ledermalpflege. Maltechnik-Restauro,
111–114.
Berardi, M.C., Nimmo, M. and Paris, M. (1990) The
Seventeenth-century Flock-leather Wall Hangings of
the Chigi Chapel in Ariccia: A Case Study. In Preprints
of the ICOM Committee for Conservation 9th Triennial
Meeting, Dresden, II, pp. 611– 615. Los Angeles:
ICOM.
Berardi, M.C., Nimmo, M. and Paris, M. (1990) Parati in
cuoio a cimatura. Cenni su una tecnica poco nota e
problemi di conservazione. Rivestimenti murali in carta e
Cuoio: tecniche esecutive, conservazione e restauro, pp.
5–24. Roma.
Berardi, M.C., Nimmo, M. and Paris, M. (1993) II
cuoio dorato e dipinto, richerche e conservazione.
Materiali e strutture. Problemi di conservazione, III(3),
95–129.
Bergeon, S. (1990) France, XVIIème siècle–Tenture de
Scipion. In ‘Science et patience’, ou la restauration des peintures,
pp. 236 –239. Paris.
Bilson, T. and Bonnot, C. (1997) The Transfer and
Restoration of an Eighteenth Century Gilt Leather
Screen. In Postprints of the ICOM Committee for Conservation
Leathercraft Working Group interim meeting
Amsterdam 1995 (P.B. Hallebeek and J.A. Mosk, eds),
pp. 6 –14. Amsterdam: ICOM.
Calnan, C.N. (1992) The Conservation of Spanish Gilt
Leather – An Introduction. In Conservation of the Iberian
and Latin American Cultural Heritage. Preprints of the
Contributions to the Madrid Congress 1992 (H.W.M.
Hodges, J.S. Mills and P. Smith, eds), pp. 23–26.
London: IIC.
Dudley, D. (1981) Conservation of Leather Wall Hangings
in the James J. Hill Mansion. Journal of American Journal
of Conservation, 20, 147–149.
Erlande-Brandenburg, A. and Guichard, R. (1992) Une
experience de restauration à la Bibliothèque Nationale.
Historique et description: la tenture de cuir peint des
héros romains d’après Goltzius. Techniques utilisées.
Revue de la Bibiotheque Nationale, 2, 33–39.
Hallebeek, P.B. and Soest, H.A.B. van (1978) Gilded
Leather. In Preprints of ICOM Committee for Conservation
5th triennial meeting, pp. 1–8. Zagreb: ICOM.
Hallebeek, P.B. (1980) Restoration and Conservation of
Gilt Leather, Part II. In Conservation Within Historic
Buildings, pp. 164 –165. Preprints of the Contributions
to the Vienna Congress. London: IIC.
Hallebeek, P. and Keijzer, M. de (2002) Conservation
Procedure Based on Methodical Research to Remove
an Alkyd Resin from a Gilt Leather Wall-hanging. In
Preprints of ICOM Committee for Conservaton 13th triennial
meeting Rio de Janeiro, II, pp. 770 –776. London:
James & James.
Hejtmanek, R. and Lepeltier, C. (1988) Restauration d’un
fragment de tenture en cuir doré: étude des produits de nourriture
et d’assouplissement pour le cuir ancien. Paris.
Jagers, E. (1980) On the Deterioration after Treatment of
Painted Leather Wall Hangings in Three Castles in
Rhineland. In Conservation Within Historic Buildings,
pp. 166 –167. Preprints of the Contributions to the
Vienna Congress. London: IIC.
Jagers, E. (1987) Die Konservierung von Ledertapeten –
ein Unfallstudie. In Conservation-Restoration of Leather
and Wood. Training of Restorers (Sixth Internat. Restorer
Seminar, Veszprem), pp. 225–232. Budapest.
Konigsfeld, G. (1989) Anmerkungen zur geschichte
der Herstellung, zu Eigenschaften und Fehlern des
Leders, Probleme der Lederpflege. In Restaurierung
van Kulturdenkmalern. Beispiele aus der Niedersachsischen
Denkmalpfleg (H.H. Moller, ed.), pp. 327–333.
Hameln.
Gilt leather 91
Lonborg Andersen, V. (1997) Remounting Gilt Leather
Tapestries with Velcro. Conservation of Leathercraft and
Related Objects. In Postprints of the ICOM Committee for
Conservation Leathercraft Working Group interim meeting
Amsterdam 1995 (P.B. Hallebeek and J.A. Mosk, eds),
pp. 121–122. Amsterdam: ICOM.
Moris, B. (1991) De restauratie van goudleer in het
museum Plantin-Moretus. Cultureel Jaarboek Van de stad
Antwerpen, IX, 41– 42.
Moroz, R. (1996) Die Trockenreinigung von
Lederobjekten. Restauro, 102(4), 242–247.
Moroz, R. (1993) The Conservation of the 18th-century
Leather Tapestries Covering a Travelling Chest. In
Preprints of the ICOM Committee for Conservation 10th
triennial meeting Washington DC, II, pp. 651– 655. Paris:
ICOM.
Moroz, R. (1997) The Formation of Cracks on Leather
with Respect to Gilt Leather. In Postprints of the ICOM
Committee for Conservation Leathercraft Working Group
interim meeting Amsterdam 1995 (P.B. Hallebeek and
J.A. Mosk, eds), pp. 19–25. Amsterdam: ICOM.
Muller, D. (1986) The Degreasing of a Set of Gilt Leather
Wall-hangings in the Rijksmuseum. In On Ethnographic
and Water-logged Leather. Proceedings of ICOM Committee
for Conservation Symposium, pp. 11–16.
Amsterdam.
Muller, D. (1987) Das Entfetten von vergoldetem Leder.
Die Ledertapeten im Raum 259 des Rijksmuseum.
Maltechnik, 93, 47–52.
Mors, B. (1991) De restauratie van goudleer in het
museum Plantijn-Moretus. Cultureel Jaarboek van de stad
Antwerpen, IX, 41– 42.
Nimmo, M., Paris, M., Rissotto, L. et al. (1996) Tensioning
Gilded and Painted Leather. In Preprints of ICOM
Committee for Conservation 11th triennial meeting Edinburgh,
II, pp. 751–758. London: James & James.
Nimmo, M., Paris, M. and Rissotto, L. (1999) Tensioning
Gilded and Painted Leather. Part 2: First Verification of
Supporting Structures with Elastic Tensionsing. In
Preprints of ICOM Committee for Conservation 12th triennial
meeting Lyon, II, pp. 697–701. ICOM.
Paris, M. (1997) Tensioning Gilded and Painted Leather:
A Research Project. In Postprints of the ICOM
Committee for Conservation Leathercraft Working Group
interim meeting Amsterdam 1995 (P.B. Hallebeek and
J.A. Mosk, eds), pp. 15–18. Amsterdam: ICOM.
Peckstadt, A., Watteeuw, L. and Wouters, J. (1992) Conservering
van het goudlederbehang van de dekenij van
Zele. Monumenten en Landschappen, 11(6), 55– 61.
Philippe, M.M.J. (1952) Le traitement des cuirs de tenture et
la façon de cordove conservés au Musée d’Ansembourg à
Liege. Bulletin des Musées de Belgique, 1, 96–100.
Pracher, P. (1974) Konservierung des Ledertapeten aus dem
Schlösschen Veithöchstein. Maltechnik, 3, 144–148.
Pracher, P. (1989) Die Ledertapeten aus Schloss Jever und
aus das Kloster ‘Zur Ehres Gottes’ in Wolfenbuttel.
In Restaurierung von Kultulrdenkmalern. Beispiele aus der
Niedersachsischen Denkmalpflege (H.H. Moller, ed.),
pp. 339–344. Hameln.
Reff, R. and Pavel, V. (1983) Restaurarea unor piese de
piele din secolul al XVII lea. Revista Muzeelor si
Monumentelor, 48–54.
Rosa, H. (1996) Gilt Leathers and the Problems of their
Conservation. In Postprints of the International Conference
on Conservation and Restoration of Archive and Library
Materials, Erice (Italy).
Schulze, A. (1988) Die Restaurierung von Ledertapeten –
Literaturstudie. Dresden.
Schulze, A. (1989) Leather Tapestry of Moritzburg: Its
Actual Situation, and First Results of Restoration. In
Postprints of the ICOM Committee for Conservation
Leathercraft Working Group Symposium, pp. 171–180.
Offenbach am Main: ICOM.
Schulze, A. (1997) Die Ledertapeten im Schloss Moritzburg.
In Denkmalpflege in Sachsen 1894–1994 (H. Magirius
and A. Dulberg, eds), pp. 229–240. Weimar.
Soest, H.A.B. van (1972) Over goudleer en zijn conservering.
Vereniging Musea Restaurateurs en Technici, 4–20.
Soest, H.A.B. van (1975) Goudleer. Spieghel Historiael, 10,
36 – 46.
Soest, H.A.B. van (1975) Enkele historische aspecten van
de goudleerfabricage. Oud Nieuws, 8(3), 24 –33.
Soest, H.A.B. van (1976) Het goudleer in Huize
Voormeer. Bulletin van de Koninklijke Nederlandse
Oudheidkundige Bond, 75, 297–302.
Soest, H.A.B. van (1976) Beknopte beschrijving van de
restauratie aan het goudleer van het Frans Hals
Museum te Haarlem. Oud-Nieuws, 9(1), 28–34.
Soest, H.A.B. van and Hallebeek, P.B. (1975) Goudleeren
behangsels. Haarlem/Amsterdam.
Soest, H.A.B. van (1980) Restoration and Conservation
of Gilt Leather, Part 1. In Conservation Within Historic
Buildings, pp. 162–163. Preprints of the Contributions
to the Vienna Congress. London: IIC.
Soest, H.A.B. van, Stambolov, T. and Hallebeek, P.B.
(1985) Die Konservierung von Leder. Maltechnik
Restauro, 91, 49–54, 57– 65.
Soest, H.A.B. van and Hallebeek, P.B. (1984) Chemical
Solutions of Problems Encountered in the Conservation
of Old Leather. In Preprints of the ICOM Committee
for Conservation 7th triennial meeting Copenhagen
1984, II, pp. 16 –18. ICOM.
Soest, H.A.B. van, Stambolov, T. and Hallebeek, P.B.
(1984) Conservation of Leather. Studies in Conservation,
29, 21–31.
Sturge, T. (1999) Gilt Leather Wall Coverings: Some
Options for Repair. In Postprints of the Conservation of
Decorative Arts Conference, London, pp. 65– 69. London:
UKIC.
Szalay, Z. (1980) Conservation and Restoration of
Dyed and Embossed Leather Objects. In Conservation
Within Historic Buildings, pp. 168–169. Preprints
of the Contributions to the Vienna Congress.
London: IIC.
92 Conservation of leather and related materials
Gilt leather 93
Talland, V., Mangum, B., Tsu, C.M. and Fullick, D. (forthcoming)
The Conservation of Leather Wallhangings at
the Isabella Steward Gardner Museum. In Postprints of
the ICOM Committee for Conservation Leathercraft Working
Group interim meeting Brussels 1998.
Thomson, R.S. (1999) Choices in the Treatment of Gilt
Leather Wallhangings. J. Soc. Leather Technologists and
Chemists, 84, 20.
Torre, S. de la (1970) Conservacion de cordobanes y
guadameciles. Informes y trabajos del institito de conservacion
y restauracion de obras de arte, argueologia y etnologia,
Madrid, pp. 91–96.
Tsu, C.M., Fullick, D., Talland, V. and Mangum, B.
(1999) The Conservation of Leather Wallhangings at
the Isabella Steward Gardner Museum. Part II. In
Preprints of ICOM Committee for Conservation 12th triennial
meeting Lyon, II, pp. 708–713. ICOM.
Winter, J. and West Fitzhugh, E. Some Technical Notes
on Whistler’s ‘Peacock Room’. Studies in Conservation,
30, 149–154.
Wouters, J. (1986) De restauratie van het goudleder behang
van het Museum het Erasmushuis te Anderlecht. Brussels.
10.1 The cuir bouilli technique
Cuir bouilli is a Norman French term that translates
into ‘boiled leather’. It describes the process used to
change flexible leather into rigid, moulded and often
intricately shaped objects like firemen’s helmets,
drinking vessels and boxes. The term directly suggests
that boiling water was used to manipulate the
properties of leather in a similar way to embossing,
but the nature of the technique has never really been
established.
Surviving objects and a number of historical
accounts of methods for moulding leather give us
many indications to the processes involved. However,
the term cuir bouilli has been used to describe all manner
of moulded leather objects, which exhibit the
familiar, rigid character, but which vary greatly in
style and function. There are distinct physical and
visual differences in these objects, which indicate that
methods for making cuir bouilli consisted of a number
of different techniques which can be related to other
leather moulding processes.
10.2 Leather moulding techniques
The familiar leather moulding techniques such as
embossing and lasting rely on the use of mild heat
and water to manipulate the properties of leather.
These moulding and shaping techniques exploit the
plastic character of vegetable-tanned leather when
it is softened by water. When water is applied to
leather it becomes malleable and easy to mould and
it will retain this moulded shape or ornamentation
when it dries. The ability of leather to do this derives
from the action of warm water on the fibrous structure
of its collagen chains and on the thermoplastic
characteristic of vegetable-tanned leathers. However,
once the process of moulding leather in this way is
complete, and the object is dried, the structure of
the leather is unaltered and it remains flexible unless
coated with a stiffening medium or mounted on a
backing material.
The nature of cuir bouilli leather after-treatment
differs in the fact that the leather is rigid and water
resistant. This indicates that when leather is moulded
using water and higher temperatures, a chemical reaction
occurs which permanently alters the structure
of the leather. If one were to follow strictly the
implied definition of the term, then leather would be
boiled in water to achieve this alteration to its chemical
and physical properties. This treatment though
would result in the leather shrinking irretrievably
and becoming brittle as it dries. Historical texts
describe three main methods called the cuir bouilli
technique which were used to harden and mould
leather objects.
10.3 The origins of the cuir bouilli
technique
John Waterer, who published many significant texts
on the history of leather craft techniques, suggested
the primitive method of heating water in skin bags
over a fire, as the origin of the technique.
The early origins of the cuir bouilli technique are
established by the finds of silver drinking vessels intact
with mineralized organic deposits, thought to be the
remains of leather cups.1
Another important early evidence
of the technique was the discovery of an Iron
Age leather shield complete with its wooden former
in a peat bog in Ireland.2
It is claimed that these
shields, called bucklers, were made entirely from wet
94
10
Cuir bouilli
Laura Davies
Cuir bouilli 95
vegetable-tanned leather that had been pressed into
moulds and dried in a warm place until they were
rigid. However, the shield had survived two and a half
thousand years, without losing its original rigid character
and it is therefore most likely that some form of
hardening technique had been used to provide this
incredible durability. The shield displays the popular
use of leather for making protective clothing and
armour. It was ideally suited to the purpose because it
could be moulded into close fitting, lightweight but
rigid protective forms that allowed greater freedom of
movement than metal.
Accounts of the methods employed for manufacturing
such armour indicate that a variety of different
moulding techniques were employed to achieve
this rigidity. Leather horse cuirasses, sheaths and
scabbards were made by laminating strips of leather
with glue onto a textile support which may have
been shaped over a mould (Cameron, 1998). Such
leather is treated in no other way, but the resultant
rigid material has often been misleadingly described
as cuir bouilli. It is the surviving leather fire helmets
and porters hats dating from the sixteenth to nineteenth
century, however, which clearly define the
use of the cuir bouilli technique. Moulded leather
helmets were in use during the great fire of London
in 1666 and continued to be used until the outbreak
of the Second World War. Their use was popular
until their replacement with heavy duty plastics,
because they protected the head and did not conduct
heat like metal versions. These helmets were
often coated with pitch to provide added protection
and make them more waterproof (Figure 10.1).
The manufacture of these helmets is paralleled by
techniques used to make military helmets in nineteenth
century America.3
The technique used to
make such helmets involved immersing oak bark
vegetable-tanned cow hide into hot water (or raising
the temperature of the water to this point with the
leather already immersed). The leather would be
removed as it began to shrink and it could be
moulded immediately into the desired shape over a
wooden former. The finished article could then be
stitched while still wet to form a helmet or vessel-like
structure, and held in place over the former to dry.4
A variation of this technique is associated with the
manufacture of bottles called blackjacks, bombards
and costrels (Figure 10.2). The earliest written reference
to leather bottles is in the record of the Guild of
Bottellars of 1373.5
These vessels were made from
oak bark-tanned cattle hide and were very strong
and substantial. Their manufacture and use was a
Figure 10.1 Cuir bouilli leather porter’s hat from Billingsgate fish market.
96 Conservation of leather and related materials
consequence of the scarcity of other materials for
domestic utensils. Towards the end of the sixteenth
century large pitchers were made of earthenware and
the craft was eventually replaced by the expansion of
the stoneware industry. Originally these objects were
hand sewn but later examples are made with two
seams riveted together by copper alloy studs.
The manufacturing technique used to make such
bottles involved wetting the leather with cold water
and then exposing it to a heat source. This was
achieved either by the use of actively applied heat
with the leather stretched over a wooden last, or by
passively applied heat with the shaped leather heated
in an oven.6
The original technique would also have
included a process where small vessels whose openings
were too small to admit any type of former
were shaped and sewn when wet, filled with sand to
form a temporary firm support and then heated or
baked to make the structure permanent. Once the
vessel was dried the sand could be poured out.
Another method for hardening leather involves
the use of materials such as waxes, resins, fats and
flour pastes applied to bulk and harden leather. This
impregnation technique has been explored by scientists,
conservators and practising artists. The
process involves the application of a hot resinous
mixture onto a previously wetted leather surface.
This technique has been called ‘pitching’ leather
and has been documented during the manufacture
of cuir bouilli boots popularly called postillions’ boots
which consisted of coating leather with such materials
as heated colophony pine resin mixed with
beeswax and lamp black pigments (Figure 10.3).7
The boots would be constructed with their grain
surface inside so that the mixture could be easily
absorbed into the exterior flesh side. They were
extremely strong and warm and would be lined with
quilted leather filled with wool for added insulation.
Each of these methods described were practised
by highly skilled, master craftsmen who passed on
their knowledge to apprentices orally. They have
not been outlined specifically in any text. In practice
they are very similar to other leather moulding
techniques but share the characteristic that they are
Figure 10.2 Cuir bouilli leather. (Courtesy Museum of
London)
Figure 10.3 Postillion’s boots with cuir bouilli leg
protectors.
all based on processes which permanently alter the
physical and chemical characteristics of leather. It is
for this reason that much confusion has arisen in
coming to a single simple definition of cuir bouilli.
10.4 Changes undergone by the leather
in the cuir bouilli process
The physical and chemical changes of leather subjected
to the cuir bouilli process are determined by
the action of heat and water on the unique leather
structure and the thermoplastic nature of excess
vegetable tannin, particularly condensed tannins,
within that structure.
It is necessary to understand these changes in the
material in order to anticipate its process of deterioration
and propose appropriate conservation treatments.
Cuir bouilli leather is made from vegetable-tanned
leather whose manufacture and chemical structure
has been well documented. During the tanning
process chemical bonds are introduced between tanning
agents and leather fibres which increase the
chemical and physical stability of the collagen fibres.
This network prevents the fibrous structure of leather
from collapsing as water is lost. Vegetable tannins
from oak bark consist of large phenolic molecules
predominantly of the condensed tannin type. They
are weakly acidic and through hydrogen bonding are
able to bond efficiently with the collagen protein
molecules. This action displaces water from the reactive
groups and the hydrophobic areas of the tannin
and protein are then drawn together by van der Waals
forces. The collagen/tannin framework is therefore
strongly networked, but at the same time flexible and
relatively stable to hydrolysis by water.
The nature of the condensed tannins used in the
manufacture of authentic cuir bouilli leather greatly
influences the final properties of the material. For
heavy duty purposes, leather is sometimes deliberately
subjected to large quantities of the tanning
material, with an excess left in place to make the
leather more rigid. It is thought that much of the
tannin may be physically held within the structure
of the leather, but be chemically independent of it
(Reed, 1966). The high molecular weight of these
tannins dispersed within the fibre spaces of the
leather could account for the restricted movement
of the leather and an increase in stiffness.
When vegetable-tanned leather has been saturated
with water and heated to a temperature around
75–90°C it begins to shrink (Bickley, 1991). The
exact temperature will depend on a wide number of
factors such as the type and amount of tanning
material present, the rate of heating, etc. At this point
of shrinkage temperature, the chains of the collagen
molecule, which are normally held in an extended
form by hydrogen bonding, become unstable as
the energy input exceeds that of the hydrogen bonds
holding the molecular shape together. Above this
point, therefore, there is a sudden release from the
extended form of the collagen molecule and the
leather becomes incredibly elastic as the chains
retract and shrink. As it cools the hydrogen bonds
are able to reform between the realigned collagen
molecules in a tighter formation. In this case if the
leather has fully shrunk, when it dries it becomes
inelastic. If the leather is heated to just below the
shrinkage point, the bonding is weakened but not
fully released allowing limited realignment to take
place in a more controlled manner. In this case the
new dense strong network makes cuir bouilli leather
rigid and strong.
Alternatively, if the heat source application is
limited to only the surface of the wet leather then it is
possible that this shrinkage solely occurs in the outer
layer of the leather, producing a surface hardening
effect. The leather could therefore have an altered
rigid outer layer and a less affected internal area, the
combination of which produces a very strong
structure.
The influence of heat on the condensed vegetable
tannins within the leather structure is an important
factor in the hardening of the leather, as these large
molecules behave thermoplastically. If there is an
excess of tannins present then they allow the structure
of the leather to be moulded when hot, but as
they cool they contribute to the hardening of the
leather by supporting the fibres in a strong matrix in
their new alignment. It is thought that the oils, resins,
and waxes used in the impregnation technique of cuir
bouilli manufacture would behave in a similar way.
The effects of the shrinkage temperature and the
tanning process can therefore have a profound effect
on leather, which is irreversibly altered during the
process of making cuir bouilli. This has implications
for some of the recommended treatments for conserving
objects made from this material.
10.5 Conservation of cuir bouilli
10.5.1 Stability
The condition of cuir bouilli leather can be detrimentally
affected by environmental damage factors and by
Cuir bouilli 97
restoration techniques. All leather in museum storage
is susceptible to decay in the presence of atmospheric
pollutants, light and fluctuating climatic conditions.
But it is generally found to be the surface treatments
applied to cuir bouilli leather objects during manufacture,
maintenance treatments throughout their use
and subsequent conservation processes which alter its
original appearance.
Cuir bouilli leather is generally found to be resilient
to attack by the atmospheric pollutants such as sulphur
dioxide, which causes the common form of
chemical decay in vegetable-tanned leather called
red rot. This could be because the acidic pollutants
cannot penetrate the dense structure. It remains
relatively stable in a fluctuating environment but
has been known to progressively harden and crack
over time. This deterioration can be attributed
to fluctuations in the environment but can also
be caused by the routine application of leather
dressings more appropriate to conventional leather
conservation.
10.5.2 Damage caused by old treatments
A misconception regarding cuir bouilli is that leather
dressings should be applied to lubricate the leather.
This treatment is intended to impart flexibility and
enhance the object’s appearance by saturating the
grain surface. However, this material was never
meant to be flexible and most cuir bouilli leather
objects have characteristic darkened surfaces. These
dark surfaces are partly derived from the alteration
in the colour of leather when it is heated but are also
a result of the original application of surface finishes
and coatings to cuir bouilli after manufacture. The
presence of these materials also has implications for
the conservation of cuir bouilli objects.
Many of the conservation dressings used on
leather may have a long-term detrimental effect on
the material they are meant to be preserving. There
are an enormous number of oils, waxes, natural and
synthetic fats and resins that are recommended
in conservation literature for the care and preservation
of leather. However, their use on museum
objects has been shown in some cases to actually
cause damage to both the body and surface of the
leather (Soest et al., 1984). Most leather dressings do
not penetrate into the leather and as they are reapplied
they accumulate as an excess on the surface.
This alters the ability of the leather to regulate its
moisture content relative to the environment, eventually
resulting in it becoming brittle and prone to
cracking.
These mixtures of materials eventually deteriorate,
however, and alter the surface appearance of the
leather. As they oxidize they can become brittle,
discoloured and, as they lose their original properties,
becoming sticky and gummy, they imbibe dust
and dirt. For the preservation of cuir bouilli leather it
is recommended these dressings are removed in
order to preserve both the body and surface of the
leather. This treatment also ensures that the original
nature and surface quality of cuir bouilli leather can
be appreciated.
The removal of non-defined layers of treatment
from an original surface is very difficult. Historic
references can provide information about the
components of original coatings but there are an
enormous variety of modern leather dressing/
improving treatments, made up of complex mixtures
of materials which have been used to conserve this
material. They are therefore extremely difficult to
identify and isolate during cleaning. However, with
careful solubility testing and awareness of the quality
and appearance of original coatings cleaning can be
very effective.
10.5.3 Original treatments of cuir bouilli
leather
Cuir bouilli objects were finished or dressed according
to their intended purpose. If bottles or buckets
were intended to hold liquids then cuir bouilli leather
was lined on the internal flesh side with pitch, resins
or waxes. The exterior of vessels was often coloured
black with dye or pigmented wax, or varnished to
make an enamelled or Japanned surface (Seeley,
1991). Linseed oil and bitumen coating is known to
have been another alternative. Oils, waxes and resins
were applied to objects like cuir bouilli fire helmets
and coach horsemen’s boots where water splashes
would be a regular occurrence.
Some of these coatings may survive intact and are
visible on objects, whereas others may be completely
hidden by later conservation dressings and
their presence may not be immediately apparent. The
conservator must be aware of this when evaluating
the possible removal of surface layers in a treatment
proposal.
10.6 Case study of the conservation of
cuir bouilli leather
The Museum of London have a comprehensive collection
of cuir bouilli objects including fire helmets,
98 Conservation of leather and related materials
porters’ helmets, postillions’ boots and bottles that
provide a fantastic reference to the cuir bouilli technique.
In particular they represent a complete range
of the surface treatments applied to this material
either as original manufacturing preparations or later
conservation treatments which help enormously
with the evaluation of treatments. The following
case study of the conservation of a cuir bouilli fire
helmet from this collection will outline a method
for evaluating the surface finish of cuir bouilli. Visual
and analytical methods were employed to investigate
a possible technique for identifying and removing
layers of leather dressing from original coating
materials.
The fire helmet which was thought to be dated
around the early eighteenth century was made from
a cow or horse hide (Pyne, 1808) which had been
hardened using the cuir boulli technique. The entire
crown and brim of the hat was constructed from
four pieces of leather which would have been saturated,
heated and then stretched and stitched over
a wooden block or former. The seams of the sections
were exaggerated to give a deep, cockscomb
raised crown. A strip of leather had also been added
between each section to reinforce these areas. The
stitches would have been completed and trimmed
while the leather was still wet. This is apparent
because the stitches have shrunk into the leather.
These helmets were then lined with a quilted inner
skull cap made from sheepskin padded with vegetable
fibre or woollen wadding. A small space was
allowed above the lining to provide an air gap,
which would both insulate the helmet and ensure
added protection from a blow to the crown of the
helmet.
The helmet had an outer coating which was very
black, shiny and evenly applied to the surface of the
helmet. The leather had become very friable at the
edges and in places the coated leather surface had
become completely detatched from the leather, lifting
the grain layer with it to reveal the flesh layer
below. After careful evaluation of the coating several
factors indicated that this was not original:
(a) The nature and appearance of the surface was
unusually black and shiny when compared with
coatings on similar objects in the collection.
(b) The coating covered original physical damage,
probably caused by a blow to the helmet, which
should have disrupted the surface.
(c) There was no evidence of the shiny black coating
near the tight corners of the construction of
the helmet, around the underside of the brim or
underneath the obvious museum restoration of
the shoulder flap.
(d) Also there was evidence of raised lettering
underneath the outer coating.
10.6.1 Analysis and use of non-invasive
xeroradiographic imaging
In addition to these subjective methods of assessment,
the use of analytical techniques was considered. The
helmet was xeroradiographed and the results not
only showed the detail of manufacturing techniques,
such as stitching and quilting, but also revealed the
presence of bold white lettering on all four sides of
the helmet (Figure 10.4).
Cross-sections were prepared in the same way as
for conventional pigment identification, from small
samples taken from the surface of the leather helmet.
These were examined in order to assess the
nature of the coatings below the surface layer. These
showed that the black outer coating, which fluoresced
slightly under the UV microscope, was very
thin, even, black and synthetic in appearance. This
layer covered three further layers of a thick, resinous
and waxy material which was pigmented with earth
brown and lampblack particles.8
This indicated that
the layer below the black outer coating was a substantial
surface treatment and highly likely to be the
original surface of the helmet.
10.6.2 Removal of inappropriate surface
coatings
The cross-sections proved that it was possible to
distinguish between the layers of coatings on cuir
bouilli objects. This information was used to aid the
removal of these disfiguring surface coatings to
reveal the original layers below. Because of the
complex chemical nature of the coatings, cleaning
tests were carried out using a variety of different
solvents, solvent mixes and solvent gels. The composition
of the outer coating demanded that the solvent(s)
used in its removal had to have both polar and
non-polar characteristics. Chlorinated hydrocarbon
solvents, used in the past to remove old dressings
and coatings on leather, are no longer an option as
their use is proscribed by environmental regulations.
After several cleaning tests it was found that
benzyl alcohol was an effective alternative solvent,
being both efficient and controllable when applied
on cotton wool swabs. This solvent contains an aromatic
benzene ring, appropriate for the removal of
non-polar materials and a single alcohol side group
Cuir bouilli 99
100 Conservation of leather and related materials
Figure 10.4 Xeroradiograph of the helmet showing construction of helmet and lead white lettering on original
surface of the helmet. (Courtesy Barry Knight, Science Conservation Department, English Heritage)
Figure 10.5 Cuir bouilli leather fire helmet after cleaning.
Cuir bouilli 101
that gives the solvent a sufficient level of polarity to
dissolve some polar materials.9
During cleaning,
swabs used to remove the coating were rolled onto
an absorbent paper and at the point where the
blue/black outer coating changed to brown, the
cleaning was stopped. The xeroradiographs were
also used as a reference to assist with the cleaning of
the lettering.
The final appearance of the surface of the helmet
after cleaning was both pleasing and far more
convincing as an original coating. The interpretation
of the lettering revealed that the helmet had
been used by a member of the voluntary fire brigade
attached to a parish, in this case St Katherine Cree
Church in the City of London (Figure 10.5 ).
A reassessment of the nature of cuir bouilli shows
that it is necessary to re-evaluate traditional conservation
treatments of this material. It is no longer
acceptable to continue to apply leather dressings to
a material that derives little or no benefits from its
application. In most cases it is preferable to remove
such coatings. It has been proved possible to crosssection
and use UV microscopy to determine original
surface finishes from later treatments, which
can then be removed using appropriate solvents.
This removal of these non-original surface coatings
not only prevents the substrate of the leather from
deterioration but reveals the true quality of these
fascinating objects.
Endnotes
1. 1848 discovery of a silver rim from a fourth century
cup in Benty Grange. Waterer, J.W. (1946) Leather in
Life Art and Industry. London: Faber and Faber.
2. Discovered in Clonbrin, Co. Longford, Eire, 1908.
Now kept in the National Museum of Ireland,
Dublin. Waterer, J.W. (1981) Leather and the Warrior:
An Account of the Importance of Leather to the Fighting
Man from the Time of the Ancient Greeks to the
Second World War. Northampton: Museum of
Leathercraft.
3. Storch, S.O.P. (1989) Military Leather Objects in
South Carolina State Museum Collections:
Manufacture. Condition. Treatment. In International
Leather and Parchment Symposium. Offenbach am
Mein, May 8–12.
4. The technique of hardening leather by saturating it
in cold water and then exposing it to a heat source
like a blow torch or oven is still used in the twentyfirst
century. Beaby, M. and Richardson T. (1997)
Hardened Leather Armour. Leeds: Royal Armouries
Yearbook.
5. Waterer, J.W. (1946) Elric colloquy, eleventh century
Guild of Bottellars 1373. Dialogues of the allied
group of craft guilds known as Archbishop Elfric’s
Colloquy dating from the eleventh century.
6. Baker, O. (1946) Blackjacks and Bottles. Unpublished
document. Cheltenham Spa: W.J. Fieldhouse Esq
and J. Burrows Co. Ltd.
7. The ‘pitching’ of carriage men’s boots using an
impregnation technique as described in ‘Art Du
Cordonnier’ De Garsault, 1767, was successfully
replicated using authentic methods and materials by
Conservators and Curators at the Centre of
Calceology and Historical Leather Works in
Lausanne, Switzerland. De Garsault. (1767) Art Du
Cordonnier. Facsimile Reprints. In Arts du Cuir
(1984). Geneva: Slatkine.
8. The cross-sections were interpreted by Professor Jo
Darrah, Senior Microscopist and Conservation
Scientist at the Victoria and Albert Museum.
9. COSHH assessments should be carried out before
undertaking cleaning work with this substance.
Benzyl alcohol is harmful by inhalation and if swallowed.
It has a toxicity level of LD50 1230mg/kg
oral, rat. There is no evidence of carcinogenic,
mutagenic or teratogenic properties.
References
Baker, O. (1946) Blackjacks and Bottles. Unpublished document.
Cheltenham Spa: W.J. Fieldhouse Esq and
J. Burrows Co. Ltd.
Beaby, M. and Richardson, T. (1997) Hardened Leather
Armour. Leeds: Royal Armouries Yearbook.
Bickley, J.C. (1991) Vegetable Tannins. In Leather, its
Composition and Changes with time (C. Calnan and
B. Haines, eds), pp. 18–21. Northampton: Leather
Conservation Centre.
De Garsault (1767) Art Du Cordonnier. Facsimile
reprints. In Arts du Cuir (1984). Geneva: Slatkine.
Landman, A.W. (1991) Lubricants. In Leather, its
Composition and Changes with Time (C. Calnan and
B. Haines, eds), p. 29. Northampton: Leather
Conservation Centre.
Pyne, G.B. (1808) The Costume of Great Britain, p. 38.
London: William Miller.
Reed, R. (1966) Science for Students of Leather Technology,
pp. 154 –258. Oxford: Pergamon Press.
Seeley, N. (1991) Enamelled, Japanned and Patent
Carriage Leather. In The Conservation of Leather in
Transport Collections, p. 23. UKIC Conference
Restoration 91. London: United Kingdom Institute for
Conservation.
Soest, H.A.B. van, Stambolov, T. and Hallebeek, P.B.
(1984) Conservation of Leather. Studies in Conservation,
29(1), 21–31.
Storch, S.O.P. (1989) Military Leather Objects in South
Carolina State Museum Collections: Manufacture,
102 Conservation of leather and related materials
Condition, Treatment. In ICOM International Leather
and Parchment Symposium, p. 222. Offenbach am Mein,
May 8–12.
Vincent, J. (1990) Structural Biomaterials, p. 64. Princeton
New Jersey: Princeton University Press.
Volken, M. (1995) The Conservation of a Pair of Bucket
Top Boots. Gentle-Craft Centre for Calcecology and
Historical Leather Works. Lausanne, Swtizerland.
Leather Conservation News, 11(1, 2).
Waterer, J.W. (1946) Leather in Life Art and Industry.
London: Faber and Faber.
Waterer, J.W. (1981) Leather and the Warrior: An Account of
the Importance of Leather to the Fighting Man from the Time
of the Ancient Greeks to the Second World War.
Northampton: Museum of Leathercraft.
A full assessment of any object prior to conservation,
whether it be made from leather or any other
material, will require an appreciation of how that
object was made. A specialist leather conservator
will therefore need an understanding of the methods
employed by leatherworkers. In addition, conservation
and restoration treatments may require repair
and replication of damaged and missing areas so
knowledge and some experience with the techniques
and tools of leatherworking are essential.
11.1 Leatherworking tools
This list of tools is a small part of a very large catalogue.
For each type of tool there are many variations
depending on the actual trade and individual
craftsperson. Leathers vary in substance, texture and
size, products and patterns vary in size, function also
varies. Most tools are designed specifically for the
intended job and many have not changed through
the ages in their use, and skills are handed down
from generation to generation. Leather after all is
man’s earliest natural material for clothing, shoes
and containers. The qualities of leather are unique
and when it is made up the product reflects this.
Tools of the trade should ideally be of good quality,
as inferior steel tools will result in substandard
work. It is important that these are cared for and well
maintained. Individuals frequently ‘customize’ tools
according to the task in hand and they will have a
wide range to satisfy the needs and requirements of
their own highly skilled and specialized trade. It is in
the interest of the craftsperson that their tools are
kept in good condition as most leatherwork has to
be precise in taking measurements, cutting and
making up.
11.1.1 The awl
This consists of a small wooden handle with an interchangeable
pointed blade. There are two types of
blade; a diamond-shaped blade used to penetrate
the leather at a particular angle and for the preparation
of hand stitching, and a round, pointed blade
generally employed to mark positional points and to
make small holes in the leather.
The diamond-shaped blade is often used in conjunction
with ‘pricking irons’ or a stitch marker.
The stitching awl, as its name suggests, is designed
specifically for hand stitching. The interchangeable
blade is diamond shaped and will vary in size according
to the stitch size and the substance of the leather.
The awl is pushed through the leather at an angle following
the pattern of the pricking iron (see below)
making a long slanting shape. These blades are inserted
into a small wooden handle that fits comfortably into
the palm of the hand. The handle has indentations
around the circumference in which the thread is
wound and enable the worker to pull hard enough to
tighten the stitches and form a firm line of stitching.
11.1.2 The knife
There are so many categories of knife it would be
difficult to justify the space to describe them all.
Ultimately knives have two uses, to cut the leather
and reduce the thickness/substance when a fold or
join is required. The name, size and shape of the
knife depend upon the length of cut, the substance
of the leather and the trade.
(a) Head knife. For a long cut the saddler will use a
head knife. This half moon-shaped knife has,
extraordinarily, survived from very early ages.
There are different versions of the head knife, the
103
11
The tools and techniques of leatherworking:
correct tools ؉ skills ‫؍‬ quality
Caroline Darke
single, with a quarter circle, hooked blade and the
double, with a semi-circular blade, half the size of
a round knife. The blades can also be used to
pare down the thickness of leather.
(b) Clicking knife. This is traditionally employed by
shoemakers, with the name derived from the
clicking noise the blades make when the ‘cutters
or clickers’ either change their blades or cut
around the curves of leather and patterns. There
is a choice of two types of blade, a hooked type,
with a vertical blade used to cut easily around
curves and contours and thicker leathers and a
straight blade, mainly used on thinner leathers,
paper and linings. This latter is often used in
conjunction with a straight edge steel rule for a
precise, straight cut. Sometimes a wooden handle
with a mechanism enables the blades to be
changed and screwed tightly into place for
safety. In this case the sharp end of the blades
may be inserted inside the handle when not in
use, hence protecting the sharp edge. The clicking
knife is not entirely confined to the shoe
trade, many others use it. If a large production is
required, then the patterns will be cut out using
steel press knives and a press. This is clearly
much quicker than cutting out by hand.
(c) Paring or skiving knives. These are made out of high
quality steel, as the edge must be razor sharp. (A
wide hacksaw blade sharpened at one end with
a piece of leather wrapped around the handle is
often made as a cheaper but not inferior substitute.)
The blade is sharpened differently to the
clicking blade either at a right-handed or lefthanded
angle. The angle varies from 45 degrees to
75 degrees according to the desires of the individual.
The edges are sharpened on fine emery for a
rough skive. For a smooth edge and skive a whetstone
is used. In most cases the bevel is on one side
only with the reverse side quite flat. There is a
definite art to skiving and once mastered it can
be invaluable in all areas of leatherwork and adds
quality to the product. The main use is to reduce
the substance/thickness of leather when joining
two strips (this join is better skived at an angle) or
reducing the edge prior to a turnover. It can be
time consuming and unless the worker is skilled
can be risky as the leather can be cut accidentally
in the wrong place.
11.1.3 The strop
This is necessary whenever clicking and other knives
are used. The blades have to be sharpened frequently
for an efficient cut. Most clickers will wear their
blades down to very different shapes and angles
depending on their own individual techniques. The
strop is approximately 35cm ϫ 5cm ϫ 1cm in
thickness with a strip of emery cloth on the one side
and a strip of buff leather on the other. Alternatively,
one surface of the leather is treated with an emery
paste of the desired coarseness. The blade is sharpened
with the desired bevel on both sides using the
emery cloth first followed by the buff side. The
coarseness of the emery cloth leaves a slightly serrated
edge to the blade which has a saw-like action
and will last longer than a razor edge.
11.1.4 The bone folder or crease
(Figure 11.1)
This is an excellent, underrated tool, with endless
uses. As the name suggests it is a folding tool made
from pieces of bone, hardwood, horn or occasionally
ivory. Nowadays it is often made from plastic or
nylon but these lack the superior qualities of bone.
Bookbinders originally used it for folding very thin
leathers and papers. The typical folder used in the
bookbinding industry is rounded at both ends. For
making leathergoods the bone folder has a smooth
pointed end with a wide bevel on one side and
slightly flattened on the back. This smooth point
prevents any damage to the leathers when either
marking positional points on the grain side or when
pushing out corners. With such a smooth point
there is no fear of penetration through the leather.
Likewise when lifting leather when turning it on
to reinforcements.
A notch may be found on the side of a folder
which is used when an edge is rubbed down to close
the fibres for a smooth result.
11.1.5 The steel rule
This is usually about 90cm long and marked with
centimetres and millimetres for accurate measurements.
It is also used as a straight cutting edge.
11.1.6 The dividers (compass)
A divider is an instrument with two adjustable hinged
legs both ending in points, thus varying from a compass
which has one point and the other designed to
take a marker such as a pencil. The most common
divider will have one point with a flat side which acts
as a guide along the edge of the leather and the other
with a rounded point ensuring accurate and repetitive
measurements. It also enables positional points such as
104 Conservation of leather and related materials
screw holes, stitching lines, the width of straps, etc.,
to be marked accurately.
The length of tool varies according to the span
required. A bag maker will use a fairly long pair of
dividers whereas a shoemaker will require a short
span only.
11.1.7 The revolving hole punch
This implement is a simple tool owned by many
households for the job impossible to do properly with
any other tool. It has six differently sized punches,
selected by revolving them around to the desired position.
With a scissor action it will cut the hole in the
material cleanly and efficiently.
11.1.8 The hammer
For leatherworking this tool preferably has a slightly
domed face. It can be employed to reduce the substance
of leather in preparation for stitching, although
care must be taken not to bruise the work. Varieties of
hammers are used across the trades but they are generally
used for a similar purpose. To protect delicate
work the head will often be covered with a piece of
leather.
11.1.9 The race
This specialist tool is used to make a groove or a
channel in a U or V shape when pulled over the surface
of the flesh side of leather. It is used by a saddler
on thick leather in preparation for making a sharp
bend in the leather. It has the same effect as a score
on paper when a neat fold is required.
The shoemaker will use a channel to prepare for
a line of stitching which is to be sunk below the
surface of the leather or for decoration.
11.1.10 The clam
This is a large, wooden, tweezer-like tool. Held
between the knees it clamps on to the work allowing
the craftsman to have two hands free for stitching.
The holding ends are usually covered with
leather to protect the piece being stitched.
11.1.11 The edge shave
These come in many sizes according to the thickness
of leather, and the size and shape of bevel required.
They consist of a slender, curved shank with a groove
The tools and techniques of leatherworking 105
Figure 11.1 Bone folders.
on the upper side forming a chisel-shaped cutting
edge set into a wooden handle.
The hand cut edge tool is particularly vulnerable
to wear and damage. If special care is taken to prevent
this, the smooth bevel made along the top edge of a
piece of work prior to polishing with an edge shave
will guarantee a smooth aesthetically pleasing finish.
The harness maker, shoemaker and the belt maker
all use this tool.
11.1.12 The crease iron (Figure 11.2)
This tool is used to burnish an edge or mark a line
parallel to the edge of a piece of work. It is used
by shoemakers, saddlers, bag makers and others.
According to the task in hand, the metal head comes
in various types and shapes. The two most common
are the single-line creasers without a guide which
are suitable for general creasing on turned edge articles
and the double line irons which have a fixed or
adjustable fence which is used as a guide along the
edge of the leather. The screw crease is adjustable
allowing the worker to choose the distance of the
crease line from the edge. The different-shaped
heads can be used for cut-edged work, box work
and types of ornamentation.
Creasers can be made of steel, wood or bone. The
steel ones have a curved shank set in a wooden handle.
They are often heated and used on dampened
leather to make a stronger impression. Vegetabletanned
leathers when wet will mark badly from a
metal head so it is necessary to use a bone or
wooden folder.
Although there are so many types of crease iron
they all have the common element of a blunt blade,
to ensure that the leather surface is not damaged.
Lines produced by crease irons can be for decoration
or as a guide or channel for stitching. They are generally
used by craftspersons making leather goods
from relatively thick leathers, i.e. harness makers,
and shoemakers.
Crease irons must not be confused with the edge
irons which are a different type of tool used by shoemakers.
As with crease irons there are many variations
of edge iron. Essentially they do a similar job
but are a chunkier looking tool. The heads, usually
made in seven widths, are rectangular in crosssection
and set in short wooden handles. The longerhandled
irons are known as jigger or waist irons. The
purpose of the edge irons is to set the edge of the
shoe to improve the appearance.
11.1.13 The stitch marker (Figure 11.3)
As the name suggests this is a tool used to mark a
line of stitching. It is a disc with blunt points around
106 Conservation of leather and related materials
Figure 11.2 Crease irons.
the edge mounted into a wooden handle. It is often
confused with a dressmaker’s tracing wheel that has
spiked points. Each point is equidistant allowing the
marks on the leather to be at the correct stitch length.
A leatherworker will have a range of different stitch
markers according to the stitch length required. The
rowels do not penetrate the leather. This tool is a
marker only, and is followed by the use of an awl.
11.1.14 The pricking iron
The ‘pricker’ is a toothed punch and is employed to
achieve uniformity of stitch size. It is available in different
stitch lengths. There are two types, one with
approximately ten stitch marks and the other with
only three. The latter is for corners and curves. The
tool is placed carefully on the leather and gently
hammered to make an impression which can be
pierced later with a stitch awl. It is important that the
marker does not penetrate the leather as this weakens
the areas between the stitches. The next time the
tool is placed on to the leather it is positioned in
the last two stitch impressions to give an accurate
continuous mark. The impression the stitch marker
makes is at a diagonal slant so when the awl is pushed
through the leather at this angle it gives the stitch an
oblique pattern.
11.1.15 The needle
Needles come in various lengths and sizes according
to the use, the leather and thickness of the thread.
There are two main types, a diamond shape with a
sharp end enabling penetration of soft leather, and a
rounded shape with a blunt end requiring preformed
holes or slits. These are prepared with the aid
of pricking irons or stitch markers to mark the
leather, and awls to penetrate the leather. The shoemaker
traditionally used a bristle in place of a needle,
in conjunction with an awl. With awkward corners
and curves a bristle is preferable to a needle as it is
flexible and will bend. Today nylon bristles are sometimes
used as a substitute for the natural product.
Long quilting needles are used for quilting saddle
panels, girth straps, etc. and half round needles can
be used, mainly for concealed stitching.
Collar needles are made from heavy gauge steel
and have diamond-shaped ends. They are used primarily
for edge stitching. These needles can take
leather thongs as well as the heavy thread that are
also for decorative edging.
The panel needle is similar to the collar needle but
is bent. It is used for sewing in the panel of a saddle.
For hand sewing glovers use an eyed needle with
a round butt and a three-sided point which is used
The tools and techniques of leatherworking 107
Figure 11.3 Stitch marker.
for the penetration of the leather. The three-sided
point will cut through the fibres of the leather.
Furriers use a round needle or a three-sided needle
for heavier work.
11.1.16 Thread
For hand sewing threads are traditionally made from
linen and are waxed every time the length of thread
is used. The wax keeps the thread intact while
stitching and grips the leather.
11.2 Adhesives
There are a number of categories of adhesives used
by leatherworkers. Using the terms employed in the
trades these include: animal glue, fish cement and
starch pastes, rubber solution and latex, which are
natural adhesives, and neoprene and PVA emulsions
which are synthetic. The qualities they possess are
tenacity and bond strength; elasticity, the pliability;
mobility, the ease with which they can be applied;
and compatibility, the power of entering the structure
of the leather.
The choice of adhesive therefore will depend
entirely on the type of work being undertaken and
strength of adhesion required. The need may be for
a total bond or a temporary hold prior to stitching.
It must be noted that natural glues and pastes can be
susceptible to climatic conditions or insect damage.
(a) Starch pastes are prepared by boiling and simmering
wheat, rye or other flours with water to form
a thick smooth paste. They are easily applied by
brush over large areas if correctly cooked. They
are not considered very strong adhesives but are
very penetrative and in the case of leather they
soften the fibres allowing it to be shaped to a new
form. They have thus been traditionally used for
covering metal purse and handbag frames, as well
as moulded articles. When dry they are fairly stiff
without being brittle.
(b) Animal glue is made from bones, trimmings and
other waste parts, boiled gently for a long time
and then allowed to cool and solidify. It is supplied
in block or a granular powder form. Animal
glue is non-penetrative but quite strong. It is softened
by warming and applied in a runny condition.
Once applied it cools and dries fairly
quickly when it becomes hard and brittle. Thus it
is suitable only for stiffened work. Nowadays animal
glue is rarely used because it is inconvenient
to prepare and keep in a good condition.
(c) Fish glue or cement is made from gelatine extracted
from fish skin and waste dissolved in acetic acid
with an added preservative. It is not often used by
leatherworkers but is extremely tenacious and
inelastic. It is used mainly for attaching small
metal corners and ornamental parts to leather,
although it is not totally effective and small rivets
or the like are generally used as an added precaution.
It is a very penetrative glue making it difficult
to use in the case of thin leathers. It can cause
irreparable damage if accidentally brought into
contact with the surface. A coating of shellac varnish
was often applied to metal parts to assist adhesion
and avoid rusting caused by the cement.
(d) Rubber solution gives a low strength, temporary
adhesion. It is a contact glue and generally holds
the work in place prior to machining.
(e) Latex is a thin liquid made from the milk of the
rubber tree and preserved in ammonia. It is very
strong and flexible when dry. Because of its penetration
it is inadvisable for use on thinner leathers.
Latex is often used as an alternative to rubber solution
as it is water based, safer and more convenient
to use.
(f ) Neoprene is a very strong synthetic rubber solution,
and if the leather is suitably prepared the
bond can be permanent.
(g) Polyvinyl acetate (PVA) is a smooth, creamy
white, liquid adhesive. It is very strong and flexible
when dry. It is a one-way adhesive and allows
for movement and adjustment of the components.
It is also suitable for large areas.
(h) Double-sided tape is now used as an alternative to
rubber solution as a temporary holding adhesive.
It is quicker and easier to use but expensive, and
if the wrong type is used will coat the machine
needle with the sticky substance thus causing
problems with the stitching.
Editor’s note: The adhesives described above relate to
those used both historically and currently by the various
trades involved with the manufacture of leather
goods. It is suggested that the reader should also see
the section on adhesives used in conservation treatments,
Chapter 13, and the section on animal glues
and collagen products as described in Chapter 18.
11.3 Reinforcements
These are used to strengthen an article partially or all
over, or as a support for softer leathers when a firmer
look and feel are required. The area of an attachment
108 Conservation of leather and related materials
such as a handle or closure will generally be reinforced
and the area where a seam has been skived to reduce
the thickness will also require a strong woven material
to prevent weakness. There are many types of
reinforcement depending on the trade and function
of the product. The following list relate mainly to
the bag, light-leather goods and similar trades.
(a) Boards. These are used for reinforcing heavy
leather goods. These include tip, split cane, plywood,
fibreboard, millboard, leather board,
strawboard and wood pulp boards. These were
used prior to the much lighter and stronger plastics
becoming available. Many boards, both
heavy and light weight, are stronger in one
direction than the other and if used in the wrong
direction will result in cracking. It is important
therefore to discover the ‘roll’ or ‘machine direction’
of the board prior to cutting.
(b) Papers. Unglazed papers with absorbent features
are often used which will make up for the deficiency
in strength of the leather. These include
kraft brown, stout brown, white cartridge, sugar,
blotting and felt papers. The use of highly finished,
non-absorbent paper will result in cockling
and shrinking and cause a ‘rattle’ noise to the final
product which is an unwanted characteristic.
(c) Woven fabric materials. These are used mainly for
strengthening purposes. They have greater
strength than leather and will not be weakened
by stitching. These fabrics may also be used to
strengthen a paper or board to increase its serviceability;
for instance preventing cracking on boards
in areas subject to constant bending as on a strap
or handle. Thick leathers are skived at the seams
to reduce their substance but as this weakens
the leather, strength can be added with a woven
fabric. The fabrics are manufactured mainly from
cotton, linen and hemp. Most have been dressed
or finished which aids in the cutting and reduces
fraying. Other woven materials introduced in
the mid-1900s were dressed with low melting
point adhesives suitable for leathers. An iron-on
backer will add body to the leather but care has
to be taken not to use leather with a loose structure,
as this will tighten the flesh side causing a
wrinkled effect on the grain side.
(d) Non-woven materials. These are used for the same
purpose as the woven fabrics but with the advent
of man-made fibres provide additional properties
similar to leather but with strength the leather
lacks. Non-woven fabrics are also available with
an adhesive coating.
(e) Wadding. This is usually made from waste cotton.
It is available in sheets with a kind of skin on
one side allowing easy separation of the layers.
This enables the craftsperson to select the thickness
of wadding required for any particular job.
For example, where protection is required many
layers can be used.
(f ) Foam. This has generally replaced the use of cotton
wadding. It will give a soft look and feel
supplementing the properties of both leathers
and woven materials. It also is used for padding.
It is more effective in conjunction with soft
leathers and is often used in combination with
chipboard for butted bags.
11.4 Techniques
11.4.1 Skiving
This is a process of reducing the thickness or substance
of the leather; this is attained by hand or with
a skiving machine or a combination of both. Skiving
is usually carried out on the edge of leather. If, however,
an overall reduction of thickness is required this
will be carried out on a splitting machine.
Skiving around the edges is generally used for the
turnover method of construction, which is butted.
If the leather is skived too thin there is a risk that
this will weaken the leather and cause the machine
line to split.
Similarly, skiving for a turned seam must not be
too thin as the result will be floppy and mediocre
and can cause the seam to tear when the bag is
turned the right side out.
Skiving by hand is laborious but where a small or
intricate piece of skiving such as a join on a strap is
required the result is superior to a machine skive.
11.4.2 Preparation
As the name suggests, this is the preparation of the
pieces once the components have been cut out and
possibly marked. It is an essential part of the making
up of a product and can often be overlooked resulting
in poor inefficient work.
11.4.3 Sewing – stitch formation
(a) Saddle stitch. This technique is used on most
hand-stitched products where two flat pieces of
leather are sewn together. The method will vary
slightly with different trades. The shoemaker,
having marked the stitch, will attach a blunt
The tools and techniques of leatherworking 109
needle or bristle to either end of the thread and
holding one needle in each hand, with the work
held between the knees or using a clam, push
the awl through the leather. As the awl is withdrawn
one of the needles is passed through, to
be followed by the second needle from the other
side. The thread is then pulled firmly and tightened
to form an even stitch. It is important that
the method is repeated in the same sequence for
each stitch to ensure neatness and consistency.
This form of stitching is considered to be very
neat and strong and has been a method adopted
by saddlers and other leatherworkers.
(b) Box stitch. This style is used on boxes and containers
where the stitching is on the corner of
the work and the two pieces of leather are at
right angles to each other. It is sewn in the same
way as the saddle stitch but at an angle. Firm
leather is preferable for this particular style of
stitching and a mould is often used to hold and
support the work instead of a clam.
(c) Butt stitch. A butted seam is used on many traditional
objects such as shoes, collar boxes, etc.
where the edges are butted together and the
needle is pushed through the middle of the
leather forming a row of stitching either side of
the join. The seam normally lies flat as opposed
to the box stitch. The term ‘split stitch’ is often
used for this particular join.
(d) Back stitch. This term is used where the stitch is
longer on the underside, with the same appearance
on the topside. The long stitch at the back
of the work can strengthen the seam reducing
the possibility of cutting through thin leather.
11.4.4 Decorative stitching
(a) Thonging. This is often used when there is no
machinery available. The work is sewn together
by means of strips of leather or braid passed
through previously made holes or slits. The
thong is a substitute for thread and is now available
by the metre, but in the past the leatherworker
would have cut the length of thong
required from a circle of leather. This method
enabled long strips to be obtained and eliminated
joins. Some leathers have more strength
than others due to the tightness of the fibre
structure. Leather is probably more practical for
making thongs than braid due to its strength.
Thonging requires little training although it is a
skill passed down from generations and can most
typically be seen used by many civilizations such
as in Native American clothing, saddles and
containers. Used in conjunction with a pricking
iron, awl and special thonging needle there are
many fancy and complex styles.
(b) Quilting. This is the term used to describe the
decorative stitching to hold padding in place.
(c) Rounding is the process of wrapping leather
around a core and stitching it to form a cylindrical
strap or handle.
11.4.5 Machine stitching
Since the mid-nineteenth century, the advent of the
sewing machine has seen the demise of hand stitching
in many trades. According to the type of material and
its setting various stitching styles can be produced.
(a) Corner stitch. This is the machine version of the
box stitch where the two edges of a box or case
are butted at right angles and stitched through the
middle, to form a stitch line either side of the join.
(b) Chain stitch. One thread only is used to form a
chain on the underside of the work. This type of
stitching is often found on work produced using
early sewing machines.
(c) Lock stitch. This is a two-thread type of stitching
where the top needle of the machine feeds the
thread through the material where it links with
the bottom thread and embeds the stitch in the
centre of the material. Both tensions of the top
and bottom must be equal to achieve an even
looking stitch.
(d) Top stitching. This is a final stitch used on the
topline of both a bag or shoe where the last row
of machining completes the closing. This can
often be used to stitch the lining in at the same
time and in the case of handbags, the handle and
the shoe, the straps as well. It can also be a term
where the binding is stitched to an edge.
11.4.6 Decorative machine stitching
(a) Fancy and mock. These terms are used where the
stitching is used for a non-functional effect.
There are times when making a bag where
functional stitching is not possible and where
the components are glued into place. However,
the design requires the visual appearance of
stitching. This is when fancy or mock stitching
is employed.
(b) Cable. This is a term used normally by shoemakers
and bag makers where the stitching is
longer and the thread is thicker than actually
required for strength, thus producing a heavier
110 Conservation of leather and related materials
looking line of stitching. This technique is known
in the bag trade as a saddle stitch although the
stitching is often alternate with a gap between
one stitch and the next.
11.4.7 Seams and construction
Most seams are common to all leatherworking professions
but differ in the way they are named which
often derives from the French. There are many reasons
for the type of seam chosen. These include the
style required by the designer, the material, the
skills of the maker and the machinery available.
(a) Boot. This is a term one would naturally associate
with the shoemaker, it is therefore surprising
that it is more often found being used by a
handbag maker. If it is too bulky or thick, the
joining of a seam will be butted edge to edge
and sewn together by means of a strong piece of
lining or thin cloth at the back of the work thus
producing a very flat seam. Alternatively the
two edges are skived, placed face to face, sewn
together and then turned back. Because the skiving
can weaken the leather a strip of reinforcement
is placed over the back and machined
either side of the seam. The term silk seam is the
shoemakers’ name for this technique.
(b) Bound seam. This term is used when a piece of
leather is used to cover a raw edge, often where a
style line or a definition to a seam is required. A
butted seam will be bound, either in thin leather
or with a contrast colour. Two versions can be
found. In the first there is a special attachment on
a machine which will stitch a tape or thin strip of
leather over the edge of the work. Alternatively
French binding, generally found on handmade
goods, is a technique where the edge is bound in
such a way that the stitching is not visible thus
achieving a softer look to the binding.
(c) Brooklyn seam. This is yet another version of the
silked seam but paper or tape is stuck over
the seam.
(d) Brosser or round seam. This is where the leather is
placed with the wrong sides together and the
stitches cover the edge often with fancy stitches.
This seam is used by glovers.
(e) Closed. This method is not dissimilar to a boot
seam but the components are faced right sides
together, machined with a small seam allowance,
opened and flattened.
(f ) Faced or butted edge. This is a term used to describe
two edges that are sewn together face to face. On
a structured bag the edges of the leather are
skived and turned on to reinforcement on both
sides, placed face to face and machined close to
the edge. Otherwise it may be raw and can be
machine or more generally hand stitched. This
can be of any style of bag and is possibly the
most used, although since the 1990s with the
introduction of a specialist machine, a lapped
raw seam can be seen on many quality bags.
(g) French or invisible seam. Here, two pieces of
leather are stitched face to face along one edge. A
reinforcement is laid parallel to the line of stitching
and the seam is taken around the stiffening
and glued down on the other side. The material
on the unstuck side is able to hinge on the stitch
line and opened out. This seam has no visible
stitching and is generally used for side gussets or
can be used as a styling or decorative seam.
(h) Glove. This is a generic term used in shoemaking
and originates from one of the many stitches used
on a glove. The machine has twin needles on the
top but a single thread from the bottom thus
making a slight ridge between the two lines of
stitching. For a more defined ridge a cord can be
run through between the two rows of stitching.
(i) Inseam. This term is used when the leather is
stitched with the right sides facing and then
turned. It is widely used by glovers.
( j) Jean or roll seam. This method is named from the
similarity to the seams in jeans. It is used for joining
one piece on top of another. It is necessary
to use this method when a flat join is required,
especially when joining curves. Reinforcement is
usually needed. It is useful for decorative purposes
and panelling. It is a stronger seam than the open
seam and probably stronger than the boot seam.
(k) Lapped/overlay. Here the component pieces are
placed one on top of the other and machined or
stitched through either with a single or double
seam. The underside is usually skived to reduce
the bulk of the seam and the overlay skived
when appropriate. A relatively new machine has
been introduced which will stitch in this way
and has quite dramatically changed the styles
available to a handbag designer.
(l) Moccasin. This is a fancy but functional seam
achieved when the shoe is constructed in a way
that one side of the leather has to be gathered on
to an apron top. It can either be stitched with an
open seam or the top leather from the apron
folded over to form a binding.
(m)Open or flat seam. As its name suggests this is the
reverse of the closed seam. For shoemakers it
shows on the outside of the upper whereas the
The tools and techniques of leatherworking 111
handbag maker will have the open seam showing
on the inside. It is a seam used to join soft
materials of most types of tannage, vegetable,
chrome, and semi-chrome, providing the leather
is not liable to crack. Two pieces of leather are
placed face to face and machined together, folded
back and glued if required. It can then be top
stitched and finally turned right side out thus
hiding the seam.
(n) Piped seam. This is where a separate piping is
inserted between the turned seams and will often
be included in a style to add strength and a definition
to the shape of the bag when particularly soft
materials are used. They can also add to the visual
appearance by using a contrast colour or material.
(o) Pique. This is similar to the lapped seam where
one edge is lapped over the other with only one
edge showing but making a flat seam. It is used
by glovers.
(p) Prix-seam. This term is derived from the French,
as are most of the glove seams where two edges
of the leather are held edge to edge with the
wrong sides facing and stitched together leaving
a raw edge. This style is generally used on heavier
gloves especially gentlemen’s gloves.
(q) Raw/cut edge or bound. A craftsperson with
limited equipment can use raw edge construction
although it is now used by most levels of the
market. The leather is not skived and the edge of
the leather must be of hard or firm substance. A
vegetable-tanned leather is ideal. Both edges are
stained and polished and can be machined, hand
stitched with a glove or harness stitch or thonged
by punching the edges with holes and lacing
together with a thick thread or narrow strip of
leather. An alternative is to bind the edge with
a strip of leather or material to neaten it.
(r) Silked seam. As a means of strengthening the
seam the closed seam has a woven silk tape placed
on the wrong side with two rows of stitching
either side of the join to hold it in place. A row
of zigzag machining can also be used. This is predominately
found in boot manufacture. A gent’s
shoe will have it showing on the right side with
leather instead of the tape for added strength.
This is similar to a boot seam.
(s) Sprung seam. Sewing two different shapes together
can give an extra dimension to the product. It is
used for both footwear and bag making. It is not
always necessary to use the same type of seam.
(t) Turned. The term describes the making and
turning of the product from the wrong side of
the work to the right side. Often used on soft
materials of most types of tannage, vegetable,
chrome, and semi-chrome, providing it is of a
non-cracking type. Placing the wrong sides
together using a flat seam to stitch the two
pieces together joins the components. The seam
can be stuck down with an adhesive if appropriate.
Piping can be inserted for extra definition.
(u) Turned over edge. This construction is, as it
describes, an edge turned over generally on to
reinforcement; this can mainly be a board or a
fabric with ‘iron on’ properties depending on
the substance of the leather and the look of the
product. This method requires a high level of
skill, the maker has to skive the edge, prepare
and machine. There are materials which do not
lend themselves to this style simply because
skiving is not always possible, this leads to bulky
seams and on the corners an uneven turnover.
Plastics and chrome-tanned leathers are typical
of this group of materials.
Bibliography
The following reference works may be useful to the
reader requiring further information concerning
techniques for leatherworking and craftsmanship.
Attwater, W.A. (1983) The Technique of Leathercraft. London:
Batsford.
Cherry, R. (1979) Leathercrafting: Procedures and Projects.
Texas: Tandy Leather Co.
De Recy, G. (1905) The Decoration of Leather. London:
Constable.
Double, W.C. (1960) Design and Construction of Handbags.
London: Oxford University Press.
Freidrich, R. (1986) Cuir – Tradition, Création. Dessain
et Tolra.
Hamilton-Head, I. (1993) Leatherwork. Poole: Blandford.
Michael, V. (1993) The Leatherworking Handbook. London:
Cassell.
Moseley, G.C. (1945) Leather Goods Manufacture. London:
Pitman.
Salaman, R.A. (1985) Dictionary of Leather-working Tools.
London: Unwin Hyman.
Waterer, J.W. (1946) Leather and Craftsmanship. London:
Faber & Faber.
112 Conservation of leather and related materials
12.1 Introduction
The overriding general principles, ethics and standards
of practice for conservation are summarized in the
‘Codes of Ethics’ for the care of objects and collections
drawn up and ratified by the International Council of
Museums Committee for Conservation (ICOM-CC),
and national institutions such as United Kingdom
Institute for Conservation (UKIC) (now the Institute
of Conservation) American Institute for Conservation
(AIC) and Australian Institute for the Conservation of
Cultural Material (AICCM). Conservation professionals
will be aware of these and will have been
trained to carry out their work with reference to the
philosophies expressed in these standards.
The book, Caring for the Past, Issues in Conservation
for Archaeology and Museums (Pye, 2001), focuses on
the practical concerns and ethical dilemmas of
conservators having to treat objects in a variety of
circumstances. Some of these are governed by the
necessity to make the object fit for continued use
rather than static museum display. Conservation
processes which change the object or its environment
and lead to the long-term survival of the object are
discussed in relation to the original purpose or function
of the object and also its current situation in a
museum or collection. This book is essential reading
for all conservators, and also for those considering
the issues and treatments discussed in this chapter.
Conservation treatments and principles of care
applied in situations where leather objects may still
be in use or where they are in private collections,
historic houses or other places out of controlled
museum environments can often cause dilemmas
and conflicts of opinion. Standard museum practices
and treatments may simply be unworkable in nonmuseum
situations and compromise solutions may
often have to be reached and adopted by the conservator
in order to secure the best treatment or
environment possible for the object concerned.
The following points will need to be considered
and may help the conservator select the most appropriate
treatments, evaluate general care requirements
and make informed recommendations to the client
for the long-term survival of the object within the
context in which the object is kept or used.
12.2 Objects in use
The use to which the object is put is of prime importance
as is the way it will be handled and cared for
after treatment. There is no point in carrying out a
delicate conservation repair on a piece of upholstery
that is going to go into a family home and be used,
at best, sat on regularly or, at worst, as a trampoline
by small children.
Communication with the owner or curator responsible
for the object is vital to find out what they
expect from conservation, and to determine what
conditions the object is returning to. An owner may
have unrealistic expectations of what can be achieved
considering the current condition of the object.
Museums have very different conservation needs
from private individuals who are still using and enjoying
their objects. It also has to be established who
will be caring for the object. Will it be looked after
by professionals in a museum or a historic house?
Is it in the care of an owner who will treat it in a
way which is appropriate to its state? Will it be
handled by untrained staff, who may lift the object
inappropriately?
For example, if an object has a handle, but this is
fragile, it is very difficult to ensure that untrained
113
12
General principles of care, storage and display
Aline Angus, Marion Kite and Theodore Sturge
staff do not use it. It is easy to provide detailed advice
on the future care of an object after treatment, but it
is much more difficult to ensure that this is followed.
As a result, a more pragmatic approach may
be required, and the question ‘What would happen
if ?’ should be asked. If an object is likely to break
when a very weak handle is used, the resulting damage
could be extensive. This may lead to a decision
to carry out a stronger but more invasive repair than
might otherwise have been chosen. Alternatively it
might be better to replace the original handle if it
cannot be strengthened, thereby reducing the risk.
However, such decisions should not be made without
considerable thought and consultation. Such
treatments should be fully documented and the
original handle should be retained and kept carefully
with the object should the situation change in the
future and the original handle need to be put back.
12.3 Display or storage?
Is the object to be displayed or stored? If it is going
to be stored for the foreseeable future, the prime
need is for it to be stable and for the components to
be secure so that they are not lost. The object needs
to be in a fit state for handling, but an aesthetically
attractive appearance is not a high priority.
It may be that the needs of objects which are to
go on display will be the same as those to be stored,
but they may differ in various aspects. Objects on
display must be readily intelligible. For example, an
object with a picture on it may be perfectly stable
but if there is distracting damage to the image, it may
be difficult to interpret. Inpainting, but not overpainting,
to make an image readable may therefore
be appropriate before it is displayed.
12.4 Levels of treatment
Good practice and theory require that all conservation
treatments should be reversible, but to some
degree all are irreversible and the most appropriate
and least invasive treatment should be chosen.
Conservation of an object aims to ensure that the
object is brought to a state where it is stable and as
far as is possible safe from further deterioration. At
its most simple, this could mean storing the object
in a box in the correct environmental conditions.
The treatment of pests and mould in leather is
essential. The stabilization of red-rot may also be
appropriate, as may the securing of loose sections of
leather or a flaking surface. However, the application
of surface finishes or the inpainting of damage may
not be considered fully compatible with best conservation
practice.
Full restoration is at the other end of the scale. In
the case of a chair, for example, this could involve
refinishing the wood, a full rebuild of the underlying
upholstery and a new leather covering. While
this will give a very serviceable object, it will lose
much of its feeling and appearance of age, and render
it of less value as an historic object.
Usually, treatments fall between these two
extremes. Some restoration work may be considered
necessary to give the object structural integrity, to
assist interpretation, or simply to make an object
more visually attractive. Filling a hole in an object
such as a leather screen may increase its strength and
reduce the chances of further damage. It may also
reduce the visual distraction caused by the area of
loss, allowing the object to be viewed as a whole.
The decision to inpaint the fill may well relate to the
nature of the object. It is likely that the owner of a
gilt leather screen will regard it as a work of art and
will want nothing which will distract from the overall
appearance of the object. However, an assumption
that this will be required should not be made
without consulting the owner or curator, who may
prefer a simple background colour.
The context in which an object is to be displayed
is significant and may affect the level of work carried
out. For example, if a leather bag is being displayed
in a museum in a leatherworker’s workshop, as part
of a social history display, it does not need to appear
pristine. However, if the display is of a leathergoods
shop, it needs to look plausible as shop stock. Any
surface treatments applied to achieve this may not
be actively conserving the object, instead they would
serve an aesthetic function.
12.5 Handling by the public
Repeated handling and direct access by the public
may cause excessive damage and this may influence
decisions on the level of treatment to be undertaken.
For example, boxes, cases or trunks which open and
are accessible on open display may prove irresistible
to visitors. If a box has leather hinges or straps, or
perhaps an overhang around the edge of the lid, casual
opening and closing by people passing by can rapidly
lead to damage. The object either needs to be
moved from open display, or those responsible must
realize that in time the leather may be damaged
114 Conservation of leather and related materials
beyond repair with replacement the only remedy.
This does not sit comfortably with the concept that
museums should preserve objects, as far as possible,
for ever. Even if the harm caused in this way can be
repaired this will never remove the underlying damage.
A tear can be repaired but the object will never
be as good as it was before it was torn. Accessibility
is desirable but repeated handling should be avoided.
12.6 The ‘finish’
The final finish or dressing given to an object as part
of the conservation process is an issue that requires
consideration. A finish or dressing is often applied
for aesthetic reasons rather than on conservation
grounds. A leather dressing may brighten the object
and give it a ‘finished’ look, but may not actually
contribute to its conservation. Finishes may lead to
problems in the long run, so care should be taken.
Dressings may absorb dirt and may create a tacky
surface. If they contain inappropriate ingredients or
if too much is applied these may spew onto the surface.
Spew is a white surface deposit of free fatty
acids which may be confused with mould.
Dressings should never be applied to the front or
back of painted leather, be it gilt or otherwise. The
oils and fats in them can migrate into the paint and
varnish layers, causing irreversible discolouration
and softening of the varnish. This may not happen
immediately, so testing at the time of application
cannot be relied on.
There is a long tradition of applying varnishes
based on oils and resins, both natural and synthetic,
to leather objects. Many of these are now giving
problems because they have discoloured. Their
removal from an object can be very difficult or even
impossible, particularly from gilt leather. Gilt
leather is problematic because the original varnishes
applied over the silver to give the golden colour are
often soluble in the same solvents needed for the
removal of the over-varnish. The long-term consequences
of any non-essential finish should be carefully
considered.
It is possible to refinish leather completely using
modern materials, and there are firms which specialize
in this. They very often strip the original
surface coatings completely in order to provide a
uniform key for the replacement pigmented finish
layers. It is very unlikely that this would be appropriate
for historic material, but items such as modern
sofas may well benefit and be given an extended
life. It should be remembered, however, that many
rare treasures on display in museums today were once
in day-to-day use and only considered ordinary.
12.7 Preventive conservation
12.7.1 Environment
Leather does not differ greatly in its preventive
conservation needs from other organic materials.
However, it responds quickly to changes in the
environment, so additional care is required.
The relative humidity (RH) of the room where
the leather is located will affect it. If it is too damp,
above 65%, mould may form and stain the leather.
If the room is too dry, below 40%, the leather may
lose some of its flexibility and become more prone
to cracking and tearing. Changes in humidity also
lead to significant changes in area. For example,
leather mounted on a screen can become very tight
in dry conditions, leading to splitting and pulling
away from the edges. This also makes it more vulnerable
to knocks. On the other hand, if the atmosphere
becomes too damp, the leather on the screen
will expand and it may sag. Leather accommodates
the slow swing of seasonal RH change, but extremes
of RH and sudden changes cause damage. A further
consideration is that many leather objects are composite,
and may include several differing materials in
their construction. These materials may have very
different RH requirements. In this instance environmental
conditions will need to be maintained which
will cause as little damage as possible to all materials
included.
Room temperature does not in itself make a great
difference. However, it is so closely linked to relative
humidity that it has to be considered. The problem
can be particularly acute when large rooms,
used perhaps for functions, are unheated most of the
time and then boosted to a high temperature when
the room is being used.
All light is harmful and it can lead to a change in
the colour of leather, particularly that which has
been dyed, and may also affect decorative finishes
such as paint. Ideally, the lux level should be kept to
50 or less but a higher lux level is sometimes suitable
for a limited display time. The most damaging source
of light for leather is direct sunlight. In addition to
the lux level being very high, the leather will absorb
heat from the sunlight very rapidly. A gilt leather
screen which is exposed to direct sunlight will
rapidly become noticeably warm, and loosely fixed
leather can become drum tight in less than an hour
General principles of care, storage and display 115
and then the risk of damage to the object becomes
very high. Prolonged exposure to sunlight can lead
to vulnerable leathers becoming literally burnt.
Spotlights should be avoided as they can cause similar
problems and localized hot spots.
Dirt is difficult to remove from the grain crevices
and cracks in leather, and is also problematic on the
flesh side. It can come from a variety of sources,
common ones being open fires, people’s hands and
general airborne dust. This last can be exacerbated
by poorly filtered air conditioning. Air dragged into
a museum in the middle of a city is likely to be
dirty. If the air conditioning filters are only working
at 90% efficiency, the 10% of dirty air that gets
through into the building can rapidly build up in
the galleries. The more that can be done to protect
objects the better, be they on display or in store. It
is preferable and cheaper to prevent contamination,
rather than to have to undertake frequent cleaning
programmes.
12.7.2 Pests
Regular inspection and insect pest monitoring is
desirable so any infestation may be noticed quickly
and early remedial treatment undertaken. Protection
from damage by other pests such as vermin, or cats
or dogs if the object is in a domestic environment,
should also be ensured.
It should be noted that careless handling and
clumsy usage of an object by curators, owners and
other people can also cause serious damage to a
fragile object.
12.7.3 Storage and display
Good storage and display can do much to protect
objects from damage. The essential requirements are
suitable environmental conditions including providing
protection from light, from atmospheric pollution
and from general dirt and dust. Providing
sufficient space and support and thus preventing
crush damage is also essential. Boxing an object
carefully is often a storage solution that will go a long
way to addressing several of the above requirements.
One issue which is sometimes raised in relation to
the storage of leather is the use of acid-free tissue
and card. Leather by its nature is an acidic material
and it is likely that old vegetable-tanned leathers will
have a pH in the range of 2.5– 4. As a result, the use
of acid-free packing materials is likely to be of
limited benefit. However, if the object also contains
acid-sensitive materials such as paper or textile, it may
still be advantageous to use acid-free packing materials,
but the benefit is likely to be limited by the
acidic nature of the leather itself.
The ideal form of storage provides support to the
whole shape of the object. Any interior voids should
be padded which will give protection from crushing.
However, the object also needs to be accessible for
study and to monitor its condition. If the packaging
is too complex and time consuming to open and
close, damage may be caused during the process of
unpacking. In addition, the packaging components
may not be properly reinstated after inspection.
All storage solutions must be clearly labelled and
indexed. A great deal of time can be saved and damage
prevented if the desired object can be located
quickly and easily. If it is necessary to disassemble an
object for storage, a reassembly diagram should be
packed in the box with it as well as included in the
notes. For smaller items, a sturdy box will usually
give the best protection, provided it is not overfilled
and the contents are not inappropriately mixed, with
a heavy object overlaying a fragile one. As well as
giving good physical protection against knocks and
dust, a box provides its own microclimate and gives
some buffering against changes in temperature and
humidity. It is also easy to transport and avoids the
necessity of handling the object.
Where boxed storage is not practical, open
shelves, racks, cupboards and open storage have to
be considered. Shelves in a dustproof cupboard or a
roller rack with doors provide the best protection.
Roller racking takes up less space and is cheaper in
the long run. However, initial cost often leads to
open shelving being used instead. Provided that the
shelves are not overfilled, they offer reasonable protection
from knocks. Unfortunately, they only give
limited protection from dust and covering the
objects adequately can be difficult. Sheets of tissue
paper have a limited life, and cotton or Tyvek dust
sheets can be difficult to manoeuvre in a tight space
without damaging the objects under them. Items
should never be stored directly on the floor if it can
possibly be avoided because of the danger of flooding
and accidental mechanical damage.
To sum up, the display needs of leather are not significantly
different from those of objects made from
other organic materials. Where appropriate the
object needs to be supported to prevent collapse or
damage, cushioned from environmental extremes
and be protected from soiling. Appropriate handling
while the object is being moved is of course also
essential.
116 Conservation of leather and related materials
12.8 Shoes
Shoes are easily crushed and whether they are in
storage or on display, they should be lightly padded
out to hold their shape. The padding should hold
them in their original shape, if unworn, or to the
shape of the last wearer, and the ankles and legs of
boots should be supported. If the leather is stiff it may
be necessary to humidify it first. Acid-free tissue paper
is the most easily moulded to the shape of the shoe or
boot. Care needs to be taken to avoid overpacking as
this can lead to distortion and loss of the individual
shape worn into the shoe by the original owner.
Shops and warehouses have long known that the most
efficient storage is individual boxes for shoes and
boots (ankle and knee sized). If bigger boxes holding
more than one pair are used, it should be ensured that
they are shallow so that the shoes cannot be stacked
on top of one another. Shoes often have non-leather
components, and if they are on display this needs to be
taken into account. For example, textiles may be
more sensitive to light than leather, and if these are
present particular care should be taken to keep the
lighting down to 50 lux. Some shoes are finished with
a bright, shiny, patent finish. This can soften and
become sticky over time so care should be taken to
ensure other components do not rest on these finished
surfaces, nor should shoes of this nature be wrapped in
tissue paper. Silicone release paper should be used if
such dust covers are to be employed.
12.9 Gloves
As a general principle gloves may be padded or lightly
stuffed using rolls or ‘sausages’ of acid-free tissue paper.
The tissue rolls should never be forced into the fingers
but rather slid gently into place. Gloves of some age
may have hard creases or fold lines formed at the sides
so great care should be taken not to introduce too
much support into the gloves causing strain or cracking
along these lines. It is inevitable that gloves will
have creases formed at the sides; the purpose of the
padding is to lessen the damage caused to the leather or
fabric. If the gloves are brittle no attempt should be
made to introduce padding. This danger may often be
reduced by humidifying the leather before padding.
12.10 Leather garments
The care needs of leather clothing, whether on display
or in store, do not vary dramatically from that
of other types of costume. The most significant factor
to take into account is weight. An item such as a
leather coat may be very heavy. If it is hung on a
plain wooden hanger for any length of time, the
weight can quickly start to pull the shoulders out of
shape. The ends of the hanger will push up into the
shoulders, leaving a visible area of distortion which
in time will wear through. If hangers are used they
should be carefully padded with inert materials and
shaped to fit the coat. Buff leather coats and very
heavy items of leather clothing should be stored on
a customized specialist mannequin to provide
adequate support. Alternatively, it may be more
appropriate to store a garment flat in a box, provided
it does not need to be folded, as this, too, can
cause creases and distortion. Any necessary folds
should be softened by packing them with rolls of
acid-free tissue. Hats and helmets can be stored in
boxes, but with soft leathers or headwear with vulnerable
parts or trimmings it is preferable to store
them on head-shaped or purpose-made supports.
12.11 Luggage
Luggage tends to have had a chequered history and
may have spent long periods in attics when not in
use, in less than ideal environmental conditions, but
generally away from the more aggressive and catastrophic
elements of deterioration. The principle
risk with luggage is that it may crush if it is stacked.
Leather suitcases are heavy and if they are stacked,
be it for storage or display, they will scratch one
another and the corners of the smaller ones will press
into the surfaces of the larger ones and distort them.
Although it is tempting, it is not a good idea to use
historic luggage as storage boxes. Soft leather bags
should be padded lightly to keep them in shape. It
should be ensured that the handles are not used to
move the luggage around, and luggage should also
be kept off the floor out of the way of mops and
vacuums. Ideally, luggage should be stored on shelves
without stacking and with protection from dust and
light.
12.12 Saddles
Poor storage of saddles can lead to severe damage
(fig. 12.1). The nineteenth century racing saddle
shown in Figure 12.1 had not been supported
or protected for many decades prior to acquisition
by a museum. The damage shown is typical and
General principles of care, storage and display 117
demonstrates what can happen when a saddle is stored
unsupported. It had rested on the floor with the
flaps folded under, and was heavily soiled. Layers
of degraded newspaper probably originally intended
as a protective wrapping had not improved matters.
Saddles are composite objects and in addition to the
leather components there is often wood, fabric,
padding and metalwork present. The organic materials
in the saddle are susceptible to insect attack and mould.
Care needs to be taken, when bringing all new
items into a museum collection or conservation studio,
that fresh infestations are not introduced. Items
such as saddles are often stored, prior to their acquisition,
in areas such as barns and outhouses and so
are very vulnerable to infestation. Figure 12.2 shows
the same saddle with associated racing boots and
whip after conservation.
The requirements for the storage and display of
saddles are very similar. They need to be supported
underneath so that the flaps and straps are free to
hang down without distortion. There are two basic
designs of support available on the market at present.
One is free standing while the other screws
onto the wall like a very large coat hook. Both are
shaped roughly to resemble a horse’s back and they
are usually made of tubular metal. This creates two
problems in that individual saddles do not always fit
very snugly onto the support and may slip off, and
the narrow rods do not spread the load equally. The
pressure points may, over a period of time, distort
the padding on the underside of the saddle. Therefore
the supports should be padded to fit individual saddles.
This will help them to sit more securely on the
support and lessen the chance of pressure damage. A
custom-made saddle support gives the best possible fit,
and provides more scope for its design if it is to go on
display. The simplest way to make one is to build up
layers of Plastazote, an inert closed cell polyethylene
foam, or a similar material which can then be carved
into shape. If wished, this can then be covered with a
fabric such as unbleached calico.
Saddles in store need to be protected from dust.
A simple dust sheet can be used, but a made-tomeasure
loose cover is preferable. These can be made
from a fabric such as unbleached calico or Tyvek
with Velcro closures.
12.13 Harness
Harness is awkward to store. It is designed to go
around the curves of the horse’s body, and does not
118 Conservation of leather and related materials
Figure 12.1 Nineteenth century racing saddle as acquired by the National Horseracing Museum, Newmarket.
readily lie flat. If stored on open shelves it tends to
become entangled with itself and other items.
Probably the least potentially damaging solution for
the harness is to keep it in a large, shallow, flat box
or tray. However, these can be difficult to move
about. The alternative to storing it flat is to hang it
up over curved blocks with a radius of at least
8–12cm to spread the load. Some harnesses are finished
with a linseed oil-based patent finish similar to
that found on shoes. The same precautions should
be taken.
12.14 Screens, wall hangings and
sedan chairs
The storage of screens can be difficult. There is a
strong temptation to lean them up against a wall,
but this puts all the weight on one fold and, unless
they are protected with boards, they are vulnerable
to knocks. Vertical racks are a better solution, as
they provide all-round protection, but sliding them
in and out of these racks can be awkward. If space is
available the best solution is to store them flat on
long span shelving. The protection provided is good
and it is relatively easy for two people to lift them
out and stand them up.
The leather on screens is very vulnerable, particularly
that on the two outer folds. If it gets too dry it
will become very tight and may split. When tight, it
is also more vulnerable to knocks than when it is
relaxed. ‘Too dry’ here refers to the moisture content
of the leather, which is governed by the relative
humidity in the room, rather than the absence or
otherwise of dressings. It is also possible that the
tension will distort the frame, leading to joints
breaking. Screens may be as high as 3 metres, and
this makes them difficult to move around. They are
best carried, folded flat, by two or more people.
Screens should be handled as little as possible as fingernails
can scratch or even go through the leather.
The display and use of screens needs some care.
Sources of heat, including lights, radiators, fires and
sunlight need to be avoided as these can rapidly dry
out the leather and cause excessive tension. Sometimes
screens are displayed flat against a wall. They
can be held in place with cords or some other device.
However, if something goes amiss and the screen
starts to fall away from the wall, it can become dangerous
and unwieldy, especially if it is very large.
General principles of care, storage and display 119
Figure 12.2 Saddle after conservation, together with associated racing boots and whip.
Screens are designed to stand on the floor in a zigzag
position, and this is probably the safest for them.
Damage to hinges and frames should be repaired to
maintain a stable configuration.
Members of the public may present an added
hazard. Sometimes their reaction to being told that
‘this painted screen is made of leather’ is to poke it
in disbelief. Wall hangings are also at risk from the
temptation to touch and prod the material. It may
be advisable to ensure that the leather is displayed
out of reach, or to cover accessible areas with glass
or acrylic sheet. Care should be taken that this is not
in contact with the leather and can be removed for
cleaning. Wall hangings and panels are susceptible to
damage from moisture. This can be as insidious as a
slightly higher RH between the back of the leather
and an outside wall leading to secret mould growth,
or as disastrous as a leak running down the wall.
Loose leather wall hangings are usually stored flat as
separate sheets of leather, often in plan chests. They
should be interleaved with acid-free tissue paper and
clearly labelled. Care should be taken that too many
sheets are not piled one on top of another.
Sedan chairs are generally made using patent
leathers. In addition to the difficulties associated with
this material they present many similar problems to
screens and wall hangings. The leather panels are
under tension and are very vulnerable to accidental
damage. Sedan chairs should preferably be stored
and displayed slightly off the floor to protect them
from mops and vacuum cleaners, and away from a
thoroughfare.
12.15 Carriages and cars
Barns and garages do not provide ideal storage conditions,
being susceptible to extremes of temperature
and humidity through the year, and wide fluctuations
throughout each day. The objects are also more
accessible to a variety of pests such as mice nesting
in upholstery, bird droppings, etc. and the associated
damage they cause. The size of carriages means that
this type of storage is often the only option, so the
leather should be monitored carefully for deterioration
and infestation, and protected from falling or
windblown debris and leaks. A regular cleaning
schedule should be built into the monitoring system
so that debris is removed before it can attract further
pests. Cars present similar problems, and in addition
enclosed cars can set up their own microclimates.
The leather hoods on cars and carriages are especially
problematic. If they are left up they are under
a great deal of tension and tend to split, and if they
are folded down they get brittle along the folds and
split. It is advisable to decide whether to have the
hood up or down, and leave it there as moving it
around just makes the situation worse. If it is necessary
to fold the hood up and down, or actually to
use the vehicle, it may be better to think of replication
with the original stored appropriately.
12.16 Conclusion
While it is accepted that preventing damage is more
desirable and cheaper than expensive conservation,
objects will inevitably suffer some damage caused by
use and wear. It is better for the long-term survival
of the object to encourage careful and limited use
and to educate the owner how to limit the damage
while still continuing to enjoy the object, fulfilling
its intended function.
The ideal environment will usually be 50 –55%
RH, 50 lux or less, 18°C, combined with protection
from dust, handling and pests. Although this may be
unachievable in domestic, non-museum or alas many
museum contexts, a clean and stable environment
where the object may be regularly inspected and an
owner or curator who understands the ideal to aim for
and what to do when something is going wrong, will
go a long way to prolong the survival of the object.
Reference
Pye, E. (2001) Caring for the Past, Issues in Conservation for
Archaeology and Museums. London: James and James.
120 Conservation of leather and related materials
13.1 Past conservation treatments
13.1.1 Introduction
When examining an object it is frequently detectable
that previous conservation treatments have been
carried out. Sometimes these treatments may have
been undertaken at a time before precise records
were kept detailing which chemicals, adhesives and
methodology were used. Identifying which chemicals
and methods have previously been used is essential
before further conservation is carried out but
defining past treatments on leather can sometimes
be problematic. Included here are the results of surveys
that identify many of the treatments, chemicals
and adhesives which have been used at various times
in the conservation of objects made from leather
and skins. The results of these surveys provide an
overview of procedures that may have been carried
out to a leather object in the past and a starting
point for the conservator who has to deal with an
object that has obviously been treated but for which
there are no existing records.
Some of the earliest treatments for leather were
devised from those developed for the care and preservation
of bookbindings and include the application
of fungicides and insecticides and the use of buffer
salts to impart resistance to acidic atmospheric attack
(Plenderleith and Werner, 1971). Many of these treatments,
such as the use of Lindane, pentachlorophenol,
p-nitrophenol and orthophenyl phenol would now be
considered unacceptable for health and safety reasons.
The first comprehensive work devoted solely to
the care of leather was A Guide to the Conservation
and Restoration of Objects Made Wholly or in Part of
Leather by John Waterer (1972) and for a generation
this became the standard reference work.
13.1.2 1982 Jamieson survey
In 1981, immediately after the formation of the
Leather Conservation Centre Trust, a worldwide survey
was carried out by F. Jamieson, a recently retired
leather chemist with an interest in historical matters,
to look at the current methods being used for the
conservation of leather objects, to identify areas for
future research and to determine whether there was a
requirement for a specialist institution where research
training and practical work could be undertaken.
Sixty-nine museums in the UK, USA, Canada, Spain,
Australia, the Netherlands and Germany took part in
this survey and a detailed report was presented to the
trustees. The major results of this report were summarized
by Jackman (1982). The materials used at the
time are listed below.
Bavon ASAK APB. Leather lubricating compound.
Alkenyl succinic acid derivative. Soluble in white
spirit and Genklene (1,1,1-trichloroethane).
British Museum Leather Dressing. Standard recipe:
20g anhydrous lanolin.
15g beeswax.
30g cedarwood oil.
330ml hexane.
Connolly’s Leather Food. A dressing for hide upholstery,
leather goods and clothing. Preparation containing
lanolin, beeswax, water, morpholine and white spirit.
Disinfectant 1473. Used as a fungicide. Constitution
not known.
Dowicide A. Water soluble fungicide. Sodium salt of
orth-phenyl phenol.
Facteka A. Granular cleaner in fine and coarse grades
suitable for cleaning suedes or leather with abraded
121
13
Materials and techniques: past and present
Marion Kite, Roy Thomson and Aline Angus
surface. Rubber-like material made from vulcanized
rape oil.
Genklene. Non-flammable solvent. 1,1,1-
trichloroethane.
Hydrophane. Liquid leather dressing based on linseed
oil.
Invasol S. Water soluble leather lubricant. Synthetic
anionic oil.
Lipoderm Liquor SA
Lipoderm Liquor LPK. Water soluble leather lubricant.
Synthetic anionic oil free of natural fat.
Lissapol N. Non-ionic detergent.
Neutralfat SSS. Water soluble leather lubricant.
Stabilized olein soap which on drying loses its emulsifying
property so that it no longer promotes
absorption of water.
Plexisol. Consolidant for leather affected by red rot.
Polyacrylate resin preparation containing 25% solids.
Must be diluted with Genklene before use.
Pliancreme. British Museum Leather Dressing in the
form of a cream, emulsified with water, containing
a fungicide.
Pliantex. Consolidant for leather affected with red
rot. Polyacrylate resin preparation containing 25%
solids. Must be diluted with Genklene before use.
Pliantine. Traditional British Museum Leather
Dressing.
Polydiol 400 and 1000. Impregnating material.
Polyethylene glycol waxes.
Preventol L. Fungicide. Sodium salt of chlorinated
phenol.
Santobrite. Fungicide for leather. Derivative of
pentachlorphenol.
Vulpex. Material for cleaning leather articles.
Potassium oleate soap. Soluble in water or white
spirit.
13.1.3 1995 survey
In 1995 members of the International Council of
Museums Committee for Conservation (ICOM-CC)
Leather and Related Materials Working Group participated
in a survey to find out and record the treatments
which had been used on leather, prior to this
date, by members of the conservation profession.
The results were published as part of the post-prints
for the interim meeting of this working group (Kite,
1995). The methods of application of these past
treatments were also recorded if known. The aim
was to assist conservators when faced with problems
which may have been caused by these treatments.
The possibility of problems with past treatments had
already become a reality and was demonstrated on
collections of shoes which were frequently found
after prolonged storage to have spews and sticky, oily
deposits on them. These problems were also found
on many other leather objects which were known to
have been treated and conserved within the previous
20 years or so.
The results of this survey are reproduced here,
with comments as to efficacy of the treatment which
were made at the time. This serves as a record for
the current reader and as background before further
discussing current methods of conservation.
Aluminium alkoxide, 1% in mineral spirits: used as a
chemical stabilizing retanning agent for red-rotted
vegetable-tanned leather, having no consolidative
effect. In addition to having a buffering effect the
aluminium ions crosslink with the collagen and vegetable
tannins increasing the shrinkage temperature.
Bavon leather lubricants based on alkylsuccinic acid.
Bavon ASAK ABP: leather lubricant applied from a
solvent solution. Provides good flexibility at low
levels of use. Based on synthetic paraffin long chain
polymers with non-ionic water in oil emulsifying
agents. Soluble in white spirit, petroleum spirit or
1,1,1-trichloroethane, used in 2–25% solutions
(10% is normal).
Painted on leather with 15 minute intervals
between coats (ten coats normally sufficient to allow
manipulation). Very brittle leather may be immersed
and soaked.
Bavon ASAK 520S: highly polar leather lubricant
based on an alkylsuccunic acid modified to give
complete water solubility. Used on intestines, bladders
and other fine membranes. Very effective on
drumskins and can be used on objects particularly
when reshaping; water content being used to advantage.
5–20% solutions. Often useful to start at 5%
working up to 20%. Can produce a spew over time,
which can be removed with white spirit.
Bedacryl 122X: polymethacrylate ester: a consolidant
for wood and some types of leather. Supplied in a
mixture of xylene and n-butanol, or xylene and cellosolve
acetate, or a petroleum solvent. Cellosolve ϭ 2
ethoxy ethyl acetate.
122 Conservation of leather and related materials
Beva 371: a heat seal adhesive dissolved in a petroleum
fraction. A blend of ethylene-vinyl acetate
copolymers, ketone resin and paraffin.
DDT (dichloro-diphenyl-trichloroethane): now banned
but older collections may have been treated with it
as an insecticide. Used on skins, leather and wool.
p-dichlorobenzene (PDB,1,4-dichlorobenzene, one of
three isomers): mothballs.
Draftclean: ground rubber.
Ethylene glycol: solvent, substitute for glycerol in
conjunction with olein soap for softening ethnographic,
semi-tanned leather.
French chalk: used to clean feathers, fur and chamois
leather.
Fuller’s earth: used as a powder cleaner for feathers,
fur and chamois leather, often mixed with magnesium
carbonate. Sprinkle over feather, leave overnight
and then brush off. Also used mixed to a stiff dryish
paste and brushed onto surface, left to dry then
brushed or vacuumed off. Only suitable for strong
good condition furs.
Invasol S: used as a leather lubricant. Miscible in
water (up to 20%); apply in several coats with swabs.
Softens leather well but it has been recorded that
light-coloured leathers darken.
Isopropanol or isopropyl alcohol (2-propanol): solvent used
to soften and swell leather: employed in aqueous mixtures
to soften hard and brittle parchment. Properties
intermediate between ethanol and acetone.
Lanoline, anhydrous: used as a leather lubricant.
Magnesium carbonate: an absorbtive cleaner, particularly
for feathers, fur, chamois leather.
Opodeldoc: soap liniment of the following composition:
Camphor 40g
Oleic acid 40g
Alcohol (90%) 7000ml
Potassium hydroxide solution 140ml
Rosemary oil 15ml
Purified water to1000ml.
PEG 400, polyethylene glycol 400 (25–35% in tap
water): impregnation period between one and five
weeks. Used for treatment of waterlogged archaeological
leather.
Pliantine (British Museum Leather Dressing, standard
and special G): thick brownish liquid: lanolin, cedarwood
oil, beeswax, 1,1,1-trichloroethane. Special
G omits the beeswax. Used as a dressing for hard,
brittle leather.
Pliantex: flexible polyacrylic resin based on ethyl
acrylate. Supplied as a 30% solution in ethyl acetate.
Used for the consolidation of fragile leather, particularly
where ‘red rot’ is present. The polymer is stable
in light and is flexible. It is not swelled by water and
is non-tacky. The material will not harden because
no C¨C double bonds remain in the polymer
molecule. Because of this, subsequent polymerization
of the dried film cannot occur. Ageing does
not produce crosslinking with its lack of solubility.
It is diluted 1:4 for use. Diluents are esters, ketones
and aromatic hydrocarbons. Produces a very soft
flexible film after the evaporation of the solvent
(Waterer, 1972).
Renaissance wax: microcrystalline wax used for cleaning
and sealing leather, wood, ivory and metals.
High shine can be achieved, useful for patent leather.
Saddle soap (Proparts): commercial leather cleaner.
Alkaline pH 9–10. Based on neatsfoot, cod or
sperm oil, emulsified with soap in water to produce
an emulsion fatliquor. Considered obsolete by 1995
as extremely alkaline when pH 4 – 6 is most
favourable for leather. Spew formation can occur
and in time stiffen the skin.
Silicone leather wax: used as a leather cleaner and
lubricant.
Tannic acid, gallotannin, gallotannic acid: sometimes
used as a retanning agent to treat archaeological
leather. Dissolved in alcohol or acetone.
Thymol: fungicide for leather, furs, paper, parchment.
1,1,1-trichloroethane: solvent, component of most
leather dressings.
Vulpex (potassium methyl-cyclohexyl-oleate): soap; for
leather, featherwork, etc. where use of water is
impractical. pH 10.5–11.5; soluble in white spirit,
trichloroethane or water.
White spirit BS245 (Stoddard solvent): mixture mainly
of alkanes of boiling range 150 –200°C. Miscible
with acetone. Used as a solvent, for dry cleaning
and leather treatment.
13.1.4 2000 list
In 2000 Sturge presented a list of materials with a
summary of their properties and methods of application.
These had all been used in the conservation
Materials and techniques: past and present 123
of a number of leather objects featured in a collection
of case studies (Sturge, 2000). All the objects
had been conserved within five years of the publication.
This list covers a wide range of materials used
at the Leather Conservation Centre at this period
but was not intended to be a comprehensive survey.
However, it gives a wide ranging overview.
13.1.5 2003 Canadian Conservation
Institute (CCI) survey
In 2003 the results of further research were presented
by Jane Down at the Adhesive and Leather
Symposium prepared for the Library of Congress
Preservation Directorate in partnership with the
Folger Shakespere Library (Down, 2003). From this
the following treatments may be added to the above
list as having been used in the conservation of leather
and skins.
Glue. Animal glue has been of importance to the
bookbinder for many years. Glue-based recipes contain
plasticizers, preservatives, perfume, thickeners and
in some cases extenders. An early recipe for bookbinders’
glue has the following ingredients: gelatin,
water, yellow rosin, methylated spirit and glycerine.
Gelatine. This has been used to repair vellum. In order
to increase the flexibility of the adhesive, two drops of
a 2% aqueous sorbitol solution are added to each
100ml of a 9% edible gelatine solution. The mixture
is warmed in a water jacket for use, because if gelatin
is boiled, it will darken and lose adhering power.
Rubber cement. Reported by Julia Fenn (1984) that the
Royal Ontario Museum has several examples of skin
and leather artefacts with hardened black stains – the
results of repairs using rubber cement. Its advantages
were that the adhesive was flexible, easy to apply and
had good adhesion. The use of this material is no
longer recommended.
Soluble nylon (N-meythoxymethyl nylon). This was
first recommended in 1958 by Werner as a consolidant
for objects with powdery surfaces that require
soaking to remove soluble salts. This material is no
longer recommended.
13.2 Notes on treatments in use in
2004 – additional information
13.2.1 Introduction
Much of the information in this section is based on
the work published by Sturge (2000).
It is accepted that the first priority before any
treatment is undertaken is to assess the condition and
identify the tannage of the leather. Second, to determine
if the object has been treated on a previous
occasion and identify what has been used in this
treatment if possible. The condition of the surface of
the leather and the ongoing effects of any previous
treatments, especially if oiling has been used, will
have an effect on the current method chosen. If the
grain surface is lifting and scuffed, it can snag the cotton
wool of the swabs used in cleaning with solvents.
If the leather is very deteriorated, it may be possible
to consolidate first and clean once the surface is a little
more sturdy. It is important to ensure that a consolidant
has been chosen that can be cleaned through,
and that the cleaning method is compatible with the
consolidant. It may be necessary to carry out tests on
a small area before proceeding generally with the
treatment. Comments on methodology of use have
been included in the following section as an aid for
the conservator and to provide a record.
13.2.2 Dry cleaning
A good brush vacuuming can be very effective and may
be all that is required.
Smoke sponges (dry cleaning sponges of vulcanized
natural rubber) are very useful for surface cleaning
and the dirty surface of the sponge may be shaved or
snipped off as work progresses.
Wishab erasers (sulphur and chlorine free) have proved
useful. They are available in three hardnesses.
Groomstick (molecular trap, made from natural rubber,
neutral pH). This must be used with caution
and the surface of the leather must be in good sound
condition and firm. Groomstick is tacky and its use
can result in damage and the lifting of any loose
fragments from a friable leather surface.
Glass bristle brushes. These are used on very rare
occasions and should be used with extreme caution
as they are abrasive to the leather surface. In certain
circumstances they may be the only treatment that
works to remove stubborn surface deposits and soils.
They are used particularly for thick suedes and
should not be used on fine leathers or fine suede
surfaces. Glass bristle brushes should be employed
with extreme care and the correct personal protection
worn. Gloves and eye protection must be worn
as well as a mask. A thorough cleaning of the object
and the work area after use is essential.
124 Conservation of leather and related materials
13.2.3 Wet cleaning and solvent cleaning
Aqueous cleaning. Cotton wool swabs moistened
with deionized water have been used to remove surface
soiling but care must be taken not to wet the
leather if water is being used in this way. The aim is
to soften and remove the dirt, not to soak the
object. Overwetting the leather may cause all manner
of problems including distortion, discolouration,
hardening, movement of salts and tannins, tide
marks, etc.
Water and ammonia. Water with the addition of a
very small amount of ammonia has also been used.
The ammonia is more aggressive to the dirt than
water alone but is harmless to the leather in low
concentrations. When used extremely diluted, to
almost a homeopathic level, good results may be
obtained. Tests should be carried out to determine
the appropriate strength which should be as low as
possible while still effective. The ammonia should
be added to a measured amount of water a drop at a
time. All water-based treatments should be used
with caution, but water with a little ammonia may
also in some circumstances be used as a cleaner for
varnished and painted leathers. However, ammonia
in too high a concentration can adversely harm
some painted surfaces.
Water and detergent with a little non-ionic detergent
or wetting agent have been used. The detergent
helps the water to wet, soften and break down nonpolar
soiling more easily. It is essential to remove
the residual detergent with a swab moistened with
deionized water.
Water and alcohol. A 50/50 mix of water and alcohol
is favoured by ethnographic conservators in some
instances where this has been found to be more
effective than water or alcohol alone.
Polar organic solvents. The use of materials such as
ethanol, isopropyl alcohol, acetone and other polar
organic solvents is sometimes necessary to remove
soils. Such materials must be employed with care as
these products can dissolve oils and tannins in the
leather and harm finishes.
White spirit (Stoddard’s solvent) being non-polar and
slow evaporating is the mildest organic solvent for
use with leather. Mineral spirit has a similar solubility
profile, and does not smell as much. It contains less
aromatic hydrocarbons and is therefore sometimes
less effective. White spirit is generally the starting
point for solvent tests, and is used for the majority of
solvent cleaning of leather. Small objects which
have been overdressed may be immersed in a bath of
white spirit (or mineral spirits) to try to remove the
excess oil. This can be necessary as an oily surface
will resist all attempts at consolidation and repair.
Excessive dressings also attract dust, can be unsightly
and may cause damage to the object by accelerating
the degradation of sewing threads used in the construction
of the object.
White spirit and water. It has been found that a 50/50
mix of water and white spirit, with a small amount
of detergent to form an emulsion, is an effective
cleaner for gilt leather and other leathers with
painted or varnished surfaces. The mixture may be
applied with swabs or soft cloths, and then carefully
rinsed off with a little distilled water, ensuring that
the leather at no time becomes wet.
Toluene is an aromatic non-polar solvent which is
effective for cleaning leather. It has particular health
and safety implications and appropriate safeguards
should be taken, as is the case with many organic
solvents.
13.2.4 Proprietary leather cleaners
Proprietary leather cleaners must be used with
caution as it is sometimes difficult to confirm the
ingredients.
Leather Groom (oleaic acid soap with small quantities of
neatsfoot oil and silicone oil). This is an effective mild
cleaner for smooth leather surfaces. It is used as a
mousse so is difficult to overapply. It was originally
developed to clean and condition motorcycle leathers.
In some instances it may disturb or remove surface finishes
so testing of the product before use is essential.
Microcrystalline wax has some light cleaning properties
attributed to the white spirit in its formulation.
13.2.5 Humidification
Leather becomes more malleable when humidified
so raising the humidity renders it more receptive to
reshaping. As it dries after reshaping the leather may
set in its new shape naturally or it may need to be
weighted or otherwise restrained and prevented
from returning to the previous deformed state. A
way must be devised to hold the leather in place as it
is dried out, often with the aid of dry blotting paper.
If using non-permeable weights, like glass, it is necessary
to keep changing the blotting paper layers or the
moisture will be trapped and unable to evaporate.
Materials and techniques: past and present 125
The aim of the process is to raise the general humidity
without soaking the leather. While leather reacts
well, in general, to a rise in humidity caused by the
presence of water vapour, it will react very badly to
getting wet through the action of liquid water.
Degraded leather will have a lower shrinkage temperature
than new leather so this should be borne in
mind. Heat treatments should never be used at high
humidity as leather is likely to shrink if heat is
applied when it is wet.
Large commercially supplied humidification chambers
built to a high specification, which can provide
precisely controlled levels of humidity and temperature,
are excellent but may not be available to all
conservators. Good results can be obtained using a
small homemade humidity chamber, constructed
using racking, retort stands, polyethylene, Perspex
or other materials available in most conservation
studios. A relatively inexpensive ultrasonic humidifier
may be used to provide the humidity source.
For smaller objects, a plastic box with melinex or
polyethylene film over the top and the ultrasonic
humidifier feeding in may be adapted. Another
solution would be to introduce a bowl of wet cotton
wool into a simply made polyethylene chamber.
In other circumstances areas of an object may be
locally humidified using an ultrasonic humidifier.
Flat objects can be humidified using a semi-permeable
membrane such as Goretex or Sympatex, or using
damp blotting paper with a separating layer of soft
cotton fabric or Reemay. If damp blotting paper is
used care must be taken to ensure that the leather is
only subjected to the humidity and that it is not in
direct contact with the blotting paper, nor that the
blotting paper is too wet resulting in the separating
layer or cloth becoming soaked through.
There is always a danger of mould growth being
set off by a rise in humidity. Awareness of this and
regular inspection of the object during the humidity
treatment is essential. Humidity treatments should
be carried out for as short a period as possible. If
necessary, a series of treatments may be undertaken
involving gradual reshaping carried out in stages.
Humidification should not be hurried nor taken
to excess resulting in wet leather. The leather may
want to return to an even earlier state than that
which it is intended to achieve.
One should always be aware that the shrinkage
temperature of badly degraded and old leather can
be extremely low. It should not even be left near a
window while it is humidified where it is in danger
of being warmed by the sun.
13.3 Repair materials
A wide range of materials have been used for repair
patches, strip lining or full supports.
New leather of similar tannage to that used on an
object may have compatible properties, but generally
will have a completely different appearance. It is often
impossible to match one or two hundred years of
wear with a new piece of leather. Modern tanning
methods produce a very different looking product,
and sourcing suitable compatible leather is difficult.
However, a compatible leather does give a good
robust repair that will react to changing conditions in
a sympathetic way.
Polyester sailcloth has been used to support leather in
the past, for instance in the relining of screens. It is
very heavy and does not move at all with the
leather, for instance as humidity changes take place.
Spun-bonded polyester fabrics, e.g. Reemay, Ceerex,
Vilene. This is a modern alternative and has frequently
been used in recent times. It is available in a
variety of weights and because it is spun bonded has
no nap or direction of weave. These materials are
light in weight and easy to use, with just enough
‘give’ to move with the leather rather than imposing
its own priorities on the leather. These materials
have been used for a complete reline or for small
repairs.
Japanese tissue paper is ideal where a less robust repair
is suitable. A good thick handmade paper is easy to
use, and has a pleasant ‘organic’ appearance which
often resembles old partially degraded leather. It is
easy to colour and will stick with most adhesives. It
is useful where a sacrificial repair is required as it is
generally weaker than the leather. If a thin repair is
needed, it is in many cases stronger than leather
pared down to a similar thickness.
A woven textile can be used. There is a danger though
that over time the weave will evidence through the
leather or impose its own tensions on the object.
13.4 Adhesives
There is a range of reversible adhesives which may
be used depending on the circumstances, e.g. the
condition of the leather, working conditions and the
conditions which the object will be returning to.
126 Conservation of leather and related materials
Beva 371 is supplied as a paste or as a pre-cast film.
It is a mixture of ethylene vinyl acetate resin, polycyclohexanone
and paraffin wax. It was developed
for use in the conservation of paintings. The paste is
dissolved in toluene, so needs to be handled with
care and fume extraction. Beva is frequently used in
the dry form using heat to set it which makes a
good strong bond. It can be bonded to the backing
fabric first which is then cut to size and shape.
When bonding leather to leather it can be difficult
to get sufficient heat in between the layers to melt
the Beva, but it is good if the repair material is thin.
Poly vinyl acetate and ethylene vinyl acetate emulsions. Any
general-purpose PVA or EVA used in the conservation
world would most likely be suitable although
there are specific ones supplied for leather conservation.
PVA M155 is a general-purpose dispersion with
good tackiness when wet. A water reversible PVA,
M218, is very similar to M155, but is considerably
easier to clean up after use. Vinamul 3254 is an EVA
copolymer dispersion, with good flexibility and water
resistance. It is not as easy to reverse as other adhesives,
but in many cases can be peeled away carefully if
necessary.
Acrylics. Lascaux 498HV and 360HV (butyl
methacrylate copolymers, thickened with acrylic
butyl-ester). These are supplied as a creamy emulsion,
and can be solvent reactivated if necessary.
These do not have the tackiness when wet as the
above-mentioned PVA adhesives which makes repositioning
easier. Acrylics have been found to make a
good bond for flat objects. The 498 grade dries fairly
hard, while the 360 is softer and slightly tacky when
dry. The two grades are used as a mix to get the
flexibility of the 360 with the strength of the 498.
These acrylics are easy to remove, either with solvent
or by peeling, as the adhesive does not readily
penetrate the leather. The Lascaux acrylics are water
resistant when dry, but can be solvent reactivated
with acetone or toluene. The solvent reactivation is
useful to form a fast stick without involving further
moisture. Water can lead to problems with the
expansion of the leather. Generally this is not a problem,
and the moisture content of emulsion adhesives
can be beneficial in helping to relax the leather, but
expansion caused by water can throw joins and splits
out of alignment. The back of the leather and the
repair fabric are coated with the resin mix and left
to dry thoroughly before solvent reactivating. Various
solvents can be used, depending on what is needed
and what kind of extraction is available for use.
Acetone gives a quick, but not sticky bond, although
it should be used with caution. Toluene gives more
tack and a longer working time.
Paraloid B72 is rarely used as an adhesive for leather
as it lacks the required degree of flexibility. It has,
however, been used as a consolidant.
Wheat starch paste. This may be bought ready made,
although it is preferable to make it as required. It
will not bond well with synthetic fabrics. As an
adhesive it has very little bulk but a good contact
between the two surfaces being stuck is essential. Its
high water content can cause problems, but it has
good reversibility and long-term stability.
Sodium carboxy methyl cellulose (CMC) is supplied as a
powder and is prepared as a 1 to 5% dispersion in distilled
water. This material is useful when facing
objects such as gilt leather screens to enable repairs to
be carried out from the reverse side. The moisture
content of any adhesive must, however, be borne in
mind when treating degraded leather. CMC is also
used as a thickening agent for dispersion adhesives
like Vinamul 3254. It increases the viscosity and
working time by retarding the drying point.
Animal glues. These can be difficult to use for the
repair of leather as generally they have to be applied
hot, and most have a high moisture content. The
shrinkage temperature of the leather concerned is
an important factor if animal glues are to be considered
as an adhesive option. Leather that has been
stuck with animal glue in the past is often found to
have become embrittled, and the bond has failed.
13.5 Surface infilling materials and
replacement techniques
Leather is often chosen as it can give a pleasing finish
but is frequently hard to match the original texture.
Modern tanned leathers have a very different handle
and appearance to historic leathers particularly if
they are degraded and it can be difficult to source
compatibly tanned skins.
Japanese tissue is often used as an alternative to leather
where a thin fill is required. It can be coloured to tone.
Beva 371 can be used as an infilling material. It
bonds well, is plastic and flexible and moves with
the leather. It can be painted, moulded and matted
to blend with the leather surface. Beva may be
Materials and techniques: past and present 127
prepared to be used as a hot melt filler as described
by Sturge (2000).
13.6 Moulding and casting materials
and techniques
Conservators will each have their own preferred
moulding materials subject to availability and individual
experience. One product is Steramould, a
silicone rubber moulding material developed for
hearing aids. It is considerably less expensive than
the dental materials often recommended in the literature.
It can leave an oily mark on unfinished
leathers so tests should be carried out before use.
Fills can be made from solid Beva 371 to match
original printing or tooling of the leather. The original
is first moulded with Steramould with a piece
of glass pressed down onto the silicone to give it a
flat surface for working on. When the silicone rubber
has hardened and been removed, solid Beva can
be melted into the mould under silicone release
paper. The moulded form can then be cut to fit and
adhered into the gap in the object. The Beva fill can
be inpainted to tone with the original.
13.7 Consolidation techniques
Consolidation is an option for leather which is
badly degraded. Sometimes consolidation will need
to be carried out to give a firm surface for repairs to
attach to or for cleaning to be undertaken. It may be
that it is not the leather itself which requires consolidation
but the painted surface decoration. A variety
of consolidants are available to the conservator.
Paraloid B67 in white spirit. This is occasionally used
as a consolidant for painted surfaces on leather. It is
generally only used as a final coating to give protection
to the surface or to reform a disrupted varnish.
Klucel G can be dispersed in ethanol. It is sold as
Cellugel ready dissolved in isopropyl alcohol. It has
been used for the consolidation of friable and flaky
surfaces on leather. It holds a degraded surface
together but does not penetrate to any extent into
the leather structure.
Pliantex ( flexible ethyl acrylate resin). Used until 2004
when it ceased to be commercially available.
SC6000 (an acrylic wax blend) is used primarily as a
surface coating material. It does, however, have a consolidative
effect on the surface. Blends of SC6000
with Klucel G and isopropyl alcohol have been used
widely in the United States to consolidate the surfaces
of red-rotted bookbinding leathers. These appear to
penetrate the fibrous structure to some extent and
give a semi-matt natural appearance (see Chapter 21).
Lascaux wax-resin adhesive (443–95) has been used as
a consolidant for flaky paint on leather.
Gelatine. This has been used particularly for consolidating
bookbindings or by conservators trained in
that speciality. Gelatine films are not particularly
flexible and are probably most suitable for objects
such as the coverings of book boards which are
fixed and not intended to flex.
13.8 Dressings and finishes
The overapplication of dressings to leather can often
cause irreversible damage so they should not be
applied as a routine treatment and in many circumstances
should be avoided entirely.
Traditionally dressings were applied in an attempt
to slow down deterioration, improve the appearance
and to restore some strength and flexibility.
The long-term effects of overoiling leather are that
oils and fats can encourage bio-deterioration, spew,
oxidize and stiffen the leather, discolour and stain it,
leave a sticky surface and wick onto nearby material,
soften the original finishes and decoration, attract
dust and impede future conservation treatments.
The solvents present in many dressings can affect
surface finishes, wet, swell and deform the leather,
dissolve or dislocate the original components. The
use of dressings therefore may lead to many disastrous
side effects. Each object is different, so there
can be no cure-all routine treatment. Unfortunately
dressings have in the past being used as standard
treatments over the whole of a collection resulting
in some of the problems we have today.
Saddle soap contains soaps but is mostly emulsified
oils. It is very alkaline with a pH 9 to 10, which can
lead to a lowering of the shrinkage temperature of
the surface of the leather. It is intended to be used
on modern equestrian leathers as a lather or foam
and to be washed off thoroughly. This technique is
not ideal for historic objects. It can result in darkening
and its application involves excessive wetting.
Although it appears to clean leather it can be pushing
the dirt further into the surface. It may even
be the cause of the fine cracking of the surface
sometimes seen on old leathers.
128 Conservation of leather and related materials
Pliantine (British Museum Leather Dressing) contains
beeswax, lanolin and a small amount of cedar wood
oil. It has a bad reputation for being overapplied and
becoming a darkened and sticky dust trap, but if
applied sparingly to sound leather and worked in
well, it can be satisfactory.
National Trust Furniture Polish (natural colour). This is
not strictly a dressing but a wax-based surface coating.
In most cases, leather does not need a heavy
waxing and a cloth which has previously been used
with a wax polish on furniture will generally have
enough residual polish remaining on it to give a
sheen without the danger of overapplication. Any
good quality uncoloured polish of this type will give
a similar result. If the leather is firm enough, a hint
of wax followed by a good buffing can make a huge
difference to the appearance.
Microcrystalline wax also gives a pleasant sheen, but
must used sparingly. If overapplied, it can stay slightly
tacky and can leave residues in the cracks. These can
be removed with white spirit or mineral spirits.
SC6000. A commercial surface finish containing wax,
acrylic resin and isopropyl alcohol, supplied in the
form of a cream. It dries to a shiny and hard surface.
References
Down, J. (2003) Adhesive Research and Some Aspects of Skin
and Leather Bonding. Unpublished report presented to
Adhesive and Leather Symposium at the Library of
Congress. Canadian Conservation Institute.
Jackman, J. (1982) Leather Conservation, A Current Survey.
London: The Leather Conservation Centre.
Kite, M. (1995) Some Conservation Problems Encountered
When Treating Shoes. ICOM Committee for Conservation
Leathercraft Working Group interim meeting Amsterdam
pp. 91–95 ICOM.
Plenderleith, H.J. (1946) The Preservation of Leather Bookbindings.
London: The British Museum.
Sturge, T. (2000) The Conservation of Leather Artefacts. Case
Studies from the Leather Conservation Centre. Northampton:
The Leather Conservation Centre.
Waterer, J.W. (1972) A Guide to the Conservation and
Restoration of Objects Made Wholly or in Part of Leather.
London: Bell.
Materials and techniques: past and present 129
14.1 A brief history
Taxidermy as we know it today, that is the dried or
preserved skin of a vertebrate modelled to represent
the living animal, dates from the latter half of the
eighteenth century. Prior to that attempts had been
made with varying degrees of success to preserve the
whole creature by some form of evisceration and
drying. While these were sometimes successful in
the short term, most succumbed before long to the
ravages of insects and damp, leaving dotted across
Europe, a handful of specimens from the seventeenth
century. The only example of this method to
survive in the UK and indeed probably the oldest
preserved bird is the Duchess of Richmond’s African
Grey Parrot in Westminster Abbey, which died in
1702. However, by the mid-eighteenth century
Bécoeur had discovered arsenic as a preservative and
this, coupled with widespread agreement that specimens
should be skinned completely, meant that the
many examples which survive from the late eighteenth
century/early nineteenth century are prepared
in a manner which differs little from those used
today for birds and smaller mammals.
As the nineteenth century progressed, so too did
taxidermy methods and by 1851 many taxidermists
were able to exhibit work of a high standard at the
Great Exhibition in London. Whereas much early
work had been on birds and small mammals, now a
full range, from fish to large mammals, was on show.
This necessitated more varied preservation and preparation
techniques. The publicity achieved at the Great
Exhibition led to taxidermy’s heyday from about
1870 through to the First World War. This period
saw the opening of many public museums, a vogue
for the natural sciences and a craze for birds (or parts
of ) as a fashion item.
As the world opened up, colonists expanded into
lands from which a stream of big game trophies
started to flow. So popular was taxidermy by the
1870s that General George A. Custer was collecting
and mounting his own trophies while campaigning
in Dakota. In the UK, shooting a tiger while visiting
or working in India seemed to become an essential
part of life for the upper classes. These, usually
prepared as rugs, often with the head mounted with
the mouth open, were eventually sent back home to
serve as domestic obstacles for future generations.
Museums and wealthy collectors sent expeditions to
search far flung corners for new rarities and to this
day there are species which we only know from a
few preserved skins collected at this time. Indeed,
famously, the last two specimens of the now extinct
great auk (Alca impennis) were killed to be mounted
and sold to collectors. The extinction of the passenger
pigeon (Ectopistes migratorius) in 1914 was not
due to overcollecting but taxidermy had enabled
the preservation of several hundred specimens from
a population, which numbered tens of millions only
50 years before. We can at least see these today, unlike
the dodo, which became extinct too early for taxidermy,
leaving only one poor specimen in Oxford.
This was destroyed in 1755 leaving as its legacy a
continuing debate as to the true appearance of the
species.
Changing tastes and the Great War finally brought
a halt to the boom, which in the UK had seen almost
every town have at least one taxidermist. The larger
and more reputable firms survived into gradual
decline in the interwar period until the coup de grâce
of the Second World War, which left only the two
large London firms of Rowland Ward and Gerrard &
Sons, plus a handful of small operators. North
America with its huge wilderness areas and ‘frontier’
130
14
Taxidermy
J.A. Dickinson
culture did not suffer in the same way and hunting
and fishing trophies remained popular with many
companies supplying a demand which is today probably
larger than ever. The latter decades of the
twentieth century have seen a revival in Europe with
a new generation discovering taxidermy in an age
when there is the threat for many species that only
the preserved specimen may be left for posterity.
14.2 Taxidermy terms
The language of taxidermy uses the following terms.
GRP. Glass-reinforced polyester, what is commonly
called fibreglass.
Hide paste. Usually based on Dextrin plus, possibly,
whiting, talc and fine papier mâché.
Base. That to which the mount is fixed, often made
to represent the ground but can also be a branch,
artificial rock, or simply polished wood.
Mount. Taxidermists call the finished specimen a
mount. They also refer to ‘mounting’ a specimen.
Form. Usually for mammals, this is what the skin is
fitted onto.
Pickling. The method of preserving a skin by soaking
it in a solution such as salt/alum or carbolic acid.
This will not endow any of the qualities of a dressed
skin.
Tanning. Taxidermists commonly use this to mean
dressing.
Prepare. To mount a specimen.
14.3 Birds
14.3.1 Methods
X-rays have revealed that the early taxidermists
employed a variety of methods as each experimented
with this new subject. It was only with the publication
of manuals that methods became standardized.
Whatever method chosen, the bird would be skinned,
usually by ventral incision, and the skull, legs and
wing bones retained in the skin but scraped clean of
meat. The inside may have had some of the excess fat
and tissue scraped away, if time permitted, but the skin
was often not washed as drying plumage was time
consuming and difficult. At this stage a preservative,
usually either a dry powder or an arsenic-based soap
might be applied to the inside and sometimes the
feathers would be treated to a wash containing either
arsenic or ‘corrosive sublimate’ (mercury (II) chloride).
Next, one of two methods would normally be
used to mount the bird:
1. Soft stuff. Wires would be inserted through the
foot, up the sinew tract at the back of the leg and
probably bound onto the femur and tibia. Wires
might be fixed into the wings in a similar manner.
One or sometimes two or more wires would
now be inserted through the tail, on up the neck
and out the top of the skull. All these wires would
now be twisted together in the body area and the
skin would be filled out with chopped tow ( jute
strand), wool, cotton, grass or anything else considered
suitable. After stitching up, the bird would
be fixed to a base by its leg wires, modelled into
shape and left to dry.
2. Bind up. Wires would be similarly placed in the
legs but then a body, sometimes approximating in
size to the bird’s own but often ovoid, would be
made by binding hay, wool, wood wool, tow or
carved peat. Through this would be put a wire,
which was wrapped with cotton, tow, wool, or
similar, to make a neck. This was then inserted
into the skin with neck wire coming out of the top
of the skull and the leg wires clenched through the
body. Again, after stitching of the skin and fixing
to a base, it would be modelled into shape.
At this stage, with either method, glass eyes would
have been fitted. Sometimes they would be simply
on a bed of cotton wool held in by the skin. Others
would be modelled in with clay and sometimes a
rock hard mix of plaster and animal glue secured
them.
When dealing with very old taxidermy, however,
one should always be prepared for the unusual. In
the mid-nineteenth century the English naturalist
Charles Waterton prepared a large collection of
birds, which are hollow!
Most birds are now mounted using a hard body,
often still made of bound wood wool but increasingly
made from balsa wood, Styrofoam or moulded
polyurethane (PU) foam. Tow is still widely used to
make necks and leg muscles and, while clay is the
main method of setting eyes, epoxy putty is increasingly
used. Some eyes, traditionally glass, are now
made from acrylic. Skins themselves, if properly
prepared using mechanical wire brushes and washed
in a scouring agent such as Pastozol AZ or biological
Taxidermy 131
detergent, are virtually fat free, though nothing
seems to be known of the long-term effects of such
treatments.
14.3.2 Problems
Due to the use of arsenic and mercury (II) chloride
as feather washes on some specimens, all old birds
should be handled with caution. Measures such as
wearing latex gloves and a dust mask should be taken.
Museums may wish to use X-ray fluorescence to
determine the extent of arsenic in larger collections.
Provided common sense is used there should be no
great threat. Indeed Morris (1982) found that the
life span of a random sample of taxidermists born
between 1782 and 1908 averaged 76.4 years with
50% passing the age of 80.
It is only in the last 50 years that most taxidermists
have had access to deep freezers and modern
equipment and chemicals for cleaning and drying.
Prior to that, the taxidermist had to work fast to
preserve the specimen and usually the best way to
do this was to mount it as quickly as possible. Once
this was done, it would dry out before it could
decompose. Even though they might have been
treated with a preservative on the inside, the skins of
many old specimens are little more than raw dried.
Inevitably, the speed of this process meant that many
corners were cut, the worst being the failure to
remove fat and properly degrease skins. In species such
as waterfowl, the fat layer within the feather tracts
can be at least 5–10mm thick. This fat appears to
oxidize with age and creates what is commonly
called ‘fat burn’. This can cause damage within only
a few years of preservation and causes the skin to
become very brittle and will either split or break
into pieces if the specimen is touched or vibrated.
Individual feathers will come away with a crusty lump
of usually rusty-coloured skin attached. This problem
does not seem to be reversible and is difficult to
treat successfully. If the bird has been mounted with
a firm form inside it is possible to fix small areas
of damage with a suitable adhesive such as PVA. In
some cases it may be possible to strengthen the
whole of the inside of the skin by injecting small
amounts of a consolidant such as Paraloid B72.
Old bird mounts which have remained in their
original cases or glass domes are usually fairly clean
but collections of uncased mounts like those in
many museums can often be quite dirty. Most fresh
bird skins can be washed by immersion and the
plumage dried and fluffed to leave it in perfect condition
because, while the skin is flexible, the feathers
can all be separated and each dried individually. In
dry, immovable skin, it is not possible to achieve the
necessary movement of each feather that allows it to
be fluffed up as it dries. Given these conditions, little
more than surface cleaning by wiping should
usually be attempted, particularly by the inexperienced.
If washing is to be undertaken it is usually
best done using a neutral detergent in small patches,
drying each before starting the next. Even then, a
small area should always be tested first as some feathers
react badly to water. The fringes of feather tips,
particularly if they are abraded or light damaged, of
some species of Accipitridae, Falconidae, Glareolidae,
Columbidae and Upupidae can curl when washed,
though circumstantial evidence suggests that this may
be partly due to using a too alkali detergent. Should
this happen it is sometimes possible to reduce the
curl by carefully wrapping the affected area in wet
tissue which when dry can be left in place for up to
several months. In many cases, wiping with a solvent
merely forces the dirt into the feather. In these cases,
dirt will only be removed by flushing in a suitable
extraction bath. However, it is probably best, in most
instances, to avoid this unless absolutely necessary.
Besides dirt, the problem found most obviously
in bird mounts is that of leg wires (usually ungalvanized)
rusting, erupting and splitting through the
back of the legs. Often these wires will break off at
the foot if the specimen is removed for repair. In all
but the largest birds, it is usually possible to discard
this wire and replace it with a new one fitted into
the metatarsal by drilling through the base of the
foot. The rust-damaged area can then be repaired
and remodelled.
14.4 Mammals
14.4.1 Methods
Initially, small mammals were prepared in a similar
way to that described for birds with the addition
that the nose, lips, ears and toes had to be skinned
out and modelled to avoid shrinkage and distortion.
It was quickly found that anything larger than a fox
needed a much stronger, more rigid framework to
prevent them sagging under the weight of materials
used. Larger mammals also had skin which needed
immersing in a pickle to fix it and also needed shaving
down to allow the pickle to penetrate and to
help prevent shrinkage as it dried.
Many of the early, large mammal mounts were
fairly crude but from the mid-nineteenth century
132 Conservation of leather and related materials
Taxidermy 133
standards improved steadily and by the 1880s competent
mounts were being produced. These commonly
used a method of a centre board shaped as a
silhouette of the neck and body to which metal rods
bent to the shape of the legs were fastened. The skull
and sometimes the leg bones were attached, and leg
muscles and body were created by binding on straw,
hay, or wood wool. Often, this was covered with a
layer of clay to smooth it out and allow some detail
to be shown. The better taxidermists improved on
this by using plaster and scrim instead of clay to
strengthen and provide a firm base to fix the skin to.
Sometimes a layer of papier mâché–glue–plaster
composition would be applied under the skin at
mounting. Folds, wrinkles, etc. could be modelled
into it before it set helping to hold the details in
place as the skin dried.
In the early twentieth century the great American
Carl Akely (1864 –1926) introduced modern taxidermy
by producing highly detailed plaster or glued
paper forms cast from an anatomically accurate clay
sculpture. The ‘Akely method’ meant that more than
ever skins had to be dressed or tanned, not merely
pickled, and some taxidermists turned to the methods
used in the fur trade. Thin, supple skins which
hardly shrink on drying allow detail to be modelled
in by gluing them on to hard forms without the risk
of them splitting. Trophy heads of big game were
prepared in the same way as large mammals, with
similar variations in technique. In North America
the ‘Akely method’ meant that forms for both full
mounts and trophy heads could be mass produced
and firms very quickly became established supplying
taxidermists with a range of forms for species both
large and small. For many years these were hollow
and made of glued paper up to 5 or 6mm thick, but
from the 1970s they have slowly been superseded
by high density PU foam. This trend has spread to
Europe and most countries with commercial taxidermists.
The market for these forms is large – firms
can supply almost any species from a squirrel to a
polar bear. There remains, however, some doubt as
to the longevity of PU which may present interesting
problems in the future. Individual taxidermists
also create ‘one-off ’ forms from GRP, others carve
forms from Styrofoam and some still resort to the
bind up method. Many ears are now filled with GRP,
epoxy putty or custom-made plastic liners. The
preparation of skins is becoming much more uniform
with most species above squirrel size being
tanned with Lutan FN, a low basicity aluminium
tanning complex.
Figure 14.1 Trophy heads of Argali sheep showing badly soiled condition (left) and after cleaning (right).
14.4.2 Problems
Many old mounts and especially trophy heads become
very dirty due to years of open display. After
ascertaining the condition of the skin and hair and the
type of form used, it may be possible to remove much
loose dust by gently brushing and blowing followed
by further cleaning as for furs and skins. However,
certain ungulates such as sheep of the genus Ovis and
some deer of the genus Cervus have hair which
becomes very brittle with age and these should on no
account be treated by brushing. With most mammals,
and particularly trophy heads, it is possible to wash the
whole mount by spraying with warmish water containing
a suitable detergent and gently working the
hair with a sponge to loosen the dirt. The whole
mount can then be rinsed thoroughly with running
water. Brittle-haired species in particular can be
cleaned in this way as the hair becomes much more
pliable while wet. When rinsed, the hair can be ‘blotted’
with towels and then dried fairly quickly with
warm air. It is important to dry as soon as possible to
prevent the skin and any modelling materials such as
clay from absorbing water. For other methods see the
section on cleaning in Chapter 15.
One of the commonest problems in taxidermy,
particularly in larger species, is skin splitting. This
generally occurs for one of two reasons:
1. The whole mount is unstable or has been removed
from its base allowing it to wobble whenever it is
moved. Eventually this leads to the skin splitting in
areas of movement. This type of problem can only
be addressed by first stiffening the mount and preventing
further movement. If the mount is not on
a base, simply putting it on one may cure the problem.
If, however, the form inside the skin is not
rigid – perhaps a too soft ‘bind up’ or leg rods too
thin – the solution may be achieved in a variety of
ways. With small specimens, it may be possible to
identify points of movement and to inject Polyfilla,
or similar, into and around these areas using a
syringe and large bore needle. In larger species,
such as bear and tiger, I have successfully stiffened
soft, straw bodies by driving lengths of plastic piping
into areas of movement and pouring in a two
part PU foam mix. Using a low rise foam in small
pours it is possible to impregnate a large area of a
body or leg until it becomes rigid. The same
method will also stiffen sagging necks.
2. The skin has not been prepared properly and
shrinks because it is too thick; has been incorrectly
dressed or only pickled; has been stretched to fit a
form that is too large. Any one or combination of
the above can cause splits to appear almost anywhere
on a specimen. Where the skin has not
been glued to a solid form, shrinkage usually first
shows itself by the bursting of stitched seams.
Even if the skin is glued to a form, this will not
prevent splitting if the skin is incorrectly prepared
and/or is overstretched. Splits and bursts
are also likely to happen due to large fluctuations
in relative humidity (RH) and high temperatures,
and even a well-prepared skin can be damaged by
the expansions and contractions of a large bound
body covered with a thick layer of clay.
Whatever the cause of splitting, an assessment must be
made of the skin’s condition in order to determine
what method will be used to effect a repair. If the skin
is in good condition and appears to have been well
prepared, it may be possible to soften it down using
damp cloths and stitch it together. It may, of course,
be necessary to soften a quite large area in order to get
enough stretch. At the same time, if the mount has a
solid form a suitable ‘hide paste’ such as Dextrin may
be used to prevent the skin from shrinking back.
Crucially, any such repair must be allowed to dry out
slowly to reduce further shrinkage. When softening
any mammal skins, it is important to remember that
old skins are often acidic due to being pickled with salt
and alum and care must be taken to avoid ‘acid swell’,
which causes the skin to become very rubbery and
weak. To reduce the risk of this, salt should be added
to softening water at a ratio of 50g per litre.
Where the condition of the skin will not allow it
to be stitched together, then it may be possible to
disguise splits by patching. This can be achieved with
bits of skin from the same species, if available, and it
is always useful to have a collection of aged skin from
unwanted specimens. Unlike furriers, taxidermists
have never dyed skins so most old mounts have faded
in varying degrees, often unevenly, which makes
matching in far from easy. If no skin or hair is available,
then an alternative may be found; natural or synthetic,
it does not matter as long as it can be made to match.
This may be achieved on hard forms by simply
gluing in place, having first made sure that the surrounding
skin is similarly held. On soft mounts,
Polyfilla can be injected into and around the split in
sufficient quantity to create a firm base to which
adhesive will adhere. The split can then be patched as
above or can be ‘haired’ by painting with a suitable
adhesive (PVA) in small amounts and laying in tufts
of hair. Sparsely haired species such as apes can be
‘haired’ using a two part unfilled PU tinted to the
skin colour as the adhesive. This will grip the hair
134 Conservation of leather and related materials
Taxidermy 135
easily but then set quickly. Sometimes it is possible to
use a longer hair, which can be trimmed to length
when dry. If it is necessary to dye or colour hair
completely to match, this is best done before patching
takes place. As few mammal hairs are single
coloured, dyeing can only be used for base colouring
after which airbrushing can be a useful technique.
Patched areas can have markings and other detail
added in situ by this method. On species with sparse
coarse hair the airbrush with acrylic paint can be
very effective and easily reversed.
There may arise instances when the mount is in
such poor condition that simple ‘repairs’ are not sufficient.
Very occasionally even historic specimens can
be completely taken apart and remounted. However,
the costs of such an undertaking mean it is only likely
to be considered for very important specimens. An
excellent account of the renovating of an extinct
quagga (Equus quagga) is given by Rau (1993). Suffice
to say this type of project should only be attempted
by those with great experience.
Initially, mammal ears were left untouched because,
being composed of skin and cartilage, they might
dry without rotting. The drawback is that any ear
larger than a squirrel’s quickly distorts badly as it
dries. To avoid this, the ear must be ‘skinned out’.
This involves either separating, from inside, the skin
of the back of the ear from the cartilage or, better still,
removing the cartilage completely. Either way, a
stiffening and shaping substance can then be introduced
into the ear. Older mounts often have just clay
and the retained cartilage, but many from the twentieth
century have a liner made of lead or paper often
accurately shaped or, at least, a non-hygroscopic
‘compo’ mix, together with a larger wire rod to provide
rigidity while setting. Often these rods were
driven through the tip of the ear, down the length
and into the form. Their legacy is a wealth of heads
with rusty damage patches to the back of each ear
tip. Ears which have not had the cartilage removed
can become distorted over time. These can be
reshaped to some degree by softening and clamping
between shaped wooden formers while they dry. If
kept at a steady RH, they may retain this shape.
14.5 Fish
14.5.1 Methods
It is undoubtedly the case that attempts were made
to preserve fish in the eighteenth century but it is
Figure 14.2 Ear of antelope from rear showing traces of iron oxide in line along the centre leading to a damaged area
where the rusted wire has broken through the weakened skin.
136 Conservation of leather and related materials
only from the mid-nineteenth century that fish of
any quality and in quantity are to be found.
Traditionally, until the late twentieth century, fish
were prepared by skinning along the lateral line on
the non-show side and removing the body. As much
flesh as possible was taken from the head without
skinning (as this is nearly impossible), the inside of
the skin was scraped clean of fat and tissue and an
arsenic mix might be put on the inside. The commonest
method of mounting was then to fill the
skin with sufficient sand or damp sawdust to recreate
the body, stitch up, model into shape and leave
to dry. Larger species such as tunny (Thunnus sp.)
would require a body form and be mounted in much
the same way as mammals. At this stage, it might be
given a carbolic wash over the outside and a coat of
shellac would help to hold the scales in place. This,
no doubt, helped to mask the smell and keep off flies
as it dried and fleshy areas of the head shrank. When
dry, these might be modelled back with a glue/
plaster mix, sometimes with papier mâché.
After drying, the sand, if used, was emptied out
and the now discoloured, faded specimen might be
painted to resemble itself in life. Often this was a
cursory effort and more usually it would receive
another coat of shellac to enhance any markings in
the skin and impart a ‘fishy’ gloss.
The use of silicone rubbers has enabled fish to be
reproduced in GRP in minute detail and all museums
and many taxidermists now use this method. A few
die-hard anglers, however, still want their actual fish
and today many are prepared by replacing the real
head with a cast copy fixed to the skin. This itself
may be mounted on an accurate PU form that
requires only some adhesive to attach the skin. Most
specimens are now completely painted with several
layers of paint to replicate the living fish.
14.5.2 Problems
Fish skin and bone are inherently oily and the
preservation method described leaves relatively large
amounts of fatty tissue in the fins and, of course, the
whole skull with much untouched skin. Within
decades, discolouration and eruptions through the
skin can appear. These take the form of dark brown
sticky globules of oxidized oil or fat, sometimes
forming little runs. In smaller specimens, these may
dry out and can be removed with a blade but in larger
ones they may remain very sticky and are difficult to
Figure 14.3 Stitching a split in relaxed skin behind the eye of an antelope.
remove even with solvents. In larger, oily species,
the whole specimen may be subject to ‘fat burn’
leading eventually to its total disintegration. It is
probably not possible to maintain the original
appearance of such a specimen and, if it is of historical
or scientific value, consideration should be given
to moulding it to make a GRP replica before it
deteriorates too far.
14.6 Care
As most museums are aware of the environmental
requirements of their collections and have in many
cases addressed these needs the following points are
intended for the guidance of those who care for
taxidermy in the domestic environment. Museum
curators should refer to the Manual of Natural History
Curatorship (Stansfield et al., 1994).
14.6.1 Light
(a) Ultraviolet light (UV) is the commonest cause
of irreversible damage.
(b) For display, try to use areas that have as little natural
light as possible.
(c) Never display by using picture lights, spots, etc.,
which are used as main room lighting.
14.6.2 Temperature
(a) Ideal ambient temperature is 18–22°C.
(b) Avoid high temperatures.
(c) Avoid hot spots, i.e. above radiators.
(d) Lower temperatures (13–15°C) are acceptable if
the RH is low.
14.6.3 Relative humidity
(a) Ideal RH is 50% Ϯ 5%.
(b) Avoid fluctuations in RH. It is better to have a
slightly high or low level that is steady.
(c) Lower RH is acceptable at lower temperatures.
(d) High RH is particularly bad as it promotes
bacterial and mould growth, which can destroy
specimens. This process is speeded up when
combined with high temperatures.
14.6.4 Storage
(a) Always store in darkness, by covering if necessary.
(b) Taxidermy in cases and domes is always easier to
maintain. These can be put in a black bag if a
Figure 14.4 Soiled study skin of a garganey, showing test cleaned area on breast.
Taxidermy 137
138 Conservation of leather and related materials
Figure 14.5 Study skin of a blackheaded gull suffering from extreme ‘fat burn’ which has so damaged the skin that
the specimen is falling apart.
Figure 14.6 A mounted tuna showing on the lower half areas of oxidized oil/fat leaching through the paint.
Figure 14.7 Tail end of tuna, showing areas of filler and paint being cracked and lifted by oxidizing fats underneath.
Figure 14.8 Detail of above.
Taxidermy 139
140 Conservation of leather and related materials
dark cupboard is not available. Ensure cases are
well sealed.
(c) Larger uncased specimens should be bagged or
covered to keep off dust. This should be done
simply so they can be checked for insects.
14.7 Preservatives
Bowditch (c.1821)
‘Receipt’ for making arsenic soap, invented by
Bécoeur, apothecary at Metz.
Camphor 5 ounces
Arsenic in powder 2 pounds
White soap 2 pounds
Salts of tartar 12 ounces
Lime in powder 4 ounces
Wood (1877)
Take half an ounce of corrosive sublimate
Take half an ounce of white arsenic
Take four drachms of spirits of wine
Take half an ounce of camphor
Take six ounces of white Windsor soap
Davie (1894)
Arsenical soap
White soap 2 pounds
Powdered arsenic 2 pounds
Camphor 5 ounces
Subcarbonate of potash 6 ounces
Alcohol 8 ounces
Browne (1896)
Alcoholic solution of mercury, one part in 1000.
For preventing and arresting mildew, and for external
use upon skins
Methylalcohol, 90 –95% 1 pint
Bichloride of mercury 10 grains
Non-poisonous preservative powder (M.B)
Pure tannin 1oz
Red pepper 1oz
Camphor 1oz
Alum (burnt) 8oz
Preservative for mammals
Alum (burnt) 4 parts
Saltpetre 1 part
A mixture made of the above proportions, with the
addition of hot water and a little bichromate of
potassa, makes a very fine bath in which to plunge a
thick or slightly tainted skin.
Davis (1907)
Preservative powder for small skins.
Saltpetre 1oz
Burnt alum 5oz
Plaster of Paris 4oz
Naphthalene 11
⁄2 oz
Rowley (1925)
Dry arsenical mixture for poisoning the interior of
small fresh bird and mammal skins.
White arsenic (arsenious oxide) 3 parts
Powdered alum (aluminium sulphate) 1 part
Tan liquor for fur dressing.
Water 1 quart
Salt 1 pound
Alum (aluminium sulphate) 1 pound
Dissolve by heating, cool and 1
⁄2 fluid oz
add, Sulphuric acid (commercial)
Formic acid 4 fluid oz
Hyposulphite soda 4oz
Flour (dry) 1
⁄2 pint
Fat liquor.
Water 1 quart
Laundry soap, sliced 1
⁄2 cake
Stearic acid, shaved the same bulk as soap
Carbonate soda 1oz
Neats foot oil 4 fluid oz
(castor oil gives fine results and is easily obtainable)
Boil and stir until dissolved 1 tablespoonful
then add, Ammonia
(commercial)
References
Bowditch (1821) Taxidermy: or, The Art of Collecting,
Preparing and Mounting Objects of Natural History.
London: Longman, Rees, Orme, Brown and Green.
Browne, M. (1896) Artistic & Scientific Taxidermy and
Modelling. London: Adam and Charles Black.
Davie, O. (1894) Methods in the Art of Taxidermy.
Columbus: Hann & Adair and H.T. Booth.
Davis, W.J. (1907) Bird and Animal Preserving and Mounting.
Hythe and London: J. & W. Davis and Elliot Stock.
Morris, P. (1982) On the Supposed Occupational
Hazards of Being a Taxidermist. Guild of Taxidermists.
Newsletter, 9, 36 –37.
Rau, R.E. (1993) Remounting the Quagga. Breakthrough
Magazine, 34, 54 –57.
Rowley, J. (1925) Taxidermy and Museum Exhibition. New
York: D. Appleton and Co. Ltd.
Stansfield, G., Mathias, J. and Reid, G. (1994) Manual of
Natural Curatorship. London: HMSO.
This chapter deals with furs and fashionable dress made
from the skins of fur-bearing mammals. Additional
information will be found in the chapters dealing
with ethnographic materials and taxidermy as the
methods of skin preparation used for objects which
fall within these disciplines will differ considerably
from those used for furs in fashionable dress. Basic
information on structure and morphology of hair is,
of course, common to all. Methods of cleaning, conservation
and general care may also be applicable
across the disciplines.
This chapter is divided into three sections. Section
15.1 describes the history of fur use in the context
of species availability at certain times and its use in
fashionable dress. Section 15.2 describes hair structure
and morphology, fur-skin dressing and dyeing
methods, furriery techniques including the ‘dropping’
or ‘stranding’ of skins and the method of making
up furs into finished garments. Section 15.3
deals with practical conservation issues and describes
briefly the cleaning and repair of furs as it is carried
out by furriers to make clear how and why this differs
from the conservation approach. The damage
to furs that conservators may encounter is discussed,
and the ways in which conservators repair furs and
solve some of the care and conservation problems
are described. Case histories of treatments are discussed
as examples to illustrate further the conservation
of fur within museum collections.
Personal feelings concerning the morality or
desirability of wearing fur have no place here, as it is
an indisputable fact that fur is an important part of
the history of dress across many cultures. Conservators
will therefore need to be as knowledgeable
about fur as any other skin material, animal product,
or any other organic material they may come across
during the course of their work.
15.1 History of fur use
15.1.1 Introduction
In the latter years of the twentieth century and early
years of the twenty-first, the wearing of fur as an
item of fashionable dress is an emotive subject.
Many museums do not have a collections policy
which positively includes fur, and those which have
it among their collections rarely show it or actively
encourage its acquisition.1
The reason is often given
that it is impossible to store but this is not the case.
Although not readily acknowledged there is often a
quantity of fur in most textile collections which
include dress and accessories and this should not be
dismissed lightly. There may be hats, muffs, tippets,
collars, or whole garments such as coats, jackets and
stoles. Items may be edged or trimmed with fur.
They may also be lined with fur, either whole or
part garments, or accessories such as gloves, boots,
etc. Fur has often been used on ceremonial robes
and as part of military uniforms and will thus be
found in most, if not all, collections dealing with this
type of dress. For example, coronation mantles and
ceremonial robes were trimmed with ermine and
other furs. Guards’ ‘bearskins’ or shakos are made
from the skins of American brown bears (Euarctos
americanus), busbies of the hussars troopers are made
of hair-seal (Phocidae sp.) as are those of the rank and
file of the fusilier regiments (Sachs, 1922) and flying
helmets from the period of the First World War and
141
15
Furs and furriery: history, techniques and
conservation
Marion Kite
the early years of aviation are lined with rabbit fur
(Oryctolagus cuniculus sp.).
It is not only the textile conservator who might
have to treat fur. Conservators working with ethnographic
materials will certainly have to treat fur, so
will conservators working with mixed collections of
organic materials, possibly furniture conservators,
those working with archaeological materials, natural
sciences and taxidermy collections and possibly other
disciplines too.
In ethnographic objects from diverse cultural origins
fur is abundant, as it is in taxidermy specimens.
It has been used in furniture; in the late eighteenth
and early nineteenth centuries travelling trunks were
covered with and lined using the pelts of fur seals
(Otariidae sp.) (Ewing, 1981). Occasionally archaeological
fragments may also be found and several
fragments have been discovered with various Iron
Age finds – bog bodies (Glob, 1971).
15.1.2 Background and history
Unto Adam also and to his wife did the Lord God make
coats of skins, and clothed them.
Genesis. Chapter 3 verse 21
The practice of wearing furs is as old as humanity.
Some method of dressing skins was discovered early
in history as a skin flayed from an animal and used in
its rough state would quickly go hard or if dried
slowly without further treatment to preserve it, would
putrefy. In neither case would it be of any use.
The discovery of a 5000-year-old body (now
known as the Ice Man) preserved in a glacier at
Hauslabjoch across the border of the Austrian/
Italian South Tyrol gave evidence of fur being worn.
The man was found fully clothed, and although the
clothing was not completely preserved, his upper
garment was described as of leather – and as fur
which had lost its hair and was probably similar to a
cloak or cape. Photographic evidence taken prior to
disturbing the body showed that it was made of fur.
In the course of recovery and stabilization the hair
of the fur had come out and is now present as separate
clumps (Spindler, 1994).
Found with the body of a woman discovered in a
bog in Huldre Fen at Rainten, Djursland, in Denmark
was the most complete woman’s costume of Iron Age
date yet discovered. She was discovered wearing a
lambskin cape and another cape as an outer garment
(Glob, 1971).
Another body of an Iron Age man, dating from
some 2200 years ago and found in a peat bog at
Tollund in Jutland in 1938, was discovered wrapped
in animal skin. This was identified as some kind of
sheepskin and had pieces of cowhide sewn onto it
(Glob, 1971).
Arctic peoples and others from cold climates have
of course chosen fur for warmth and protection but
throughout history the wearing of furs in fashionable
society has been synonymous with wealth, luxury
and status.
In classical antiquity the Phoenicians, Assyrians,
Greeks and Romans all used furs and the British fur
trade began at least 2000 years ago. When the Romans
arrived in Britain they traded furs for British wool
and metals. Later, Norse traders brought exotic luxuries
including furs from Russia and Armenia which
they traded through London and were imported
through Queenhythe docks in the city. The AngloSaxons
and Normans wore furs and as London
developed it became the centre of the world fur
trade. By the thirteenth century furs from northern
Europe, Scandinavia, Russia and the Baltic lands
were traded through London and a business community
of merchants and furriers developed. The
Peltry in West Cheap is mentioned in 1274 and the
shops and homes of skinners extended south from
Cheap near the banks of the river Walbrook to the
Thames (Veale, 1966).
From the fourteenth century onwards the
Hanseatic League, founded by wealthy merchants,
formed one of the great trading organizations of the
world and furs were one of their principal commodities.
Squirrel skins, sables and others from
Russia and the Baltic lands were marketed through
the City of London and the Worshipful Company
of Skinners of London were one of the earliest
medieval guilds drawing up regulations for fur trading
and manufacture of skins into furs. The Craft
Guilds had enormous power and ensured fair trading
and quality control. The Skinners originated as
a guild of furriers and were granted their charter by
Edward III in 1327. Their coat of arms depicts three
ermine caps tasselled and enfilled with gold crowns
supported by a lynx and a marten. A lynx also forms
the crest. Ermine was the most esteemed fur in
which the skinners dealt at the time, and lynx and
marten were also highly valued as the wearing of
them indicated social prominence, success and
wealth. Edward III ordered that no person of an
income under £100 per year should wear fur except
lamb, coney, cat and fox under penalty of forfeiture
and that ermine was to be worn by royalty only
(Baldwin, 1926).
From early on the upper classes had tried to limit
the wearing of furs by the lower classes in order to
142 Conservation of leather and related materials
maintain and protect their own status and the exclusivity
of certain furs. The wearing of furs was strictly
forbidden to the church, however in 1127 the Council
of London allowed abbesses and nuns to wear the furs
of lambs and cats only (Sachs, 1922). These must
have been the lowest class of furs at the time.
In 1555 the British owned Muscovy Company
was formed and opened new sources of trading in
Russia. Beaver, hunted to extinction in the British
Isles, but long valued as one of the principal furs and
also used for making fur-felt hats, was available in
quantity (Spriggs, 1998).
In Tudor England furs were thought to benefit
the health. Skins of wildcat were supposed to cure
rheumatism and gout, and mouse skins were thought
to cure chilblains (Veale, 1966).
Furs were used as political and royal gifts with
Russian sables being the most valuable. In 1587 Czar
Ivan the Terrible gave to Elizabeth I four timbres
(bales of 40 skins) of very rich black sables, six
well-grown white spotted ‘Luzerance’ (lynx) and
two gowns of ermines (Veale, 1966).
In the sixteenth and seventeenth centuries the
wearing of furs in Europe was strictly controlled
and Laws of Sumptuary dictated what estate of man
could wear which fur; with the highest ranking
having permission to wear furs of the greatest rarity
and value.
Squirrel skins were much in demand by the
upper classes and the skins of the grey squirrels with
white bellies (not an indigenous species of the British
Isles but imported from northern Europe) were versatile
giving a variety of different decorative effects.
They were known as vair if used whole, gris if only
the backs of winter skins were used, poppel for the
light skins of early summer, rovair for autumn skins
where streaks of red appeared in the grey backs,
minever if only the bellies were used (white with a
little grey surrounding) and pured minever if the white
bellies were used with all the grey trimmed off
(Veale, 1966).
It is from a misunderstanding when the story of
Cinderella was translated into French by Charles
Perrault in 1697 that her slippers became lined with
verre and not vair. Henceforth her slippers were glass
and not made with the fur that would befit a young
woman of a suitable social status to marry a prince.
In the late sixteenth century, with a view to seeking
new territories and to fish the North American
fishing grounds which were already known as exceptional,
expeditions were sent to North America and
Canada. It was by chance trading with the native
peoples that the inexhaustible wealth of fur resources
was discovered. In 1608 De Champlain, the leader
of a French expedition, established a fur trading
post at Montreal and trade was initially dominated
by the French until the final conquest of Quebec in
1659. In 1670 Charles II granted a charter to the
Hudson’s Bay Company giving it a monopoly of
trade and commerce in the lands within Hudson
Straits. The first auction of Hudson’s Bay pelts took
place in 1672 in Garraways Coffee House in Change
Alley, Cornhill, in the City of London.
Today the main auction houses are based in
Scandinavia, Russia and North America but London
commodity brokers are still responsible for more
than 50% of the world trade in fur at a primary or
wholesale level.
Throughout the earlier part of seventeenth century,
before the Hudson’s Bay Company came into
being, most furs continued to be supplied from
northern Europe. Both men and women wore furs
and throughout seventeenth and eighteenth centuries
sables continued to be the most valuable. By
the eighteenth sumptuary legislation had been abandoned
but sable (Martes zibellina), ermine (Mustela
erminea) and squirrel (Sciurus vulgaris) were only
affordable by the most wealthy. Furs continued to
be used as linings. Fur muffs of varying styles and
sizes were in fashion for men and women from the
end of the seventeenth century throughout the eighteenth
century. For men they were usually worn tied
round the waist with a sash and for a time they
became very large, almost pillowcase size. This was
particularly an Italian fashion. In the eighteenth
century the most popular furs worn by men were
ermine and squirrel, but fox (vulpes sp.), lynx (lynx
sp.) and others were also worn. For women, the
contrast of textiles and furs became a fashion focus
with luxurious velvets and rich silks being complemented
by the choice of furs. In 1771 a sack back
dress of pastel velvet trimmed with sable was
admired by Lady Mary Coke at the court in Vienna
(Ribeiro, 1979). A dress described by Mrs Delany in
1742 consisted of ‘dark green velvet trimmed with
ermine, and an ermine petticoat’ (Llanover, 1861).
Towards the end of the century when the silhouette
changed, bulky fur linings of cloaks for outdoor
wear were replaced by edgings only.
In the eighteenth century fur muffs were often
perfumed. Sable and ermine remained the most
exclusive and light white furs such as ermine and
arctic fox were particularly fashionable for the
wealthy, and appear in many eighteenth century
portraits. Squirrel and lynx were also popular in the
first quarter of the eighteenth century (Ribeiro,
Furs and furriery: history, techniques and conservation 143
1997). In the early eighteenth century rabbit was
worn by those of the poorer classes who were able
to afford it but it became a fashionable choice by
higher social classes by the end of the century.
Such was the fascination with fur that some silks
were woven with patterns imitating fur worked into
the design (Figure 15.1).
Until the mid-nineteenth century the primary
use of furs in fashionable dress was as linings and for
making accessories and for trimming gowns. Rarely
were complete garments fashioned from furs with
fur being used as the outside material except in certain
European countries including Hungary where
the suba (a type of cloak) was worn (Ewing, 1981).
The dictates of the sumptuary laws had long ceased
to apply and furs were an indispensable item of luxury
and a way of displaying wealth now being accumulated
by the newly prosperous middle classes. However,
it was not until around the mid-nineteenth
century that fur coats or jackets came into being in
their own right as an item of fashionable dress for
women.
Seal skin from the fur seal (Otariidae sp.) was one
of the first furs to be used for coats as a method had
been perfected for removing the harsh top hairs and
refining the processing to give a light pliable skin.
Sealskin was plentiful and had a beautiful rich velvety
appearance when dyed black.
By the late nineteenth and early twentieth centuries
a huge variety of furs were available and in
demand by fashionable society. By 1880 all sorts of
oddities were worn including cats heads, stuffed
squirrels, tiny cubs or bears, small stuffed monkeys
and also mice as trimmings. These were particularly
used for hats and worn together with any number of
stuffed birds, wings and feathers already applied to
hats. Large animal skins had become fashionable for
home decoration; whole specimens of stuffed bears
and lions plus the skins of lions, bison, tigers, leopard
and polar bears had become fashionable accessories
in the domestic environment.
J.G. Sachs writing around 1922 states that over
100 species of fur-bearing mammals were used in
the fur trade from the following classes – rodents,
felines, canines, weasels, bear/racoon group, marsupials,
ungulates and sundry, which correspond to
none of the above but includes fur seals (aquatic mammals),
moles (underground mammals) and monkeys
(primates but usually only the colobus).2
Now comparatively few species are available to
the fur trade as they are protected and come under
the control of CITES (Convention on International
Trade in Endangered Species) which regulates world
trade in threatened and endangered species. The
world populations of endangered and at-risk species
are monitored and the Red List of most vulnerable
species facing extinction is constantly being updated.
A leopard skin coat or tiger skin rug seen today
may give rise to a feeling of horror and sadness knowing
how few individuals of the species are left in the
wild, but the wearing and owning of a leopard skin
or ocelot coat was an expression of superior taste and
elegance at the time they were fashionable. In 1956
J.G. Links, head of the fashion house of Calman
Links, a director of the Hudson’s Bay Company and
President of the British Fur Trade Alliance, wrote:
The buyer of such a coat generally has considerable
experience and sophistication in the world of fashion as
well as a number of other fur coats. She therefore wants
the best and nothing but the best will do. The price of
a fine leopard coat can easily exceed that of mink.
(Links, 1956)
144 Conservation of leather and related materials
Figure 15.1 Detail from eighteenth century silk dress,
V&A collection.
Today, this subtle message has been lost to the casual
viewer and we only see in each coat the wanton
killing of several specimens of what is now an
endangered species. Conservators treating furs, and
those treating bird skins and feathered objects too,
are likely to come upon examples of many endangered
or protected species and should be aware that
it is important to identify and safeguard the longterm
survival of these examples. A leopard skin coat
is much like the dodo. We will not see its like again.
In the 1960s designers targeted the youth market
with less costly furs such as rabbit. Particular designs
and colours were also tailored to the young and
these became known as ‘fun furs’. They were accessible,
fashionable and relatively inexpensive.
In the last quarter of the twentieth century there
was a marked decline in the wearing of fur in the
UK but since the mid-1990s a resurgence has
occurred with 150 of the world’s top fashion designers
showing fur in their 1997 collections, Dior, John
Galliano, Alexander McQueen, Gucci, Givenchy,
Valentino to name a few. In 1999 240 leading
designers included fur in their collections.
15.1.3 Husbandry and harvesting
The skins of fur-bearing mammals are taken when
they are in their prime. In the wild they are usually
in their best condition during the winter months
when it is coldest. The fur covering on the animal is
then at its most abundant and best colour, and the
skin is at its thinnest and most supple. In spring the
animal will moult and have a thinner covering of
hair for the summer months. The skin will also
undergo changes and begin to take on a reserve of
fatty tissue. In autumn the animal will grow a new
winter coat and the skin will again change and the
fatty tissues in the skin dissolve. These seasonal
changes affect the quality, colour and grade of pelt
which in turn affect the value. Prime skins are the
best and therefore of the highest value.
It was not until the latter part of the nineteenth
century that commercial raising and breeding of furbearing
animals was introduced. In America the first
experiments in mink (Mustela vison) farming were
undertaken in 1866 followed in 1887 when silver
fox (Vulpes vulpes) farming was begun; however, in
the UK fur farming was not undertaken until the
early twentieth century.
Commercial farming began slowly and tentatively
and was not always successful. Many species
breed only once a year and only certain species do
well in captivity in pens. Animals that are confined
are also more prone to disease, parasites and bacterial
infections. Good husbandry, sanitation, feeding
and management are essential and the early fur
farmers had a great deal to learn in understanding
the animals’ habits and general characteristics. They
also needed an understanding of genetics and a
planned and well-recorded breeding programme in
order to have the likelihood of breeding good stock
and not to in-breed too closely and thus have
unplanned mutations and weaknesses occur in successive
generations. Today with all the benefits of
modern science, zoos are still struggling with breeding
certain animals in captivity and are not always
successful.
‘Pelting’, the taking of the skin, is only done
when the fur is at its best quality and colour and a
diseased and stressed animal will not be of any use to
the furrier as the animal’s health and condition is
shown in the quality of its fur.
In the wild furbearers will produce indefinitely if
their habitat is viable. For species that are still
hunted, population and habitat management ensures
this viability. This is achieved by scientific monitoring
by professional wildlife biologists and governmental
regulations which allow for a certain number
of a species to be harvested each year without causing
threat to the survival of that species.
Today the most common farmed furs are mink
(Mustela vison) and fox (Canidae sp.). Other species
farmed on a smaller scale include nutria (coypu,
Myocaster coypus), chinchilla (Chinchilla lanigera),
fitch (polecat also known as foul marten, Mustela
putorius), sable (Mustela zibellina), and finnraccoon
(Tanuki Nyctereutes procyonides). From a scientific
point of view, fur animals that have been domesticated
(farmed) for more than ten generations are
considered to be so far genetically removed from their
ancestors that they must be treated as a fully domesticated
subspecies.
Fur farming is regulated and in the European
Union, Council Directive 98/58 sets down rules covering
the welfare of farmed animals, including furfarmed
animals. Directive 93/119 deals with the
slaughter and killing of fur and other farmed animals.
In North America, fur farmers also follow strict
codes of practice and conform to provincial, state or
national animal welfare and other regulations.
The most significant change in the long history
of the fur trade is that by the end of the twentieth
century 85% of the world’s commercial furs were
produced on farms.
In November 2000 a bill to ban fur farming in
England was passed by Parliament and came into
Furs and furriery: history, techniques and conservation 145
force at the end of 2002 forcing the 13 mink farms
to close down.
It is useful to the conservator to know what are the
most likely species which may be found in fashionable
dress and when they were used. It does not,
however, preclude any of the 100 or so species
appearing in an object but it may be relevant to know
when a particular species was fashionable and available
in order to help pinpoint the likely date of the object
concerned, and how the fur may have been processed.
15.1.4 Some fashionable furs and dates
15.1.4.1 Later middle ages and into sixteenth century
Lynx (Lynx sp.)
Genette (Viverra genetta)
Ermine (stoat; Mustela erminea)
Mink (Mustela vison)
Lettice (skins of the snow weasel; Mustela sp.)
Sable (Martes zibellina)
Squirrel (English, European, Russian, Sciurus sp.)
Coney (rabbit; Oryctolagus cuniculus)
Lamb (Ovinae sp.)
Wolf (Canis lupus)
Hare (Lepus europaeus and Lepus timidus)
Fitch (polecat; Mustela putorius)
Shankes or budge (kid; Caprinae sp.)
Leopard (Panthera pardus)
Otter (Lutrinae sp.)
Swan (Cygnus sp.) is also listed in the Wardrobe
Accounts of Queen Elizabeth I, 1561 and 1590, and
was prepared by her skinner William Jurden (Arnold,
1988).
15.1.4.2 Sixteenth and seventeenth centuries
Squirrel (English, European, Russian; Sciurus sp.)
Ermine (stoat; Mustela erminea)
Beaver (Castor canadensis)
Lettice (skins of the snow weasel; Mustela sp.)
Mink (Mustela vison)
Sable (Martes zibellina)
Marten (Martes americana)
Foynes (stone marten; Martes foina)
Budge (lamb skin; Ovinae sp.)
Fitch (polecat; Mustela putorius)
Lamb (Ovinae sp.)
Otter (Lutrinae sp.)
Fox (Canidae sp.)
Genette (Viverra genetta)
Coney (rabbit; Orctolagus cuniculus)
Cat (Felidae sp.)
Lynx (Lynx sp.)
Hare (Lepus europaeus and Lepus timidus)
15.1.4.3 Nineteenth century
In 1851 the Hudson’s Bay Company exhibited at
the Great Exhibition and showed examples of the
following furs from Canada:
Racoon (Procyonidae sp.)
Beaver (Castor canadensis)
Chinchilla (Chinchilla lanigera)
Bear (Ursidae sp.)
Fisher (Martes pennanti)
Fox (Canidae sp.)
Red (Vulpes vulpes)
Cross (Vulpes vulpes)
Silver (Vulpes vulpes)
White (Alopex lagopus)
Grey (Vulpes cinereoargenteus)
Lynx (Lynx sp.)
Marten (Martes americana)
Mink (Mustela vison)
Musquash (muskrat; Ondatra zibethica)
Otter (Lutrinae sp.)
Fur seal (Oteriidae sp.)
Wolf (Canis lupus)
Furs from the rest of the world were also shown and
included:
European marten
Stone (Mustela foina)
Baum (Mustela martes)
Squirrel (Sciurus sp.)
Fitch (polecat; Mustela putorius)
Kolinsky (Mustela sibirica)
Ermine (stoat; Mustela erminea)
Blue fox (Alopex lagopus)
Astrakhan (karakul lambs; Ovis aries)
Leopard (Panthera pardus)
Coney (rabbit; Oryctolagus cuniculus)
Genet (Genetta ginetta)
Sable (Martes zibellina)
15.1.4.4 Twentieth century
In 1922 the skins of the following animals were
available and regularly used (Sachs, 1922):
Badger
Canadian (Taxidea taxus)
Japanese (Meles ankuma)
Russian (Meles meles)
Bear
Black (Ursus americanus)
Brown (Ursus arctos)
146 Conservation of leather and related materials
Grizzly (Ursus arctos)
White (Ursus mairtimus)
Beaver (Castor canadensis)
Cat
Wild
European (Felis sylvestris)
North African (Felis sylvestris lybica)
North American (Felis rufus)
House (Felis catus)
Civet (true civet cat; Viverra zibetha)
Chinchilla (Chinchilla lanigera)
Dog
Chinese (Canis familiaris)
Ermine (Stoat; Mustela erminea)
Canadian (Mustela nivalis)
Russian (Mustela nivalis)
Fisher (Martes pennanti)
Fitch (polecat; Mustela putorius)
Fox
Blue (Alopex lagopus)
Cross (Vulpes vulpes)
Grey (Vulpes cinereoargenteus)
Kit (Vulpes velox)
South American (Dusicyon sp.)
Red Australian (Vulpes vulpes)
Russian (Vulpes sp.)
Japanese (Vulpes sp.)
Japanese fox (a species of racoon dog; Nyctereutes
procyonides)
Goat
Grey (Caprinae sp.)
Black (Caprinae sp.)
Guanaco (Lama guanicoe)
Hamster (Cricetus cricetus)
Hare (Lepus europaeus and Lepus timidus)
Kid (Capra hircus)
Kolinsky (Mustela sibirica)
Lamb
Persian (Ovis aries)
Broadtail (Ovis aries)
Leopard (Panthera pardus)
Lynx, Canadian (Felis lynx)
Marmot (Marmota sp.)
Marten (Mustela martes)
Mink (Mustela vison)
Mole (Talpidae sp.)
Monkey (Colobus polykomos, C. angolensis, C. satanus
and C. guereza)
Musquash
Southern (Ondatra sp.)
Nutria (Myocaster coypus)
Oppossum
American (Didelphis virginiana)
Australian (brushtail possum; Trichosurus vulpecula)
Otter, Canadian (Oryctalagus canadensis)
Rabbit
White (Oryctalagus cuniculus)
Chinese (Oryctalagus cuniculus)
Raccoon (Procyonidae sp.)
Sable (Martes zibellina)
Sea otter (Enhydra lutris)
Seal
Hair (Phocidae sp.)
Fur (Oteriidae sp.)
Skunk (Mephitis sp.)
Squirrel (Sciurus sp.)
Thibet (Caprinae sp.)
Tiger (Panther tigris)
Wallaby (Macropodidae sp.)
Wolf (Canis lupus)
Wolverine (Gulo gulo)
15.1.4.5 Late twentieth and early twenty-first
centuries
At the close of the twentieth century and the beginning
of the twenty-first century the following animals
were readily available to the fur trade. Many
previously used species are now protected, i.e. monkeys,
civet, large cats including ocelot, jaguar, and
sadly several appear on the CITES Red List:
American marten (Canadian sable; Martes zibellina)
Australian opposum (Trichosurus vulpecula)
Beaver (Castor canadensis)
Chinchilla (Chinchilla lanigera)
Coyote (Canis latrans)
Fisher (Martes pennanti)
Fitch (polecat; Mustela putorius)
Fox (Vulpes sp.)
Lamb (Ovinae sp.)
Lynx, Canadian (Lynx lynx)
Marmot (Marmota sp.)
Mink (Mustela vison)
Mole (Talpidae sp.)
Musquash (muskrat; Ondatra zibethicus)
Nutria (coypu; Myocaster coypus)
Rabbit (coney; Oryctolagus cuniculus)
Raccoon (Procyonidae sp.)
Sable (Martes zibellina)
Squirrel (Sciurus sp.)
Ermine (Stoat; Mustela erminea)
Weasel (Tanuki, Nyctereutes procyonides)
Others may be available as part of licensed animal
population management programmes – culls:
Seals (Phocidae sp., Oteriidae sp.)
Bears (Ursus arctos and Ursus americanus)
Furs and furriery: history, techniques and conservation 147
15.2 Structure, morphology, dressing
and making
15.2.1 Definitions and terminology
Understanding the differences in terminology used
in describing fur and its preparation as opposed to
the preparation of leather is an essential introduction
to the art and science of fur dressing.
In common usage the word ‘fur’ is used to
describe the hairy outer coat of certain mammals.
To the fur trade the term ‘fur-skin’ is most usually
used and applies to the hairy outer coat of a mammal
which is inseparably attached to the skin proper.
To a fur-skin processor (or fur-dresser) and to the
furrier concerned with the manufacture of fur garments,
etc. ‘fur’ applies to the hairy outer coat of
mammals used in the fur trade. Included in these are
sheep and lambs which by convention are commonly
described as possessing wool.
The term ‘pelt’ is generally used to refer to the
leather side of the ‘fur-skin’, which is also referred
to as ‘skin’.
Fur-skin processing or ‘dressing’ refers to the
preparation (dressing) and dyeing of raw fur-skins
for the purpose of making them non-putrescent and
suitable for commercial use.
The term ‘fur’ also refers to the ‘down’ or ‘undercoat’
of a skin while ‘hair’ refers to the longer stiffer
guard hairs which are the outer covering or top
hairs. During fur processing sometimes these guard
hairs are removed to expose the soft underfur. Some
animals only have hair, e.g. horses and cows have no
fur, only hair.
To the leather trade ‘pelt’ is commonly used to
designate the hide or skin prepared for tanning by
removal of the hair or wool, epidermis and flesh.
‘Skin’ is used to describe the outer covering of an
animal of the smaller kind, e.g. sheep, goats or of
immature animals of larger species such as calf and
pony; also the skin of a fur-bearing animal dressed
and finished with the hair on, e.g. sheepskin.
‘Hide’ is the outer covering of a fully grown animal
of the larger kind, e.g. cattle, horse, camel, elephant.
In the leather industry a ‘dresser’ is distinguished
from a ‘tanner’ in that the dresser carries out the
finishing of tanned or semi-tanned leather and
this includes dyeing, glazing and the final finishing
processes as required before the skin is marketed
(sheep, horses and cattle are treated both by skinners
and leather dressers for different purposes).
There are few differences across the continents
in the manner in which raw skins were and are
commercially prepared. The differences lie primarily
in the recipes used for the dressing.
15.2.2 Brief history of fur-skin processing
and dyeing
The discovery of alum as a preservative was probably
made by the Chinese who claim to have used furs
for 3000 years. Alum is an important substance in
the history of leather and fur-skin dressing.
Sylvia Matheson in her publication Leather in the
Lands of Ancient Persia gives a first millennium BC
Babylonian recipe for processing very special leather
(Matheson, 1978). It reads:
The skin of the kid thou shalt feed with the milk of a
yellow goat, and with flour; thou shalt anoint [it] with
pure oil, ordinary oil, and the fat of a pure cow. Thou
shalt dilute alum in pressed grape juice, then fill the
surface of the skin with gall nuts of the tree-cultivators
of the Hittites.
It is logical to assume that as the Babylonians used
and traded furs, a recipe similar to this would have
been used for their preparation and dressing.
By Roman times a distinction was made between
tanners (coriarii) and fur-skin dressers (pellioni) and it
was recognized that each was a separate distinct skill
and process. In addition to dressing, pellioni included
in their activities the making up of certain items and
a general trading in fur-skins.
Tanners concentrated on bark tanning and tawyers
concentrated on those skins for which the use of
alum and oil was more suitable. Among these were
fur-skins. (Tawe comes from the Anglo-Saxon meaning
to prepare.) The word ‘tawyer’ has long been
associated with alum dressing (Kaplan, 1971).
By medieval times the furrier combined the
activities of fur-skin dresser with that of manufacture
of garments and trimmings. The guilds covered
many branches of a particular trade and it was considered
fraudulent practice to dye fur-skins. However
this practice did not include trimmings matched to
a garment and dyed to red, blue or green, only the
practice of dyeing to cover up natural faults in a skin,
light spots or patches with the intent to deceive.
Black dyeing was especially forbidden and remained
so until the seventeenth century.
According to the records of the Skinners Company
alum and oil were used for fur dressing but by 1593
alum dressing had been partially replaced by oil.
The method used for preparing fur-skin was to
stretch the skin on a frame and sponge the flesh side
several times with a solution of alum and salt, or oil.
148 Conservation of leather and related materials
Lightweight fur-skins such as squirrel, beaver and
fox were first greased with oil, butter or other fatty
substances and trampled with bare feet in a barrel
until the skin was rendered pliable. Fleshing with a
scraper then followed.
In the seventeenth, eighteenth and nineteenth
centuries dyeing was less restricted although still
controlled. Black and brown were dyed onto furskins
using plant products such as logwood, sumac
and gallnuts together with mineral substances such
as verdigris, iron filings, alum, or copper scale. The
processing method of ‘foot tubbing’, trampling
greased fur-skins in a barrel, to make them pliable
was carried on until into the twentieth century.
Very little changed for nearly 300 years. By the
mid-nineteenth century demand for furs had
increased to the extent that large factories employing
hundreds of workers were set up in Europe to
process furs rather than small workshops with only a
small number of craftsmen. Methods of dressing
were still dependent on alum, salt and natural fats,
and for dyeing upon vegetable products and metal
salts. The fur seal which became popular around
1847 was dyed by repeated brush applications of dye
in order to preserve the leather from damage by the
strong dye, the composition of which was based on
that used in the French silk industry (Kaplan, 1971).
By the end of the nineteenth century mechanization
of some processes had taken place. The ‘foot tub’
was replaced by wooden ‘kickers’ derived from the
textile trade’s ‘fulling’ mills and cleaning drums
were rotated by power-driven belts. The discovery
of synthetic coal tar dyes by Perkin in 1856 had no
immediate application in fur dyeing and it was not
until the end of the century when oxidation dyes
were patented that coal tar derivatives could be
applied to furs. The use of para-phenylene diamine
enabled a greater range of colours to be obtained
on fur.
15.2.3 Hair and fur fibres
The structure of mammalian skin has been described
in detail in Chapter 1 but for the purposes of this
chapter, I shall briefly revisit it in the context of
fur/hair.
The mammalian skin is constructed mainly from
a series of interlaced protein fibres of which the four
main types are described as follows:
1. The hair fibres rooted in the follicles of the epidermis.
These are frequently described as ‘fur’.
2. Muscle fibres fixed between the grain and the
base of the hair follicles.
3. Collagen fibres forming the bulk of the grain and
corium, and constitute what is generally known
as the pelt or leather.
4. Elastin fibres lying mainly on the grain and flesh
layers.
The fibre, described variously as hair, wool or fur
depending on the animal type, is composed of the
protein keratin.
The fur-skin processor deals with the keratin
fibres and the three other types of fibrous proteins in
an inseparable form, his aim being to maintain and
enhance not only the properties of the fur fibre but
equally the skin fibres.
The function of these keratin fibres is to serve as a
protection for the skin and to insulate against weather
and other hazards of the environment. This is true of
warm climates as much as cold; fur-covered tropical
animals are insulated against strong sun and heat.
Keratin fibres are themselves poor conductors of
heat. The air trapped between the fibres helps to
form an efficient insulating layer, preventing rapid
loss of heat which is why animals from cold regions
are more fully furred than those from warm climates.
Certain species of mammals, such as pigs, have very
little hair and in this case a layer of fat under the skin
plays the role of temperature regulator. Some aquatic
mammals such as seals possess both a well-developed
fur fibre and a considerable layer of fat.
The hydrophobic nature of keratin preserves the
skin from direct contact with water.
15.2.4 Keratin
Keratin is the generic term applied to chemically
related resilient protein materials including hair,
scale, hoof, horn, nail, claw, beak and feathers.
Proteins are materials formed by amino acids
linking together to form complex high molecular
weight natural polymers.
A typical protein chain may be represented by
ˆNHˆCHR1
ˆCO.NH.CHR2
.CO.NH.CHR3
.COˆ
where R may be the same or different organic
radical. It is the type and distribution of these different
organic radicals which gives each individual
protein or group of proteins their characteristic
properties.
The amino acid composition of the keratins is
complex and has been described by Vincent (1978).
All keratins contain significant amounts of the
diamino acid cystine, which enables the formation
Furs and furriery: history, techniques and conservation 149
of particularly stable covalent chemical linkages
between adjacent protein chains of the material.
| |
CH.CH2SˆS.CH2.CH
| |
Chain 1 Chain 2
Keratin can therefore be considered a long chain protein
that owes much of its properties to the disulphide
bond of cystine. A typical molecular weight of the
individual keratin chains varies from 2000 to 12000.
The disulphide link SˆS between adjacent
polypeptide chains also accounts for the complete
insolubility of keratin in polar solvents, and its
limited lateral swelling and high wet strength.
In addition to the strong covalent disulphide links
there are a large number of relatively weak hydrogen
bonds between adjacent protein chains. Most hydrogen
bonds are disrupted at temperatures between 40
and 60°C, which is why heat or steam can successfully
be used to relax keratin enabling it or objects
made from it to be shaped or moulded. Keratin is
remarkably chemically stable to changes in relative
humidity (RH) and not easily damaged by chemical
attack. It is, however, damaged by strong acids and
alkalis and reducing agents and is particularly vulnerable
to poor handling practices and insect attack.
The keratins are subdivided into two groups: soft
keratins (epidermis or skin layer) containing low
levels of sulphur and hard keratins (hair, horn, etc.)
containing more than 3% sulphur. The roots of the
hair are more susceptible to chemical attack than the
mature fibres because some of the cystine has not
yet formed crosslinks and still exists as side chains.
15.2.5 Morphology of hair
Each hair is composed of three sections, the shaft,
the root and the bulb. Hairs are formed from the
epidermis. In the place where the hair is to appear,
the epidermis becomes thicker and forms an indentation.
This deepens into the derma to constitute a
follicle. Hairs are always fixed obliquely in the surface
of the skin and can be straightened, in life, by the
contraction of the small muscles (erector pili) which
are attached to the follicle. These come into effect
when the animal is attacked or afraid. When the
contraction ends, elastic fibres (elastin) surrounding
the sheath of the hair return it to its original position.
Cold operates in the opposite direction, realigning
hairs so as to increase the volume of air trapped
between them and thus diminish heat loss from
the body.
The character and appearance of hair fibres differ
from species to species and also within the same
animal.
Hair, examined under the microscope, is formed
of three distinct layers: cuticle or exterior, corticle
or cortex and medulla (Figure 15.2).
15.2.5.1 Cuticle
The cuticle is formed in small scales and is composed
of horny flat cells. The form of the cells varies
according to the species and also according to the
type of hair, e.g. guard hairs or fur. The disposition
of scales may differ from root to tip.
(a) Scales may surround the shaft completely in
ring form, the upper part of the scale covering
the lower part of their scale directly above it.
This type of structure is more often encountered
in soft underfur.
(b) Scales do not entirely surround the shaft but
have the same form covering one another. This
usually occurs in guard hairs, which are generally
more lustrous than those of the first category (a).
(c) Scales may be placed side by side without overlapping.
This occurs usually in ‘feeler’ hairs.
150 Conservation of leather and related materials
Cuticle
Cortex
Medulla
Cuticular scale
Pigment granules
Figure 15.2 Diagram showing morphology of hair.
The cuticle preserves the interior of the hair from
destructive action. The lustre of the hair depends
upon scale structure. The system of cuticle cells
forming the imbricate (overlapping) surface of animal
hair is responsible for the greater resistance to motion
in tip to root direction. Gloss/lustre is dependent on
the degree of light reflectance from the surface of the
fibres and is highly prized by the furrier as a measure
of quality. Two factors are involved, (a) the structure
of the scales of the individual fibres, and (b) the parallelism
of the fibres as a whole. If the fur fibres are
untidy and run in random directions, light is scattered
upon the surface and the fur looks dull, while if
the fibres lie straight and parallel a good gloss is
obtained.
15.2.5.2 Cortex
Below the cuticle lies the corticle layer, which consists
of cells composed of fibrils and microfibrils in an
amorphous matrix. The cells are positioned along
the axis of the fibre and are surrounded by cementing
material composed of amorphous keratin. The
cells themselves are crystalline in form and constitute
about a quarter of the total material. The thickness
of the cortex varies with the species. In the hair seal
96% of the total diameter of the fibre is cortex, in the
squirrel 34% and in reindeer hair it is absent entirely.
The resistance of hairs depends on the development
of the cortex. The outstanding feature of poor wear
is a high percentage of medulla, with very little or
no cortex and little cuticular layer. Reindeer hair is
therefore very brittle while hair seal is very resistant.
15.2.5.3 Medulla
In the interior of the cortex there is usually the
medulla composed of polyhedral cells, which may
also enclose pigment cells and bubbles of air. The
diameter of the medulla varies according to the
dimensions of the hair shaft and often the medulla is
absent from the tip. In underfur the medulla is less
well developed than in guard hair. Some hairs have
no medulla at all.
The results of chemical treatments and dye absorption
will to a large part be determined by the properties
of these histological phases (Kaplan, 1971).
Pigment granules are distributed in the cortex
and sometimes in the medulla of most animal fibres,
and are responsible for the wide and varied range of
colours of fur-bearing mammals. These granules are
protein and known as melanin. The colour of the
pigment may appear as black, brown, reddish-brown,
yellow or red. The pigment is insoluble in most solvents
and is resistant to concentrated acids but may
be dissolved in alkalis. It is the distribution and
quantity of the pigment together with the colourless
air bubbles in the hair fibre, which account for
the wide variation of hair colour in animals. The
colour is partly due to pigmentation and partly light
interference.
15.2.6 Fur-skin dressing
15.2.6.1 Introduction
Very little has been written on the subject of fur
preparation and finding detailed information about
the practical aspects of fur dressing and furriery
requires a long literature search for the conservator
who may have to treat fur in the course of their professional
activities. The fur trade has been in decline
for a quarter of a century and although it is now on
the increase due to an upturn in the fashionable status
of fur, the militant stance taken by many anti-fur
protesters has made it is almost impossible to find a
furrier to talk with in person about the subject.
The author has found only five books published
in English which describe in detail the methods
involved with the processing of furs (Austin, 1922;
Kaplan, 1971; Rosenberg, c.1920; Bacharach, 1930;
Samet 1950). There are also a few publications
in Russian and German (Pense, 1955; Hahn and
Weigelt, 1967). All of these were published prior to
1971.
15.2.6.2 Dressing
For in-depth descriptions of the processes of fur
dressing I refer the reader to Kaplan (1971); Austin
(1922) and Bacharach (1930). The following, however,
is an introduction for the conservator who will
need to know something of the methods used for
fur preparation and dyeing, especially during the last
two centuries: this being the most likely era from
which furs will date that the conservator has to treat.
Awareness of these processes will enable the conservator
to understand the likely degradation processes to
expect and also help them work out a suitable and
compatible method of cleaning and further treatment.
The priority in fur-skin dressing is the preservation
of the fur properties but as the skin and fur are
inseparable all processes must be compatible to both
and not cause damage to either.
The dressing must be sufficiently permanent to
withstand the wetting and drying processes used in
Furs and furriery: history, techniques and conservation 151
the manufacture of fur garments and accessories and
the end result should be a supple, pliable skin, of
good tensile strength to hold the stitching. The
dressing should not be too heavy, nor should it be
elastic so the skin holds its shape after stretching,
and the natural gloss, colour and quality of the fur
should be maintained. The fur and skin should be
able to withstand normal wear and storage and
subsequent cleaning by accepted fur trade methods
(Kaplan, 1971).
15.2.6.3 Soaking
Fur-skins arrive at the skin dresser in a raw dry state,
either opened flat, an incision having been made
down the centre of the flank, or cased, the skin having
been removed by cutting across the rump and
hind paws then peeling the skin off. Some may have
been salted. Most of the adhering fatty tissue has
been scraped away before drying. The first operation
is soaking to restore to the dried collagen
approximately the amount of water it had in life and
ready the skins for the mechanical and chemical
treatments to follow. Salt is added to the soak. Some
longhaired fur-skins are not immersed but are wetted
by applying water or salt solution to the raw pelt
either by brushing or by means of a poultice of wet
sawdust. Skins may need to be ‘drummed’ (treated
in a revolving drum) after soaking in order to remove
excess water prior to fleshing. They may also need
‘caging’ (treated in a revolving cage to free them
from the sawdust).
15.2.6.4 Fleshing
The next stage is fleshing: the removal of the thin
protein membrane layer which separates the skin
proper from the fat layers and organs of the body. In
the past this was done by hand working the skins
over a curved knife for small skins or over a beam for
larger skins. Today this process is done by mechanical
blades but still requires a skilled operator. It is
important to remove this layer as it is not readily
permeable and could inhibit the following chemical
treatments. Great care has to be given to this process
as cutting too deep will expose the roots of the hair
and this will lead to hair loss at a later stage.
15.2.6.5 Unhairing
The process of mechanical unhairing is resorted to
in the case of skins possessing longer top hairs purely
for the purpose of improving the general appearance
of such skins. The types of skins which undergo this
process are beavers, seals, otters and nutria. These
have a growth of hair which is pulled leaving the
underfur. In such cases the pile becomes shorter and
closer.
15.2.6.6 Pickling
The fleshed fur-skin is now ready for the chemical
treatment, which is the basis of skin dressing. Pickling
prevents bacterial attack and contributes to the
hydrolytic breakdown of the non-collagen interfibrillary
material within the skin structure. The oldest
and best-known method of pickling is the use of
‘Leipzig dressing’. This is a mixture of sulphuric
acid and salt, and replaced the earlier method of
treating with a mixture of organic acids derived
from fermenting bran. This pickle may be applied
to fur-skin either by immersion in vats or by brush.
Immersion has the disadvantage of leaving the hair
in an acid state and if left with an excess of acid
remaining in the pelt, there is a danger that over time
it will be damaged. It is customary to add ammonia
to the oil at the oiling stage to neutralize the excess
acid. The brush method is usually used for longhaired
fur-skins. Other acids may also be used for
pickling, i.e. formic, acetic, lactic and glycollic.
Kaplan, writing in 1971, commented that due to the
risks involved with sulphuric acid it was replaced
with safer organic acids (Kaplan, 1971). Kaplan also
comments that fur-skins dressed using an acid pickle
are light and soft but will dry hard if they later
become wet and are subsequently dried. Furthermore
he comments that acid pickling is useful for
opening up the collagen fibres but that a water stable
dressing must be used in the subsequent treatment.
An alternative pickling method is to use an alum
pickle. This gives a more resistant leather and is less
stretchy. Aluminium salts do not enter stable combinations
with collagen, unlike chrome salts. Solutions
of alum or aluminium sulphate with salt are used
and the skins are usually treated by soaking in vats.
Formaldehyde produces a dressing which is not
reversed by soaking in water but it was not until the
1920s that this was used in fur-skin dressing. It is
used in conjunction with other dressings.
15.2.6.7 Chrome tanning
Chrome is only used for processing fur-skins in special
cases. Chrome-tanned fur-skins have a higher
shrinkage temperature than any other type of dressing,
they are resistant to bacterial attack, are durable
and may be prepared with considerable softness and
pliability. They do not, however, have the correct
152 Conservation of leather and related materials
‘handle’ for the fur trade. Chrome-tanned skins are
thicker and heavier than acid- or alum-dressed skins
and have less stretch when damped. Chrome also
imparts a blue/green tone to the skin and fur, and
renders them unsuitable for bleaching with hydrogen
peroxide. It is therefore rarely used except in
cases where they will be dyed with acid or other
textile dyes in the temperature range of 60 –80°C,
which is well above the shrinkage temperature of
acid or alum dressing (Kaplan, 1971).
Chrome is now generally used for sheepskins
with the wool on or for processing deerskin.
15.2.6.8 Oiling
The last process of fur dressing, prior to dyeing, is
oiling. Its purpose is to lubricate and prevent adhesion
between the fibres of the pelt substance during
the drying of the wet pickled fur-skin. Mechanical
milling or ‘kicking’ follows the application of oil or
fat to the pelt. This is the more modern method
replacing ‘foot tubbing’. It is essential that all parts
of the pelt are lubricated and the penetration and
distribution of the oil have a profound effect on the
handle and physical properties of the dressing. The
final part of the dressing process involves mechanical
treatments to remove excess oil from the fur and
the pelt and the stretching of the pelt. The skins are
(‘drummed’) treated with dry sawdust in large
revolving drums and then (‘caged’) treated in revolving
cages as part of this mechanical process.
15.2.6.9 Beating
Beating the furs may follow which involves beating
them with rattan canes to remove the last of the
dust. This process may be carried out by machine or
by hand. Beating may be done as part of fur processing
but it is also done by furriers as part of routine
maintenance of furs. The reason is not only to
remove dust but also to free the fur fibres, breaking
up the adherence of one fibre to another.
It is a process to be carried out with sensitivity as
the ferocity of beating a strong pelted fur such as
seal would undoubtedly do harm to a delicate fur
such as chinchilla. The rhythm of hand beating was
described to the author by a furrier as being like a
paradiddle which is a basic drum roll of alternate
double beats.
15.2.7 Dyeing
The process of dyeing furs is covered in depth by
Austin but for the conservator I have included a
brief introduction (Austin, 1922). Austin states:
‘Natural furs of the more valuable kinds are above
comparison with the majority of dyed furs.’
However, natural colours are not always in fashion
and also show wide differences in individuals
from the same species or may be of uneven colouring
within one individual. Usually the purpose of
dyeing fur-skins is to improve their appearance and
hence the value. Occasionally furs are dyed in high
colours – red, yellow, blue and green – in order to
accommodate the demand of fashion, for example
the fun furs which appeared in 1966 in order to
bring fur to the fashion conscious young. These
were most often rabbit but ermine, white fox, beaver,
hare, lamb, kid, and squirrel have also been dyed a
wide range of colours according to the demands of
fashion.
About two thirds to three quarters of furs are
dyed. Some such as fisher, leopard and ocelot are
never dyed and others such as Persian lamb, astrakhan
and caracul are always dyed (Kaplan, 1971; Austin,
1922).
Many of the more valuable furs are ‘blended’ by
skilled application of fast dyes by hand to the tips of
the hair only, in order to even out the colour differences
and visually blend them together.
Many of the cheaper furs have been dyed and
otherwise treated (plucked, sheared, etc.) to imitate
furs of the rarer and more costly kind. Marmot, red
fox, rabbit, hare, muskrat, squirrel, opossum, and
racoon have all been used to imitate others such as
mink, sable, marten, seal, chinchilla.
Dyeing furs is a complex process as the hair and
pelt have the capacity to take up dye differently with
the pelt absorbing dye much more readily than the
hair. Different hair types also respond to dye differently
with the top hair being more resistant to taking
up dye than the underfur. The lustre of the hair
can easily be adversely affected by harsh chemicals
and dyestuffs and the temperature of the dyebath
must not be greater than 35°C in most cases as the
pelt will shrink and dry hard. The shrinkage temperature
of collagen must be considered for all
processes where heat is involved and the dye
method used must not extract any of the chemical
or other materials used in the initial skin dressing.
The dyes also need to have good light fastness and
resistance to rubbing.
Traditionally furs are dyed by the brush process
whereby only the tips of the upper part of the hair
are coloured, or by dipping where the entire fur
including the leather is dyed. In many cases the use
of both methods is necessary as dipping serves to
Furs and furriery: history, techniques and conservation 153
give the overall required colour and then tipping
refines this by treating only the upper part of the hairs.
There are three stages to the dyeing process:
1. Killing.
2. Mordanting.
3. Dyeing or colouring.
15.2.7.1 Killing
The purpose of killing is to render the fur fibre more
receptive to subsequent mordants and dyes. Affinity
for dye particles and salt solutions varies from fibre
to fibre. The underfur is more receptive than the
guard hair and the hair tips of the underfur are more
resistant than the basal part. The horny nature of the
keratin fibre has much to do with this. The surface
of the hair is also covered with a fine coat of fatty
material which renders the hair impervious to dye
solutions. Alkaline solutions may be used to degrease
the hair and to reduce these differences of affinity by
hydrolytic breakdown of the cystine SˆS linkages.
Modern killing treatments also include oxydizing
agents or reducing agents as an alternative.
15.2.7.2 Mordanting
Pretreatment of fur-skins with metallic salts is one of
the oldest dyeing techniques. It is accepted as a general
rule with certain exceptions that colours produced
on mordanted fur-skins are faster than on
unmordanted. In addition, dyeings on mordanted
fur-skins are more intensive and require less dyestuff.
15.2.7.3 Dyeing or colouring
Four classes of dyes or colouring materials are used
in fur-skin dyeing:
1. Vegetable or ‘wood’ dyes; materials of plant origin.
2. Mineral or inorganic dyes, which depend upon the
precipitation of pigmented metallic compounds.
3. Oxidation or true fur dyes; organic synthetic
intermediates (Ursol D to dye black was first
marketed about 1894).
4. High-temperature dyes; those borrowed from
the textile field and applied at temperatures
above those of oxidation dyes and belonging to a
range selected from acid, basic, vat, pre-metallized
and disperse dyes.
15.2.8 Finishing
After the furs have gone through the dyeing process
they are dried and finished. Finishing may involve
the application of a salt solution to the backs of the
skins in order to replace some of the salt lost during
the dyeing. They may also be re-oiled prior to
drumming with sawdust or sand. Drumming is an
important operation in the finishing as the hair
receives a polish and the full lustre and brilliancy of
the colour is brought out. The final action of finishing
is to stretch the furs and render them soft and
flexible.
15.2.9 Pointing
Pointing is a process which may have been carried
out to any of the silky longhaired furs which have
been dyed black, but is usually associated with fox.
In this process the furs are artificially supplied with
the silvery hairs of the badger to simulate the
appearance of a natural silver fox. Bachrach (1930)
states the process involves individually inserting hairs
using a strong waterproof glue. One, two or three
hairs are inserted at a time with single-hair work
being the most time consuming and therefore
reserved for the best skins of highest value. The
basal end of the badger hair is dipped into the glue,
and blowing aside the fur fibre the end is set as low
as possible into the peltry near the skin. The author
has found no record of the glue recipe but most
likely hide glue was used possibly with the addition
of formaldehyde to crosslink the glue and make it
insoluble in water (Figure 15.3).
Conservators should be sure to identify furs
which have been pointed prior to carrying out any
cleaning.
15.2.10 Making up into garments or
accessories
The manufacture of a fur-skin garment involves selection
and matching of skins for quality and colour, cutting
the individual skins to appropriate size and shape,
sewing the skins together, damping the pelts to enable
the sewn skins to be stretched to flatten the seams and
ease them exactly into the pattern shape required,
nailing or tacking on wooden boards to retain that
shape, drying them, drumming and caging them, then
‘closing’, which means assembling, interlining, finishing
and lining the completed garment.
A cutter, a machinist, a finisher and a liner are all
involved with the making of a fur garment. All are
highly skilled but it is the skill of the cutter which is
all-important. Cutting is complex work and the
skins of each individual species of animal may be cut
and seamed in a way that differs from all the others,
although there are similarities between them all.
154 Conservation of leather and related materials
Rosenberg describes these variations for over
60 of the most popular species but I include here a
summary of the basic idea behind the art of cutting
(Rosenberg, c.1920).
The process of making up starts with a pattern, in
the same manner as making any other garment.
The cutter opens the skins by cutting them
through the flank or belly. They are then damped
and stretched out flat by hand, then trimmed by
having the poor parts, such as heads, paws and sides,
cut away. The fur varies from flatness and thinness at
the head to fullness and density at the rump. It
grows shorter the further it gets from the centre of
the back until the belly or side is hardly covered.
The more that is cut out the better will be the general
appearance and evenness of the finished garment.
It will also wear better.
There are two main systems of working which
the skins may have undergone in order to manipulate
them and join them together in the making of a
garment. The first is the ‘skin on skin’ system and
the second is ‘dropping’ or ‘stranding’. The purpose
of both is to obtain the necessary length of material
required for the garment with the minimum of horizontal
seams. An excess of these seams compared to
the usual number required for a particular fur is
regarded as a fault. Some skins such as leopard or seal
are often long enough to be made up without a join.
This author has not found any references to a
likely time when ‘stranding’ was introduced and the
technique developed as a method for joining pelts
together. Logically, the likelihood is that it was
developed after the mid-nineteenth century when
fur first began to be used as the outside material for
garments, rather than for linings and trimmings
only; and from a practical point of view it is likely
to date from about 1900 when fur sewing machines
were developed. The enormous amount of sewing
involved in stranding pelts to make a coat would
have been impractical in labour costs and time to
undertake totally by hand sewing.
The only mid-nineteenth century mink coat
examined by the author to date used the ‘skin on
skin’ method for joining the pelts.
15.2.10.1 Skin on skin
This method was used where the skins were too
small to be stranded and such an expensive and
time-consuming process was not justified. The
joining of two skins one above the other means that
rump is joined to head. As the hair on the rump is
longer than that on the head it follows that the join
will show.
The skill of the cutter is to contrive a seam that
will show as little as possible (Figure 15.4).
15.2.10.2 Dropping or stranding
The second method of joining skins manages to
avoid cross-seams altogether and it is a method used
for the more expensive skins, the value of which
will justify the extra work and expense involved. It
enables the ideal of long, slender, strands to be
achieved from short, wide skins.
The skin is cut vertically down the centre and the
cutting proceeds on one of its two halves. Working
on one of these halves the first cut is made diagonally
from the side of the skin to the centre, that is
to say from the left edge of the skin running down
to the right edge if it is the left half being dealt with,
and from the right edge to the left edge if it is the
other half. The cut starts not at the extreme edge of
the skin but sufficiently within it to prevent the two
parts, severed by this first cut, falling apart and it
ends the same way just before reaching the edge.
A second cut is made parallel to the first cut but
6mm (a quarter of an inch) below it: then another
and another until the bottom of the skin is reached.
Furs and furriery: history, techniques and conservation 155
Figure 15.3 Detail showing pointing.
Depending on the length of the finished strand
required, a piece from another skin can be grafted in
or if a shorter strand is required then a section of the
cut skin may be removed before machining so
exactly the right length can be achieved. Next the
cut skin is passed to the fur machinist (Figure 15.5).
15.2.10.3 Sewing
A fur sewing machine is not at all like a household
sewing machine and is specially designed for the
purpose of sewing fur. It has an electric motor and
two pedals, one to switch the motor on and off and
the other leading to one of the two round cups
approximately 6cm in diameter which are mounted
horizontally in front of the machine. When the
pedal is depressed the cup is brought slightly forward
and when released the cup springs back in contact
with the other cup which is fixed to the machine.
The machinist completes the cutting of the first
strip at both edges and the skin falls into three parts
(the upper part, the strip and the lower part). The
lower part is put aside and the upper part and first
strip are retained. These two parts of the skin are
pressed together again, hair side inside, ready to sew
along the cut but the first strip is slid 8mm (threeeighths
of an inch) downwards towards the lower
edge of the cut. The two pieces are inserted between
the cups which having milled edges hold the fur
securely. The edges of the fur protrude above the
cups and as the machine is set in motion the fur
pieces are driven through the machine and the
edges are oversewn. At the same time the fur itself
is prevented from springing out from between the
cut edges by means of a pin used to press it down
(Figure 15.6).
When the strip of fur has been sewn back to its
original position but 8mm further down this constitutes
the first ‘drop’. The effect has been to make
the skin a fraction longer without moving any hair
more than 8mm from its original position. Once all
the ‘drops’ have been sewn the end result will be to
have lengthened the skin considerably but it will be
156 Conservation of leather and related materials
Figure 15.4 Detail showing skin on skin method of
joining furs.
Figure 15.5 Detail showing stranding.
Figure 15.6 Detail showing fur sewing machine.
(Courtesy Stephen Kirsch)
much narrower. Once the second half has been
treated the same way and these two halves finally
joined together again then a long elegant strand will
have been completed.
Some strands will need to be made curved and
others made shorter in order to fit into the garment
pattern but it is the responsibility of the cutter to
place his cuts in such a position that they produce
the necessary shape and size strands that when they
are all fitted together they will make the finished
garment according to the pattern set out.
Once all the strands have been joined together to
make the various pattern pieces the raised seams
must be flattened and the creases and wrinkles
smoothed out. This process involves laying out the
pieces pelt side uppermost on a board, wetting out
the skin with water and then stretching the pelts and
nailing them into position. Wetting will shrink back
the pelts and the stretching and nailing process
enables all wrinkles to be pulled out and the seams
flattened as the pelts are pulled back to size and
shape and pinned or nailed in place before being left
to dry.
After drying the hair looks flattened so the next
process is to drum the pieces for an hour in sawdust
to restore the appearance of the fur. The type of
sawdust is important and neither oak nor pine is
suitable. Oak because of its high tannin content
which in the presence of traces of iron could lead to
staining of the fur, and pine because its resinous
nature could cause stickiness. Beech, birch or poplar
is used. The moisture content is particularly important
as dry fur fibres, if subjected to mechanical friction,
will develop static electrical charges and will
cling together. In the presence of oily materials
matting may take place and in extreme conditions
felting could occur. For these reasons the moisture
content of fur should not be allowed to drop below
its natural regain of 10 –12%.
Finally the pieces are interlined, usually with
domette, assembled and joined together, and then the
garment is lined and finished (Figures 15.7 and 15.8).
15.2.11 Plates and crosses
Offcuts and fragments of fur-skins left over after the
best parts have been utilized are not discarded.
These fragments may be the trimmed-away parts
left over, or from parts of the animal of less use, i.e.
ears, leg pieces, paws, underparts of the neck, etc.
These are sometimes sewn together to make crosses
or plates of fur. These large pieces made from the
tiny fragments are used in the manufacture of lower
Furs and furriery: history, techniques and conservation 157
Figure 15.7 Detail showing lining and interlining layers.
Figure 15.8 Ermine evening coat c.1935–37 French
(Paris) (T.272-1976). (Courtesy V and A Images)
priced garments and for linings. In China it is customary
to sew these into the shape of a Greek cross.
The reason being that it can quickly be manufactured
into a garment by doubling it over in half and
sewing along the sides and under the arms of the
cross which will form the sleeves (Bachrach, 1930).
The lining of a Chinese kesi robe discussed in
Section 15.3 was most likely made in this way (Kite,
1991).
15.3 Conservation and care
15.3.1 Introduction
Few pre-nineteenth century furs from fashionable
dress survive due to the ravages of moths, but from
whatever date the object originates it is important to
identify the species of animals used. It is possible that
this information is not included in the registered
description of the object.
Important items of dress made from expensive fabrics
are frequently altered during their useful lives and
an out-of-fashion fur coat may have been altered and
refashioned by a skilled furrier into a more up-todate
style. Due to the high cost of the better quality
furs this was not and still is not an uncommon practice.
Detecting evidence of such alterations in furs is
much more difficult for the conservator or historian
than it is to detect in a textile garment, and it is likely
to be almost impossible without having access to the
back of the skins to see the process of sewing and
joining the pelts. It is likely that it is only the conservator,
during the course of repair treatments, who
will have the opportunity to see the backs of the
skins. Conservators should therefore be aware of this
possibility and attentive to notice any signs of alterations.
Additional information regarding the quality
of the garment, or origin of the skins, may also be
found once the backs of the skins are examined and
the cutting and arrangement of pieces can be seen.
Skins in the raw state are often marked with distinctive
signs to indicate their place of origin. Sometimes
owner’s initials or trademarks have been used. The
Hudson’s Bay Company used a range of initials to
indicate the place of origin or province from where
the animals were trapped which served to indicate to
buyers the character of the pelts (Rosenberg, c.1920).
Fur dressers and dyers also marked the skins. If discovered
by the conservator in the process of their
work, these marks should be recorded and retained.
It is also important to note that while sewing
machines were pioneered in 1844 and in use from
the 1850s, the fur sewing machine did not come
into being until 1900, so although the linings of fur
garments were machine sewn before this date, the
fur-skins were not. Examination of the methods of
skin preparation and sewing, style and cut, as well as
knowledge of species availability, is therefore essential
in order to date a fur garment accurately.
A furrier will clean and repair damaged fur garments
in very different ways from those used by
conservators. Methods employed by the furrier
include cleaning by tumbling in drums with sawdust
impregnated with white spirit or hydrocarbon solvents
(historically, the aromatic hydrocarbon benzene,
C6H6, was used), removal of damaged areas of
skin or whole skins and replacement with new, possibly
redyeing or ‘blending’ and then refinishing with
the use of warm irons or gums to bring back the lustre
of the fur.
These are not the options available to the conservator
when dealing with museum objects and
potentially brittle, degraded fur-skins. Museum
codes of ethics and practice which govern conservators’
professional conduct make such interventions
unacceptable, also it is likely that replacement skins
to match would not be easily available and totally
unavailable under any circumstances if the item
concerned had been made from animals from a now
endangered and protected species.
A fur garment is an object which may have an
important provenance or historic significance in its
own right. Damage and evidence of use and wear
are as important in furs which have been taken into
museum collections as any other fashion item.
15.3.2 Species identification
Species identification is difficult but if it is not obvious
by the appearance of the fur and a furrier cannot
be consulted or is not familiar with a species
used in an object which might be over 150 years
old, then identification may be done with reference
to the morphology of the hair. The scale pattern and
cross-section of hair fibres differ from species to
species, so microscopic examination of a crosssection
and scale pattern may help. However, the
morphology of hair will differ within the same species
and within an individual animal so good comparative
reference materials are essential and a conclusive
result may not be obtained easily. Reference to the
following publications may be of assistance to the
conservator when attempting species identification
of furs (Blazej et al., 1989; Novak, 1987; Rogers
et al., 1989; Appleyard, 1978; Brunner, 1974).
158 Conservation of leather and related materials
Recently a method has been developed using
mass spectrometry to identify the amino acid
combination of each animal species (Liska and
Shevchenco, 2003). The method relies on good
comparative material and is currently being used by
customs officials to identify illegally taken examples
of threatened and endangered species. When further
developed and the operational time has been
reduced it will prove invaluable and a quick method
to use, and may also be of use to museum curators
and conservators for a positive species identification
of materials from animal sources.
15.3.3 Damage
The damage a conservator is likely to encounter in
furs in museum collections includes:
(a) General soiling due to use, which may include
soiling and staining with foodstuffs, make-up,
sweat or skin grease before the object was
acquired; linings may be particularly soiled
around the neckline.
(b) Surface soiling due to an accumulation of dust,
and atmospheric pollution, acquired in the
domestic environment during a long period of
inappropriate storage before the object came
into a collection, or due to years of display in
unsealed cases in the museum environment.
(c) Wear due to excessive use during the pre-accession
life of the object resulting in bald areas on the
pelts.
(d) Tears due to accidental damage during wear or
due to poor handling after the fur had reached a
fragile and unsound state.
(e) Chemical damage or physical damage occurring
during skin processing, the effects of which only
become apparent with the passage of time; this
includes rare but known occasions where the
skin has been pared away too deeply during
fleshing leading to hair loss. It also includes furs
made from pelts taken early in the season when
the animal had not completed the growing of
the winter coat and the bulbs of the guard hair
roots come through the skin. This will result in
loss of some of these guard hairs during the
dressing process and the fur will have a scanty
appearance.
(f ) Chemical damage due to the use of inappropriate
insecticides. Camphor, naphthalene and PDB
(para-dichlorobenzene) are harmful to some
colours if used with dyed skins. Naphthalene and
PDB are known to have been used in museums as
insect inhibitors until the 1970s–1980s, the use
of which may be the cause of damage now or in
the future.
(g) Light damage leading to the fading of colours or
to the yellowing of natural white peltries such as
ermine and fox.
(h) Environmental damage, poor or inappropriate
storage methods (too hot, too dry, too damp)
leading to shrinkage, hair loss, embrittlement,
mould and other damage to the pelts.
(i) Insect damage caused by moths (Tinea and Tineola
sp.) or carpet beetles (Anthrenus and Attagenus sp.).
( j) Damage to linings, either through use and wear
or due to the degradation of the lining fabric.
Silk and synthetic materials have been used for
the linings of fur garments.
15.3.4 Conservation methods
Conservation methods used to treat furs must take
into account the properties of both hair and skin
materials and what has already been done to them
during the course of the fur-skin processing and
dyeing. When considering items of dress, the linings
and any additional trimmings or components of the
object must also be taken into account and these
may need treating separately, either in situ or they
may need to be removed for treatment.
Ethically, stitching should not be unpicked unless
absolutely necessary, following usual conservation
practice; but it must be kept in mind that in many
cases where repair to skins in items of dress is
required then access to the back of the skin will be
necessary in order to carry out the repair. This will
mean that unpicking stitching and resewing parts of
the lining and interlining will be unavoidable.
Before any treatment is undertaken, and the
background information concerning date and possible
provenance has been noted, the fur and skin
should be examined closely from the hair side. If
there is a smell of naphthalene (mothballs) this
should be recorded.
By looking through the hair to the skin it may
be possible to tell if the pelt has been dyed. It
may not, however, be detectable other than by an
expert furrier if the hair has been surface dyed or
blended.
It is useful for the conservator having identified
the species to know what are the natural colours of
the animals concerned. If a fur is an unusual colour
for a species or has been prepared to look like a different
species, e.g. muskrat to look like mink, then
it is reasonable to assume that the pelt has been
dyed.
Furs and furriery: history, techniques and conservation 159
15.3.4.1 Cleaning
Clean fur should be lustrous, so a dull appearance and
an unpleasantly dry or a greasy feel to the fur will
indicate that it is dirty or dusty. Providing there is not
an overall shedding of the hair, a light vacuuming of
the fur using low suction and a protective layer of
muslin or net over the nozzle of the vacuum will
remove surface dust and particulate soiling. Light
brushing may also help dislodge particulate soils and
insect frass which tends to get trapped at the roots of
the hairs and is difficult to remove. If the fur has a
greasy feel or there are localized areas of soiling then
solvent cleaning may be carried out providing a fume
chamber or other appropriate extraction facility is
available. Working always in the direction of the hair,
swabbing with white spirit BS 245 or Stoddard solvent
or petroleum spirit is a useful method of removing
surface soiling. The fur should be colour tested
before such cleaning to ensure that if it has been dyed
the dye is stable in the solvent. The fur should not be
soaked with solvent but gently stroked with a solventsoaked
swab lifting off the soiling as work progresses.
It may be possible to place absorbent paper below each
section of hair to be cleaned and to swab out directly
onto this. The fur should be well blotted to remove
excess solvent and to speed drying. A large item may
need to be treated in sections. An arctic fox fur lining
of a large Chinese kesi robe, c.1800, was cleaned in this
manner (Kite, 1991). Where fur garments have textile
linings which require solvent cleaning, the conservator
may prefer to clean the lining and the fur as two separate
procedures, completing the cleaning of the lining
and allowing the solvent to evaporate before cleaning
the fur.
Another method of cleaning has been described
by Del Re using Stoddard solvent and Vulpex, a
spirit soluble soap (Del Re, 1988). This was used for
cleaning particularly soiled ermine.
Keratin is stable in polar solvents but if a mixture
of deionized water and detergent, or water and IMS
(industrial methylated spirit, ethanol and 4%
methanol) or IMS alone is used to clean the fur then
care must be taken to avoid wetting the skin. Tests
must be carried out prior to treatment to ensure
that dye is not soluble in whatever solvent is chosen.
A particularly soiled bearskin from the uniform of a
colonel of the Grenadier Guards was cleaned by sectioning
the hair and locally swabbing each tuft onto
absorbent paper. First, deionized water was used,
followed by a 1% solution of non-ionic detergent,
and then to rinse, deionized water was swabbed
through followed by a 50:50 mixture of water and
IMS. This last mixture was used to remove any
remaining soiling. Finally each tuft was swabbed
with IMS alone to help remove excess water. Each
tuft was then blotted thoroughly, combed and
allowed to dry naturally (Kite, 1990). Fur, which
has been cleaned using aqueous treatments, may be
dried using a cool air blower. On no account should
heat or hot air be used.
15.3.4.2 Repair methods
A full-piled skin usually possesses a thin pelt while a
thin-haired skin possesses a thick pelt. This guide is
useful to the conservator, and if the skin is aged, dry
and damaged may provide an indication to the overall
strength and fragility of the skin.
A sewn repair to a torn skin is unlikely to be an
option for the conservator working with fur garments
of fashionable dress so the choice of adhesive
and support material must be made with the nature
of the skin in mind. The adhesive must not penetrate
and impregnate the skin but it must be strong
enough to hold firmly to the back of the skin and
not peel away when the skin is flexed. The shrinkage
temperature of the collagen must be kept in
mind when a heat-set adhesive is chosen, and an
aqueous adhesive must be able to be used in a form
that does not allow the skin to become wet as there
is a risk of shrinkage and hardening on drying. The
adhesive should also be stable, non-yellowing and
able to be removed should the support need to be
taken off and the repair redone at a later date. The
support material should be strong, light and flexible
and ideally have a multi-directional non-woven structure,
compatible with the multi-directional arrangement
of the collagen fibres of the skin. Leather, gold
beater skin, Japanese tissue (kozo mulberry fibre and
mitsumata Edgeworthia papyrifera papers), Holytex,
Reemay, Tetex, Pellon, Cerex and nylon gossamer
have all been used as support materials for adhesive
methods of skin repair.
The adhesives chosen for skin repairs have included
Beva 371 (ethylene vinyl acetate), wheat starch paste,
a wheat starch paste with the addition of sodium alginate,
isinglass (sturgeon glue), Lascaux 360HV and
Lascaux 498HV (butyl-methacrylate dispersion
thickened with acrylic butyl-ester), Jade 454 and Jade
403 (polyvinyl acetate emulsion), Apretan MB Extra
(formerly Mowilith DMC2 polyvinyl acetate emulsion),
and PVA-AYF (polyvinyl acetate solution).
Several papers have been published describing
adhesive methods of repair of skins including
Lougheed et al. (1983), Dignard and Gordon (1999),
160 Conservation of leather and related materials
Dickens (1987), Kite (1990, 1991, 1999), Rae and
Wills (2002) and Richardson (2002).
Only a few, however, relate to fur items of fashionable
dress made up as described in Section 15.2
(Kite, 1990, 1991; Dignard and Gordon, 1999).
In order to carry out an adhesive repair on fur
garments of fashionable dress, usually access has to
be gained to the back of the skins. Although possible
to work from the front, inserting a patch, the
author believes that a more satisfactory result will usually
be achieved if access can be gained to the back of
the pelt. Knowing the construction of linings and
interlinings will help the conservator gauge the
amount of work needed and time to be allocated in
order to unpick stitching of these and then resew
them after the repairs have been made to the skins.
Linings may also need cleaning and repair and in the
worst cases of soiling and damage may need to be
removed, cleaned and repaired separately before
resewing into the garment.
15.3.5 Two case histories illustrating
methods
Two case histories reduced from their original published
form are included here to illustrate particular
conservation problems involving fur and the methods
chosen to solve them. For a full account of these
case histories and object treatments see the original
published works (Kite, 1990, 1991).
15.3.5.1 The conservation of an ermine lining to a
blue felt Paquin cape. French, c.1936 (T123-1980)
(Figure 15.9)
In 1990, conservation was required to the ermine
(Mustela erminea) lining of the hood from a blue felt
cape by the designer Paquin (Kite, 1990). The fur
was grubby and in some places the skins had started
to split, and in two areas of particular damage the
skins had fragmented. At some time these areas had
been stuck down to the silk lining of the fur in an
attempt to consolidate the skins. The adhesive had
become hard but fortunately had not soaked
through the skin or impregnated the fur.
The fur lining and attached ermine tie were
removed from the cape for treatment and it was
necessary to unpick the stitching and partially release
the silk lining to the fur to gain access to the back of
the skins. The adhesive was soluble in acetone and
was easily removed by localized spot treatment using
small cotton wool swabs soaked in acetone and a
scalpel blade to scrape away the softened adhesive
from the back of the skin. It was considered inadvisable
to flood the skin with acetone due to the risk
of removing oils from the skin so its use was kept to
a minimum. The general condition of the skins
appeared to be good and they were not dehydrated
or brittle. However, there was marked yellow staining
in the damaged areas. When the cape was worn
with the hood up these areas corresponded to the
neck and ear regions of the wearer so it was possible
that the owner had sprayed herself with perfume
and these stains and damage could be directly attributable
to the alcohol or other ingredient in the perfume
causing the rapid oxidation of fat in the skin
and accelerated degradation. The fur was grubby
and had some lipstick marks so was cleaned by
swabbing with white spirit BS245 onto absorbent
paper.
Beva 371 was chosen as the most suitable adhesive
for repair so a 15cm3
of Beva 371 film was prepared
by ironing it onto a square of nylon gossamer
Furs and furriery: history, techniques and conservation 161
Figure 15.9 Detail of ermine lining of hood from blue
felt cape by Paquin, 1936 (T.123-1980).
162 Conservation of leather and related materials
Figure 15.10 Detail of ermine lining of hood from blue felt cape by Paquin, 1936 (T.123-1980) showing damage to
skins.
Figure 15.11 Detail of ermine lining of hood from blue felt cape by Paquin, 1936 (T.123-1980) showing same area
after repair. Note yellowing of skin in area of damage.
between two sheets of silicone release paper. A spatula
iron set at 70 –75°C was used. The damaged fur
hood was laid out on a soft board and the tiny fragments
of skin were held in alignment using entomological
pins stabbed through into the board. By
ironing small straps of the Beva film onto each split,
gradually the damaged area was repieced and made
whole (Figures 15.10 –15.11).
From the hair side, because there were a few tufts
of hair missing, it could still be detected that there
had been damage but the skin was again sound.
The silk interlining to the fur was resewn in place
and the most severely damaged part was covered
with a new piece of silk habotai dyed to colour
match. The conserved and reassembled fur hood
lining was then restitched into the cape together
with the ermine ties.
An alternative adhesive treatment can be illustrated
with reference to the following brief case history.
15.3.5.2 The conservation of a Chinese woman’s
dragon robe lined with arctic fox fur, c.1800 –1850
(T766-1950) (Figure 15.12)
A Chinese woman’s dragon robe of yellow plain weave
silk with tapestry woven roundels and trimmings,
lined with arctic fox (Alopex lagopus), required extensive
conservation prior to exhibition in 1991. The
robe had long sleeves with horseshoe cuffs edged
with brown fur; designed to be worn turned back.
This fur was identified as mink (Mustela lutreola).
The robe and fox fur lining were grubby and in
places had a grey appearance with the worst soiling
being concentrated at the hem. The fur lining
showed extensive insect damage and was splitting
and torn. The fur trimmings to the cuffs were worn
to the skin in many places and torn.
It was necessary to treat the silk robe, fur lining
and cuff fur separately so stitching holding the fur
elements was unpicked and the furs were separated
from the robe.
Once removed the fur lining could be examined
and its condition precisely assessed. An interlining
was linked to the skin side of the fur which consisted
of layers of paper and a layer of fine yellow
silk. This was removed and retained to be sewn
back onto the fur after the fur had been conserved.
The fur lining was made from hundreds of scraps
stitched together to make three distinct bands for
each side, which were then stitched together to
make up the lining. Although the fox fur was thick
the skins were thin and papery and hair follicles
could be seen protruding through the underside of
the skins. At some time repairs had been made to
the skins using what seemed to be a starch paste and
an oriental paper similar to that used for the paper
interlining. It was not known when nor where this
was done but it was significant that the paper used
was similar to that used in the construction of the
object, suggesting that the two papers were contemporary.
These paper repairs were so damaged with
insect holes they were no longer fulfilling their purpose
so they were removed.
Working in a fume chamber the fur lining was
solvent cleaned by swabbing onto absorbent paper
using white spirit BS245. The lining was so large it
was necessary to clean it in sections waiting for the
solvent to evaporate from one area before moving
on to the next (Figures 15.13–15.15).
The adhesive and method used for the previous
paper repairs, although damaged and no longer
fulfilling their purpose, had not failed due to the
nature of the technique. Moreover, the method was
compatible with the oriental nature of the object
and had caused no obvious damage or shrinkage of
the skin where the patches had been applied.
Experiments using wheat starch and various mixtures
of wheat starch and sodium alginate were carried
out and a number of mitsumata and kozo papers
Furs and furriery: history, techniques and conservation 163
Figure 15.12 A Chinese Woman’s Dragon Robe Lined
with Arctic Fox Fur c.1800 –50 (T766-1950).
164 Conservation of leather and related materials
Figure 15.13 Detail, cleaning the arctic fox fur lining.
Figure 15.14 Detail, cleaning the arctic fox fur lining.
were examined for suitability. A mitsumata paper was
chosen. A rabbit skin was used as the test fur for
these experiments as a sample of arctic fox was not
available. The most satisfactory mixture and working
consistency of the adhesive paste was identified
and a suitable method of patch application was perfected
on the test fur to ensure that the skin did not
become too wet nor the patch, nor skin, shrink on
drying. Once the method was perfected the arctic
fox lining was repaired by the localized application
of patches and a mixture of wheat starch paste and
sodium alginate used as dry as possible (Figures
15.16 –15.17).
The silk robe was cleaned and repaired using traditional
stitching techniques used in textile conservation
and the garment was reassembled. The fur
bands from the cuffs were repaired using Beva film
carried on Remay.
15.3.6 Freezing tests of adhesives
It is important to know that adhesives selected for
use when carrying out conservation treatments to
furs will remain stable if the object has to be deep
frozen at a later date as part of an insect pest management
strategy. In 1990 some tests were carried
out. Beva 371, Silicone Adhesive SF2, wheat starch
paste and mixtures of wheat starch and sodium alginate
in various concentrations had been used for
experimental repairs on a dressed white rabbit skin.
In order to test the stability of these repairs the skin
was deep frozen to Ϫ30°C and the results published
(Kite, 1992). All the sample repairs had remained
stable. Since this time the skin has been frozen for a
second time. It is interesting to note that a recent
examination of these sample repairs, after 13 years
and many occasions of handling for teaching and
demonstration purposes, showed all the repairs still
to be stable although there was some darkening of
the SF2 adhesive. Some of the paper and paste
patches have been pulled away and manually tested
to destruction over the years but where they have
not been so mishandled they are stable and well
adhered. The author has not carried out freezing tests
on all the adhesives which may be used for the repair
of fur-skins, and suggests that this is an area where
further work needs to be done.
Furs and furriery: history, techniques and conservation 165
Figure 15.15 Detail, cleaning the arctic fox fur lining.
15.3.7 Care of furs
15.3.7.1 General storage and display
Fur garments are likely to be heavy so should be
stored on substantial well-padded hangers. Enough
space should be allowed so that furs are not packed
tightly together and crushed. Cotton lawn or Tyvec
bags should be provided to cover and enclose each
item and a label with the object number and brief
description should be fixed to the outside of the bag
for easy identification (Heiberger, 2002).
A small photograph of the item would also be
useful, included with the label, and fixed to the bag
to aid identification and help limit handling. Smaller
items and accessories are best stored separately in
boxes with the boxes clearly labelled with a small
photograph fixed to the outside of the box.
For display a garment should have adequate support
so that it is not crumpled or under stress. A
mannequin tailored to fit is appropriate for a coat
and an accessory should have a purpose-made support
or mount.
Although keratin is chemically stable all types of
fur are subject to discolouration by light; dark
colours may fade and light colours become yellow.
Ideally furs are best stored in the dark in a cool dustfree
stable environment. For long-term display low
light levels of around 50 lux have been suggested in
the past. However, in keeping with current practice
relating to museum lighting policy for works of art
on paper and similarly light-sensitive materials,
which includes textiles and furs, together with current
theories of risk assessment, an increase in light
levels is permitted calculated against less exposure
time overall (Derbyshire and Ashley-Smith, 1999;
Ashley-Smith, 1999). The RH should be stable at
around 45–55% and although water does not harm
the fur hairs, humidity levels above 65% can lead to
the risk of mould growth on the pelt. Extreme
dryness should also be avoided as desiccation can
166 Conservation of leather and related materials
Figure 15.16 Detail of damaged skin before repair. Figure 15.17 Detail of damaged skin after repair using
mitsumata paper and a wheat starch paste and sodium
alginate mixture.
lead to embrittlement and possibly tearing of the
skins. If the skins are weakened overall then the
sewn lines are particular areas of risk when handling
as they have already been physically weakened by
the perforations of the stitching. If desiccation
occurs in the pelt there is a danger of the collagen
fibres shrinking, the follicles opening and the hairs
falling out.
15.3.7.2 Pests and freezing – cold storage
Regular inspection of storage and display areas and
a pest-monitoring programme should be in place
where furs are part of the collection. Regular monitoring
for insect activity is essential as moths and
carpet beetles will eat fur, moths devouring it at the
roots then proceeding to perforate the leather.
Whenever an addition is made to a collection it is
good practice to treat that object for insect infestation
as a precaution before putting it into store with
the rest of the collection. Before treatment it should
be kept isolated until this has been carried out.
There are many publications available in conservation
literature on the topic of pest management
including Florian (1987), Child and Pinniger
(1993), Hillyer and Blyth (1992), Pinniger (1994,
1995), and Norton (1996) The opinion expressed
by writers on furs and furriery is that moths are the
most damaging risk to furs and that cold storage balanced
with a controlled atmosphere is the best remedy
(Sachs, 1922; Rosenberg, c.1920; Bacharach,
1930). If the atmosphere is maintained at a high
humidity in very low temperatures, moisture will
condense into a frost on the garment; but if a dry
atmosphere is maintained the cold air will absorb
the little remaining moisture causing the skins to
dry out and become brittle. It is therefore essential
to balance the environmental conditions when furs
are kept in reduced temperature storage and specialists
in this field should be consulted if this type of
storage is to be provided. Maintenance of furs in
reduced temperature storage of no more than 8°C
(50°F) was recommended by Bachrach as far back as
1930 but few museums have the facility for this.
Clothes moths (Tineola biselliella and Tinea pellionella)
will not breed or feed below about 10°C.
However, this temperature may not kill larvae for a
long time as they probably starve to death. The larvae
of carpet beetles (woolly bears) may be more
tolerant but the adults will not breed at 8°C.
Until the 1980s treatment for pest infestations was
carried out using methyl bromide and ethylene dioxide
but since then deep freezing of infested material
has become one of the accepted methods and is a
straightforward procedure to carry out. Deep freezing
to temperatures of Ϫ30°C for a period of
72 hours and then repeating the procedure is currently
the accepted method of dealing with insect infestations
in museums (Florian, 1987). In 2003 it became
accepted that it is unnecessary to carry out the second
freezing procedure. Anoxic treatments using nitrogensaturated
atmospheres have also been regularly and
successfully in use for a number of years (Newton et al.,
1996). An alternative for whole collections and large
quantities of fur items is to treat them using the
thermo-lignum process3
(Thomson, 1995).
Beating the fur from time to time with sticks is
advocated by furriers and is a treatment that goes
back to medieval times. William Jurden, Skyner to
Queen Elizabeth I, had the essential task of regularly
airing and beating the furs and fur-trimmed garments
to keep them free of dust, moths and fleas
(Arnold, 1988). Although beating is still carried out
by furriers today as part of maintenance it is not a
suitable treatment for fragile aged skins or museum
objects.
Endnotes
1. An exception was an exhibition held at the Museum
of London, November 2000 entitled Stolen Skins? Fur
in Fashion.
2. Rodents – e.g. beaver, muskrat, nutria, rabbit, marmot,
squirrel, chinchilla
Felines – e.g. leopards, ocelots, cheetah, lynx
Canines – e.g. wolf, dog, fox, tanuki
Weasels – e.g. otters, mink, martens, sables, fisher,
ermine, wolverine, badger, skunk, genet
Bear Racoon Group – e.g. racoon, bears, bassarisk
(ringtail)
Marsupials – e.g. opossums, kangaroo, koala
Ungulates – e.g. sheep (lambs), goats (kids), camel
family
Sundry –others.
3. There are two processes which have been trialled. The
first involves raising the temperature gradually from an
ambient temperature of 20°C up to 50°C over a
period of 11 hours, holding this temperature stable for
two hours then allowing cooling back to ambient temperature
of 20°C over 10 hours. During this time the
relative humidity is strictly controlled and raised from
50 to 60% and back again.
The second process involves flooding the chamber
with argon to give an atmosphere of less than 1%
oxygen, then heating to 38°C over a period of 8
hours, holding at that temperature for 3 days and then
cooling over a further 8 hours. During this treatment
Furs and furriery: history, techniques and conservation 167
the relative humidity is increased from 50 to 55% and
then dropped back to 50%. Both methods are useful
for fur-skins but it is the second method that could be
useful for degraded fur-skins with very low shrinkage
temperatures.
References
Appleyard, H.M. (1978) Guide to the Identification of Animal
Fibres. Leeds: British Textile Technology Group.
Arnold, J. (1988) Queen Elizabeth’s Wardrobe Unlock’d.
Leeds: W.S. Maney.
Ashley-Smith, J. (1999) Risk Assessment for Object Conservation.
Oxford: Butterworth-Heinemann.
Austin, W.E. (1922) Principles and Practice of Fur Dressing
and Fur Dyeing. London: The Library Press Ltd.
Bachrach, M. (1930) Fur, a Practical Treatise. London:
Prentice-Hall Inc.
Baldwin, F. (1926) Sumptuary Legislation and Personal
Regulation in England. Baltimore: Johns Hopkins Press.
Blazej, A. et al. (1989) Atlas of Microscopic Structures of Fur
Skins. Amsterdam: Elsevier.
Brunner, H. (1974) The Identification of Mammalian Hair.
Melbourne: Inkata Press.
Child, R.E. and Pinniger, D.B. (1993) Insect Trapping in
Museums and Historic Houses. International Conference
on Insect Pests in the Urban Environment, Cambridge,
UK.
Delany, Mrs (1861) The Autobiography and Correspondence
of Mary Granville, Mrs Delany. Rt Hon Lady Llanover,
ed. London: Bentley.
Del Re, C. (1988) Technology and Conservation of Five
Northwest Coast Head-Dresses. Symposium 86, The Care
and Preservation of Ethnological Materials, pp. 53–61. C.C.I.
Derbyshire, A. and Ashley-Smith, J. (1999) A Proposed
Practical Lighting Policy for Works of Art on Paper at
the V&A. Preprints of the ICOM-CC 12th Triennial
Meeting Lyon, 3 September 1999, pp. 38– 41.
Dickens, J. (1987) The Development of a Treatment to
Re-secure Mats of Insect-damaged Fur. Ethnographic
Conservation Newsletter, 4, 18–19.
Dignard, C. and Gordon, G. (1999) Metal Ion Catalised
Oxydation of Skin: Treatment of the Fur Trim and
Collar on a Velvet Cape. The Journal of the Canadian
Association for Conservation, 24, 11–22.
Ewing, E. (1981) Fur in Dress. London: B.T. Batsford Ltd.
Florian, M.L.E. (1987) Methodology Used in Insect Pest
Surveys in Museum Buildings – A Case History. Preprints
of the 8th Triennial Meeting, pp. 1148–1174. ICOM-CC
Sydney, Australia.
Glob, P.V. (1971) The Bog People. London: Paladin.
Hahn, H.G. and Weigelt, G. (1967) Chemische Technologie
der Rauchwaren-zurichtung and-veredlung. Leipzig: [n. pub.].
Heiberger, B. (2002) Caring for Fur at the Museum of
London. In The Conservation of Fur, Feather and Skin
(Margot Wright, ed.). Seminar organized by Conservators
of Ethnographic Artefacts held at Museum of
London, 11 December 2000, pp. 88–92. London:
Archetype.
Hillyer, L. and Blyth, V. (1992) Carpet Beetle – A Pilot
Study in Detection and Control. The Conservator, 16,
65–77.
Kaplan, H. (1971) Furskin Processing, pp. 13, 113, 137.
Pergamon Press.
Kite, M. (1990) A 1740s Horse-Hair Hat, a Busby c1827
and a Fur-Lined Cape c.1936. Preprints of the ICOM-CC
Conference held in Dresden, August 1990, pp. 645–650.
Kite, M. (1991) The Conservation of a Wet Weather Hat
from the Uniform of a Marshal General of the
Portuguese Army, and a Chinese Fur-lined Kesi Robe
c. 1800. Preprints SSCR Conference, Paper and Textiles:
the Common Ground, held in Glasgow, September 1991,
pp. 105–115.
Kite, M. (1992) Freezing Test of Leather Repair
Adhesives. Leather Conservation News, 7(2), 18, 19.
Kite, M. (1998). Fur. ‘Core’ Conservation and Restoration of
Objects of Cultural Patrimony, pp. 17–20. France. Spring
1998.
Kite, M. (1999) The Conservation of a 19th Century
Salmon Skin Coat (626–1905) Preprints of the ICOM-CC
12th Triennial Meeting Lyon, 29 August –3 September 1999.
pp. 691–696.
Links, J.G. (1956) The Book of Fur. James Barrie.
Liska, A.J. and Shevchenko, A. (2003) Proteomics, 3, 19–28.
Lougheed, S., Mason, J. and Vuori, J. (1983) Repair of
Tears in Fur Skin Garments. Journal IIC-CG. 8 & 9,
13–22.
Matheson, S.A. (1978) Leathercraft in the Lands of Ancient
Persia. Vic: Colomar Munmany.
Norton, R.E. (1996) A Case History of Managing
Outbreaks of Webbing Clothes Moth (Tineola Bisselliela).
Preprints of the ICOM-CC 11th Triennial Meeting,
Edinburgh 1996, pp. 61– 67.
Novak, M. (1987) Wild Furbearer Management and
Conservation in North America. Ontario: Ministry of
Natural Resources.
Pense, W. (1955) Rauchwaren. In Handbuch der
Gerbereichemie und Leqerfabrikation (W. Grassman, ed.).
Band 111, Wein: Springer.
Pinniger, D.B. (1994) Insect Pests in Museums, 3rd ed.
London: Archetype.
Pinniger, D.B. (1995) Friends of the Dodo – Recent
Advances in the Detection and Control of Museum
Insect Pests. Proceedings of the 11th British Pest Control
Association Conference, London 1995.
Rae, A. and Wills, B. (2002) Love a Duck: The
Conservation of Feathered Skins. In The Conservation of
Fur, Feather and Skin (Margot Wright ed.). Seminar
organized by Conservators of Ethnographic Artefacts
held at Museum of London, 11 December 2000,
pp. 43– 61. London: Archetype 2002.
Ribeiro, A. (1979) Furs in Fashion. The Connoisseur,
December, pp. 226 –231.
Richardson, H. (2002) The Conservation of Plains Indian
Shirts at the National Museum of the American
168 Conservation of leather and related materials
Indian, Smithsonian Institution. The Conservation of
Fur, Feather and Skin (Margot Wright, ed.). Seminar
organized by Conservators of Ethnographic Artefacts
held at Museum of London, 11 December 2000,
pp. 7–24. London: Archetype.
Rogers, G.E. (ed.) (1989) The Biology of Wool and Hair.
London: Chapman and Hall.
Rosenberg, C.J. (c1910) Furs and Furriery. London: Sir
Isaac Pitman and Sons Ltd.
Sachs, Captain J.C. (1922) Furs and the Fur Trade. London:
Sir Isaac Pitman and Sons Ltd.
Samet, A. (1950) Pictorial Encyclopedia of Furs. New York:
Arthur Samet.
Spindler, K. (1994) The Man in the Ice, pp. 135–138.
London: Weidenfeld and Nicolson (translated from the
German by Ewald Osers).
Spriggs, J.A. (1998) The British Beaver – Fur Fact and
Fantasy. In Leather and Fur, Aspects of Early Medieval
Trade and Technology (Esther Cameron, ed.) pp. 91–101.
London: Archetype.
Thomson, R.S. (1995) The Effect of the ThermoLignum
Pest Eradication Treatment on Leather and
Other Skin Products. Report 1995. Leather Conservation
News, 11, 11–12.
Thomson, R. (1998) Leather Working Processes. In
Leather and Fur, Aspects of Early Medieval Trade and
Technology (Esther Cameron, ed.). London: Archetype.
Veale, E.M. (1966) The English Fur Trade in the Later
Middle Ages, pp. 16, 44, 193. Oxford: Oxford University
Press.
Vincent, J. (1972) Structural Biomaterials. Princeton N.J.:
Princeton University Press.
Furs and furriery: history, techniques and conservation 169
16.1 Exotic skins
16.1.1 Introduction
Collecting today is increasingly popular and it is
therefore not surprising to find beautifully crafted
leather articles in museums and other collections, be
they public or privately owned. A fair proportion of
these will be made from exotic leathers, distinguishable
from mammalian leather by their interesting
surface texture, such as scales or quill pips and by
their fascinating natural markings.
16.1.2 Origins and history of exotic
leathers
The use of exotic skins dates no doubt back to prehistory,
well before the discovery by Europeans of
tropical areas of the world, with hunter–gatherer
tribes utilizing the skins from reptiles, birds, fish and
amphibians for adornments to their clothing or for
their head-dresses as well as for covering such articles
as drums. These skins were mostly dried and made
supple by scraping the flesh side and applying various
animal fats, methods that preserve the skin without
imparting a tannage.
The supply of exotic skins in bulk, especially to
tanners in the United Kingdom, started towards the
end of the nineteenth century from countries
within the Empire situated within tropical regions.
Rain forests, savannas, lakes, rivers and the sea contained
wild species with skins large enough to be
commercially usable in the manufacture of leather
goods. The import of East Indian tanned buffalo
hides and goatskins provided the framework for the
trade in exotic skins to commence, exported either
air-dried, in a raw, wet-salted condition or pre-tanned
in a local tannery.
France initially obtained its supplies of exotic skins
from its colonial empire within Africa where the
rivers and lakes yielded an abundant supply of crocodile
skins.
The expansion of the trade soon necessitated
searching other areas apart from Africa and the Far
East for supplies. Exotic skins were imported from
South and North America, and from other tropical
or subtropical areas.
16.1.3 Uses of exotic leathers
Tanners of exotic skins and manufacturers of finished
articles made from these normally understand exotic
leathers as those made from either reptiles, birds, fish
or amphibians. For any skin to be commercially usable
it has to satisfy the following requirements:
(a) The available area of skin must permit a manufacturer
of finished leather articles to cut the
components with a minimum of waste. It follows
that the larger the leather article, such as a
handbag, the larger the exotic skin has to be,
except where a design is used permitting smaller
pieces to be stitched together. This tends to
increase labour costs but cheapens the article.
(b) The physical strength and properties of the skin
must match the wear and tear and flexing
requirements of the finished article. Reptile skins
with their tightly woven fibre structure are
immensely strong, particularly with a skin which
is relatively thick, such as crocodile. The skins of
170
16
The tanning, dressing and conservation of exotic,
aquatic and feathered skins
Rudi Graemer and Marion Kite
The tanning, dressing and conservation of exotic, aquatic and feathered skins 171
birds, such as ostrich or emu, have a looser fibre
structure as have fish which results in a lower tensile
strength. To improve flexing of the leather,
the tannery will fatliquor the skins. Exotic skins
have good resistance to scuffing with lizard skins
among the best compared to leather made from
domestic animals.
(c) The leather made from exotic skins has to be ‘in
fashion’ – that is to say, it is promoted in the
world of fashion as the ‘in’ material to be used. As
such it must be available in fashionable colours
and in the desired surface finish, such as bright,
shiny, metallic, matt, or dull, such as suede. The
tanner has limitations imposed on him by the
nature of the skin as well as fashion demand, with
crocodile leather for handbags, invariably finished
by glazing, giving a brilliant finish. Most
reptile leather is finished in this way, but fashion
dictates will force the tanner to apply matt finishes
or even buff off the surface layer, to give a
‘Nubuk’ finish. Bird and fish skins were nearly
always finished matt after tanning, their fibre
structure being too loose to be glazed, but modern
finishing systems allow more shiny effects if
not the brilliant results obtained from glazing.
16.1.4 Preparing the raw skins
The flaying of raw, exotic skins differs from type to
type with belly-cut being the norm for many species,
leaving the back of the animal in the centre of the
leather. Skins which can be back-cut, such as
pythons (Python sp.) or Teju lizards (Dracaena sp.,
Tupinambis sp.) from South America, have their
belly scales in the middle of the leather. These are
widely used for American cowboy boots with the
wide belly scales running down the centre of the
boot and vamp. Rattlesnakes (genus Crotalidae), in
the raw, dried state, are also used, mostly belly-cut
in the manufacture of these boots.
Crocodiles and alligators are very heavily ossified on
their backs which makes this part of the skin impossible
to tan and soften. For this reason only the sides
and belly are used in the tanning process (Figure 16.1).
Lighter ossification is also present in the belly of some
species which, if not too severe, can be softened by
the tanner with acids. Matt finishing of heavily ossified
caiman skins resulted in the ‘wild’ crocodile popular
for making handbags in the 1970s.
16.1.5 Tanning and dressing
Tanning exotic skins follows the same basic processes
as the tanning of mammalian skins. After thoroughly
soaking air-dried skins, they are immersed in a solution
of sodium sulphide to remove the keratinous
surface layer of the scales, which is the equivalent to
the hair and epidermis of mammalian skin. The
equivalent with birds are the feathers and with fish
the scales.
After bating and pickling with acid follows
the important bleaching process which removes,
Figure 16.1 Crocodile handbag and shoe with snakeskin trim.
if required, the natural pigmentation, a process
demanded either by fashion or if the design is not
particularly attractive.
With the demand mostly for glazed reptile leathers,
the traditional chrome tannage cannot be used or
only as a pre-tannage on crocodile leathers. A vegetable
or synthetic tannage is applied instead. These
plump up the leather enabling it to withstand the
high pressures imparted by the cylindrical glazing
jack made from glass, agate or steel, which is dragged
across the skin by the glazing machine at high speed.
As a result of using these vegetable and synthetic
tanning materials certain disadvantages affecting the
preservation of the final finished leather manifest
themselves. The different finishing methods also affect
the fastness to different agents. Of these the following
have to be noted.
16.1.5.1 Light fastness
Collagen, the leathermaking protein, is in itself not
fast to light. It will yellow on exposure. This is aggravated
by the presence of natural fats. Leather tanned
with synthetic tanning materials, even of reasonably
good light fastness, will therefore turn yellowish.
Reptiles are often tanned with their natural markings
emphasized by the use of synthetic tanning materials
and will therefore yellow with age. This also affects
pastel shades. Most vegetable tanning materials, used
mainly for darker colours, will redden on exposure.
This is not a problem on colours such as black, dark
brown or navy. Light browns, greens or greys will,
however, darken. To give these leathers the brilliance
in colour, the tanner uses cationic dyes in the finishing
coats, notorious for their poor light fastness.
Unfortunately pigments that are light fast produce a
muddy, dull looking finish when glazed.
No such constraints exist for matt-finished leathers,
such as ostrich (Struthio camelus), various species of
sharks, caiman (Dracaena sp.) and occasionally other
reptiles. These can be chrome tanned and moderately
pigmented to improve light fastness.
16.1.5.2 Water resistance
Glazed leathers will dull when exposed to dampness.
Traditionally, this finishing method, which as
its name suggests gives a very high gloss, involves the
application of a surface coating based on casein,
originally hardened with formaldehyde. This can
no longer be used for health and safety reasons.
Alternatives do not harden the film sufficiently to
prevent water spotting, although a thin spray of
nitrocellulose-based lacquer over the finish will
improve matters. Matt finishes can be made quite
fast to water with nitrocellulose- or urethane-based
emulsion sprays, but it should be borne in mind that
leather has pores and all finished articles have seams.
A detailed account of the production of leather from
lizard skins is given in The Reptile Skin by Fuchs and
Fuchs (2003). This work also provides essential reference
material for collectors, curators and conservators
seeking to identify species.
16.1.6 Conservation
Described above are the practical constraints to the
conservation of finished leather articles made from
exotic leathers during the twentieth century. Treatment
strategies will of course depend on many factors
and repair and consolidation methods will be
selected as appropriate to the object concerned, the
way the skin was processed and the date the object
was made. Most likely methods chosen will be
drawn from treatments used for other leathers.
Of interest is the conservation treatment undertaken
to a Romano-Egyptian cuirass and helmet made
from crocodile skin, discussed by Wills (2000). Also,
the conservation treatment undertaken to a python
skin chair by Sturge (2000).
16.1.7 Conclusion
Today the world is quite rightly talking of the vital
necessity of the conservation of living creatures.
The commercial pressure on some of the species,
the spread of humanity as well as the destruction of
habitat through the exploitation of timber in the
tropical rain forests resulted in the Washington Conference
and the setting up of CITES. This organization
has been controlling the trade over the past 25
years with licences and prohibiting the trade where
species are endangered. Unfortunately some countries
have found ways of circumventing these regulations
and exotic leather articles are still on sale
in shops in ‘touristy’ areas of the world. Farming of
some species has, however, led to particular successes
with crocodiles and ostrich, with their leathers
and the finished articles, although expensive, freely
available.
Exotic leathers with or without their natural
markings, in their many colours, textures, metallic
effects and finishes have no doubt tempted many
customers in the past century to purchase leather
goods made from these (Figures 16.2 and 16.3). I
hope customers of today will find equal pleasure
from just watching these beautifully marked and
172 Conservation of leather and related materials
The tanning, dressing and conservation of exotic, aquatic and feathered skins 173
coloured, living animals in a diversity that is perhaps
unequalled.
16.2 Aquatic skins
The use of fish skin and the skins of aquatic
mammals and other marine vertebrates as a leather
product dates back some 2000 years when Native
Americans were using it to make pouches (Neergaard,
1991; Ingram and Dixon, 1994). In England in the
fifteenth century gauntlets and bags were being
made from fish skin leather and in the seventeenth
century eel and whale were tanned (Ingram and
Dixon, 1994). It is recorded that in 1627 a Canadian
tanner bought a book covered in cod skin (Ingram
and Dixon, 1994).
In the nineteenth century the use of fish skin
leather may not have been usual but neither was it
uncommon. At a maritime exhibition held at the
Westminster Aquarium in London in 1886 a
Norwegian exhibitor showed a variety of tanned fish
skins among which were flat fish (order Pleuronectiformes)
prepared for gloves, skins of soles (family
Soleidae) prepared and dressed for purses, skins of eels
prepared and dried for braces and upper leather for
shoes made from ‘white fish’1
(Unattributed, 1880).
The skins of beluga or white whale (Delphinapterus
leucas) were being tanned in Bermondsey, London,
in 1887 producing a supple, beautiful and high quality
leather for use as uppers and in the manufacture
of ‘bespoke’ boots. Laces were cut by hand from the
whole length of the skin and are described as unsurpassed
in wear (Unattributed, 1888). These laces
were the customary choice and quality for army officers’
boots. A commercial fish skin tannery was still
in operation in Kingston, Surrey, UK, until 1950.
A patent was taken out concerning the making of
shoes at Gloucester, Massachusetts, using the skins
of cusk or torsk (Brosme brosme) and in Colbourn,
Canada, an industry was said to be carried on using
the skins of ‘siluroids’ (i.e. catfishes) for glovemaking
(Unattributed, 1880).
Figure 16.2 Nile crocodile skin (Crocodylus niloticus).
Figure 16.3 Waistcoat by Jean Muir c.1960s using skin
of Python reticulatus.
174 Conservation of leather and related materials
In the nineteenth century the skins of sharks and
whales were tanned and some were used for shoes,
but mostly in Europe they were used for covering
high quality boxes and cases and for industrial uses.
In the late 1940s approximately 800000 sharks
were caught annually by the Japanese and their skins
tanned for the shoemaking industry producing 2
million pairs of shoes or one third of the Japanese
annual requirement.
The use of untanned fish skin in the form of shagreen
(shark and ray skin) is well known in many
cultures, and it has been used for binding ceremonial
sword hilts in Europe and by the Japanese for
the handles of samurai swords.
In the late nineteenth century and early part of
the twentieth century ‘shagreen’ was used in furniture,
most notably by the French cabinetmaker
Ruhlman, and on decorative boxes and instrument
cases and even in jewellery. The skin of the blue
shark (Prionace glauca) was used for this purpose
(Unattributed, 1880).2
A fish called chat (Scyliorhinus
canicula, contemporary name Squalus catulus) was
used to make a product known as ‘peau de roussette’
used for cases and other articles but also known as
shagreen (roussette is the French name for dogfish)
(Unattributed, 1880). Dogfish skin has been widely
used as shagreen and has been called ‘peau de chien
de mer’ and ‘chien marin’. Another species of dogfish,
spotted dogfish or bull huss (Scyliorhinus stellaris),
was also used under the name of ‘roussette tigrée’
and in France went under the name of ‘Galuchat’
when prepared as Monsieur Galuchat had done with
the dermal denticles with which they were studded,
ground down and smoothed. These were usually dyed
green and used to cover sheaths, boxes, compacts
and other small decorative fashion items, bags or
accessories. It was also coloured black, white or red
(Unattributed, 1880). As the skin was rigidly bonded
to the article, it did not have to flex and stability was
assured as long as the article was kept dry.
The dermal denticles are cartilaginous and are
not removed by the normal liming process during
the preparation of the skin which is why they were
ground down to give a smoother polished surface.
The cartilaginous material tends to take dye to a different
shade than the collagen giving an interesting
two tone effect at the surface.
In the mid-twentieth century, during World War II
when occupying forces overran Norway and
Denmark and confiscated leather made from animal
hides, cod (Gadus morhua), eel (Anguilla anguilla),
plaice (Pleuronectes platessa) and catfish (Anarhichas
lupus)3
were tanned so local inhabitants could make
handbags, belts, harness and footwear (Ingram and
Dixon, 1994). ‘Neptune’ suede, made from the skin
of plaice, was dyed bright colours and made into
wedge evening sandals. Ten to 12 skins were required
for each pair (Ledger, 1982).
16.2.1 Fish skin preparation
After World War II an investigation was undertaken
into the surviving state of the German tanning
industry. The plant owned by Johann Knecht and
sons at Elmshorn was undamaged and still commercially
producing cod and haddock (Melanogrammus
aeglefinus) skins as fancy leather for the novelty goods
trade. It is recorded that:
they obtain their skins in a salted condition. They do
not keep well unless refrigerated even when salted.
They wash the skins and give them a good liming, delime
and bate (scales not removed except as they fall off
in the process), pickle and one bath chrome tan in a
paddle, wash, neutralize, fat liquor and tack as natural
chrome, buff flesh and grain, colour flesh side, pigment
and emboss. (Schultz and Schubert, 1945)
This plant was not alone in processing fish skins
which were mostly plaice, cod and haddock often
obtained from Norwegian curers (Caunce et al.,
1946). A detailed method used for processing wetsalted
cod skins at Vibo-Schwanheim Lederwerke of
Frankfurt-am-Main is given in Caunce et al. (1946).
The finishing method describes the skins being
embossed with lizard grain on a callender embossing
machine, then given three or four applications of
colourless cellulose lacquer. This operation was performed
by hand using a cloth covered sponge to
ensure that only the raised portions of the grain
were coated. Finally the skins were dried and hot
plated at 50°C very lightly and rapidly on a hydraulic
press (Caunce et al., 1946).
16.2.2 Structure and identification
Unless the skin has a particular and easily recognizable
grain pattern, such as ray skin, or the identifiable
scale pattern remains and has not been removed or
destroyed during tanning, then close examination of
the grain surface using magnification is necessary for
a positive identification. Alternatively, identification
may be made by sampling, providing this is possible,
preparing a cross-section and examination of this.
Under magnification the surface of fish skin will
appear smooth and devoid of any follicle pattern. A
cross-section prepared from a piece of raw salmon
skin shows that fish skin has no epidermis and has a
The tanning, dressing and conservation of exotic, aquatic and feathered skins 175
layered weave structure of horizontally running collagen
fibre bundles with a small number running at a
slightly different angle. The outer surface layer much
like an epidermis is pigmented (Figure 16.4). Similar
patterns are exhibited by the skins of wolf fish and
dog fish (Figures 16.5 and 16.6).
Examples of cross-sections for comparison may
be found in Whitear (1986).
The sizes and shapes of the leather pieces may also
in some circumstances be significant in making an
identification of aquatic leather even if the species
may not be determined.
The tanning process for fish skin is complex and
species specific. Factors such as age and size of the
fish also affect the end result. The structure of fish
skin is sensitive to enzymatic attack and raw skins
will deteriorate rapidly. Fish skin collagen is easily
solublized by acids and alkalis, and can be destroyed
by anionic detergents which decrease the shrinkage
temperature (O’Flaherty et al., 1958). Care has to be
taken in handling and storage prior to tanning.
Skins can be frozen but during thawing the internal
fibres of the skins tend to break so often skins are
salted to slow down the deterioration (Ingram and
Dixon, 1994).
The shrinkage temperature of fish collagen is
considerably lower than mammalian collagen. Native
collagen of cod skin shrinks at about 40°C whereas
bovine skin requires a temperature of about 65°C.
However, the shrinkage temperature varies with the
species, with cold water species generally having a
lower shrinkage temperature, 38– 45°C for cold
water fish to 50 –56°C for warm water species
(Gustavson, 1956). It has been established that the
shrinkage temperature has a direct relationship with
the hydroxyproline content in the amino acid structure
of the collagen. Rockfish (family Scorpaenidae)
containing the lowest per cent of hydroxyproline
(7%) has the lowest shrinkage temperature (33–34°C)
while carp (Cyprinus carpio) has 11.6% hydroxyproline
and a shrinkage temperature of 57°C (O’Flaherty
et al., 1958).
Oil tannage does not raise the shrinkage temperature
but vegetable tans will raise the shrinkage
temperature by about 20°C and chrome by about
30°C.
Synthetic dyes enable the skins to be coloured to
any desired shade.
16.2.3 Fish skin in ethnographic objects
Fish skin used in clothing is much more likely to be
found with the species identified in ethnographic
collections but objects are rare (Figure 16.7).
Figure 16.4 Cross-section of salmon skin.
176 Conservation of leather and related materials
Figure 16.5 Cross-section of wolf fish skin.
Figure 16.6 Cross-section of dogfish skin, showing dermal denticle.
The tanning, dressing and conservation of exotic, aquatic and feathered skins 177
Inuit and Aleut peoples from the northwest
Pacific rim and other northern Pacific peoples have
historically used fish skins for clothing and to make
cultural objects. Yupik people of Alaska used fish
skins for raincoats, mittens and boots and as bags for
water containers.
The methods of skin preparation differ considerably
from the commercial methods described above.
A method of preparation described by a Yupik
woman from southwest Alaska and published by
Hickman is as follows. The fish were skinned, soaked
in water and scraped, some were scaled and some
were not. After scaling they were soaked in urine for
between half a day and overnight. The urine from a
small boy before weaning was described as best for
lighter skins and for tougher skins the urine from
an older boy, around the time his voice breaks
(Hickman, 1987). The longer the skin is soaked the
softer it became. A new bath was then prepared
with naphtha soap and aspen shavings then another
of clear water. Finally the skin was blotted and laid
out on a small board, the outside outermost to dry.
The purpose of soaking in urine was to open up
the skin structure. The urea content influences this.
Urea is a hydrogen bond breaker and can partially
destabilize the collagen. The urea breaks down to
give ammonia which acts as a mild alkaline treatment
of the skin loosening epidermis and opening
up the structure to allow tans to penetrate.
Another description taken from a catalogue published
by the Musée de l’Homme in Paris describes
a method used by the Ostiak people of Western
Siberia to tan the skins of sturgeons and sterletts
(Acipenseridae), burbot (Lota lota), pike (Esox lucius),
Pacific salmon (Oncorhyncus spp) and Kumza (Salmo
trutta). Translated it reads:
The skins are prepared in spring and summer by
women. The gutted fish is hung for a day or two to dry
then split down the stomach to take off the skin which
is then made dry by the sun stretched between stakes.
Sometimes they are dried by the hearth and here they
become covered with soot resulting in a skin which
is more water resistant. When dry the skin is rolled
in a ball and made supple by beating with a mallet.
The softening of certain types is finished by anointing
the skin with brains and with fish eggs. (Hickman,
1987)
The brains and fish eggs supply highly emulsified
oil which will penetrate into the skins’ fibre structure,
Figure 16.7 Gilyak embroidered salmon skin coat, nineteenth century, showing back view.
178 Conservation of leather and related materials
filming the fibres and preventing the fibres from
sticking, maintaining a flexible dry skin. The fat will
also make the final leather more water resistant. The
shrinkage temperature would not be raised by this
tannage.
16.2.4 Conservation
For many reasons, frequently due to less than ideal
storage, costume accessories come to the conservator
in a crushed and misshapen condition requiring
simple humidification and reshaping treatment
before they are fit to display. They may also need
cleaning.
When objects are made from skins it is important
to the conservator to know the genus of creature
and method of preparation originally used for the
leather, before any treatment is carried out. If it is
aquatic leather then it is important, if possible, to
identify the species and whether it is from warm or
cold waters. The significance of the shrinkage temperature
and moisture sensitivity is important both
for the possible use of humidification treatments for
reshaping and for the use of heat set adhesives and
aqueous solutions for repair.
The presence and identification of finishes is also
important particularly if hydrocarbon solvents are
being considered for use in cleaning.
In 2003 there were few published articles concerning
the conservation of fish skin and those that are
readily available deal with ethnographic materials.
The following may, however, be useful to the conservator:
Heikkanen (1978), Kite (1999), Murray
(1994) and Pancaldo (1996).
16.3 Feathered skins in fashionable
dress
The general fascination for wearing bird plumage
from beautiful, rare and exotic species is documented
from Roman times (Doughty, 1975) and the
wearing of feathers and bird skins by a fashionable
and status conscious society has continued throughout
history. Wealthy Romans and Greeks wore the
feathers of ostrich (Struthio camelus), which is still
one of the principal feathers used in the millinery
trade. References have been found in the wardrobe
accounts of Elizabeth I, to the wearing of swan skins
(Cygnus sp.) which were prepared by the Queen’s
Skynner William Jurden (Arnold, 1988).
Many different bird species from all parts of the
world have been used since, including herons, rheas,
owls, birds of paradise, kingfishers, jays, magpies and
many others (Doughty, 1975). By the late nineteenth
century the demand by the fashion industries
of Europe and America was unprecedented. In a
sale held in New York in 1888 30000 humming
birds (Trochilidae sp.) were sold in one afternoon
(Cunnington, 1953).
During the second half of the nineteenth century
many species were becoming at risk of extinction
and prominent naturalists and many others in the
United Kingdom and America had begun a movement
to protect endangered species. This directly led
to the Sea Birds’ Preservation Act being passed in the
UK in 1869. This prohibited the taking of sea birds,
which were mainly being used for millinery purposes.
Subsequent legislation in the early twentieth
century in both the UK and USA followed, radically
controlling the taking of many other species of
birds. Today, only species of domestic fowls (Gallus
sp.), peafowls (Pavo sp.), pheasants (Phasianidae sp.) and
a few other farmed species including ostrich (Struthio
camelus) are commercially available to the feather and
bird skin trades.
Accessories made using complete or part bird
skins may be found in museums large and small
where dress is included in the collections. Items that
commonly survive include muffs and possibly trimmings
from the eighteenth century, and fans, muffs,
collars, trimmings and hats from the nineteenth
and early twentieth centuries. Ceremonial and military
uniforms also may have feathers and bird skins
included. However, it is on hats worn as part of fashionable
dress that part and whole birds are most frequently
found (Figures 16.8 and 16.9).
In the Victoria and Albert Museum dress collection
there are collars of grebe skins (Podiceps cristatus),
a Victorine of male eider duck heads (Somateria
mollissima) lined with down, muffs of sundry other
waterfowl, fans with humming birds (Trochilidae sp.)
applied to them and many other small bird skin items
dating from the nineteenth century. There is an
array of whole birds, part birds and bird plumage
attached to hats including birds of paradise (Paradisaea
sp.), humming birds (Trochilidae sp.), peafowls (Pavo
sp.) and many others. Swansdown (Cygnus sp.) (skin
on) is also to be found (Figures 16.10 –16.13).
16.3.1 Processing
Methods used by Inuit and Native American peoples
for processing bird skins have been published (Oakes,
1991; Oakes and Riewe, 1996). Simple methods
involving scraping the fat and blood from the skin
The tanning, dressing and conservation of exotic, aquatic and feathered skins 179
Figure 16.8 Greater bird of paradise (female) (Paradisaea
sp.) on hat c.1940s.
Figure 16.9 Greater bird of paradise (male) (Paradisaea
sp.) on hat c.1940s.
Figure 16.10 Victorine of male eider duck heads (Somateria mollissima) nineteenth century.
180 Conservation of leather and related materials
Figure 16.11 Fan c.1887 with whole hummingbird. Figure 16.12 Peafowl muff, hat and tippet, late nineteenth
century.
Figure 16.13 Peafowl muff, showing detail of head, late nineteenth century.
The tanning, dressing and conservation of exotic, aquatic and feathered skins 181
then sucking out the remaining fat were used with
alternative treatments including the use of urine, fish
fats and roe. Methods of bird skin preparation used
by taxidermists have also been published (Gerhardt,
1989). (For recipes see Chapter 14.) However, the
author has found no direct references or published
works dealing with the processing of bird skins with
feathers in situ by fur dressers or tanners from the
commercial skin trade. References are made concerning
the processing of turkey and ostrich skins in the
twentieth century but these had the feathers removed
and were prepared as leather and tanned, not tawed
or dressed.
It is logical to assume that the methods used for
preparing bird skins with feathers in situ intended
for use in fashionable dress would be similar to those
for furs, using alum, salt and oils and maybe formaldehyde
or other pickle. Arsenic and arsenical soaps,
including mixtures of arsenic, camphor and soap,
have been used in the processing of taxidermy specimens
and there are references to arsenic being used
to dress feathers for millinery purposes (Kliot and
Kliot, 2000). In some cases however, whole or part
bird skins may have been simply cleaned and dried.
There is evidence in portraiture, and records in
the wardrobe accounts of Elizabeth I, establishing
that feathers have been dyed since the sixteenth century,
and most likely before this time, but bird skins
when used in fashionable dress have usually been
chosen for the beauty and natural colours of the
feathers and therefore are not dyed. The exception
to this is swansdown (skin on) when it has been used
to make powder puffs and trimmings which may be
found dyed a variety of pale colours. Bird skins have
also occasionally been dyed for millinery purposes
when the diversity of nature has failed to provide a
suitable tone or hue to complement the seasons’
fashionable colour palette.
In 1888 Erdmann, a German chemist, took out a
patent for dyeing furs and feathers using oxydation
dyes. Feathers were first treated in an aqueous or
alcohol solution of para-phenylene-diamine then
exposed to the slow oxidation of the air. Alternatively
they were treated in a second solution with
an oxidizing agent. Particularly suitable were ferric
chloride, permangenates, chlorates and hydrogen
peroxide (Austin, 1922). It is possible these may have
been used on bird skins.
Occasionally feathers have been decorated with
painted designs, often using metallic pigments to add
an extra sparkling decorative element. These are most
usually only found on hats.
16.3.2 Conservation problems with
bird skins
1. In many cases damage may be directly attributable
to the original processing and drying, particularly
when residual fats were not adequately
cleaned from the skin. This can lead to a condition
known to taxidermists as ‘fat burn’ which is
rapid deterioration due to the oxidation of the
fats in the skin.
2. Bird skins are thin and the feathers protrude into
the dermis. Desiccation of the skins is one of the
major problems. This can lead to the follicles in
which the feathers sit opening as the skin shrinks
and the feathers falling out. When this occurs
the only effective option is overall consolidation
of the skin and securing the feathers using an
adhesive.
3. Fading of colours due to display in inappropriate
light levels.
4. Physical damage due to wear or poor storage.
A few articles have been published concerning
the conservation of feathers including Rae and Wills
(2002), Kite (1992, 1993) and Del Re (1988).
Some of these concern objects where the feathers
have been removed from the bird skins and the
feathers alone have been used to create the object
concerned so the treatment of the skin is not an
issue. However, Rae and Wills and Del Re discuss
treatments for bird skins with the feathers in situ.
For more information on the cleaning and conservation
of whole birds and part bird skins please refer
to Chapter 14.
The use of light brushing and vacuum suction, or
organic solvent and aqueous methods of cleaning, are
likely to be the usual options considered but since the
late twentieth century experiments have been undertaken
to test the efficiency of laser cleaning methods
for feathers (Lang, 1998/99; Solajic et al., 2002).
When further work has been undertaken this could
provide a useful alternative to currently available
choices.
For general information concerning the care and
conservation of bird skins the reader should consult
Chapter 14. Additionally, in certain circumstances,
much that applies to the conservation of fur-skins
may also be applicable to the repair of bird skins.
However, it is important to note that degraded and
desiccated bird skins may be extremely fragile and
the feathers may be very easily disrupted and dislodged
from the skin by handling. The skins may
also be dry and brittle and tear easily. Expert advice
182 Conservation of leather and related materials
should be sought by the inexperienced conservator
before any cleaning and conservation of feathers in
bird skins is undertaken, and before a bird skin trimming
on an item of dress is dismantled or any stitching
is unpicked in order to gain access to the backs
of the skins to effect an adhesive repair.
Endnotes
1. ‘Whitefish’ is most likely to be referring to the
beluga or white whale; however, today it refers
to commercially exploited members of the order
gadiformes (cod and relatives).
2. Prionaca glauca. Contemporary references use
various common and scientific names, e.g. blue
dogfish or ‘whaler’ or squalus glaucus.
3. Catfish. The name used for the large order,
Siluriformes, of fishes bearing barbels or ‘whiskers’
on the head, nearly all of which are freshwater
fishes, but also used for the distinctive marine
fish Anarhichas lupus, also called the wolf-fish
which yields an attractively spotted skin.
References
Arnold, J. (1988) Queen Elizabeth’s Wardrobe Unlock’d.
Leeds: W.S. Maney.
Austin, W.E. (1992) Principles and Practice of Fur Dressing
and Fur Dyeing. London: The Library Press.
Caunce, A.E. et al. (1946) The German Light Leather
Industry. B.I.O.S. Final Report No. 1425 item no. 22,
pp. 29–30, 184. British Intelligence Sub-Committee.
London: HMSO.
Cunnington, C.W. (1953) Feminine Attitudes in the 19th
Century. London: Heinemann.
Culbertson, C.M. (1922) The Art of Ostrich Plume Making.
Melvin and Meurgotten, Inc.
Del Re, C. (1988) Technology and Conservation of Five
Northwest Coast Head-dresses. Published in Symposium
86, The Care and Preservation of Ethnological Materials.
C.C.I. pp. 53–61.
Fuchs, K. and Fuchs, M. (2003) The Reptile Skin. Frankfurt-
am-Main.
Gustavson, K.H. (1956) The Chemistry and Reactivity of
Collagen. New York: Academic Press Inc.
Hickman, P. (1987) Innerskins and Outerskins: Gut and
Fishskin. San Francisco Craft and Folk Art Museum.
Hiekkanen, K. (1980) En kvinnodraekt av fiskskinn fran
Amuromradet: konservering och undersokning.
Konservering og restaurering af laeder, skind og
pergamen, pp. 321–327. Konpendium fra Nordisk
Videreuddannelsekursus 3–14 April 1978. Lund,
Sverige: Kulturen.
Ingram, P. and Dixon, G. (1994) Fishskin Leather: An
Innovative Product. Journal of the Society of Leather
Technologists and Chemists, 79, 103–106.
Kite, M. (1992) Skin Related Materials Incorporated into
Textile Objects. Post-prints of the ICOM-CC Conservation
of Leathercraft and Related Objects Interim Symposium.
24–25 June 1992, pp. 33–35.
Kite, M. (1993) Feathers and Baleen, 2 Keratin
Materials Incorporated into Textiles. Pre-prints of the
ICOM-CC Triennial Conference, Washington 1993,
pp. 645–650.
Kite, M. (1999) The Conservation of a 19th Century
Salmon Skin Coat (626 –1905). Pre-prints of the ICOMCC
Triennial Meeting, Lyon 1999, pp. 691–696.
Kliot, J. and Kliot, K. (eds) (2000) Millinery, Feathers,
Fruits and Flowers. Lacis.
Lang, U. (1998/99) Laser in der Restaurierung.
Seminararbiet im WS 1998/1999 an der FHTW.
Berlin: Studiengang Restaurierung/Grabungstechnik.
Ledger, F. (1982) Put Your Foot Down. Melksham: Colin
Venton, p. 158.
Murray, W. (1994) Conservation of a Pair of Fish-Skin
Boots. SSCR Journal, 5(3), 13–14.
Neergaard, L. (1991) Fishskin Leather, an Old Idea that’s
New. San Francisco Chronicle, 24 May, p. 2.
Oakes, J. and Riewe, R. (1996) Our Boots, an Inuit Women’s
Art. London: Thames and Hudson.
O’Flaherty, F., Roddy, W.T. and Lollar, R.M., eds
(1958) The Chemistry and Technology of Leather. Vol. II.
Types of Tannage. New York: Reinhold Publishing
Corporation.
Pancaldo, S. (1996) Examination and Treatment Report:
A Western Eskimo Fish Skin Bag. (Unpublished
Report.)
Rae, A. and Wills, B. (2002) Love a Duck: The Conservation
of Feathered Skins. In The Conservation Of Fur
Feather and Skin (Margot Wright, ed.). pp. 43– 61.
Seminar organized by Conservators of Ethnographic
Artefacts held at Museum of London, 11 December
2000. London: Archetype.
Schultz, G.W. and Schubert, A. (1945) An Investigation
of the German Leather Industry. Miscellaneous Report
No. 2: report prepared by H.Q. Theatre Service
Forces, European Theatre Office of the Chief
Quatermaster. British Intelligence Objectives SubCommittee.
London: HMSO.
Solajic, M.R., Cooper, M., Seddon, T., et al. (2000)
Colourful Feathers. In The Conservation of Fur Feather and
Skin (Margot Wright, ed.). pp. 69–78. Seminar organized
by Conservators of Ethnographic Artefacts held at
Museum of London, 11 December 2000. London:
Archetype.
Sturge, T. (2000) The Conservation of Leather Artefacts,
Case Studies from the Leather Conservation Centre.
Northampton: The Leather Conservation Centre.
The tanning, dressing and conservation of exotic, aquatic and feathered skins 183
Unattributed (1880) The Boot and Shoe Trades Journal, 17
January 1880.
Unattributed (1887) The Boot and Shoe Trades Journal, 25
June 1887.
Unattributed (1993) Aquatic Leathers. Leather, March,
20 –21.
Vincent, J. (1978) Structural Biomaterials. Princeton, NJ:
Princeton University Press.
Whitear, M. (1986) Biology of the Integument, 2 Vertebrates.
(Bereiter-Hahn J., Matoltsy K. and Sylvia Richards K.,
series ed). pp. 8–38.
Wills, B. (2000) A Review of the Conservation Treatment
of a Romano-Egyptian Cuirass and Helmet Made from
Crocodile Skin. The Conservator, 24, 80 –88.
17.1 Introduction
A book in its entirety could be devoted to the conservation
of ‘ethnographic leather’; that is skin and
leather products of first nation, indigenous or aboriginal
peoples. However, this chapter, within the
wider context of a volume on a broad range of leather
and skin materials, is intended to serve as an introduction,
to signpost readers to other published sources. A
factor when dealing with ethnographic skin materials
is to understand them within the context of the
function or purpose of the object concerned and the
culture that made it, and the uses to which this object
was then put. The sensitive and possibly sacred nature
of some first nation and ethnographic objects must
be taken into account before any conservation
treatment is undertaken.
Material and species identification is of great
importance. Hair fibre identification can be of great
assistance as can carefully measuring the size of the
skins and having some global idea of where the item
originated when trying to identify the material
(Appleyard, 1978; Chapman, 1982). Parts from now
endangered or protected species of the animal kingdom
may be incorporated into ethnographic material.
Human remains may be part of the collections
or may be incorporated into objects.
The aim of this chapter is to highlight factors
which may influence decisions made for the conservation
treatment of ethnographic leather and skin
materials.
17.2 Ethics
Certain ethnographic objects have what can be
described as a ‘silent heritage’ relating to the use of
the object before it was collected. Within specialist
ethnographic collections the spiritual and intangible
aspects of these artefacts must be recognized and
understood to be an important element of collections
management and care. Originating cultures’ concerns
should be treated with respect and every effort must
be made not to compromise them during their handling,
storage and care, when they come within a
museum context (Patterson and Greenfield, 1998).
Certain conservation processes may be thought profane
such as handling by one gender, fumigation or
the use of non-kosher or taboo repair materials. For
example, kosher parchment should be used for Torah
repair (Thompson, 1998).
Animist societies believe that the natural world is
animated by an immaterial force, a vital breath, a
spirit. Objects made from or decorated with skins and
fur can possess the stolen talents of the creature whose
first skin it was. Objects associated with Shamanism
and Totem objects come within this category. Items
may have sacred and ceremonial functions which
should be understood before conservation treatment
is applied. Consultation with the descendants
of originating cultures is desirable and can be legally
required.
Human remains may fall to the care of a conservator,
though this is less common now that indigenous
peoples have successfully applied for repatriation of
their ancestors. Examples in the past have been
South Amerindian shrunken and Maori tatooed
heads.
17.3 Uses
Ethnographic skin materials may be found in an enormous
range of objects; shelters including tipis and
184
17
Ethnographic leather and skin products
Sherry Doyal and Marion Kite
Ethnographic leather and skin products 185
other tents, clothing including gut garments, transport
items such as animal harnesses and saddles, or
boats such as the kayaks of the Arctic or coracles of
Europe. Whole skins are typically used as vessels for
water or wine. Membranes such as stomachs are
used for bags. Skin is employed in the fabrication of
weapons, such as war clubs of stone and raw hide,
bolos and knife sheaths. Tools may also be manufactured
from skin, for example ray skins are used as
rasps by Pacific peoples. Musicians play strung gut
or stretched drum skins. Homes are furnished with
skins and pelts as floor and bed coverings and in furniture,
such as African chairs of state or raw hidethonged
seating of Asia.
17.4 Tanning methods
The various methods used for the tanning and
preparation of skins are dealt with elsewhere in this
volume. Techniques of brain or oil tannage, vegetable
tannage and the production of raw hides
are all of interest to those working with ethnographic
collections. Some skins may have little
preparation, for example bird skins may simply have
fats scraped or sucked from the skin before they are
dried.
The local availability of materials to the peoples
of a region give a specific colour and quality to the
hides and skins they prepare. This regional distinctiveness
can help the specialist provenance and give
an attribution to an object. For example, Amerindians
use plant materials including barks, roots and seeds
for tan liquors, plant additions to brain slurries for
oil tanning, and seed cones, leaf and wood for smoking.
The plants differ from one tribe to another
(Moerman, 1998).
The effect of smoking renders skins more waterproof
and can add colour. Different types of fuel
were selected to produce differing shades including
yellows ( juniper leaf ), browns (black spruce cones)
and reds. Both Amerindian and Sami peoples have
used alder smoke to add red colour to leather. These
smoked colours can be light sensitive. Sometimes
rotten wood was used for smoking. Fungal action
on the wood had the effect of removing the cellulose
leaving the lignin behind. When burned this
released phenols which colour the skin and complex
aldehydes such as acrolein which have a tanning
action (Mason, 1889).
Not all ethnographic skins are tanned. Often raw
hide is used in the manufacture of an object. The fact
that green raw hide shrinks and tightens as it dries can
be used to good technical effect. The widespread use
of raw hide strips to bind the stone and metal heads
of axes and other tools to wooden antler and bone
handles are examples of this. Raw hide items are
hygroscopic and very susceptible to changes in
relative humidity. An object can become distorted
or even split due to the tensions exerted by raw hide
subjected to inappropriate humidity, particularly
when combined with other, less environmentally
responsive materials.
17.5 Construction techniques
Skins can be sewn with sinew or tendon. Post-contact
cotton, linen and synthetic threads are used. Seams
may be constructed in such a way as to make them
waterproof, as those routinely used by Inuit when
making footwear (Oakes and Riewe, 1995). Seal
gut parkas may have a dried grass incorporated
into seams so that they swell on wetting, improving
waterproofing.
17.6 Decoration
Surface decoration on ethnographic skin objects may
be complex and incorporate beads, paint, pigment,
quill, applied feathers, applied hair, shells, metal
Figure 17.1 Model kayak, after conservation. Early twentieth century. (Collection of the late Colonel Andrew
Croft, DSO, OBE.)
186 Conservation of leather and related materials
tinklers and sundry other materials. Some large
objects with skin or leather coverings may be studded,
close nailed, have scratched or impressed decoration,
inlays and some will be inherently unstable.
Fringes can be used as a decorative effect or for
functional purposes; acting as fly swats on clothing,
animal trappings or tents or for wicking moisture
out of wet garments to assist performance in wet
conditions. Fringes and thongs are also worked into
cordage from which items such as animal halters are
made (Grant, 1972).
17.7 Conservation
17.7.1 Pre-treatment examination
Expect the unexpected; so-called exotic skins of
Europe may be commonplace in the country of
origin. Reptile, bird and fish skins and small mammals
are all used.
When ethnographic objects are presented for conservation
skins and pelts should be examined for signs
of wear which can provide evidence of use. Pigment
residues on the interior of skin garments may be
from body colouring, powder may be evidence of
pre-collection cleaning using clays and both may
preclude vacuum cleaning as part of the conservation
treatment. One author has found remains of lice,
of interest to biologists, on horse hair used to decorate
a skin garment.
Human remains, may have been consolidated in
the field.
17.7.2 Poisons – health and safety issues
Ethnographic skins and leathers, particularly those
originally acquired by natural history collectors, may
have been subject to post-collection treatments to
prevent insect and other pest damage and may harbour
residual biocides. These can include arsenic compounds,
mercuric chloride, DDT (dichlorodiphenyltrichloroethane),
naphthalene, paradichlorobenzene,
methyl bromide, thymol (3-hydroxy-p-cymene)
and ethylene oxide ( Johnson et al., 1999). These
chemicals can continue to have a deleterious effect
on life, including human health. It is suggested that
disposable gloves, dust smocks and dust masks
should be worn during handling, particularly cleaning.
Poisons may also react with objects (HowattKrahn,
1987), for example methyl bromide is said to
Figure 17.2 Large sealskin bag, hair on, after conservation. Early twentieth century. (Collection of the late Colonel
Andrew Croft, DSO, OBE.)
Ethnographic leather and skin products 187
cause leather products to give off unpleasant odour
after treatment (Florian, 1985).
17.7.3 Condition
It is important to remember that condition may vary
throughout a single skin, either because of the health
of the animal or variables in skin preparation. Wear,
dryness, cracking, damaged or brittle hair, hair slippage,
matting, insect damage, curling or straightening
of hair, acidity, shrinkage, damaged or failed seams
and splits, rips and tears may all be found in ethnographic
skin objects.
It is likely that skins will be acidic due to the
degradation or oxidation of the fats and oils used in
the initial preparation (Storch, 1987). Metal beads
and tinklers which may form part of the object may
have reacted with these oils forming acidic corrosion
products and causing staining. The acidic nature
of the object may have caused sinew or other sewing
thread to deteriorate leading to bead loss or the
cohesion of the structure to break down. Applied
copper decorations or alloys containing copper can
cause particular problems. At Exeter City Museums
a Native American dagger sheath ornamented with
brass dome-headed nails had such an excess of waxy
green deposits of cupric ester formation below the
domes that the studs were being pushed back out of
the leather.
Excess alkalinity of certain glass beads can cause
damage to the sewing threads and skin as they deteriorate.
This problem is known as ‘glass disease’ and
occurs in beads when the alkali constituents in the
glass mixture leach out to the surface of the glass in
high relative humidities (Carrol and McHugh, 2001).
17.7.4 Cleaning
Initial surface cleaning may be a simple vacuuming,
and for furs, a gentle tamping and air-blower grooming.
A hair dryer set to cold or compressed air can be
used. Fur should be blown in the direction of hair
growth. Objects can be cleaned under extraction, in
a fume hood or using a vacuum cleaner fitted with a
hose and funnel to catch dust raised. Low powered
vacuum suction cleaning can be employed assisted
with a soft brush such as a squirrel hair mop or
baby’s hair brush. Before surface cleaning by vacuum
suction it is important to inspect furs carefully.
The technique of checking or cracking skins, used by
Arctic peoples to create ventilated skins (Rahme and
Hartman, 2001), by cracking the epidermis so that
tiny flaps of skin with fur attached cover a garment,
creates a surface which is very vulnerable to damage
by vacuum suction. Slippage of fur may be an inherent
weakness in a skin resulting from unsuitable methods
of preparation. Additionally insect pests may cut fur
at the epidermis and this hair may not become
detached until disrupted by cleaning. (See chapter on
furs for further cleaning information.)
When working with deep furs such as a sheep
skin, it can be useful to build a frame with an open
weave mesh stretched over it. The skin is placed hair
side down over a light-coloured bench or onto lightcoloured
paper. The flesh side can be tamped by patting
gently with the hand or a fly swat. This releases
particulate matter from the root of the hair where it
may be causing abrasion, without disrupting the lay
of the hair. The matter sifts through the screen onto
the light-coloured surface were it can be checked for
insect debris or an unexpected amount of loose hair,
vegetable matter, etc. before it is vacuumed away.
Then the skin can be turned flesh side down onto the
table and the hair is vacuumed through the screen. If
the item is relatively robust this procedure may be
repeated until very little soiling is being released.
After initial surface cleaning further cleaning may be
required. It is important to trial clean several small areas
to help decide on an appropriate level of cleaning.
Figure 17.3 Small decorated sealskin bag, after conservation.
Early twentieth century. (Collection of the late
Colonel Andrew Croft, DSO, OBE.)
188 Conservation of leather and related materials
Aqueous cleaning is rarely suitable for ethnographic
leather but mechanical surface cleaning using soft
erasers, smoke sponges and chemical sponges is often
very effective. Materials need to be cleared from the
object by further low powered vacuuming.
17.7.5 Solvent cleaning
An author still shudders at the memory of a comment
made at the first conservation conference she
attended over 25 years ago. A speaker recounted,
with some delight, the wonderful scents of berries
and smoke released when submitting skin garments
to a solvent dry cleaning process. What materials
were being extracted? In the intervening years conservators
have learnt to do less to the items in our
care. We have learnt this from conservators before
us who were prepared to admit their mistakes or
whose mistakes have only been revealed by the
passage of time.
A suitable local solvent cleaning process for furs
with oil-adhered soiling would be the grooming of
the fur with a white flannel cloth pad moistened
with white spirit BS245 or Stoddard solvent wiped
lightly over the surface of the fur. The pad should
be changed as it becomes soiled. When the solvent
has evaporated off the fur can again be vacuumed to
remove released soiling. Stains and surface soiling can
be spot cleaned using swabs. The technique used is
to ring the stain with solvent and work inwards,
blotting to remove soiling. (For further information
see chapter on furs.)
17.7.6 Reshaping
Providing the skin is strong and not brittle and fragmented,
areas stiffened by wetting may be softened
by manipulation with a blunt tool (such as a bone
folder) to loosen and flex stiff collagen fibre bundles.
This may be assisted by the penetration of the skin
with a 70/30 (v/v) ethanol and water mix to prevent
cracking and the skin is gently manipulated
until dry (Lougheed et al., 1983).
Historically, reshaping of ethnographic skins has
been undertaken using humectants, oils, oil emulsions,
organic solvent conditioning and humidity to
soften the skins prior to the reshaping treatment
(Sully, 1992). In the past overoiling has resulted in
residual spews and overall stickiness causing problems
years after the treatments were undertaken. At the
time of writing the authors’ preferred reshaping treatment
is to humidify the skin and gradually manipulate
the object back to shape as it softens, as it reaches
equilibrium in an environment of gradually increasing
humidity. When considering humidification one
should remember that the thinner the skin the more
likely there is to be an adverse reaction to wetting
which may easily occur where direct application of
humidity is used (with a spray or ultrasonic humidifier,
for example). Semi-tanned leathers are hydrophilic
(Schaffer, 1974). Humidification should not be rushed
and should be undertaken as a gradual, controlled
process. Local treatments using humidity membranes
such as Sympatex or Gortex can be applied
to small areas such as a distorted strap. Unbuffered
acid-free tissue paper puffs, conditioned to a higher
relative humidity than the object, can be used to pad
out areas such as collapsed skin backs to masks. The
puff will gradually release the humidity into the
object. More puffs are added as the shape is eased out.
Whole object treatments can be applied in a humidity
chamber. This is, for example, particularly effective
for skin garments being brought back to shape for
mounting on mannequin figures. A chamber can be
as simple as a polyethylene tent using salts or glycerol
to set the humidity within the chamber or as
complex as fully automated electric systems.
Tears and curling edges may need to be reshaped
and flattened, subject to tests, with ethanol before
repairs are carried out (Kaminitz and Levinson, 1988).
When tears are realigned and objects are reshaped
then a method of securing and holding the object in
the desired position will need to be found. Glass
weights or small sand bags may be used where suitable
for flat items. Sand bags have advantages over glass
weights as the humidified object can dry through the
weight. Glass weights can trap evaporating moisture
causing tidemarks. For three-dimensional items,
blocking on mounts, unbuffered tissue, crushed nylon
net, or inflated polyethelene bags may all be used to
hold the object in shape. The object should be
allowed to return slowly to ambient conditions while
blocked.
17.7.7 Mounts/internal supports
Damage has frequently been done to threedimensional
skin objects by either poor storage or display
(McNeil et al., 1986; Niinimaa, 1987; Rose and
Amparo, 1992). Mounts are ideally made to provide
support both in storage and on display; however,
storage volume may be much increased by this.
A good mount can reveal much about the construction
of an object and may make invasive repairs
unnecessary. Mounts should be produced to fit the
object because skin items may stretch or take up the
Ethnographic leather and skin products 189
shape of a poorly shaped support (such as a mannequin
with a 1950s exaggerated and pointed bra shape). The
mount should provide support to eliminate sagging
and stress on the object and to avoid creases.
Successful conservation is often a collaboration
between object conservator and skilled mount
maker. For hard mounts metal and acrylic sheet
working skills are required and for soft mounts
sewing and tailoring skills. Just as important is good
information about how skin items were used or
worn. Consultation with indigena, period drawings,
photographs and anthropologists’ notes are all valuable
assets when devising a mount. The visual material
can also be displayed alongside mounted items to
further explain an exhibit.
Mannequins may be custom made from Ethafoam
plank (Larouche, 1995) or commercial mannequins
made of papier mâché can be customized with a saw
and then covered with a foil such as Moistop to seal
emissions. Either type may then be padded with polyester
felt or wadding and covered with cotton calico
or cotton stockingette. The latter has the advantage of
requiring fewer tailoring skills. The cotton fabrics can
be dyed with a conservation quality dye system to give
a range of skin or display colours. Heads, arms and
legs can be tailored in wadding and cloth over an
Ethafoam tube core. Support underpinnings or
undergarments can be made by taking a pattern from
the clothing and cutting this shape in polyester felt,
this has bulk and will stand away from the mannequin
to offer support, for a cloak or the skirt of a coat, for
example. The felt can be covered with knitted, pile or
napped fabrics used to ‘key’ into the nap surface of the
skin garment to provide a friction mount with overall
support. Alternatively the mount can be covered with
a slippery fabric such as nylon or silk if static or abrasion
is a concern. A brass pole system can be used to
secure the mount within the case. Brass can be cushioned
with Ethafoam or coated by heating and dipping
into powdered polyethylene.
For further information on mount making see
McNeil et al. (1986), Kaminitz and Levinson (1988),
Kite (1994), Kite and Hill (1999), Stephens and
Doyal (2002).
17.7.8 Mending
As a general principle, mends should be weaker than
the object being repaired. When working with material
which is subject to dimensional change it is
important that repairs rather than the object should
fail. Some conservators prefer to use like with like
materials, that is they choose materials similar to those
of the object so that the expansion and contraction
rates of the mend are similar to the object and therefore
avoid or minimize tensions between the mend
and the object. The temperature and humidity of
storage, conservation and display areas and the season
in which a mend is made all have impacts on success.
17.7.9 Repair supports
Repair supports may be used to give either a suture,
patch or full support to an object. When choosing
skin products for repairs, criteria to be considered
include trying to match the grain, weight, colour and
spine direction, and establishing which is the hair or
flesh side (Munn, 1985). Thin semi-transparent supports
include gold beaters’ skin made from cattle intestine.
This can be laminated with gelatine (Kaminitz
and Levinson, 1988). Membrane from the swim
bladders of fish including sturgeon, cod, hake and
whiting has been used (Munn, 1985) as has sausage
casing. These should be degreased with acetone or
ethanol before use and can be pumiced for better
adhesion and to cut gloss.
Synthetic web fabrics, non-woven heat-bonded
polyester and nylon also may be used. These may be
dyed to tone with the object using synthetic dye
(Munn, 1985).
17.7.10 Sewing
Tacketing or thonging (Munn, 1985), unwaxed
nylon dental floss (Kaminitz and Levinson, 1988)
and sinew (Kite, 1999) are a few of the materials
which have been used for sewn repairs to ethnographic
objects.
17.7.11 Adhesives
Much has been written about adhesives in other
chapters. However, the basic criteria for selecting an
adhesive for use on ethnographic objects include viscosity,
so that the adhesive does not carry through
the skin, flexibility, and that strength should be a little
lower than the skin to be repaired. The shrinkage
temperature of the skin to be repaired must also be
considered. Beva 371, Acraloid B72, polyvinyl
acetate, wheat starch paste, pharmaceutical clear
gelatine or parchment size are some of the most
frequent choices made (Lowenthal et al., 2003).
Many more adhesives are of course suitable in certain
circumstances (Fenn, 1984; White and Sully, 1992).
Treatment decisions will also be influenced by
how the object will be used, mounted, displayed,
travelled, or stored.
190 Conservation of leather and related materials
17.7.12 Cosmetic repairs and infills
Infills of similar weight support material can be butt
jointed (to create little tension) with a supporting
patch below. A semi-transparent overlay or a combination
of support and overlay can be employed if
the area around the loss is weak or the object so thin
that a butt joint has little strength. Synthetic furs can
be used in pelts (Nieuwenhuizen, 1998) or, for display
purposes, well-matched new fur may be temporarily
laid over insect-damaged furs.
For gap fills where leathers have shrunk and split
Beva 371, glass micro ballons and dry pigment have
been used (Nieuwenhuizen, 1998; Kronthal et al.,
2003). Also papier mâché toned with pigments.
Bulked fills can be textured using cast impression
moulds.
17.7.13 Storage
Storage should be cool, dark and well ventilated.
Items should be protected from dust by being cased,
boxed, placed in enclosed storage or stored under
cloth dust covers (Walker, 1988). Storage furniture
should be made of materials with no acidic emissions
such as stove-enamelled metal. Because of the
vulnerability of semi-tanned leathers to water damage
a store location away from overhead pipes and
water storage is much preferred. Supports are
important, especially for heavier skins and furs. To
avoid stretching, mounts or rigid supports may be
required. Stacking items without dividers should be
avoided as an impression of one object may be left
on another.
Items folded when supple may stiffen and set in
the storage position. This should be considered when
packing items. The use of unbuffered acid-free tissue
for storage of proteinaceous material should be considered
as the alkaline buffering material may leach
into the object. Sticky items may need silicone
release packaging materials. It should be appreciated
that fatty spew may pool in depressions in objects
during storage and that dust is attracted to spew.
Storage areas should be checked at least twice
yearly for evidence of insect infestation and insect
monitoring traps are recommended in storage and
display areas. Before entering the store, items may
be cycle frozen as an infestation preventive measure
(Florian, 1986). Reduced temperature storage has
been used for the preservation of oil-tanned items
(Fenn, 1985) and as a pest deterrent. However, a
breakdown of the cooling system can cause a hazard
by exposing items to extremes of relative humidity
(Lougheed et al., 1983). It should be remembered that
cold stored items should be well supported and
brought to ambient temperatures before handling as
they may be stiff and more brittle when cold (Carrlee,
2003).
17.7.14 Display
In common with most organic materials relative
humidities of 45–55% and temperatures of no more
than 21°C are suggested for the display of ethnographic
materials. Light may fade smoke-dyed
leathers and dark furs or cause light furs and repair
adhesives to yellow. A light level of 50 lux with
an ultraviolet light content of less than 75W/lm is
suggested.
References
Appleyard, H.M. (1978) Guide to the Identification of Animal
Fibres. Leeds: British Textile Technology Group.
Carrlee, E. (2003) Does Low-temperature Pest Management
Cause Damage? Literature Review and
Observational Study of Ethnographic Artifacts. Journal
of the American Institute for Conservation, 42(2), 139–141.
Carrol, S. and McHugh, K. (2001) Material Characterisation
of Glass Disease on Beaded Ethnographic
Artefacts from the Collection of the National Museum
of the American Indian. In Ethnographic Beadwork.
Aspects of Manufacture, Use and Conservation (Margot
Wright, ed.). London: Archetype.
Chapman, V. (1982) Scale Impressions of Animal Fibres:
A Simple Method. Conservation News, 18, 14.
Florian, M-L. (1985) A Holistic Interpretation of the
Deterioration of Vegetable Tanned Leather. Leather
Conservation News, 2(1), 1–5.
Florian, M-L. (1986) The Freezing Process: Effects on
Insects and Artifact Materials. Leather Conservation
News, 4, 6 –15.
Grant, B. (1972) Encyclopaedia of Rawhide and Leather
Braiding. Centerville, MD: Cornell Maritime Press.
Howatt-Krahn, A. (1987) Conservation: Skin and Nativetanned
Leather. American Indian Art Magazine, Spring,
44 –51.
Johnson, J. et al. (1999) Masked Hazard. In Common
Ground, Archaeology and Ethnography in the Public
Interest, Fall, 26 –31. Washington: NPC Archaeology
and Ethnography Program.
Kaminitz, M. and Levinson, J. (1988) The Conservation
of Ethnographic Skin Objects at the American Museum
of Natural History. Leather Conservation News, 5, 1–7.
Kite, M. (1994) Support Stands for the Storage and
Display of Hats. The Poster Summary Booklet for the IIC
Congress, Ottawa.
Kite, M. and Hill, A. (1999) Polyester Wadding, Perspex,
Vilene, Gatorfoam and Ethafoam used in the Preparation
of Supports for 3-dimensional Textiles. Post-prints of the
Ethnographic leather and skin products 191
ICOM-CC Textiles Working Group Symposium Amsterdam,
1994. London: Archetype.
Kite, M. (1999) The Conservation of a 19th Century
Salmon Skin Coat (626 –1905). Preprints of the ICOMCommittee
for Conservation 12th Triennial Conference
Lyon 1999, II, pp. 691– 696. ICOM.
Kronthal, L., Levinson, J., Dignard, C. et al. (2003)
Beva 371 and its Uses as an Adhesive for Skin and
Leather Repairs: Background and Review of Treatments.
Journal of the American Institute for Conservation, 42,
341–362.
Larouche, D. (1995) Intersecting Silhouette Mannequins.
Textile Conservation Newsletter, Spring supplement.
Lougheed, S., Mason, J. and Vuori, J. (1983) Repair of
Tears in Skin Garments. Journal International Institute for
Conservation, Canadian Group, 8 & 9, 13–21.
McNeil, K.C., Johnson, J.G., Joyce, D.J. et al. (1986)
Mounting Ethnographic Garments. Curator, 2(4),
279–293.
Mason, O.T. (1889) Aboriginal Skin Dressing: A Study Based
on Material in the US National Museum. Annual report of
the Smithsonian Institute, pp. 553–589.
Moerman, D.E. (1998) Native American Ethnobotany.
Portland, Or.: Timber Press.
Munn, J. (1985) Examination and Treatment of Vellum. In
Recent Advances in Leather Conservation. Washington: AIC.
Nieuwenhuizen, L. (1998) Synthetic Fill Materials for
Skin, Leather and Furs. Journal of the American Institute
for Conservation, 37, 135–145.
Niinimaa, G.S. (1987) Mounting Systems for Ethnographic
Textiles and Objects. Journal of the American Institiute for
Conservation, 26, 75–84.
Oakes, J. and Riewe, R. (1995) Our Boots – An Inuit
Woman’s Art. Toronto: The Bata Shoe Museum.
Patterson, C. and Greenfield, J. (1998) Storage Considerations
for Native Arts: A Joint Project between the
Denver Art Museum and the American Indian Communities.
Preprints of the Scottish Society for Conservation
and Restoration Conference Dundee (M. Wright and
Y. Player-Danhnsjö, eds). SSCR.
Rahme, L. and Hartman, D. (2001) Leather – Preparation
and Tanning by Traditional Methods. Portland, Or.: The
Caber Press.
Rose, C.L. and Amparo, R. de T., eds (1992) Storage of
Natural History Collections: Ideas and Practical Solutions.
Society for the Preservation of Natural History
Collections.
Schaffer, E. (1974) Properties and Preservation of
Ethnographical Semi-tanned Leathers. Studies in
Conservation, 19, 66 –75.
Stephens, M. and Doyal, S. (2002) Round the World on a
Mannequin. In Home and Away – Approaches to Textile
Conservation Around the World. UKIC Textile Section.
Storch, P.S. (1987) Curatorial Care and Handling of Skin
Materials: Part II Semi-tanned Objects. Conservation
Notes, 18. Austin: University of Texas.
Sully, D.M. (1992) Humidification: The Reshaping of
Leather, Skin and Gut Objects for Display. In ICOM
Committee for Conservation, Leathercraft Group Symposium
London pp. 50 –54. ICOM.
Thompson, J.T. (1998) On Restoring Sacred Objects.
Leather Conservation News, 14(2), 1– 6.
Walker, S. (1988) Using Tyvek in Protective Covers for
Artefacts. Museum Quarterly, 16(4), 23–25.
White, S.J. and Sully, D.M. (1992) The Conservation of
a Siberian Parka: A Joint Approach. In ICOM Committee
for Conservation, Leathercraft Group Symposium. London
pp. 54 –57. ICOM.
Bibliography
Other works on the preparation, use and conservation of
ethnographic skin products include the following.
Anon. (2001) Arctic Clothing from Igoolik. London: British
Museum.
Burnham, D.K. (1992) To Please the Caribou. Ontario:
Royal Ontario Museum.
Conservation Notes. Canadian Conservation Institute
Various Authors
N6/4 Care of Objects Decorated with Glass Beads
N6/5 Care of Quillwork
N8/3 Care of Mounted Specimens and Pelts
N8/4 Care of Raw Hide and Semi-tanned Leather
Fitzhugh, W.W. and Crowell, A. (1988) Crossroads of
Continents – Cultures of Siberia and Alaska. Washington:
Smithsonian Institute Press.
Hickman, P. (1987) Innerskins and Outerskins: Gut and
Fishskin. San Francisco: San Francisco Craft and Folk
Art Museum.
Hobson, P. (1977) Tan Your Hide! Home Tanning Leather
and Furs. Vermont: Storey Books.
Horse Capture, G.P., Vitart, A., Waldberg, M., et al.
(1993) Robes of Splendor: Native North American Painted
Buffalo Hides. New York: The New Press.
Horse Capture, J.D. (2000) Beauty, Honor and Tradition: The
Legacy of Plains Indian Shirt. Washington: Smithsonian
Institution.
Morphy, H. (1998) Aboriginal Art, pp. 160 –161, 337,
357, 104. London: Phaidon.
Wright, M. ed. (1998) Conservation of Leather Skin and
Hair. Conservators of Ethnographic Artefacts. London:
Archetype.
Wright, M. ed. (2001) Ethnographic Beadwork, Aspects of
Manufacture, Use and Conservation. Conservators of
Ethnographic Artefacts. London: Archetype.
Wright, M. ed. (2002) The Conservation of Fur Feather and
Skin. Conservators of Ethnographic Artefacts. London:
Archetype.
This chapter includes some of the less obvious and
unusual skin-related materials including gut membranes,
glue, gelatine, isinglass, and others which may
be the concern of conservators.
These materials may have been used in the production
of an object or may be useful materials
employed by conservation specialists during the
process of conservation of an object.
18.1 Animal glues and fish glues
Animal glue is, as the name suggests, derived from
animals and has been used since antiquity. There are
no exact records telling when and where animal and
fish glues were first used but it is known that at least
3500 years ago these glues were used in Egypt and
were made by being melted over fire and applied
with a brush (Darrow, 1930). From the first century
Roman scholar Plinius we learn that two kinds of
glue were used, taurokalla in Greek, gluten taurinum
in Latin made of the skins of bulls and ichtyokalla
made from parts of fishes (Petukhova, 2000).
Connective tissue in skin, bone and other tissue is
made up of proteins, principally collagen with small
amounts of other components including plasma
proteins and elastin.
These proteins are partly hydrolysed on heating in
water, acids or alkalis to produce a soluble product
generically known as glue. The degraded collagen
which goes into solution is concentrated by evaporation
until protein solids reach upwards of 45%.
They are then cooled and set to gel. The remaining
water is then removed and the dried product is
ground into particles ready for use. Details of the
various processes involved are given by Young
(1971).
Animal glues have a number of special characteristics,
but are unique in having three phases:
1. liquid when in hot water
2. gel when water nears room temperature
3. solid when water has been evaporated out.
Glues, as used by craftsmen and conservators alike,
include a range of products derived from a range of
animals and are of varying purity. The quality of an
animal glue is based on its gel strength. This is
determined by:
1. the source of the collagen
2. the aggressiveness of the treatment applied to
extract the collagen
3. the stage at which it is extracted
4. the amount of impurities and lesser proteins
included.
18.2 Skin glues and hide glues
Skin glues are derived from cattle and sheep skins
and are known as hide glues or parchment glues
depending on the material from which they are
made. They may contain contaminants from skin
preservatives or tanning agents. These skin or hide
glues have the highest strength of the animal glues.
Acid hydrolysis or alkaline hydrolysis can be the
method employed to break down or denature the
collagen molecules and allow the protein to be
brought into a colloidal suspension.
Glue is soluble in few solvents at room temperature
but will swell in cold water to form a gel. The gel
from animal glues will melt on heating to 30 –50°C
(Horie, 1987). The pH of hide glue is 6.0 –7.5.
192
18
Collagen products: glues, gelatine, gut membrane
and sausage casings
Marion Kite
Collagen products: glues, gelatine, gut membrane and sausage casings 193
Hide glues are used in the manufacture of wood
joinery, bookbinding, abrasive papers, gummed tapes,
and matches.
18.3 Parchment glue and
parchment size
Parchment glue was used by medieval craftsmen to
strengthen weak parchment and for patching and
joining parchments (Reed, 1972).
Over 100 years ago a recipe for preparing parchment
glue was given by Watt (1897) and involved
boiling 21 grams of parchment scraps soaked in 21
⁄2
litres water for 45 minutes, or longer if a stronger
size was required.
A general method and recipe used today is to soak
fine shavings or pieces of parchment in cold water
followed by prolonged boiling. The parchment collagen
is degraded to varying degrees from swollen,
hydrated collagen fibrils to gelatine (Haines, 1999).
Parchment glue has been used as a consolidant
and as an adhesive by conservators from many disciplines
and has been used for resizing archival papers
that have been washed.
Parchment glue and rabbit skin glues have been
used in the production of gessoes and in gilding.
18.4 Rabbit skin glue
True rabbit skin glue is made from rendered down
rabbit skins and like parchment glue goes readily
into solution. Rabbit skin glue has many applications
in fine art and especially in gilding. It is flexible
but its structural strength is weak so is not used
for gluing any material under stress.
18.5 Bone glue
Bone glues are derived from the bones, sinew and
cartilage of most farm animals. Bone glues are considered
inferior to skin and parchment glues.
Typically the pH ϭ 5.8– 6.3 (Hubbard, 1977).
Bone glues are commercially used as carton and
box adhesives.
18.6 Gelatine
Gelatine is a purified form of hide glue. It can be
rendered insoluble by reacting it with trivalent
metal ions, tannins or aldehydes. The production of
gelatin is normally brought about by giving skin and
other collagen containing materials treatment with
either lime or acetic acid, followed by heat.
Gelatine prepared with alkali has slightly different
properties to that prepared with acid. For the production
of high quality gelatin of uniform composition,
the skin of immature pigs is used, treated with
acetic acid followed by heating (Haines, 1999).
Since the nineteenth century gelatine solutions
have been used widely for adhering and consolidating
objects from many disciplines. Mercuric chloride
or formaldehyde may have been used as an
additive to inhibit mould growth (Horie, 1987). If
so, then the mercuric chloride would be detectable
using EDXRF analysis and the formaldehyde would
cause crosslinking and the gelatine to be insoluble.
From the late 1880s until well into the 1930s, costume
and accessories were decorated with sequins.
(Figure 18.1). Frequently these were made from
Figure 18.1 Evening dress by Callot Soeurs c.1922
embroidered with pearlized gelatin sequins and glass
beads. (Courtesy V and A Images)
194 Conservation of leather and related materials
gelatine which was dyed or treated with any one of a
number of coatings to simulate other materials such as
jet, mother of pearl, iridescent or coloured glass and a
range of different coloured metals. Cellulose nitrate
was one of the coatings used for pearlized sequins
(Paulocik, 1988). Gelatine is very reactive to changes
in humidity. A dramatic rise will often cause the surface
of gelatine sequins to ‘bloom’ and go dull and an
increase of as much as 25% moisture content of gelatine
at room temperature can result in the gelatine
swelling and becoming rubbery (Horie, 1987). Direct
application of water will cause gelatine to swell alarmingly
(Figures 18.2a and 18.2b). Aqueous cleaning
methods for textiles where gelatine sequins have been
used are therefore unsuitable. The use of hydrocarbon
solvents is also not usually possible as organic solvents
will dissolve cellulose nitrate and may harm the other
finishes or coatings (Kite, 1992).
18.7 Fish glue
There are two types of fish glue. The highest quality
product is known as isinglass and is made almost
entirely from the swim bladders of fish. The glue
extracted from the swim bladders of sturgeon
(Acipenseridae sp.) is known as sturgeon glue. The
swim bladders are opened, washed, stretched and
dried to produce sheets of this protein. Fine sheets
may be produced by pressure rolling after the material
has first been softened in cold water. These may
be shredded or flaked.
The second type of fish glue is a much less expensive
product and is extracted from heads, skins
and skeletal waste from cod (Gadus sp.), haddock
(Melanogrammus aeglefinus sp.) and mackerel (Scomber
scombrus sp.) and other fish as a by-product of the
fresh and frozen food markets.
In medieval Europe fish glues were used as a size
for parchment and as a medium or binder for paint.
The property of fish glue to adhere well to the
porous surface of parchment made it a useful material
for the illumination of manuscripts with gold
leaf and painting. In China it was used as a binding
medium by calligraphers.
It has been used by conservators as an adhesive
and consolidant.
18.8 Gut membrane
Gut membrane is prepared from the outer or peritoneal
coat of the caecum of bovines and is also
Figure 18.2a Detail of gelatin sequin before steaming.
known as goldbeaters’ skin. It was originally used as
a separation layer during the beating out of gold
when making gold leaf.
Goldbeaters’ skin is thin, light, strong and a fully
transparent sheet material composed of collagen.
The method of processing is described by Watt
(1897) and includes treatment by soaking in a potassium
hydroxide solution, scraping, washing, stretching
and treatment with alum.
The swim bladders of certain fish such as sturgeon
or cod have also been used to prepare an alternative
material to gold beaters’ skin. These, however, are
more yellow in colour and opaque.
In the eighteenth century gut membrane was
used to make the first balloons for manned flight. It
was also used in the construction of the first aeroplanes
in the early days of aviation history.
In conservation it is used as a support material
where a thin, strong, lightweight support is required
and is often used by bookbinders for the repair of
parchment. It has also been used for the repair of
other skin materials (Kite, 1999).
In textiles it is found as a substrate for some
types of metal threads. Beaten-out gold leaf
was applied to sheets of gut which were cut into
strips forming the filaments which were then spun
round a textile core. These membrane threads were
combined into the structure of silk fabrics. They are
often to be found in Italian silks of the fourteenth
and fifteenth centuries (Kite, 1992) (Figures 18.3
and 18.4).
This type of gold thread had the advantage of
being light and flexible and much of it could be
incorporated into the structure of a comparatively
lightweight silk. Gold leaf applied to membrane
was a cheaper metal thread as much less of the precious
metal was needed in its manufacture. Darrah
(1987) has shown there is evidence of a gilded silver
layer on some membrane indicating that gold and
silver were beaten out together from a metal block
before being laid onto the membrane; also concentrations
of copper have been found, possibly indicating
a triple layer of metal on the membrane in
some cases.
Textile conservators must be aware of the usage
of this type of metal thread and know at which
period or date to expect to find them and where on
a textile to look for them.
18.9 Sausage casings
Historically sausage casings were made from natural
intestines of bovines. Gut dressing is complex and
Figure 18.2b Detail of gelatin sequin after light steaming, showing swelling.
Collagen products: glues, gelatine, gut membrane and sausage casings 195
196 Conservation of leather and related materials
Figure 18.3 Fragment of fourteenth century Italian ecclesiastical fabric from a cope woven with membrane
metal threads.
Figure 18.4 Detail of Figure 18.3, showing membrane metal thread spun around a flax thread core.
involves 11 distinct operations in the processing,
including scouring, turning inside out, putrid fermentation,
scraping, washing, inflating, drying, measuring,
and sulphuration. The process is fully described by
Watt (1897).
Prior to the identification and outbreak of bovine
spongiform encephalopathy (BSE) in the late twentieth
century, sausage casings were also made from
the flesh splits of mature cattle skins. The flesh splits
were processed mechanically and chemically to
break them down to form a solution. Acetic acid
was used to partially degrade them and the gel
obtained was used to form the casings by means of
extrusion which were then precipitated in a saline
solution and then washed and dried.
Apart from their obvious culinary uses sausage
casings are used for backing and infilling parchment
as an alternative to goldbeaters’ skin.
References
Darrah, J.A. (1987) Metal Threads and Filaments.
University of London Institute of Archaeology Jubilee
Conference Preprints, pp. 211–221.
Darrow, F.L. (1930) The Story of an Ancient Art, from the
Earliest Adhesives to Vegetable Glue. Lansdale, PA and
South Bend: Perkins Glue Company.
Haines, B.M. (1999) Parchment, the Physical and Chemical
Characteristics of Parchment and the Materials used in its
Conservation. Northampton: The Leather Conservation
Centre.
Horie, C.V. (1987) Materials for Conservation. Oxford:
Butterworth and Co. (Publishing) Ltd.
Hubbard, J. (1977) Animal Glues. In Handbook of Adhesives
(I. Skeist, ed.), New York: Van Nostrand Reinhold.
Kite, M. (1992a) Gut Membrane, Parchment and
Gelatine Incorporated into Textile Objects. The Paper
Conservator, 16, 98–105.
Kite, M. (1992b) An Overview of Skin-related Materials
Incorporated into Textiles. Postprints of the ICOM
Leather and Related Objects Group Interim Symposium,
June 24 and 25, 1992, pp. 33–35.
Kite, M. (1999) The Conservation of a 19th Century
Salmon Skin Coat (626 –1905). ICOM-CC Triennial
Conference Lyon, 29 August–3 September 1999,
pp. 691– 696.
Paulocik, C. (1989) Of Buttons, Beads and Sequins,
Beware of Water Sensitive Embellishments. Abstract
of paper presented at Harper’s Ferry Conference in
Washington, November 1988. Leather Conservation
News, 5(2), 6 –7.
Petukhova, T.A. (2000) History of Fish Glue as an Artist’s
Material: Applications in Paper and Parchment Artifacts.
The Book and Paper Group Annual. Vol. 19. American
Institute for Conservation.
Reed, R. (1972) Ancient Skins, Parchment and Leather.
London: Seminar Press.
Watt, A. (1897) Leather Manufacture, a Practical Handbook of
Tanning, Currying, and Chrome Leather Dressing. London:
Crosby Lockwood.
Young, H.H. (1971) Glue, Animal and Fish in Adhesion
and Bonding (N.M. Bikales, ed.). New York: J. Wiley
and Sons.
Collagen products: glues, gelatine, gut membrane and sausage casings 197
The process of transforming animal skin into clean,
white sheet material suitable for writing has changed
little over the centuries. The essential stages of the
process are as follows.
19.1 Temporary preservation
Immediately the skin is removed from the animal it
is vulnerable to attack by bacteria. Inevitably there
will be a delay before the start of parchment processing.
To hold the skin in good condition during such
a delay requires some form of temporary preservation.
In warm dry climates the skin can be air dried,
but in more temperate regions salt is liberally applied
to the raw skin. The salt maintains the skin in a
sound condition while it is held for sale and transported
to the user.
19.2 Soaking
The skin is immersed in a large volume of cold,
clean, sometimes running water for 48 hours, to
wash away blood and dirt, extract the salt and rehydrate
the skin. The soak may be carried out in either
stone or wooden vats and at intervals the skins are
moved in the water either by stirring by hand or by
the use of revolving wooden paddles.
19.3 Liming
The skins are immersed in a suspension of slaked
lime for eight days (up to 16 days in cold weather)
during which time the skins are gently moved
about. The alkalinity of the lime attacks the keratin
of the hair and the epidermis, loosening them and
allowing them to be scraped from the skin.
With sheepskin, the process is somewhat different.
In order to prevent the wool being damaged by
the alkali it is loosened by a paste of slaked lime that
is applied to the flesh surface of the skin. The alkali
penetrates through the skin loosening the wool at
the roots, which is then pulled from the skin, sorted
into different grades, washed, dried and sold to the
wool merchant. The skin is immersed in a lime
liquor for a further period, after which it is split into
two layers. The grain layer is tanned usually by the
vegetable tanning process to produce skivers and the
flesh split converted into parchment.
19.4 Unhairing and fleshing
The skins are unhaired by placing them grain uppermost,
over an upright, convex curved, wooden board,
termed the ‘beam’. The loosened hair and epidermis
are scraped off using a curved, blunt-edged knife. The
grain surface is further scraped to remove residual hair
and surface grease. The skin is then reversed on the
beam and fat, muscle and loose flesh layers are cut
from the flesh surface. The skins are usually returned
to the lime for several days, after which they are
washed in water for one or two days. Today, machines
are employed to remove hair and flesh.
19.5 Drying
The quality of the parchment depends on the careful
control of the drying. The skin is suspended within
a rectangular wooden frame. It cannot be nailed to
the frame, as the shrinkage that occurs during this
198
19
The manufacture of parchment
B.M. Haines
The manufacture of parchment 199
stage of the process would cause the skin to tear away
at the nailed points. Metal clamps are also inadvisable,
as contact with the metal can stain the parchment.
The method adopted allows for the frequent
retensioning of the skin throughout the drying
period. Every few centimetres around the edge of
the skin a small smooth pebble or a ball of rolled-up
newspaper is wrapped in the soft skin tissue and the
knob so formed is secured by cord to adjustable tensioning
pegs in the wooden frame. These have been
likened to the tuning pegs of a violin. An alternative
to the rectangular frame is a circular frame made of a
flexible wood such as willow. The limed skin is suspended
within this frame using tensioning cords in
the same manner and the frame itself adjusts to the
tensions that develop as the skin dries.
While the skin is still wet it is vigorously scraped
on both surfaces, using a two-handled crescent
shaped knife (Figure 19.1). During this operation
the skin is kept wet by repeated applications of
water. Throughout the process the skin is continually
retensioned by means of the pegs. Finally the
fully taut skin is air dried. The rate of drying has to
be controlled: exposure to direct sunlight or fast
movement of air can cause the parchment to become
damaged by too high a temperature and/or too rapid
drying.
When the skin is considered to be sufficiently
dry, both surfaces are scraped and shaved, again
using the crescent-shaped knife. The thick regions
of skin are pared from the flesh surface in order to
obtain a sheet of uniform thickness. Unless the
parchment is intended for book covers, the grain
surface is also shaved to remove the gloss that is
characteristic of an intact grain. High gloss is considered
undesirable in a writing parchment.
After shaving, the dry parchment is cut from the
frame and the surfaces rubbed smooth with powdered
pumice.
Bibliography
Haines, B.M. (1999) Parchment: The Physical and Chemical
Characteristics of Parchment and the Materials Used in its
Conservation. Northampton: The Leather Conservation
Centre.
Hamel, C. de (1992) Scribes and Illuminators. London:
British Museum Press. (Medieval Craftsmen)
Kennedy, C.J. and Wess, T.J. (2003) The Structure of
Collagen within Parchment – A Review. Restaurator,
24(61).
Reed, R. (1972) Ancient Skins, Parchment and Leather.
London: Seminar Press.
Rück, P. (1991) Pergament. Sigmaringen: Jan Thorbecke
Verlag.
Ryan, K. (1987) Parchment as Faunal Record. Museum
Applied Science Center for Archaeology Journal, 4, 124–138.
Tomlinson, C. (1864) The Useful Arts and Manufactures of
Great Britain, 2nd ed. London: SPCK.
Figure 19.1 Paring the surface of the skin.
20.1 Introduction
This chapter describes the nature of parchment and
its characteristics, in particular those that have a
direct influence on its preservation and conservation.
The different forms in which parchment has
been used are summarized, and features of these that
influence preservation are included. Also included is
a review of conservation treatments and how they
have developed. The intention is not to go into significant
depth in any of the areas covered, nor to
recommend any specific practice (although a cautious
and sensitive approach is encouraged). Instead,
the purpose is to introduce the reader to the subject
and offer some direction for more detailed study or
guidance.
Parchment has been used in a number of ways
since it was first produced. A precise definition of
parchment is probably: animal skins that have been
dried under tension to produce a stiff, sheet material
with a flat, even surface. Skins of this type have been
found dating from around 2800 years ago. Parchment
produced using a lime bath in its preparation, as
described in Chapter 19, appears in recipes written
as early as the eighth century (for example, the
Lucca manuscript, Codex 490ff. 21–25) (Reed,
1972: 33) and Byzantine parchment of the sixth
century has been defined as limed skin (Wächter,
1962). Parchment-type skins have been used in a
variety of ways, but the great majority of parchment
made over the centuries has been used as a manuscript
substrate (see Figure 20.1). As a consequence
of this predominance, this chapter devotes most
attention to the conservation of parchment in manuscript
formats, but it also includes a summary of
parchment used in other formats. The intention is
to make conservators and others aware of the likely
places where this type of skin material can be found
and to alert them to its characteristics.
There is a large body of published material on
the topic of parchment and its variations, in several
languages, covering many aspects of science and conservation
and published over a period of more than
150 years (not including the many recipes for production
described over the last 1300 years). In preparing
this chapter the author has reviewed over 100 texts
from the nineteenth century to the present, most of
them English language publications and translations.
The author regrets that many more could not
be included, but hopes that the references and citations
will be useful as a select bibliography.
20.2 Parchment production and use
The English word ‘parchment’ is understood to
derive from the French parchemin and the Latin pergamentum,
which in turn derives from the name of
the Hellenistic city Pergamon of Mysia (Bergama
in modern Anatolia, western Turkey), once believed
to be the birthplace of parchment making under the
second century BC King Eumenes II. According
to Pliny (himself quoting earlier sources), charta
pergamene, or ‘paper of Pergamon’, was supposedly
invented in response to an Egyptian embargo on
the supply of papyrus to the city (Diringer, 1982).
However, the oldest examples of parchment appear
to be fragments of camel skin found in the Hebron
region of modern-day Jordan, dating from around
the eighth century BC and much earlier than that
which we associate with Pergamon (Reed, 1972:
118, 277). Skins are recorded as being used for writing
purposes as early as the Egyptian Fourth Dynasty
(c.2700 BC) (Ryder, 1991).
200
20
The conservation of parchment
Christopher S. Woods
The conservation of parchment 201
Material from these periods is understood to have
been produced by stretching and drying skins, sometimes
with the addition of vegetable or fruit infusions
that had a light enzymatic or tanning effect
(Reed, 1972: 72–120; Haran, 1991). The Dead Sea
scrolls from the Qumran caves are perhaps the most
well known of such material and are dated at around
2000 years old. Having been tanned, these might be
described more accurately as leathers, but for the fact
that they have probably been dried under tension to
produce a writing surface. This type of skin, referred
to in Aramaic as ge
wil, was not usually ‘split’ in the
way that we may associate with most parchment, but
remained the full thickness of the hide.1
The hairs
were removed and the hair side was used for writing
since it was smoother than the largely untreated flesh
side (Vorst, 1986).
From the second half of the first millennium AD,
liming appears to have become a common feature of
parchment making, with the possible exception of
Hebrew Talmudic parchment, which seems to have
begun to be made using a liming process from about
1100 AD (Vorst, 1986). The untanned skins of sheep,
goats, calves and deer have all been used to make
limed parchment and there remains some inconsistency
in common terminology used for any or all
of these. In this chapter the term parchment is used
for all of these different hide types and the term
vellum is used in its precise form as parchment made
from calfskins. The term membrane is also used from
time to time to mean a single sheet of parchment of
any form.
It is not clear where or how skins began to be limed
in preparation for parchment production, whether it
began in Islamic or European culture. It is argued that
Arabs may have adopted the practice from European
sources and added it to their existing procedures
(Haran, 1991). It has been pointed out that the use
of an alkaline process was easier to control in colder
climates, where the process could continue for longer
periods without the rapid deterioration of the fibres
that would be experienced in temperatures above
85°F, a temperature regularly exceeded in the Arab
countries of Asia Minor, and where a plentiful supply
of cold water for cooling the skins may not have been
readily available (Vorst, 1986).
Figure 20.1 There are many millions of sheets of parchment stored in archives across western Europe in the form of deeds
and charters, dating from about the tenth century AD to the twentieth. The above English document, from the reign of
Queen Anne, is very typical, being a composite object made of printed and manuscript inks on limed sheepskin, with red
shellac applied seals, a blue paper duty stamp with metal strip, and other endorsements. (Courtesy Dorset Archives Services)
The use of lime in the preparation of parchment
skins had the advantage of opening up the skin fibres
in such a way that they could be pulled more effectively
into a flat weave structure. It also produced a
pale grey or strong white colour, as compared to the
light brown or yellow colour produced by tanning
processes. An even, flat surface and white colouring
both lend themselves well to manuscript production.
Paper began to be made in the Islamic world several
centuries before the Europeans (around the seventh
century AD). Papyrus had been more commonly used
for Islamic writing material, parchment being used for
specialist purposes. A rapid expansion in the demand
for writing materials from the eighth century AD
onwards required a more readily available material.
Paper could meet this demand, and by the middle
of the tenth century AD it was in widespread use
throughout the Islamic world (Loveday, 2001). In
western European countries, parchment appears to
have been the only writing material used until paper
began to be common in the fourteenth and fifteenth
centuries, and it continued to be used for many purposes
for another 400 years after that time.
The method of producing limed parchment outlined
in Chapter 18 is a fairly standard approach, used
in similar ways for several centuries and until modern
times. The period when parchment use was predominant
in Europe, and when its production qualities
were probably at their highest, was arguably between
the tenth and sixteenth centuries AD. During this
period it was used for ecclesiastical texts, for legal and
financial records and those of the royal courts, and for
the covers of books. Its production in the United
Kingdom during the last three centuries has been
most commonly intended for use as legal documents,
Acts of Parliament, certificates and awards, for drumskins
and parts of other musical instruments, and for
specialist works of art. The use of parchment is
believed to have spread to India in the tenth century
AD, probably via Muslim invasions. However, it never
really took hold as a writing material and is more
commonly found as a substrate for paintings and ink
drawings and in musical instruments, dating from
about 1600 AD onwards (Gairola, 1958; Lokandum
and Chaudray, 1991). Parchment-like material was
also used to make shadow puppets, pots and vessels
and more recently in linings for shoes, as a support in
clothing and in some sports equipment (Lokandum
and Chaudray, 1991).
The three basic layers of a skin are the epidermis
or hair side, the middle corium layer, and the inner
flesh side. These are different for each animal type.
For fine writing purposes, it is the corium layer, in
particular from sheep, goats and very young calves,
which provides the best surface characteristics.
There remain differences between each side of each
layer, however. The hair side of the corium has a
slightly harder and shinier surface than the flesh side,
which has a softer, smoother surface, and is often
more fibrous in appearance. When preparing a skin
for parchment, its use informs the extent to which a
side is scraped, or which layer is split off for use, to
produce either a ‘hair-split’ or a ‘flesh-split’ skin. The
‘hair-split’ has more of the epidermal (hair) layer
present, the flesh side having been scraped away to a
greater extent. A ‘hair-split’ parchment is often
thicker, has a harder surface on the hair side and can
be strong enough to be used for book coverings, for
example. A ‘flesh-split’ skin has had more of the epidermal
side removed and is a softer, often thinner
material suitable for use as a writing material.
In developing its use as a writing material, different
surface characteristics were used to meet specific
needs. As mentioned above, very early parchments
were not split; the only surface smooth enough to
receive writing was the hair side. After several centuries,
the surface qualities began to be refined.
Both sides were scraped, with more of the hair side
removed, and the thin, smooth material produced
by later processes could receive ink on either side
and on both at the same time, which became an
essential feature for book production. However,
western European documents such as indentures,
charters and deeds, etc. were usually written only
on one side, almost invariably the flesh side.
The standard use of the flesh side for document
writing appears to have had an effect on the different
qualities of the sides of this kind of parchment
material over succeeding centuries. Whereas both
surfaces of earlier, refined parchments were good
enough to write upon, the hair side of later ones
used for documents is so shiny and hard that it
would have been more difficult to use it for writing.
This difference might be because the preparation
of much early European writing parchment was
intended for use in ecclesiastical settings (where
texts were often bound and both sides required).
The gradual increase in demand for parchment in
legal and court settings resulted in a separate, secular
industry producing and supplying material
more suited to these different purposes. Over the
centuries, the production methods and quality of
parchment produced for standard documents altered,
particularly between the seventeenth century and the
late nineteenth century. Later skins tend to be more
rigid, the hair side can have a pronounced waxy feel
202 Conservation of leather and related materials
and they have slightly different behavioural characteristics
(Calabro et al., 1986).
Finely split, limed vellum was used in western
Europe as a writing material from early times. It
appears, however, that sheep and goat skins gradually
became the more common writing parchment
materials, particularly those used for secular purposes
from about the fourteenth century. Vellum
from this period onwards is perhaps more commonly
associated with book coverings. For this purpose
it was not split to the same extent as sheep or
goat writing parchments. The hair-split provided the
maximum strength and resistance needed to make
a robust protection for text blocks. Its use as a book
covering was commonly in a format without boards
known as ‘limp binding’ and from the eighth century
to the seventeenth a wealth of styles were used in
this fashion throughout Europe, in leather as well as
vellum (Scholla, 2003). These limp bindings were
used for manuscript texts, first on parchment and
subsequently on paper.
In the UK, stationery bindings (blank books used
for accounts, for example) were commonly produced
in limp format from the fifteenth to the eighteenth
century, and frequently vellum covers were added to
gatherings of paper records once a suitable quantity
was reached. From around 1700 vellum was also used
as an adhered covering on boards for ledgers and
other ‘hardback’ stationery bindings. In early nineteenth
century England, for example, church registers
of baptisms, marriages and burials became standardized,
the first such consisting of printed pro-forma
pages sewn into boards covered with adhered vellum,
including green vellum (see below).
The flesh-split was also used for these and other
coverings, for both manuscript and printed texts. A
flesh-split covering can often be distinguished by a
paler colour and somewhat grainy appearance, compared
with the common yellow–brown and shinier
surface of the hair-split covers. Flesh-split covers have
often become weak and torn, especially along the
joint and spine exposed to sunlight. Frequently, older
vellum and sometimes writing parchment (often
musical manuscript or legal documents) were reused
for the covering of manuscript texts. The finer parchments
of this nature are frequently found to be damaged,
being unsuited for this purpose.
Surface characteristics of parchment sheets were
altered further by the preparation used by the scribe
or illuminator, such as ‘pouncing’ with powdered
pumice, the application of light vegetable oils, or polishing.
Different methods of preparation were used in
different parts of Europe (Bykova, 1993). Surfaces that
were intended to receive layers of pigment or gold leaf
were frequently prepared further, sometimes coated
with a mineral ‘ground’ such as gesso or bole. These
different surface characteristics all affect the ways in
which parchment responds to its environment.
Parchments were rarely coloured for use,
although manuscript membranes were sometimes
whitened further with chalk. Skins sometimes had a
patterning or colour caused by the presence of
blood in the vascular system. If the animal had died
of natural causes, or if the carcass was deliberately
beaten before being flayed, iron and other residual
blood products remained in the skin and membranes
causing strong patches of brown ‘staining’.
Byzantine and Arabic parchments intended for particular
purposes were sometimes dyed yellow (with
saffron) and in rare cases a blue–black, using dyes
from the murex shellfish (Bloom, 1989). In eighteenth
century Europe, vellum was sometimes dyed
with copper to produce ‘green vellum’. This was
most commonly used for stationery binding covers,
for wallets and for small notebooks that often
incorporated a pouch or pocket.
Other uses for both limed and other untanned,
split-skins include its incorporation in western clothing
(Kite, 1992) (see Figure 20.2), in furniture (especially
the work of Carlo Bugatti) (Giovannini, 1999; Munn,
1989), as a decorative surface covering for eighteenth
century telescopes (often green vellum), and as the
support material for seventeenth and eighteenth century
fans (Hermans, 1992). American Indian and
Inuit cultures used split sealskin for kayaks and seal gut
for clothing and bags and in African cultures a similar
material was used for musical instruments (Dignard,
1992; Kaminitz and Levinson, 1988).
Ethnographic artefacts from all over the world
often incorporate untanned skin material, such as
shrunken heads, mummified bodies (those which
do not involve tanning-type preparations) and costumes
decorated with pelts or even whole animals.
Many of these various items may not constitute
what we commonly think of as parchment, but their
qualities as untanned collagen membranes give them
similar characteristics to parchment, and their conservation
frequently involves similar considerations
to those used for manuscripts (see Chapter 17).
20.3 Chemical, physical and
deterioration characteristics
Skins are not homogeneous structures. They are
described as displaying morphogenesis, which in
The conservation of parchment 203
204 Conservation of leather and related materials
simple terms means that they are formed by living
organisms from standard building blocks (skin collagen
molecules) into varied, complex shapes, influenced
by the many changing circumstances of an
animal’s existence and growth (Harrison, 1981). This
complex variety continues to be present in skins that
have been made into parchment and the manner of
its production causes this material to display a pronounced
capacity to deform and change in different
conditions. These are key features of the physical
characteristics of parchment, and ones that need to
be borne in mind by all who must care for heritage
objects that contain or consist of parchment.
There are significant differences between skins that
have been limed and those that have been tanned.
The strong alkali used in a lime bath causes collagen
to undergo a significant degree of molecular change
that is different from the changes brought about in
tanned leather. The tanning process causes the collagen
molecular matrix to become crosslinked, so that
sites that would otherwise be available for molecular
bonding are linked to their neighbours, producing a
more robust structure with a higher shrinkage temperature
than fresh skin. By contrast, the hydrolysis
and racemization of molecules in parchment skins
causes the matrix to be expanded and weakened,
leaving it with a lower shrinkage temperature than
fresh skin (Haines, 1987). Polar sites available for
hydrogen bonding are exposed and the whole matrix
becomes highly hygroscopic.
The salting, liming and scraping or shaving process
used in the production of a high quality writing
parchment results in the removal of plasma proteins,
mucopolysaccharides, keratin, elastin and fats, leaving
an almost pure collagen fibre network with about
13% water content under normal conditions and
residual lime of about 1.6% (Haines, 1994). Skin, and
especially limed skin, is labile in heat and will shrink
in high temperatures, particularly if this is associated
with water or high relative humidity. With a shrinkage
temperature of between 55 and 60°C in new
material, and as low as room temperature in old,
decayed examples, parchment is very sensitive to some
of the uses and treatments that present a lower risk to
other organic materials such as paper and some textiles
(Haines, 1999). Because parchment consists almost
entirely of collagen, and collagen is highly sensitive to
bonding with polar molecules such as water, it is
water and aqueous solutions that place the material at
greatest risk of damaging changes. Non-polar or low
polarity solvents will not react with polar collagen.
These solvents do have the capacity to dissolve fats and
Figure 20.2 Two examples of garments employing parchment in their composition. On the left, an English bodice
from c.1660 decorated with parchment lace. On the right, a Guipure work chasuble from Piedmont dating from
1730 –40. The embroidery on the chasuble uses metal thread worked over parchment shapes and cord.
oils, and for most western parchment, this is not a
problematic feature, since such fats and oils have been
removed completely during the salting, liming and
washing processes. Early parchment was sometimes
prepared with light vegetable oils, however, and these
might be adversely affected by such solvents.
Limed skins will absorb and adsorb water in humid
environments, and lose most of this water when conditions
are drier, which means they are very sensitive
to fluctuating environments. This sensitivity manifests
itself as a change in rigidity from a relatively
rigid state in dry conditions to a markedly limp state
in damp conditions. These changes are accompanied
by significant expansion and contraction across all
dimensions. In humid conditions, new parchment has
been shown to be able to take up 10% of its weight in
additional water in one hour and, although absorbed
water is lost quite rapidly in drier conditions, additional
adsorbed water (water bonded to molecules)
takes longer to be lost and may remain indefinitely
(Woods, 1995; Berardi, 1992). During these changes,
unrestrained parchment deforms considerably,
demonstrating a typical curling and, in large sheets,
some reversion to the natural undulations of the hide.
It has been shown that temperature and humidity
fluctuation can cause dimensional changes in parchment
of nearly 4.5% (Berardi, 1992).
Parchment exposed to high temperatures and
fluctuating conditions is vulnerable to a breakdown
in the fibres in the form of a gelatinization. Examples
of parchment items exposed to high temperatures
in dry conditions are shrunken and hard, brittle
and often stuck together where they are folded, for
example. Hot, wet conditions invariably cause such
items to blacken and fuse until any adjacent faces
are inseparable and have the appearance of having
been melted together (see Figure 20.3). The same
effect can happen over long periods of time at lower
temperatures and in dry conditions, as has been
noted of fragments such as those found in caves in
Qumran and Hebron, which would have experienced
fluctuations and repeated drying and condensation
effects over many centuries (Kahle, 1986).
Wetting and subsequent uncontrolled drying of a
parchment membrane will cause it to shrink and
become transparent. This shrinkage can be uniform,
in the case of a small item, for example, or
patchy depending on the degree of wetting in any
area and also in its position on the skin. Areas
around the shoulder, flanks and butt, for example,
tend to have a more coarse grain structure and can
often be more translucent than other areas even in a
good condition parchment. Transparency tends to
be caused by the three-dimensional shrinkage in the
skin bringing wetted fibres and fibrils into contact
with one another. The increased sites for bonding
prevalent in limed skins cause the fibres and fibrils
to stick to each other if they are not kept apart
under tension during drying. Transmitted light at
the surface will not be scattered but will penetrate
the skin, giving it a translucency or even transparency.
This characteristic has been exploited in
the past to make ‘window parchment’ and is evident
in raw hide skin articles such as shadow puppets
(Reed, 1972: 143; Chaudray et al., 1991).
Parchment membranes that have been affected by
water or heat in localized areas, especially when
folded, can present significant problems for opening
and preservation. Local patches of shrunken skin
cause a wide region of distortion radiating from
The conservation of parchment 205
Figure 20.3 Fifteenth and sixteenth century account and
inventory rolls, previously stored against a brick basement
wall. Repeated episodes of moisture and probably some
heat from hot water pipes, over a long period of time, have
been the most likely cause of the ends of these rolls to fuse
together, harden and blacken. The parchment in the rest of
each roll is good, but this damage prevents them from
being opened without very serious intervention. (Courtesy
Dorset Archives Service)
them across the healthier skin (Hassel, 1999). A less
dramatic form of shrinkage and hardening is even
more common. Membranes that have been folded,
rolled or crumpled for a long time, or tightly bound
in a book, can have become sufficiently rigid as to
make opening difficult or risky. Items in this condition
are often damaged further by overenthusiastic
attempts to open them out, leading to tears and
delamination. Objects that contain parchment components
and which are exposed to liquid water can
be distorted subsequently by the shrinkage of the
parchment elements. Examples include clothing and
also vellum-covered books, especially those with the
vellum pasted down onto boards and adhered to the
spine of the text block. This can happen even in
humid environments (see Figure 20.4).
It has been noted that ‘limp vellum’ binding styles
(with no boards or adhesion) cause less damaging distortion
to their text blocks, especially when exposed
to water. For this reason and several others, the format
has been recommended as a conservation binding
style, whether using vellum or another material,
even for those items that may previously have been
bound in a different form (Reed, 1991: 217–220;
Fitzsimmons, 1986). Notwithstanding the proven
positive features of such bindings, heavy limp vellum
covers can also be found to have become shrunken
and distorted over time, frequently exposing the text
block and resulting in wear to the weaker paper,
especially at the fore edge (see Figure 20.5) (Craft,
2003; Clarkson, 1982). The choice of quality of the
covering material, and which sewing support to use
with it, are important features of these structures.
As well as being used as a total covering, whether
limp or with boards, vellum and parchment has been
used commonly for structural and decorative features
in bindings and coverings, including ‘tacketing’ (decorative
sewing), protective vellum corners for clothand
leather-covered bindings, and for thongs and
ties. The shrinkage of vellum thongs in a sewing structure
can be the cause of distortion of the spine of a
text block, similar to that described above.
Parchment membranes are as susceptible as any
other material to becoming dusty, dirty and stained.
Stains that arise because of a spillage of an aqueous
solution are problematic because the most effective
way of reducing them (using another aqueous solution)
would probably cause further damage: inks
and pigments would be at risk and the parchment
would be affected by the wetting and particularly by
its subsequent drying. Like paper and some textiles,
surface dust and dirt can also become ingrained if a
dirty membrane becomes damp or wet, and even
low polarity solvents such as alcohol and acetone
can lead some surface dirt into the fibre structure.
A common deterioration problem is microbiological
infestation. Parchment membranes contain
varying amounts of partially or completely gelatinized
collagen fibre, especially at the surfaces. This
material, and the collagen fibre matrix itself, is an
attractive medium for fungi and bacteria, which will
flourish in prolonged damp conditions (Kowalik,
1980). The effects vary depending on the length of
the episodes of growth. Minimal growth can be
observed in almost all old parchment, manifesting
itself as a slight complexion of tiny, faint black,
brown or purple speckles under the skin surface.
Badly affected membranes, with much surface
growth, will have become weakened and fibrous;
their surfaces flaked and delaminated, losing inks or
pigments in the process. Infestations can cause livid
staining of purple, bright yellow and pink. At its
very worst, a parchment membrane can be completely
destroyed by mould, rendered to dust.
Inks and pigments are often the first casualty of
the steady degradation of a surface by mould or
by expansion, contraction and distortion. Heavily
applied pigments and gold leaf crack and flake off
through the action of this movement and are undermined
by microbiological activity. Manuscript inks
often do not penetrate deeply into the fibres and are
easily rubbed off. Nineteenth century parchment in
particular seems to have a harder surface and inks do
not always adhere strongly, particularly if exposed to
water. The recipe of an ink also affects its capacity to
adhere or penetrate. Carbon inks are very vulnerable
and this will have become apparent in early times,
leading to the more common use of iron gall inks.
These in turn can be unstable and burn through
their substrate (Wächter, 1987a). Parchment appears
to be more resilient to this acidity than paper, perhaps
because of its high calcium carbonate content
deposited by the liming process, which helps to neutralize
acids. This same resilience may protect parchment
from other sources of acidity such as modern
airborne pollutants. Inks containing verdigris (copper
acetate) can penetrate strongly and pigments of
this nature can produce what is referred to as ‘copper
green’ decay, where the fibres of parchment are
weakened considerably (Fleming, 1983).
The fading of iron inks is a problem common to
paper and parchment manuscripts alike. Since at least
the early seventeenth century, gallic acid (e.g. derived
from gallnuts soaked in white wine) was used to
intensify faded inks (Petrus, 1619). Unfortunately,
after a few years the treated area discoloured to
206 Conservation of leather and related materials
The conservation of parchment 207
Figure 20.4 A good example of warped boards on a vellum-covered volume, the distortion being caused by the shrinkage
of the vellum following damp conditions. This warping exposes the text block to dust and makes handling difficult.
(Courtesy Bodleian Library)
Figure 20.5 Typical examples of English manuscript stationery bindings of the seventeenth and eighteenth centuries.
These are registers and accounts bound up coarsely into volumes using heavy hair-split vellum for their covers. The vellum
has in most cases shrunk over the years, exposing the paper text blocks, which in turn have become damaged. (Courtesy
Dorset Archives Service)
208 Conservation of leather and related materials
brown and caused the writing to be illegible. In the
nineteenth century and the first half of the twentieth
century a variety of intensifying solutions were recommended
for both specialist and domestic application,
such as tea or tannic acid, ammonia, ammonium
sulphide neutralized with lime water, and potassium
ferrocyanide.2
Most of these solutions had damaging
properties. One 1930s observer reported the application
of an aqueous solution of ammonium hydrosulphide
to intensify the ink, followed by a mixture of
tannic and acetic acids to make the reaction ‘permanent’
and counter the effects of the first solution. It
was noted that the manuscripts subjected to this treatment
‘were not very reassuring in appearance, having
great, discoloured blotches’ (Smith, 1938a).
Perhaps the most extraordinary of the various mixtures
employed were ferrocyanate solutions which
discoloured to a bright blue (of the kind used in ‘blueprint’
plans) and frequently obliterated the text
(Fuchs and Mrusek, 2002). More destructive still,
the strongly acidic solutions have caused the gradual
hydrolysation and destruction of the fibres of the substrates
to which they were applied, making them
brittle and crumbling. While paper seems to have suffered
from this decay more quickly and dramatically
than parchment, the calcium residue in the latter has
not been sufficient to resist the action indefinitely.
Although parchment is very attractive for certain
forms of mould and bacteria, it appears to be a little less
immediately attractive to insects and other, larger pests.
Parchment membranes can be grazed upon by silverfish
and nibbled by rodents, but perhaps they do not
provide sufficiently digestible nutrition, for this damage
seems to be more common and extensive in paper.
Mice and rats will use parchment, like other available
materials, for making their nests, so examples can be
found that are damaged by the urine and faeces of
these creatures. Insect damage seems to be most commonly
associated with marks caused when the skin was
part of the living animal, such as warble-fly holes in
vellum. These holes were regularly repaired as part of
the preparation of sheets for writing and often they
include aspects of historical production that are valued
by the scholar and conservator, rather than requiring a
remedy (see Figure 20.6 and Clarkson, 1992).
The format in which parchment is used is often the
cause of its damage. The sensitivity of parchment to
humidity results in distortion to a membrane where
one area is restrained or covered and another is not.
This happens in a normal way by the use of parchment
in certain forms, for example where the pages
of an early manuscript have been turned causing a
deposit of oils and dirt from the fingers of the readers.
The fore edge and especially bottom corners of manuscript
volumes frequently display this soiling and the
action has sometimes worn the skin and made it weak
and fibrous. The more oily areas in particular will not
respond as readily to atmospheric changes as the surrounding
skin because the oils block the passage of
moisture to the fibres, leading to distortion around
these areas. Distortion can also be found around repair
patches or close to the gutter of a tightly bound
book and it is common where a membrane has been
adhered to a surface under tension and part of it has
subsequently come free. This frequently leads to splits
and running tears; it can even pull a whole membrane
apart (Soest, 1989).
Many archival parchment formats are sealed documents,
such as royal charters and grants, indentures
Figure 20.6 Many kinds of hole can be found in parchment
items. These pages from an English register of baptisms,
marriages and funerals of the early seventeenth
century, include: old stitching holes, a hole that existed in
the skin before it was prepared as parchment and repaired
with a piece of older parchment before use, and holes
caused by more recent insect damage. (Courtesy Dorset
Archives Service)
and deeds. The structure and format of a parchment
document can often be determined by the manner
in which it has been sealed and so, given the enormous
quantity of such items in existence, we cannot
describe the characteristics of parchment without
making some reference to this very common format.
Seals rarely affect the chemical stability of
parchment, but especially for the more common,
pendant examples, the behaviour of sealed items
will be influenced by the presence of the weight of
the seal or many seals hanging from one edge. Seals
can be affected by the hygroscopic nature of parchment
and also by its calcium content, depending
upon their composition (there are many different
materials used in different formats). Seals should not
be removed from documents, however, since to do
so is considered a fundamental breach of their
integrity and provenance. Sealed documents should
be treated holistically, as composite items, rather
than as two separate historical and material features.
In summary, it may be said that there are two
varieties of format in which parchment presents
characteristics of which the conservator must be
aware. One format is loose or unrestrained sheets or
leaves of parchment, the other is parchment that is
adhered or partly adhered to another, less flexible
material. Both formats are profoundly affected by
the capacity of parchment to absorb and release
atmospheric moisture, and the changes in size and
shape, or tensions, that this fluctuation causes. Further
variations or influences are common to both of these
two basic formats, such as animal type, method of
production, fibre structure, the site on the hide
from which a membrane has been cut, its surface
and laminar characteristics, the effects of inks and
other applied coatings, the extent of surface damage
and fibre strength, etc. Add to these many variations
the fact that each animal skin is unique, and it can
be understood that every piece of parchment must
be approached with consideration of its own, complex,
individual characteristics.
20.4 Display and storage
The display of parchment membranes has been a
common subject for publication. The adverse affects
of excessive tension and adhesion to a rigid mount
have been observed above. To avoid the risk of tearing
caused by the natural tendency of parchment
to shrink in dry conditions, various successful methods
have been devised over the last 25 years which
involve the application of strings or even springs
around the edges of a membrane, rather like a trampoline,
which are then attached to a mount in favour
of direct attachment of the skin. These approaches
include the use of linen threads, which stretch and
shrink in opposition to the skin, allowing the membrane
to maintain an appearance of even tension during
fluctuating conditions (Clarkson, 1987). Japanese
hand-made paper strips have also been used for a similar
purpose, based upon the tendency of these longfibre
papers to accommodate the expansion and
contraction of the skin, and also an ingenious method
of using strips of polyester sheet (Mylar or Melinex)
cut into the form of ‘springs’ (Pickwoad, 1992;
Norman, 1993).
Light levels for parchment on display are the same
as for most organic materials, in particular those
with coloured pigments. Ferrogallic inks and mineral
pigments fade in strong light, so levels of 50 lux,
with no ultraviolet, are important (Myers, 1980;
BS5454:2000).
Safe storage conditions for parchment are widely
recognized as being dry (a stable point between 45%
and 60% relative humidity), to avoid the growth
of mould (BS5454:2000). Drier conditions can be
acceptable for long-term preservation, as may be
evinced by the great longevity of some extant membranes.
However, periods of use in more humid
conditions will cause the expansion and humidification
of this exceptionally hygroscopic material and
rapid changes of environment should be avoided.
Temperature control is of great significance in
maintaining a stable humidity and it is widely recognized
that lower temperatures reduce damaging
hydrolytic activity. The use of individual protective
packaging made from acid-free and buffered cards
and papers is recommended, which also has the
advantages of maintaining dark conditions and
improving environmental stability. Reduced handling
is advisable, for reasons given above.
20.5 Conservation treatments
Common features in the deterioration of parchment
can be summarized as: shrinkage and brittleness,
distortion, tears and holes, mould damage and
the weakness or loss of inks and pigments. Over the
last century many different approaches, techniques
and materials have been used to remedy these problems.
The one thing they have in common is that
they are all different; no complete sequence of treatment
or recipe of solution is repeated in quite the
same way by the different authors reviewed for this
The conservation of parchment 209
chapter, but there are common approaches or technical
‘themes’ that can be discerned. In reviewing
these approaches as trends over time, one can observe
a gradual movement towards more minimal intervention
in recent years. The rate of change in this trend
varies geographically and it has its exceptions, but
it is discernible and will form a part of the conclusion
of this work.
The trends can be divided into two strands: the different
types of material used to remedy problems and
the different approaches or attitudes towards remedial
treatment. During the mid-twentieth century there
was a general trend away from using age-old methods
that involved compatible or sympathetic materials,
towards the exploration and use of modern synthetic
materials. However, techniques for the use of these
materials continued to be guided by what might be
called the old fashioned craft production approach –
the intention to remedy all problems and return the
imperfect item to its former condition; serviceable
and ‘as good as new’. In western Europe from the
1930s to the 1980s there appears to have been an
expectation that modern chemical science would
provide the answers to problems and help conservation
‘operatives’ to remedy every imperfection
(BS4971:1973). This scientific approach becomes less
evident when we review western conservation texts
in the 1980s and 1990s,3
but from the same period we
find many published tests and recommendations for
the use of a wide variety of chemical treatments emanating
from the old Soviet Union countries.
Since the 1990s there appears to have been a gradual
return to the use of more compatible materials,
common experience having shown modern synthetics
to have undesirable characteristics. At the same
time, approaches and techniques have also changed,
becoming less invasive, the craft production approach
being no longer considered necessary or appropriate.
There have been several useful reviews of practice
over the years and reference is made to these below.
The most exhaustive review of approaches used up
until its time of publication, Dr Reed’s Ancient Skins,
Parchments and Leathers of 1972, referred to in the end
notes, provides essential historical information on the
nature and production of parchment, and also a
detailed insight into the many and varied methods
and recipes sought by ‘restorers’ to remedy every
conceivable imperfection in a membrane. Another
fascinating source is L. Herman Smith’s contemporary
description of the practices undertaken in
European archives of the 1930s, published in The
American Archivist, also referred to in the endnotes. As
well as revealing the attitudes of their times, these
reviews are invaluable as a record of the many types
of treatment and material used in the past, evidence
of which a modern conservator might find when
examining a previously restored membrane. The
different types of treatment commonly required or
encountered are grouped here into key activities.
20.5.1 Mould and fumigation
Mould growth on parchment has been treated in a
number of ways. The fluctuation of environmental
conditions in temperate climates has the tendency to
allow for episodes of mould growth to be countered
by periods of dry conditions that kill off the mould,
while leaving residues that are reactivated when conditions
become damp again. The increase in availability
of chemical fungicides during the nineteenth and
twentieth centuries has resulted in a number of
attempts to kill mould on parchment and paper items
by the use of various chemicals. These have included:
sodium pentachlorophenate (Santobrite), isopropylmetacresol
(Thymol), sodium ortho-phenyl-phenate
(Topane), formaldehyde, DDT, hydrogen cyanide,
methyl bromide, ethylene dioxide, p-chloro-m-cresol
(or 4-chloro-3-cresol) and quarternary ammonium
salts (such as Catamin-AB).4
The use of most of these
has not been satisfactory because of serious risks to
health and to the environment, in some cases the
residues of these may continue to pose a risk to users
of the items. Some have also caused heavy discolouration
(pink or blue) of the parchment (Kowalik, 1980).
In addition to these fungicides, methods of disinfecting
membranes using alcohol solutions have also been
explored (Voronina et al., 1980).
The growth of mould is a risk for all waterlogged
organic materials and parchment is no exception.
Ways of avoiding this risk have been explored,
including freeze-drying and gamma irradiation.
Freeze-drying for parchment has been shown to be
feasible but is not without its own risks and adverse
effects (Parker, 1993). Gamma irradiation has been
shown to be deleterious for paper and parchment,
although there have also been positive views expressed
for its use in large-scale emergencies (Adamo et al.,
2001; Sinco, 2000). The drying and surface cleaning
of parchment items, followed by maintenance in dry
conditions for storage and use, continues to be the
most non-invasive and effective approach to controlling
growth (Craig, 1986).
20.5.2 Cleaning methods
Surface cleaning methods for parchment tend to follow
similar practices as those used for paper. Popular
210 Conservation of leather and related materials
methods in the first half of the last century included
the use of pellets of sticky bread, rolled or pressed
on the surface; wiping with cotton wool or chamois
leather moistened with water; or swabbing with
benzene (Reed, 1972; Haslam, 1910). Most of these
approaches were gradually replaced by the use of
rubber or vinyl erasers, or just soft brushes for loose
dirt, partly because of concerns about surface abrasion
and the uncertainties over the deposit of material
attractive to fungi, and especially arising from an
increasing understanding of the risks associated with
the application of liquid water. Wet methods have
been replaced with alcohol solutions applied locally
with cotton buds, which introduce more controlled
cleaning with less risk to the surface and to the highly
hygroscopic collagen fibre.
There are other risks associated with surface cleaning
parchment. When applying dry techniques it is
easy to ingrain soft dirt into the fibres, sometimes in
streaks. Sadly, in attempting to avoid this, it is common
to apply more vigour at the outset, which in
turn risks damaging surface fibres. It is also essential
to try to avoid damaging inks or pigments, so unfortunately
the application of erasers around writing, for
example, can lead to an unattractive penumbra of dirt
around the letters. Various forms of solid eraser
(sliced or grated) and sponge rubber are commonly in
use, especially those incorporating a narrow point for
accuracy (Szcepanowska, 1992). Restricting cleaning
to gentle brushing and removal of spots of loose surface
dirt appears to be the safest intervention.
The use of laser technology for surface cleaning has
been explored in all areas of conservation, including
for paper and parchment. For some otherwise good
condition material, the removal of ingrained dirt by
this means may be less damaging than traditional
methods. Reservations about the risks to organic
materials such as parchment are not unfounded, and
it has been recognized that care in application is critical
to the success of laser cleaning of parchment
without causing damage (Kautek et al., 1997; Cooper
et al., 2000). These experiments have been revealing
and contribute to knowledge about potential methods
and limitations of conservation. It is reasonable to
question whether it is ever necessary to remove dirt
so thoroughly, particularly in cases where little or no
adverse affect may be caused by its presence.
In similar vein, it should be noted that although
there have been examples of the use of bleaching
agents to remove or reduce discolouration in
parchment, these are not common. Methods have
included hydrogen peroxide, lemon juice and even
onion juice, and complex mixtures involving soaps,
ammonia and chloramine B.5
In the paper and
manuscript field there has been a gradual trend away
from bleaching processes as conservators have learned
about the risks in their application, and perhaps
because it has been recognized as unnecessary or
inappropriate to ‘brighten’ items simply in order to
access text that is already legible. Equally, the use of
solutions to intensify faded inks, as described above,
appears to have been abandoned. Although such
chemical methods were still being explored as late as
1981 (Flieder, 1982), the use of ultraviolet light to
reveal texts had begun to replace these at least as early
as the 1930s. Smith, in his tour of European archives
at that time, observed the new use of UV equipment
in some institutions (including a malodorous cupboard
at the Bodleian Library where users would
operate a lamp (Smith, 1938b)), as well as reluctance
in some to use UV. In referring to the latter he comments:
‘… they do not take into account that the use
of ultra-violet light entails no risk whatever to the
manuscript (something which certainly cannot be
said of chemical reagents, no matter how carefully
they may be applied)’ (Smith, 1938a). Steady advances
in light technology and digital image enhancement in
the late twentieth and early twenty-first century have
made it possible to discern writing against or underneath
stains or added text, without intervention
(Mairinger, 1981–82; Fuchs, 2002).
20.5.3 Humidification and softening
As described above, parchment is commonly found to
have become less flexible or even hardened, preventing
a sheet from being viewed. In the case of large
documents, for example, the rolling and creases can
become set, causing the skin to become spring-like
and difficult to hold open without risk. An unassisted
researcher opening a long-unused, multi-membrane
account roll can appear like a person wrestling with
an octopus. In the past, it was commonly held that a
roll like this should be flattened permanently, often
involving pasting it down onto a solid acrylic sheet
lined with a woven polyester fabric, or a board
covered with waxed paper (Cockerell, 1958). After
drying, the membrane would be peeled off the lining
material, or vice versa (sometimes leaving offset
ink behind), revealing something resembling an
embossed skin table mat. These days there is perhaps
more willingness to support users in accessing difficult
items with care, in favour of reformatting the
items to meet all comers, and certainly a greater
appreciation of the need to preserve original formats
(Clarkson, 1992). When an entire collection consists
The conservation of parchment 211
of difficult but original formats, the most sensitive
(and cost-effective) approach may be to humidify
gently those that are intractable, copy the collection,
return items to their original formats, package them
and place them in a suitable storage environment
(Lindsay, 2003). This is equally applicable to single
items as to collections (Woods, 2002).
Methods of humidification vary and tend to be
determined by whether it is necessary for the general
relaxation of a whole membrane or just localized
treatment to a crease or a cockled region. People have
long recognized the capacity for parchment to
become limp in humid environments and this has
been exploited, either by placing a membrane into a
humidity chamber or into a ‘damp pack’. The precise
amount of moisture in an enclosed space necessary to
relax different weights of membrane has been considered
(Woods, 1995). Earlier methods of humidification
involving damp packs tended to place the
parchment at greater risk of getting wet on the surface,
and the introduction of different kinds of
humidity chamber must in part have been intended
to avoid this risk.6,7
In recent times, the use of ‘Goretex’
(a specialist fabric incorporating a barrier membrane
that allows water to pass through only as a
vapour) has become common as a means of humidifying
a chamber, or used in a pack in such a way that
liquid cannot come into contact with the skin
(Buchanan, 1993; Singer, 1992). Also common is the
use of ultrasonic humidifiers or nebulizers to introduce
a fine mist into a chamber (Quandt, 1996).
When humidifying parchment, especially whole
sheets, the principal concern is to avoid any application
of liquid water if possible. The energy of water is significant,
arising from its strong polar charge (Kremen
and Southwood, 1960). The reduced shrinkage temperature
inherent in parchment makes it vulnerable
to damage by the application of polar liquids, as well
as when a membrane is dried without restraint
against shrinkage (Haines, 1999). The high energy of
water can exceed the energy holding decayed collagen
molecules in an expanded structure, causing
molecules to collapse and the fibres to shrink, even at
room temperature. The structural or molecular condition
of collagen is not easily determined by visual
examination and the gradual deterioration of collagen
fibres has been shown to lead to a ‘pre-gelatine’
stage in which wetting or even high humidity can
cause apparently fibrous material to dissolve into a
gelatinous state (Larsen, 2002).
Even if this ‘pre-gelatine’ stage has not been reached,
the surface tension of water as it evaporates exerts a pull
between fibrils and fibres, bringing them together and
consequently allowing them to bond to each other.
Tensioning the skin or applying a water-soluble, lowpolarity
solvent such as alcohol can reduce this effect,
allowing the water to be removed without bringing the
fibres into contact. Tensioning literally holds the fibres
apart as the water evaporates. Alcohol mixes with water
producing an azeotropic solution with a much lower
surface tension than the water alone. The mixture
evaporates without exerting a pull on the fibres, leaving
the skin dry and largely unaffected.
Rather than risk wetting an old but otherwise
sound membrane, and having subsequently to
remove the water under controlled conditions to
minimize any further damage, it may be safer to use
an environment with a high relative humidity and
to allow the membrane to condition at its own rate.
Even after gentle humidification, however, the natural
movement of the skin as it loses moisture may
need to be restrained to avoid distortion. Various
methods have been used to restrain or tension skins
during drying, including the use of successive changes
of dry blotting paper under boards and weights,
and commonly by ‘pegging out’ a skin to place it
under tension, in a similar fashion to its original
production (see, for example, Firgure 20.7). The
risks associated with the use of presses for drying
have long been recognized (Cockerell, 1958).
Vulnerable inks and pigments can be offset, fibres
can be pinched or squashed together to cause hardening
and translucency, and the prolonged presence
of moisture can permit mould to grow. As can be
imagined, there are also risks of damage in the use of
excessive tensioning when pegging out skins, particularly
those with holes or tears; it should be remembered
that a damp skin will undergo significant
shrinkage on drying, so allowance for this movement
must be made.
Drying a moist skin between absorbent sheets and
under a board with no additional weight is a minimal
form of restraint. It will not result in a very flat, even
finish; instead some natural undulation and channels
along old folds will be maintained. In many cases this
may be preferable since it avoids unnecessarily
changing the appearance or structure of an item,
especially if it is to be returned to its original folded
or rolled format. Where a more even surface is
important, the ‘pegging-out’ approach is most effective
and there have been many variations in this
method described over the years (see Figure 20.7).8
Localized humidification has been undertaken
safely by using features of the above. Gore-tex can be
used in the form of a small poultice, for example,
and ultrasonic humidifiers can be applied in a limited
212 Conservation of leather and related materials
The conservation of parchment 213
area (Lee, 1992; Singer, 1992; Quandt, 1996). These
humidifiers produce a light steam, which is airborne
droplets of water, so this approach applied to the surface
of a skin can pose some risks both to skin and
inks if it is not undertaken with care. As well as the
risks associated with the application of liquid water,
thicker skins in particular can be vulnerable to laminar
scission and fibre damage when stretching or
tension is applied. This can be caused by incomplete
humidification of the skin, when only the surface
fibres are damp and flexible but the internal fibres
remain dry and rigid (Haines, 1994).
The characteristics of alcohol described above have
been used in local applications of an alcohol and water
solution in which the alcohol predominates (70 or
80%). Alcohol alone can do little to remove creases; it
requires the input of water to make fibres plastic
and deform under manipulation. The particular penetrative
and lubricant characteristics of isopropanol
(propan-2-ol or isopropyl-alcohol) in contrast to other
alcohols have been known for many years and have
been described in the context of parchment conservation
(Reed, 1972: 127; Ellement, 1987; Viñas, 1987).
Local application of very small quantities of 80/20
ispropanol and water, followed by light tension applied
with the fingers, can reshape a membrane with the
minimum of intervention. Moisture is carried deep
within the skin so that humidification is more effective
and uniform. However, while most iron gall ink is
found to be stable in such a solution, pigments may
not be, and shellac seals are softened and discoloured
by contact with alcohols. For these reasons, an alcohol
solution may not be suitable for relaxing an entire skin,
although such a method has its uses when trying to
soften a shrunken membrane (Viñas, 1987).
Hardened and heavily shrunken skins are usually
the result of fire or flood damage, and sometimes by
the ill-advised application of hot air to dry out wet
skins. The differences between wet and dry shrinkage
have been described in a conservation context
quite recently. The search for remedies has a longer
history. In 1924 C.G. Matthews, a public analyst in
England, published attempts to open and flatten
folded documents that had been baked inside metal
safes which had been in a fire. The most successful
approach to opening them was also the most minimal:
a gradual humidification with steam for half an
hour, removing condensation to avoid wetting, and
Figure 20.7 A common approach to tensioning a parchment membrane. Several methods based on this simple principle
have been developed over the years to control the rate of tension produced by the shrinkage, for example the inclusion
of elastic between the peg and the clip, or the use of Velcro strips instead of pegs. (Courtesy Bodleian Library)
a few hours spent conditioning in this moist environment.
With admirable restraint, Matthews was
content to observe that although ‘there was not a
very close resemblance to the original parchment …
it was distinctly legible, including the signature’
(Matthews, 1924).
Matthews had observed that humidified skin in
this state shrinks back and hardens again when it
dries, and so to keep it softened for longer he applied
glycerol. This was only a temporary expedient, however,
because glycerol eventually dries out and does
not leave behind a residue that can hold the fibres in
their expanded state (Wächter, 1962; Calabro et al.,
1986). Collagen fibres shrink when their shrinkage
temperature is reached, but at temperatures above
85°C the molecules undergo a fundamental change.
A coating of glycerol is insufficient to alter the characteristics
of a skin so severely affected.
By 1969 attempts had been made to remedy the
problem of shrunken parchment, seeking perhaps
to overcome the effects described above. These
attempts resulted in the use of ever more complex
recipes, usually involving urea (carbamide), to try to
force apart the collapsed molecules and microfibrillar
structure, and to introduce a longer lasting
replacement for the previous hydrogen bonding
that kept the molecules apart in an expanded state
(Belaya, 1969; Yusopova, 1986). However, in a
remarkably similar set of circumstances as those
described above, in 1970 restorer S. Cockerell
reported using these new solutions to soften documents
from a fire-damaged safe. After employing a
mixture of urea, alcohol and water for up to 96
hours for each item, the skins were softened with
varying success. Many remained distorted and all
were vulnerable to tearing during the process.
Cockerell observed: ‘The object of the exercise was
achieved, though it is not known yet if the documents
will remain stable’ (Cockerell, 1970).
Cockerell and others at that time may not have
been aware that, while they can look similar to the
naked eye, dry heat damaged parchment has undergone
a very different change to that which has
become hardened and shrunken by the effects of
water and uncontrolled drying. In the case of fire
damage, for example, it appears that some effects
cannot be reversed and it may be better do the minimum
necessary to retrieve information and accept
that skin affected in this way may never be the same
again. The treatment of the blackened and charred
areas of burnt parchment might also be considered
in the same vein, although it has not stopped some
people from trying mixtures of dammar wax and
alcoholic methylpolyamide (PFE 2/10) and even
melted amber oil with spermaceti wax in benzol, all
of which have been observed to have undesirable
characteristics (Yusopova, 1980).
The shrinkage and hardening of water-damaged
parchment is a problem that can be ameliorated to
some degree. The differences in the behaviour of collagen
fibres that have become hardened by excessive
heat, compared with those affected by water, have
been described (Hassel, 2003). The fibres and molecules
of a wet and dried skin will have become weakened
but the hardening may often be the result
primarily of surface tension shrinkage. Humidification
of such material can allow an area to be stretched and
retensioned to make writing legible, for example
(Hassel, 1999). Even if the skin has become very hard
there still may be the scope to introduce a ‘lubricant’
in between the still intact fibres and fibrils and with it
a new molecule which, if it is large enough and will
not itself break down or evaporate, can remain after
initial drying to keep the structure in an expanded
state, preferably with the capacity to equilibrate with
its surrounding environment.
The use of urea and glycerol for this purpose has
been demonstrated to be unsatisfactory (Calabro
et al., 1986). Greater success has been achieved with
the use of low molecular weight (200) polyethylene
glycol (Viñas, 1987; Calabro et al., 1986). The process
takes a very long time (months) to complete but
appears to cause the adsorption of this relatively
large molecule into the structure, even to the extent
of reintroducing opacity as well as (a rather limp and
peculiar) flexibility. PEG 200 does not dry out in
the way other solvents will and it effectively replaces
lost hydrogen bonding and bound water in the skin
with its own, artificial form of ‘hygroscopy’. The
very slow rate of change that the skin undergoes
means that it may be many years before items
treated with PEG display any evidence of change
that differs from a ‘natural’ membrane and it may
not be possible to attribute such a change to the
PEG rather than the long-term effects of the shrinkage
that the skin had suffered before its treatment.
As has been noted, however, the use of isopropanol
in preparation for immersion in PEG so often results
in sufficiently beneficial softening effects as to render
the PEG treatment unnecessary (Viñas, 1987).
Although the useful characteristics of isopropanol
and PEG have been reported widely, some interest
in urea and glycerol has continued (Dobrusina and
Visotkite, 1994; Stancievicz, 1996).
As described already, it is not always easy to identify
how far advanced is the decay of the fibres in a
214 Conservation of leather and related materials
parchment membrane. The physical characteristics
of a ‘healthy’ parchment are self-evident – the skin
is strong, dense, opaque and flexible, even if it has
tears or holes. Decay associated with a hardened and
shrunken skin or a fibrous structure can be misleading
and difficult to diagnose with accuracy. It is not
obvious how low its shrinkage temperature has
reached and humidification or semi-aqueous treatments
can result in a greater level of shrinkage and
brittleness than might have been anticipated.
Before the late 1990s, it had been possible to test
the shrinkage temperature of new material in a laboratory
setting, but this method was not applicable for
historic manuscripts or artefacts (Haines, 1987).
Subsequent advances in testing have provided conservators
with the means to identify the shrinkage
temperature of a few fibres removed from a skin, by
microscopic observation of the contraction of the
fibres, and at the time of writing, a major research
project is under way in Europe, which seeks to provide
a method of evaluating the extent of decay of
collagen in a skin (Larsen, 2002).
20.5.4 Consolidation of weak parchment
Consolidation techniques have been applied both to
the treatment of flaking media and to decayed
parchment substrate. It is commonly found that the
weakening of one is closely associated to the condition
of the other, particularly when mould has been
an active cause of decay. Equally it may be observed
that, even for very specific, localized pigment reapplication,
the search for a suitable consolidant necessarily
involves an appreciation of its effect upon
both. This is especially the case for flaking manuscript
ink because the weakness frequently occurs
uniformly throughout the text and it is often necessary
to consider the application of a coating to most
or all of a membrane. For an item with a healthy
parchment substrate, this presents the conservator
with a very difficult dilemma.
For parchment which itself has become weak and
friable, the most common approach has been the
application of a very light gelatin solution, frequently
made from parchment itself. Gelatinous solutions
have been used in a variety of recipes and for different
purposes for centuries (Reed, 1972: 220). The
advantage of using such a solution is deemed to be its
compatibility with the parchment itself. A ‘size’
made from ground parchment shavings, or bits of
fish swim bladder (isinglass), contains pieces of fibre
and connective tissue (elastin) that make it an effective
consolidant and adhesive. The membrane being
treated will have contained similarly gelatinized
fibres when new. Weakness and loss of cohesion
across a skin may even be attributable to a loss of this
substance through the activity of mould or bacteria.
Various methods of applying gelatinous consolidants
have been described, from direct brushing onto
the surface or under lifting inks, to the application of
a fine, alcoholic mist (Quandt, 1991; BS4971:2002).
Vacuum suction tables are often used during this
process, to control the application of the consolidant,
to hold the membrane flat during treatment, and to
control its drying. Some of these treatments have
been developed for use on membranes with significant
losses, to infill holes as well as to consolidate a
fibrous skin (Bëothy-Kosocza et al., 1990).
The greatest risk in using a parchment size as a
consolidant for friable skin is of shrinkage and brittleness
being caused by the application of too much
size or too much water, usually because the precise
concentration of such a solution is not easy to control.
There is also a risk to pigments: parchment size
may maintain a degree of alkalinity from the lime
content of the skin, which can adversely affect the
nature of a coloured medium. For this reason some
people prefer to use a consolidant made from isinglass
or a purified gelatin (Quandt, 1996). There is
a range of purified gelatins produced from hides of
different animals, with alpha- or beta-form amino
acids (depending on whether the hides were
reduced in an acid or alkali process). These gelatins
are produced with different Bloom numbers, which
means that the strength of the resultant gels in solution
is different, with the higher Bloom number
producing stronger gels. This variation provides a
measure of control and precision in mixing tailored
solutions for different circumstances. However, the
essential requirement for a partially aqueous solution
remains, and it may be this that prevents the use
of gelatin for consolidation in some cases.
With the notable exception of the Vatican Library,
many European archives and libraries in the 1930s
moved away from the tried and tested use of gelatinous
solutions for consolidating weakened membranes
(Smith, 1938c). From this time until the
mid-1970s a common approach was the use of a plasticized
synthetic solution in non-aqueous solvent.
This extended also to the lamination of membranes
between supporting layers of material (dealt with in
more detail below). Various synthetic solutions were
used and most were found to be unsatisfactory or
even disastrous. In the 1930s, several institutions were
reported as having routinely used solutions of cellulose
nitrate or cellulose acetate (‘Zapon’ and Cellon)
The conservation of parchment 215
or copal-resin varnish (Kopallack) (Smith, 1938).
The instability and destructive capacity of these
solutions had already been observed by 1937 (Grant,
1937). It is perhaps not surprising therefore to find
no reference to their use beyond the 1950s. A nonaqueous
solution of amide polymer (Nylon) was a
popular consolidant from the 1950s to the 1970s and
its use was reported in a variety of contexts (see also
below).
The decay properties of many synthetic solutions
caused them to be rejected for use in the conservation
of organic materials generally, including parchment.
However, synthetic consolidants continued to
be used in later years with the availability of commercial
acrylic powders or solutions, alone or added to
fibre pulps (such as Plexigum) (Sievers, 1985). The
application of a uniform coating of a synthetic plastic
polymer to the entire surface of a skin changes its
physical and hydroscopic characteristics, even causing
it to be hydrophobic (Wouters et al., 1995). There
might be circumstances where such an excessive
intervention may be the only way of saving a crumbling
item with inks or pigments that would be
unstable in a gelatin solution, for example, and it is
worth noting that parchment that has become so
severely decayed has lost much of its hydroscopic
nature anyway. Conservators would be understandably
reticent, however, to ‘seal’ a membrane inside a
plastic medium, for example; experience has shown
us that such an approach can subsequently be found
to be regrettable (Smith, 1938; Wouters et al., 1992).
Other non-aqueous consolidants for fibrous parchment
have been tried, including hydroxypropyl cellulose
ethers (the Klucel range) (Boyd-Alkalay and
Libman, 1997). The long-term behaviour of these is
uncertain (see also section 20.5.5). Early attempts at a
minimal intervention by placing weakened fragments
between layers of glass or plastic sheet proved problematic
(Boyd-Alkalay and Libman, 1997). The most
sustainable approach to the preservation of weakened
parchment would appear to involve non-invasive
means (e.g. surrogacy, packaging and stable storage),
and if necessary remedial treatments with known and
compatible characteristics.
For the most precious items, it may be appropriate
to place parchment inside a case or enclosure without
oxygen. In 1974 Dr Reed set out a design for a
glass enclosure containing nitrogen gas, but it is not
known whether any of these were ever used (Reed,
1972: 208). More recently, the use of anoxic environments
for organic materials has been explored using
a variety of large- and small-scale systems (Stiber,
1988; Carrió and Stevenson, 2003).
20.5.5 Consolidation of inks and pigments
Several different solutions have been tried and evaluated
to consolidate flaking inks and pigments. These
have included mixtures of natural and synthetic gums,
waxes, polyvinylacetate (PVA) or cellulose derivatives
(Marconi, 1962; Yusopova, 1980; Guiffrida,
1983). Most reviewers over the years have expressed
a preference for a gelatinous consolidant.9
However,
there have been several attempts to find suitable consolidants
that avoid risks associated with gelatinous
and other aqueous mixtures, in particular for the
consolidation of heavily pigmented illuminations
where the use of aqueous solutions may be damaging,
and for supporting areas damaged by copper green
decay. Unsaturated fluorocarbon polymer derivatives
such as fluoron F-24L and fluorolon H6 mixed with
vinylacetate solution (CVEB) have been tried but
caused discolouration (Bykova, 1993; Yusopova,
1980) (fluorocarbon polymers include Teflon, a
well-known non-stick coating). Soluble nylon
(commercial products such as Maranyl) dissolved in
alcohol was recommended and its use commonly
reported.10
Unfortunately it was soon found to discolour
and become irreversible.11
Also tried were
alcohol solutions of copolymers of vinylacetate with
ethylene, mixtures of cellulose ethers in methylene
chloride and methanol, and acrylic polymers such as
Paraloid B-72 (Bykova, 1993; Tanasi et al., 1985).
The use of cellulose ethers continues to be tried,
such as aqueous solutions of methylcellulose (Tylose)
and hydroxypropylcellulose (Klucel G) in a nonaqeuous
solvent. The stabilization of some flaking
pigments using Klucel G in ethanol has been described
as beneficial as a pre-treatment before the use of gelatine,
especially where the pigment will be adversely
affected by even slight presence of an aqueous consolidant
(Quandt, 1996). Tests of both of these have had
mixed results, some showing undesirable characteristics
(Chahine et al., 1991; Botti et al., 1996).
Localized coating of parchment fibres with such
plastics may cause an imbalance of hydroscopic properties
across a skin, leading to deformation as described
earlier. However, it is also frequently the case that a
heavily pigmented area, often with a layer of gesso or
other ground below the pigment, is already behaving
differently to surrounding areas and this difference
may have contributed to the flaking of the pigment.
Equally the decay of collagen can cause a significant
reduction in its hydroscopic characteristics. Coating
an area like this may make no significant change to
the characteristics across the skin, but such a change
may not be apparent until after the application.
216 Conservation of leather and related materials
The conservation of parchment 217
Dimensional characteristics will be different for each
individual item and no general rule can easily be
applied for local consolidation treatments.
20.5.6 Repairs and supports
As with so many other conservation treatments for
parchment, methods applied to support weak parchment,
fill holes and repair tears have been many and
varied. The repair of tears and holes was an important
aspect of preparing skins for use, so many examples of
how this was done can be found when examining
manuscripts of all ages. The variations of approach
have employed both adhesive and non-adhesive
techniques, both in production and in conservation.
The adhesives used have been varied and their characteristics
are a major feature of any consideration of
treatment.
Methods of repair used in centuries past were
principally twofold. Edges were joined or rejoined by
stitching them together (using raw hide strips or linen
or hemp twine) or gelatine-based glues were used,
alone or mixed with other constituents. The rejoining
of torn edges has also been undertaken in the past
using only acetic acid (Reed, 1972: 224). The acid
melts the fibres at the edge and provides tacky gelatinous
surfaces that will stick together. However, the
continuous action of the acidity, the damage caused
in application and long-term discolouration of the
parchment make it inappropriate for use.
Stitching as a remedial conservation treatment
continued until quite recently. It might be described
as being derived from early craft production methodology,
having been used in the scriptorium to prepare
membranes. Methods are described in several published
sources.12
Its use as a conservation treatment
appears to have become uncommon from the mid-
1980s, probably because the puncture of original
material ceased to accord with contemporary ethics.
It seems to have been restricted to situations in which
an adhered repair was not deemed to be sustainable
(Munn, 1989).
Clearly the opportunity to reuse existing holes in a
membrane may make stitching acceptable, and of
course the rebinding of an old codex is a context in
which the use of stitching is appropriate. Wherever
original stitching exists it is usually recorded in detail
and may be preserved in situ if it poses no threat to
the item.
Old patches and adhered joins are also preserved
and recorded. They are either found as an essential part
of membrane preparation (and so text may run over
them) or can be an important feature of the historic
structure or use of the item. For these reasons, the
separation of joins or removal of patches is rarely
undertaken except when they place the item at risk
of continuing damage. The most common such
exceptions involve the reversal of poor quality repairs
made in fairly recent times (probably during the last
50 to 100 years). The perceived risk often arises from
the decay properties of an adhesive and/or its application,
or when the patch itself is causing damage or
covering text.
The qualities of repair adhesives have been the
subject of much consideration over the years. Early
adhesives were usually gelatine based, often a thick
version of parchment size. They were frequently
mixed with honey and vinegar to adjust their properties
for use and many further variations on the theme
have been reported, which include the addition of
egg white, gum Arabic and starches (Reed, 1972:
220 –224). Modern refinements have been made to
the additives, using synthesized or purified versions,
such as sorbitol and acetic acid (Cains, 1983).
During the twentieth century it became common
practice in UK institutions to use starch pastes instead
of gelatine glues and this had its own effect on how
the membranes were treated. Starch is not a high tack
adhesive and the difficulty in applying a patch, for
example, necessitated the excessive wetting and flattening
of both old and new parchment in order to
ensure that the patch maintained an even contact
with the membrane surface while the paste dried out
(Woods, 1995). It became the practice to adjust the
surface of the new parchment (and sometimes the old)
to make this easier. This involved abrading (‘buffing’)
the surface with sandpaper so that it became fibrous,
the fibres ensuring good absorption and adhesion.
This process was even mechanized in one UK institution,
where a sanding machine was made to increase
production of prepared skins for lining and patching
(Smith, 1938). Membranes were wetted excessively
and so dried out to a stiff, sometimes shrunken and
brittle state. Excess starch was commonly sanded off to
improve the appearance of the finish. Because the
original membrane had to be stuck down with paste
onto a sheet to hold it flat during the process, this
sanding was an essential feature of the procedure to
remove starch from the reverse. Items treated in this
way have a rough, hardened feel, their lateral dimensions
are usually smaller than before treatment, they
are often more translucent than previously, and
sometimes they have ‘blistered’ areas where the skin
has dried inconsistently.
Once practitioners had learned this method it was
often applied routinely, even to skins that had only
small tears or holes. Despite the presence of published
alternatives from the 1930s onwards, it was only in
the late twentieth century that this practice in the UK
began to be replaced by more compatible and minimal
methods, and when it was more widely recognized
that excessive intervention was unnecessary for
the majority of parchment manuscripts.
Collagenous glues such as gelatine continue to provide
compatible, sympathetic and minimal options for
the adhesion of tears and patches and their method of
application has been described in detail. The high
tack properties of gelatine make it possible for only
the smallest amount of adhesive to be applied and
because it does not display syneritic properties (it does
not release water as a liquid as it sets), the parchment
does not become wet in the process of adhesion. Care
is needed to avoid using too much gelatine, and to use
it at the correct application temperature to avoid penetration
and consequent translucency. Only very small
amounts are necessary and are applied in such a way
that the glue has dried and become tacky at the time
the surfaces are brought into contact. This combination
of features results in an adhesive that sets almost
immediately and without the excessive contraction
during drying that occurs with so many other colloidal
solutions such as starches and the cellulose
ethers, and which in turn avoids the risks of distortion
around a patch or repair. Various substances
have been added to gelatine adhesives, in order to
make the adhesive liquid at room temperature.
These include natural products such as honey and
flour, and more recently the cellulose ethers. There
does not appear to be any published comparative
information describing the long-term behaviour of
these mixtures.
Other adhesives have been tried as an alternative to
gelatine, such as commercial heat-activated adhesives,
proprietary starch pastes, methyl polyamide mixtures,
and PVA emulsions.13
Given the widespread recognition
of the risks associated with heat in contact with
parchment, it seems in retrospect surprising that heatactivated,
pressure-applied adhesives should, in the
past, have been used in the treatment of this material,
and perhaps not surprising that they are no longer
advocated (Powell, 1974). PVA emulsions have been
used with a variety of patching materials such as
goldbeaters’ skin and Japanese paper.14
The PVA
emulsions do not display the hydroscopic properties
usually required for treatments to parchment and are
commonly understood to have undesirable decay
characteristics, including irreversibility. In spite
of the fact that newer PVA polymers have been
developed that are intended to be reversible (e.g.
ethylvinylacetate or EVA), and in the absence of any
long-term ageing data in this context, it is reasonable
to question their longer-term properties. It has been
suggested that tears might be readhered using minute
strings of a Nylon material activated by ultrasound.
While the material might be reason for concern, the
use of ultrasound instead of heat to melt a dry-state
adhesive momentarily is worthy of further investigation
(Mayer, 2002).
The reversibility properties of an adhesive are an
important consideration. It may be possible to effect
a successful repair to parchment using a very dry
starch paste, for example. However, the reversal of
an aged starch adhesive invariably involves the application
of water. A patch may be successfully removed by
the application of humidity alone, but removal of the
adhesive residue, where it has been determined that
this continues adversely to affect the behaviour of the
membrane, can require the application of liquid
water, so placing the membrane at further risk. The
advantages of collagen as the basis for an adhesive, in
addition to its ageing properties and compatibility,
include its inherent molecular capacity to be broken
down and subsequently to undergo a partial reformation.
This means a collagenous source can readily be
melted and dissolved in hot water but parts of its
peptide structure can reassemble as it sets (Veis and
Cohen, 1960). Once set, it can subsequently be softened
in conditions of high humidity (such as in a
humidity chamber or pack).
Various materials have been used for patches and
other means of filling lacunae. Similar to the consolidation
referred to above, the infilling of holes and
weakened areas has frequently been undertaken using
a thick suspension of a pulped material. Parchment
glue (thicker parchment size) has been used in centuries
past for filling small holes, sometimes mixed
other organic constituents such as casein and egg
white, and sometimes substituted by a solution of
reduced and acid-dissolved collagen (Reed, 1972:
222–226). In more recent times, various methods
have been described using suspensions of parchment
fibres, alone or with the addition of paper fibres, and
in aqueous or water/alcohol solutions. These methods
are frequently employed on a suction table or even in
a leaf-casting machine, usually masking off all but the
area to be filled (Wouters et al., 1995).
The most common and ancient method of infilling
larger holes has been the use of new parchment
applied with a gelatine-based glue. There have been
variations during the last 75 years, such as the common
use of starch pastes as the adhesive in UK
archives as described above, and the use of Japanese
218 Conservation of leather and related materials
papers for patches in many European archives.
Compatibility and a very long precedence of stability
are sound reasons for using parchment, adhered
with gelatine. However, new parchment is much
more rigid compared with an old and possibly
weakened membrane, and softer, more flexible infill
materials are justifiable. Japanese paper, while being
a very different material, has the advantage of being
long fibred, stable, soft and, if used carefully, has the
capacity to absorb atmospheric moisture without
causing distortion to the membrane. Parchment can
be pared to make it thin, softer and translucent, so
for sound membranes it is still a suitable material. Its
excessive whiteness when new can be overcome by
the use of skins toned during production (usually
with coffee) or subsequently (Cains, 1983).
In the past, weak areas have most often been supported
with a finely split parchment or the prepared
lining of bovine intestine, known as ‘goldbeaters’
skin’. Like parchment, goldbeaters’ skin has been
used for many hundreds of years and if applied with
a small quantity of gelatine glue can remain stable,
sympathetic and strong for very long time indeed –
even over several centuries (Wächter, 1962). It is
almost completely transparent and extremely thin. A
similar material made from fish swim bladder has
also been used as an alternative (Cains, 1983; Munn,
1989). Both of these materials continue to be used
and will be found referred to in many of the references
noted herewith, which include some very
detailed descriptions of ways in which they have
been applied.
Although repairs using goldbeaters’ skin have
withstood the test of centuries, for much of the
twentieth century there was a trend in trying to find
new ways of supporting torn or weak skins, including
lamination with materials such as papers and plastics
such as polyvinylchloride (Reed, 1972: 232–233).
Japanese tissues or papers were used in France from at
least the 1920s and in Dutch archives its use can be
traced back to 1858 (Smith, 1938). The thin paper
was adhered to both sides of a weak membrane using
a wheat starch containing alum, and then the fibres
sandpapered off to reveal the surface and writing. In
France and Germany, a transparent paper, referred to
as ‘parchment paper’ and probably similar to a ‘glassine’
paper, was used from about 1927 (Smith, 1938).
From at least the 1930s until the 1980s, silk chiffon
was widely used in UK institutions to cover
weak paper documents. The practice, called simply
‘silking’, was sometimes extended to parchment,
although its use for this material was not so common
as for paper. It involved the pasting of a layer
of silk chiffon to the written faces of a manuscript,
often in combination with a backing layer and
patches (and sometimes edge ‘framing’) using new
parchment.15
For larger membranes linen was the
preferred alternative to new parchment, being a
cheaper material. The fine silk gauze was used to
ensure that text was visible.
The use of silk as a support was slow to disappear
(it was still being used in some archives until at least
the early 1980s), even though it had been observed
to discolour and decay (Reed, 1972: 232). It was
substituted with a synthetic alternative referred to as
‘bonded fibre fabric’, an alkali-modified cellulose
tissue (Viscose) commonly used for producing tea
bags (Cockerell, 1958). In spite of the problems of
bringing heat into contact with parchment, a few
practitioners in the 1970s chose to use paper tissues
which they coated with commercial emulsions that
could be activated by heat and pressure (Powell,
1974).
Lamination with the use of plastic films was common
for paper manuscripts from the 1930s to the
1960s and its use was extended to parchment in
some institutions in Europe. In Germany, cellophane
was used for a range of documents in the
1930s, although it was observed to cause the manuscripts
to have an unattractive wrinkled surface. At
the same time in the United States a cellulose acetate
film was in use, but it does not appear to have been
applied to parchment. In Europe in the 1950s a selfadhesive
polyvinylchloride (called Mipofolie) was
sometimes used for parchment. These PVC films
proved to discolour or cause deterioration and later
had to be removed (Wächter, 1987b).
Another common alternative to goldbeaters’
skin, used from the 1970s if not before, was a form
of reconstituted collagen. It was commonly purchased
from the food industry in tubular form
and produced for sausage casings (Reed, 1972:
226 –229). Lengths would be slit to produce a sheet,
washed, dried and pounced, patches cut to size and
then pasted with starch or parchment size over the
affected area of parchment (Guiffrida, 1983). It was
thought appropriate because of its translucency and
the fact that it was derived from skin materials (it
actually consisted of about 50% collagen, 20% glycerol,
some methylcellulose, 1.5% inorganic matter,
0.5% fat) (Woods, 1995). However, its appearance
and yellowing colour, and the comparative qualities
of goldbeaters’ skin, have caused it to fall into
disfavour.
The undesirable characteristics of these various
methods and materials had been described already
The conservation of parchment 219
by the 1970s. Referring to the use of starch, silk,
paper tissues and sausage casings, Dr Reed pointed
out in 1972 that: ‘Although it is possible to restore
volumes in serious need of repair to forms which
look “as good as new”, it must be remembered that
in twenty years’ time they will require further attention.’
He goes on to describe how difficult they are
to reverse, which could have been as much the
result of inappropriate adhesives as the laminate support
materials themselves (Reed, 1972: 231).
20.6 Conclusion
In times past, parchment has been a precious commodity,
in particular as a vehicle for dissemination
of thought to the privileged few who could read
and write. Over the passing centuries it became
more and more commonplace, although still prized
as the most appropriate material for records or
agreements and contracts to be kept for generations.
Paper has replaced it for all but the most exceptional
writing and printing purposes, as have other materials
where it was used in clothing, book covers and
so on. The rapid decline in production of parchment
during the twentieth century means that it is
now largely a material of the past and this may make
it precious to us once more.
Parchment could be described as a contradictory
material. It has characteristics that make it sufficiently
robust to have withstood many centuries,
often in fairly good condition where use has been
low. It can resist acid hydrolysis and can be strong
enough to be used as a hardwearing book covering.
However, it is damaged by water, heat, mould and
regular and insensitive handling, common features in
the existence of any item over centuries. The information
and decoration that it usually carries is easily
lost. Most notably (in this context) it can be damaged
by ill-advised conservation treatments. It has
often been seen as just another kind of paper, or
even leather, and suffered from inappropriate categorization
and lack of awareness of its nature and
idiosyncrasies.
In some respects, parchment could be used to
characterize the remarkable variety and excesses of
the development of conservation in the twentieth
century. In common with so many other areas of
conservation, as conservators have been able to learn
in ever-greater detail about its nature and peculiarities,
so their understanding of the importance of
minimal intervention and sensitivity has grown and
this is to be welcomed.
Acknowledgements
The author wishes to thank the various kind people
on three continents who responded positively when
seeking sources; Marion Kite, Trevor Miles, Robert
Minte and Sabina Pugh for helping to find images
and for comments to the text, and most especially
Ange Tack of the Bodleian Library for patiently and
cheerfully hunting down so many of the texts listed
below.
Endnotes
1. The term ‘split’ is used for a skin reduced in thickness
either by literally splitting or delaminating
layers with a knife or machine, or by shaving and
scraping the sides. It is not easy to tell the difference
between a skin that has been literally split apart from
one that has been scraped down, especially as the
surfaces on both kinds were subsequently shaved
further in final preparation, and sometimes also by
the scribe or other user. For further information on
the different ways that skins have been reduced in
thickness see: Reed, R., Ancient Skins, Parchments and
Leathers, Seminar Press, London 1972, pp. 54 and
121; and Haines, B., Parchment, Leather Conservation
Centre, 1999, pp. 3–7.
2. For examples of different methods used, see:
Haslam, J., The Book of Trade Secrets, Recipes and
Instructions for Renovating, Repairing, Improving and
Preserving Old Books and Prints, London 1910, p.
43; Langwell, W., The Conservation of Books and
Documents, London 1957, p. 48; and Smith, Manuscript
Repair in European Archives, I Great
Britain, The American Archivist, Vol. I, Number 1,
1938, p. 16.
3. Compare ibid. with the Foreword of BS4971:1988
Repair and allied processes for the conservation of documents,
BSI, London 1988.
4. See, for example: BS4971:1973, Recommendations for
repair and allied processes for the conservation of document,
Part 1. Treatment of sheets, membranes and seals, BSI,
London 1973, p. 5 and Bond, M., The Record Office
House of Lords, Report for 1952, London: Record
Office, 1953.
5. For respective examples see the following: Reed, R.,
Ancient Skins, Parchments and Leathers, Seminar Press,
London 1972, p. 215; Wächter, O., The Restoration
of the Vienna Dioscorides, Studies in Conservation, 7,
1962, p. 25; and Yusopova MV Conservation &
Restoration of Manuscripts and Bindings on Parchment,
Restaurator, vol. 4, Number 1, 1980, p. 62.
6. Examples of old damp pack methods include: Reed,
R., Ancient Skins, Parchments and Leathers, Seminar
Press, London 1972, p. 211; Powell, R., Case History
of Repair and Rebinding of an Eighth Century
220 Conservation of leather and related materials
Vellum Manuscript, in Smith, P. (ed.) New Directions
in Bookbinding, 22, 1974, p. 181; and, Guiffrida, B.,
Book Conservation Manual, Part Four: The Repair
of Parchment and Vellum in Manuscript Form, The
New Bookbinder, 3, 1983, p. 31.
7. Detailed descriptions of humidity chambers for
parchment include: Cains, A., Repair Treatments for
Vellum Manuscripts, The Paper Conservator, 7, IPC
1983, pp. 20 –21 and Clarkson, C., A Conditioning
Chamber for Parchment and Other Materials, in
The Paper Conservator, 16, IPC 1992, pp. 27–30.
8. For examples ancient and modern, see the following:
Cockerell, D., Condition, Repair and Binding,
in Milne, H., Skeat, J., Scribes and Correctors of the
Codex Sainaticus, British Museum, London 1938,
pp. 84 –85; and Mr Cockerell’s ‘stretching frame’
was designed to carry out both humidification and
stretching at the same time. Its use at the Public
Record Office, London, and the revealing staff perception
of its limitations are described in Smith, L.,
Manuscript Repair in European Archives, I Great
Britain, The American Archivist, Vol. I, Number 1,
1938, p. 7; Cockerell, S., The Repairing of Books,
London 1958, pp. 73–74; and Burns, T. Bignell, M.,
The Conservation of the Royal Charter and Great
Seal of Queen’s University, The Paper Conservator,
17, IPC 1993, p. 9.
9. For example, see: Wächter, O., The Restoration of
the Vienna Dioscorides, Studies in Conservation, 7,
1962, p. 25; Guiffrida, B., Book Conservation
Manual Part Four: The Repair of Parchment and
Vellum in Manuscript Form, The New Bookbinder, 3,
1983, pp. 36 –38; and Quandt, A., Recent Developments
in the Conservation of Parchment Manuscripts,
The Book and Paper Group Annual, 15, 1996, pp. 1–2.
10. For examples, see: Gowers, H., Treatment of a
Manuscript, Museums Journal, Vol. 58, March 1959,
p. 280; Report of the Annual Repairers’ Meeting in
Society of Archivists Journal, Vol. III, Number 3, 1966,
pp. 153–154; BS4971:1973, Recommendations for repair
and allied processes for the conservation of document, Part 1.
Treatment of sheets, membranes and seals, BSI 1973, p. 7
De-acidification of Paper 7.1; and Powell, R., Case
History of Repair and Rebinding of an Eighth-century
Vellum Manuscript, in Smith, P. (ed.) New Directions in
Bookbinding, 22, London 1974, p. 181.
11. For a review of the use of soluble nylon see: Paper
Conservation Catalog, AIC Book and Paper Group
1994, pp. 23–24.
12. For example, see: Cockerell, S., The Repairing of
Books, London 1958, p. 71; Guiffrida, B., Book
Conservation Manual Part Four: The Repair of
Parchment and Vellum in Manuscript Form, The
New Bookbinder, 3, 1983, pp. 27–28; and Cains, A.,
Repair Treatments for Vellum Manuscripts, The
Paper Conservator, Vol. 7, IPC 1983, pp. 18–19.
13. For an example of the use of commercial emulsions
and PVA, see: Powell, R., Case History of Repair
and Rebinding of an Eighth-century Vellum
Manuscript, in Smith, P. (ed.) New Directions in
Bookbinding, 22, London 1974, p. 181.
14. For example, see: Bienvenida, V., Procedencia: patrimonio
cultural manuscrito miniado, en pergamino, s
xvi (Processes used on an illuminated 16th-century
parchment manuscript), Centromidca 1984.
15. For a description of these methods see: Smith
(1938), Manuscript Repair in European Archives, I
Great Britain, The American Archivist, I(1), 5–8.
References
Adamo, M., Brizzi, M., Magaudda, G. et al. (2001)
Gamma Radiation Treatment of Paper in Different
Environmental Conditions: Chemical, Physical
and Microbiological Analysis. Restaurator, 22(2),
107–131.
BS5454:2000 (2000) Recommendations for the Storage
and Exhibition of Archival Documents. London: BSI.
BS4971:1973 (1973) Recommendations for the Repair
and Allied Processes for the Conservation of Documents.
Part 1: Treatment of Sheets, Membranes and
Seals. London: BSI.
BS4971:2002 (2002) Repair and Allied Processes for the
Conservation of Documents – Recommendations,
13.5 Consolidation. London: BSI.
Belaya, I. (1969) Softening and Restoration of Parchment
in Manuscripts and Bookbinding and Instructions for
the Softening of Parchment Manuscripts and
Bookbindings. Restaurator, 1(1), 20 – 48, 49–51.
Bëothy-Kozocsa, L., Sipos-Richter, T. and Szlabey, G.
(1990) Parchment Codex Restoration Using Parchment
and Cellulose Fibre Pulp. Restaurator, 11(2), 95–109.
Berardi, M. (1992) Why Does Leather Deform? Some
Observations and Considerations. Leather Conservation
News, 8(1), 12–17.
Bloom, J.M. (1989) The Blue Koran. In Les Manuscrits du
Moyen-Orient: essais de codicologie et de paléographie
(Deroche, F., ed.). pp. 95–99. Istanbul and Paris.
Botti, L., Impagliazzo, G., Montovani, O. et al. (1996)
Investigation of Some Polymers for the Protection of
Paint Films. In Proceedings of the International Conference
on Conservation and Restoration of Archive and Library
Materials. pp. 563–581 Rome: Instituto Centrale per la
Patalogia del Libro.
Boyd-Alkalay, E. and Libman, E. (1997) Conservation of
the Dead Sea Scrolls at the Laboratory of the Israel
Antiquities Authority. pp. 211–213. London: IPC
Conference Papers.
Buchanan, A. (1993) IPC Humidification Meeting. Paper
Conservation News, 66, 11–12.
Bykova, G.Z. (1993) Medieval Painting on Parchment:
Technique, Preservation and Restoration. Restaurator,
14(3), 188–190.
Cains, A. (1983) Repair Treatment for Vellum Manuscripts.
The Paper Conservator, 7, 17–22.
The conservation of parchment 221
Calabro, G., Tanasi, M.T. and Impagliazzo, G. (1986) An
Evaluation Method of Softening Agents for Parchment.
Restaurator, 7(4), 169–180.
Carrió, V. and Stevenson, S. (2003) Assessment of Materials
used for Anoxic Microenvironments. In Conservation and
Science 2002. Proceedings of the conference held
Edinburgh 2002, pp. 32–38. London: Archetype.
Chahine, C., Rottier, C. and Ruoy, D. (1991) Effects of
Adhesives on the Mechanical Properties of Parchment.
Sauvegarde et Conservation des Photographies, Dessins,
Imprimés et Manuscrits, pp. 139–146. Paris.
Chaudray, M., et al. (1991) In Pergament: Geschiste, Struktur,
Restaurung, Herstellung (Rück, P., ed.). pp. 315–322.
Sigmaringen: Jan Thorbecke Verlag.
Clarkson, C. (1982) Limp Vellum Binding – and its Potential
as a Conservation Type Structure for the Rebinding of Early
Printed Books. Hitchin: The Red Gull Press.
Clarkson, C. (1992) Rediscovering Parchment: The Nature
of the Beast. The Paper Conservator, 16, 5–26.
Clarkson, C. (1987) Preservation and Display of Single
Parchment Leaves and Fragments. In Conservation of
Library and Archive Materials and the Graphic Arts
(G. Petheridge, ed.). pp. 201–209. London: IPC.
Cockerell, S. (1958) The Repairing of Books. London:
Sheppard Press, pp. 74, 75, 230.
Cockerell, S. (1970) A Note on the Conservation of
Some Parchment Documents Damaged by Fire.
Business Archives, 33, 18–19.
Cooper, M., Spoertun, S., Stewart, A. et al. (2000) Laser
Cleaning of an 18th Century Parchment Document.
The Conservator, 24, 71–79.
Craft, A. (2003) The Conservation of Limp Vellum
Books at the National Archives. ARC, 172, 11–13.
Craig, R. (1986) Alternative approaches to the Treatment
of Mould Biodeterioration – An International Problem.
The Paper Conservator, 10, 27–30.
Dignard, C. (1992) Tear Repairs of Skins with Minimal
Access to their Backs: The Treatment of a Kayak. Leather
Conservation News, 7(2), 1–8.
Diringer, D. (1982) The Book Before Printing. New York:
Dover, pp. 170 –171.
Dobrusina and Visotkite (1994) Chemical Treatment
Effects on Parchment: Properties in the Course of
Ageing. Restaurator, 15(4), 208–219.
Ellement, P. (1987) A Note on the Structure of Vellum
and the Effects of Various Solvents. In Conservation of
Library and Archive Materials and the Graphic Arts
(G. Plenderleith, ed.). pp. 199–200. London: IPC.
Fitzsimmons, E. (1986) Limp Vellum Bindings: Their
Value as a Conservation Binding. Restaurator, 7(3),
125–142.
Fleming, L.E. (1983) Conservation of Oriental Miniatures.
Eastern Pictorial Art Conservation News, 2, 12.
Flieder, F. (1982) L’analyse et la revelation chimiques des
encres metallo-galliques. Restaurator, 5(1–2), 57– 63.
Fuchs, R. (2002) The History of Chemical Reinforcement
of Texts in Maunuscripts – What Do We Do Now? Care
and Conservation of Manuscripts, 7, 159–170.
Fuchs, R. and Mrusek, R. (2002) New Methods of Reflectography
with Special Filters and Image Processing
Techniques. Care and Conservation of Manuscripts, 7,
212–213.
Gairola, T.R. (1958) Journal of Indian Museums, 14 –16,
43– 45.
Giovannini, A. (1999) Die Restaurierung von Zwei mit
Pergament Überzogenen Möbeln von Carlo Bugatti,
pp. 61– 65. IADA Preprints.
Grant, J. (1937) Books and Documents, Dating, Permanence
and Preservation, p. 194. London: Grafton.
Guiffrida, B. (1983) Book Conservation Manual Part 4:
The Repair of Parchment and Vellum in Manuscript
Form. The New Bookbinder, 3, 30 –37.
Haines, B. (1987) Shrinkage Temperature in Collagen
Fibres. Leather Conservation News, 3(2), 1–5.
Haines, B. (1994) The Physical and Chemical Characteristics
of Parchment, Casings, Goldbeater’s Skin and
Gelatin. In Conservation for the Future (C. Woods, ed.).
p. 26. Dorset: AIM Proceedings. Society of Archivists.
Haines, B. (1999) Parchment. Northampton: Leather
Conservation Centre.
Haran, M. (1991) Technological Heritage in the Preparation
of Skins for Biblical Text in Medieval Oriental
Jewry. In Pergament: Geschiste, Struktur, Restaurung,
Herstellung (P. Rück, ed.). pp. 35– 43. Sigmaringen: Jan
Thorbecke Verlag.
Harrison, L. (1981) Physical Chemistry of Biological
Morphogenesis. Chemical Society Review, 10(4), 491.
Haslam, J. (1910) The Book of Trade Secrets. Recipes and
Instructions for Renovating, Repairing, Improving and
Preserving Old Books and Prints. London: Haslam and Co.,
pp. 10, 11.
Hassel, B. (1999) Conservation Treatment of Medieval
Parchment Documents Damaged by Heat and Water,
pp. 253–256. Preprints of the 9th IADA Congress.
Hassel, B. (2003) Heat Damaged Parchment. Papier
Restaurierung, 3(4), 31–38.
Hermans, J. (1992) Fans on Skin: Their Conservation and
Storage. Postprints of the ICOM Committee for
Conservation Leathercraft and Related Objects Group
interim meeting, pp. 42– 44.
Kahle, T.B. (1986) State of Preservation of the Dead Sea
Scrolls. Nature, 321, May 8 and citing Plenderleith, H.J.
(1955) Discoveries in the Judean Desert 1. Qumran Cave 1.
Kaminitz, M. and Levinson, J. (1988) The Conservation of
Ethnographic Skin Objects at the American Museum of
Natural History. Leather Conservation News, 5(1), 1–7.
Kautek, W., Pentzien, S. and Krüger, J. et al. (1997) Laser
Cleaning of Ancient Parchments. Lasers in the Conservation
of Artworks, pp. 69–78. Vienna.
Kite, M. (1992) Gut Membrane, Parchment and Gelatine
Incorporated into Textile Objects. The Paper
Conservator, 16, 98–105.
Kowalik, R. (1980) Decomposition of Parchment by
Micro-organisms. Restaurator, 4(3– 4), 200 –208.
Kremen, S. and Southwood, R. (1960) The Influence of
Hydrogen Bonding on the Solvent Dehydration of
222 Conservation of leather and related materials
Hides and Skins. Journal of the American Leather Chemists
Association, 55, 24 – 40.
Larsen, R. (2002) Improved Damage Assessment of
Parchment. Care and Conservation of Manuscripts, 7, 29
and plates III and IV.
Lee, L. (1992) The Conservation of Pleated Illuminated
Vellum Leaves in the Ashmole Bestiary. The Paper
Conservator, 16, 12.
Lindsay, H. (2003) Preservation Microfilming and
Digitisation at the London Metropolitan Archives. The
Paper Conservator, 27, 47–57.
Lokandum, B. and Chaudray, M. (1991) Parchment in
India – Some Observations. In Pergament: Geschiste,
Struktur, Restaurung, Herstellung (P. Rück, ed.).
pp. 315–322. Sigmaringen: Jan Thorbecke Verlag.
Loveday, H. (2001) Islamic Paper – A Study of the Ancient
Craft. Don Baker Memorial Fund, pp. 12–23.
Mairinger, F. (1981–82). Physikalische Methoden zur
Sichtbarmachung verblasster oder getilgter Tinten
(Physical Methods of Making Faded or Obliterated
Inks Visible). Restaurator, 5(2), 45–56.
Marconi, B. (1962) Use of Wax for Fixing Flaking Paint.
Studies in Conservation, 7(1), 17–21.
Matthews, C.G. (1924) Notes from the Reports of the Public
Analysts, pp. 516 –517.
Mayer, M. (2002) Ultrasonic Bonding. Papier Restaurierung,
3(4), 19–22.
Munn, J. (1989) Treatment Techniques for the Vellum
Covered Furniture of Carlo Bugatti. The Book and
Paper Group Annual, 8, 27–38.
Myers, M. (1980) Storage of Leather Objects. In
Conservation and Restoration of Leather, Skin and
Parchment. Copenhagen.
Norman, D. (1993) Mounting Single Leaf Parchment and
Vellum Objects. V & A Conservation Journal, 9, 10 –13.
Parker, A.E. (1993) Freeze Drying Vellum Archival
Materials. Journal of the Society of Archivists, 14(2),
175–188.
Petrus Maria Caneparuis (1619) De atramentis cuiuscunque
generic, p. 179. Venice. (Ad intraurandas literas ex
antiquitate fere abolitas – How to Freshen up Letters
from Antiquity that are Almost Erased.)
Pickwoad, N. (1992) Alternative Methods for Mounting
Parchment for Framing and Exhibition. The Paper
Conservator, 16, 78–85.
Powell, R. (1974) Case History of Repair and Rebinding
of an 8th Century Vellum Manuscript. In New
Directions in Bookbinding (P. Smith, ed.), 22, 181.
Quandt, A. (1991) The Documentation and Treatment of
a Late 13th Century Copy of Isidore of Seville’s Etymologies.
The Book and Paper Group Annual, 10, 164–195.
Quandt, A. (1996) Recent Developments in the
Conservation of Parchment Manuscripts. The Book and
Paper Group Annual, 15, 1–12.
Reed, R. (1972) Ancient Skins, Parchments and Leathers.
London: Seminar Press.
Reed, R. (1991) Some Thoughts on Parchment for
Bookbinding. In Pergament: Geschiste, Struktur, Restaurung,
Herstellung (P. Rück, ed.). pp. 217–220. Sigmaringen:
Jan Thorbecke Verlag.
Ryder, M. (1991) The Biology and History of Parchment.
In Pergament: Geschiste, Struktur, Restaurung, Herstellung
(P. Rück, ed.). pp. 25–33. Sigmaringen: Jan Thorbecke
Verlag.
Scholla, A. (2003) Early Western Limp Bindings: Report
on a Study. Care and Conservation of Manuscripts, 7.
Museum Tusculanum Press, pp. 132–158.
Sievers, J. (1985) Fehlstellenergänzung bei Pergament
durch Anfasern. Maltechnik-Restauro, 19, 63– 66.
Sinco, P. (2000) The Use of Gamma Rays in Book
Conservation. Nuclear News, 38– 40.
Singer, H. (1992) The Conservation of Parchment Objects
using Gore-Tex Laminates. The Paper Conservator,
16, 40 –45.
Smith, L.H. (1938a) Manuscript Repair in European
Archives II: The Continent; France, Belgium and the
Netherlands. The American Archivist, 1(2), 51–57, 64–67.
Smith, L.H. (1938b) Manuscript in European Archives I:
Great Britain. The American Archivist, 1(1), 6 –19.
Smith, L.H. (1938c) Manuscript Repair in European
Archives II: The Continent: Italy. The American Archivist,
1(2), 70 –75.
Soest, H. van (1989) Researching the Conservation and
Restoration of Parchment. ICOM Arbeitsgruppe Leathercraft
and Related Objects, International Leather and
Parchment Symposium, pp. 94 –103.
Stancievicz, J. (1996) The Conservation of a Hebrew
Manuscript Number 802238, an Evaluation of the
Method. Restaurator, 17(2), 66 – 67.
Stiber, L. (1997) Thomas Jefferson’s Rough Draft of the
Declaration of Independence: The Evolving Condition
of an American Icon and Implications for Future
Preservation. In The Proceedings of the Fourth International
Conference of the Institute of Paper Conservation ( J. Eagan,
ed.). pp. 53– 63. London: IPC.
Szcepanowska, H. (1992) The Conservation of 14th
Century Parchment Documents with Pendant Seals.
The Paper Conservator, 16, 86 –92.
Tanasi, M.T., Vallone, L., Impaglazzo, G. et al. (1985) A
propositio di un intervento strordinario di restauro:
recupero di un documento in pergamenta dell’archivo
do stato di Torino. (An Exceptional Restoration:
Recovery of a Parchment Manuscript from the Torino
State Archives.) La Conservazione delle Carte Antiche,
5(9–10), 37– 45.
Veis, A. and Cohen, J. (1960) Reversible Transformation of
Gelatin in the Collagen Structure. Nature, 186, 720 –721.
Viñas, V. (1987) The Use of Polyethylene Glycol in the
Restoration of Parchment. In Conservation of Library and
Archive Materials and the Graphic Arts (G. Plenderleith,
ed.), pp. 195–197. London: IPC.
Voronina, L., Nazarova, O. and Petushkova, Y. (1980)
Disinfection and Straightening of Parchment Damaged
by Micro-organisms. Restaurator, 4(2), 91–98.
Vorst, B. (1986) Parchment Making – Ancient and Modern.
Fine Print, 12(4), 209–210.
The conservation of parchment 223
224 Conservation of leather and related materials
Wächter, O. (1962) The Restoration of the Vienna
Dioscorides. Studies in Conservation, 7, 23–25.
Wächter, O. (1987a) The Malicious Metallic Inks.
Maltechnik-Restauro, 23(3), 19–23.
Wächter, O. (1987b) The Delamination of the
Carolingian Evangelary from the Treasure of the
Cathedral of Essen. Maltechnik-Restauro, 23(2), 34 –38.
Woods, C. (1995) Conservation Treatments for Parchment
Documents. Journal of the Society of the Archivists,
16(2), 223, 228–229.
Woods, C. (2002) The Role of Modern Reprographics as
a Tool for the Conservator. Care and Conservation of
Manuscripts, 7, 84 –91.
Wouters, J., Gancedo, G., Peckstadt, A. et al. (1992) The
Conservation of the Codex Eykensis: The Evolution of
the Project and the Assessment of Materials and
Adhesives for the Repair of Parchment. The Paper
Conservator, 16, 68.
Wouters, J., Peckstadt, A. and Watteeuw, L. (1995)
Leafcasting with Dermal Tissue Preparations: A New
Method for Repairing Fragile Parchment and its
Application to the Codex Eyckensis. The Paper
Conservator, 19, 7.
Yusopova, M.V. (1980) Conservation and Restoration of
Manuscripts and Bindings on Parchment. Restaurator,
4(1), 58– 61.
21.1 Introduction
Randy Silverman
Successful conservation of leather bookbindings,
unlike the treatment of many other types of cultural
artefacts intended primarily for exhibition and storage,
requires books be returned to a functional state.
Traditional leather rebacking – the repair of damaged
hinges and headcaps with new leather onto
which original leather is reattached – produces aesthetically
appealing results due to leather’s ability to
blend new and old materials sympathetically. While
still a stock option, the disadvantages of using leather
as a repair material, including chemical instability of
vegetable-tanned skins and loss of physical strength
resulting from overparing, have forced conservators
to re-evaluate this choice over the past 20 years.
What has emerged is a variety of conservation alternatives
that achieve functionality, durability, and
aesthetic compatibility more quickly than traditional
methods. Most significantly, contemporary conservation
options for treating leather bookbindings tend to
minimize the intervention, ensuring repairs preserve
the integrity of historic books.
The following short essays reflect crosscurrents
in conservators’ innovative approaches to reattaching
boards, repairing joints and headcaps, and consolidating
desiccated book leather. Collectively, they reflect a
common interest in substituting cellulose for collagen
when choosing a repair material to increase the
chemical stability and physical durability of the resultant
work. These developments include a range of
bookbinding techniques, including: Cains’ joint tacketing;
Ruzicka, Zyats, Reidell, and Primanis’ work
with consolidants, Puglia and Anderson’s solvent-set
book repair tissue, Etherington’s Japanese paper hinge
repair, Minter and Brock’s cloth hinge repair, and
Zimmern and Minter’s development of board slotting
machines. They also address the problem of treating
inherent vice in historical bookbinding leathers,
especially in skins produced during the past
200 years, through the use of chemical consolidants
such as Klucel G, SC6000/Klucel and Lascaux
498 HV. The synergism underlying these trends
reveals the creativity afoot in book conservation
internationally.
21.2 Binding solutions to old
problems
Anthony Cains
21.2.1 Introduction
In his tribute to the historian Maurice Craig, the late
William O’Sullivan recalled searches made together
in the Long Room at Trinity College, Dublin, looking
for rare bindings (O’Sullivan, 1992; Cains, 2000).
During that time, they sheltered their discoveries in
a seventeenth century armoire in the office of the
librarian H.W. Parke. He wrote: their objective was
to give some measure of protection to a few of the
better-preserved fine bindings, which, like those on
all Long Room books, had suffered severely from
the polluted atmosphere of the city since Victorian
times. O’Sullivan also made observations on the relative
condition of different skin covering materials,
comparing the robust, early seventeenth century
vegetable-tanned calf to the mid-eighteenth century
calf which ‘crumbled’; the ‘morocco’ which resisted
225
21
Conservation of leather bookbindings: a mosaic
of contemporary techniques
pollution better than the calf, and vellum which
weathered best of all.
It will be observed, however, that vellum, long
exposed to light and heat, was often found to be brittle
and cracked, while tawed skin survived largely
intact although its exposed surface would erode with
the loss of the grain layer.
Referring to the manuscript collection in his
charge, O’Sullivan lamented the large-scale rebinding
events of the eighteenth and nineteenth centuries, the
decay of those bindings despite their relatively sheltered
existence in the Manuscript Room, and the low
standards of twentieth-century commercial binding
that led the librarian to suspend all binding and repair
in 1950. The work of conserving early Irish manuscripts
at Trinity College Dublin (TCD) begun in
1952 by Roger Powell, and the establishment of the
Conservation Department (1972–74), were due in
no small measure to Dr O’Sullivan’s efforts.
The Long Room project to survey, clean and conserve
the collection was started in 1979–80, and the
oak sash windows were then covered with ultraviolet
(UV) filtering acrylic sheets in addition to the holland
blinds (Cains and Swift, 1988). In preparation
for this task, a number of consolidants and leather
dressings were tried on typical examples of historic
vegetable-tanned leathers, particularly calf and sheepskin.
The project needed a treatment that contained
neither water that would darken the degraded leather
nor oil that would stain the text paper, and one that
could be handled by the intelligent but unskilled
hands of college students employed during summer
vacation. Of the several cellulose ethers that Margaret
Hey introduced in the TCD Library Conservation
Department workshop for paper sizing/consolidation
trials, Klucel G (hydroxypropylcellulose) in ethanol
proved the most effective, and provided the essential
process and the foundation for the project.
21.2.2 Klucel G
As the product guide notes (Hercules Incorporated,
1979), Klucel has excellent binding properties. Following
the publication of a brief report on the use of
Klucel G as a consolidant for degraded leather (Cains,
1981), prompt feedback was elicited from colleagues:
Dr Anthony Werner (a TCD graduate) stated the
process proved effective in the treatment of Polynesian
grass skirts using isopropanol as the solvent, while
bookbinders working in an archive commented it
worked well on reverse calf and sheep. Dr Nicholas
Pickwoad noted some problems with skins darkening,
possibly due to the Klucel G solution being
overexposed to the atmosphere before being applied
to leather by his (volunteer) staff. In their product
guide (Hercules Incorporated, 1979: 7), the Hercules
Company note the following:
Moisture Absorption: Klucel absorbs moisture from
the atmosphere, as do other water-soluble materials. The
amount absorbed depends on the relative humidity and
temperature of the environment. As packed, moisture
content of all grades does not exceed 5% by weight,
and is generally between 2% and 3%. It is suggested
that Klucel be stored in tightly closed containers and in
a dry atmosphere to prevent any increase in moisture
content.
Equilibrium moisture content at 50% RH and 73
F. (23 C.) – 4%
Equilibrium moisture content at 84% RH and 73
F. (23 C.) – 12%
Instructions for dissolving Klucel G are also given in
the product guide. The solvent is agitated, preferably
in a laboratory mixer, and the product added
slowly to the vortex. During the mixing, the powder
may coagulate but these gel lumps will eventually
dissolve to form an even, viscous solution.
As a further precaution, one may elect to use a dry
alcohol and to desiccate the Klucel G powder. For
the Long Room project, however, the solution was
prepared using industrial-grade denatured ethanol
(IMS 100 @ 20°C toilet grade) containing only a
trace of water, a solution that has proved reliable over
the years.
The writer believes the source of the water causing
the darkening of leather following an application
of Klucel G relates to the environmental conditions
in which the work is undertaken. As an example,
two equally degraded, mid-nineteenth century volumes
bound in half calf were removed from a very
dry storage environment at TCD. In preparation
for a summer class to be taught in Italy, one of the
volumes was treated with Klucel G in the TCD
workshop which satisfactorily consolidated the
leather without its becoming darkened. Several days
later, in the warm, humid environment north of
Rome, the same Klucel G solution was used to
treat the second volume, but this leather darkened
perceptibly. Because of this and similar experiences,
it is recommended that subject material be preconditioned
prior to treatment in a drying cabinet
or air-conditioned room at a relative humidity less
than, say, 40%. The moisture content (EMC) of the
subject leather can be checked with a suitable moisture
meter (Aquaboy type) in a range of less than 6%.
226 Conservation of leather and related materials
The project was conducted in a closed-off cabin
area in the Long Room, a relatively dry and stable
environment compared with the conservation workshop.
In monitoring the project, blackening of the
leather was not observed except when too much
flour paste had previously been applied to secure
torn flaps or labels. Blackening is frequently seen on
old rebackings when a paste-wash has been applied
in an attempt to consolidate the powdery leather.
21.2.3 Application of Klucel G
Sufficient Klucel G 5–10 –15g/l is shaken and
decanted into a beaker for the day’s work in hand.
While it can be applied with a well-used, 55mm
wide, Japanese brush of the type called Shiro-Ebake,
these brushes are rather expensive and may be substituted
with a regular one-inch paint brush. With the
fore edge down on the bench, brush the solution
onto the spine and caps, which will be immediately
absorbed by the areas lacking grain. On the sides
where the grain is intact, surplus Klucel G is removed
with a cotton wool pad worked in a circular or in a
figure-of-eight motion (rather like applying French
polish to wood). This serves the purpose of cleaning
the cover and leaving it without smears. The board
edges and turn-ins are then treated, using the opportunity
also to remove soil and size the brittle paper
areas of the pastedowns and flyleaves. This is best
done using another brush and container of Klucel G
for paper only (5g/l). If you are not familiar with
the leather of the subject, spot-test an area before
applying the consolidant.
The gains made by the treatment, other than cosmetic
improvements, occur in the reading room
where the treated material is cleaner to handle and
reduces the soiling of reading cradles and padded
supports. In the conservation workshop, consolidation
of desiccated leather provides the foundation
for other leather treatments, such as facing, and does
not interfere with them.
21.2.4 Facing degraded leather
A review of the author’s paper on facing, given at the
Institute of Paper Conservation Manchester 1992 conference
(Cains, 1992), is now timely. Regarding the
casting of the tissue: by reducing the water by half
when diluting the two acrylic dispersions, a fatter resin
layer results which sticks and detaches more readily
than the standard heat/solvent set recipe given.
Standard tissue: Plextol M 630 one part; Plextol B
500 two parts; and water six parts.
Facing tissue: Plextol M 630 one part; Plextol B
500 two parts; and water three parts.
The latter should not be used on endpapers because
too much resin is present to be discharged by simply
swabbing with acetone. It may only be used if
the subject paper can be immersed in acetone to dissolve
the residual resin. This new proportion was
determined after a trial on Victorian leather by John
Gillis of the TCD workshop.
After applying the Klucel G to the leather, it should
be allowed to dry thoroughly before adhering facing
tissue to the areas of the binding to be lifted and
underlaid with new conservation leather (Cains,
1994, Figures 5 and 6). The main purpose of the
facing technique is to remove the spine leather
intact whatever its condition (Cains, 1981), to gain
access to the sewing structure for repair (see joint
tackets below) or disbinding, and to prevent loss and
fragmentation of the cover during repair.
21.2.5 Technique
For raised bands, cut pieces of tissue to fit the panels
and separate strips to overlay the bands. If the joint is
to be underlaid, the band strips should stop short of
the joint by 6 to 8mm; this area will be overlaid by
the new leather but underlaid at the panels.
The spine is dampened, not flooded, with ethanol
and each piece of facing is activated with ethanol. As
it softens, it is applied to the surface of the leather
and pressed home with a pad of cotton wool and
then firmly pressed with the fingers. When the
facing has dried superficially, but the leather is still
moist, the process of lifting can commence. The
idea is to perform the ‘surgery’ while the system is
soft and flexible.
The preferred tool for lifting the leather is a bookbinder’s
paring knife of the German pattern made
from a high-speed steel, machine hacksaw blade. The
profile and rigidity of the blade is important for
controlling the process. Flexible, disposable blades
are not recommended.
Following the removal of the spine in one piece –
or if this proves difficult, lifting of each panel and
one-band segment, which should be identified by
numbering on the tissue – the flesh side is levelled by
sanding and paring. What often happens with ancient
calfskin is the grain layers will separate from the flesh
layer, in which case one may elect to remove it entirely
or reattach it, particularly if this separation is localized.
The flesh may be consolidated with Klucel G.
If one chooses to remove a degraded and damaged
Conservation of leather bookbindings: a mosaic of contemporary techniques 227
fleshing, it may be peeled away leaving the (tooled)
grain layer secured to the facing. In preparation for
replacing the spine onto the new leather, every scrap
of tissue not supporting leather is cut away with a
scalpel. The spine can be glued directly to the dry
rebacking leather. A better approach would be to
mount the spine onto a suitably coloured Japanese
paper, allow time to dry, pare, and then mount onto
the new rebacking leather. This is a valuable approach
if the surviving grain is rather lace-like, and provides
a support and release layer for the future. Before
facing the entire spine, the labels should be faced
and removed. In the case of only partial detachment
of the grain layer (Cains, 1994, Figures 5 and 6), the
flesh should be glued down and allowed to dry before
adhering the grain layer to its support. Only when
all work has been completed and thoroughly dried is
the tissue removed with acetone or xylene.
21.2.6 Treatment of the boards
When applying tissue to areas of the board to be
repaired and underlaid with new leather, care must
be taken to avoid tide marks from localized application
of ethanol. It is recommended the tissue be
activated with ethanol and applied without prewetting
the leather. It may be pressed into place with
a pad dampened with the solvent and then fingered
to secure.
21.2.7 Adhesives
The traditional adhesive for new leather is flour
(wheat starch) paste, a thick mixture (12% weight/
volume) thinly applied. Moisture from the new
leather must not be allowed to come into contact
with the exposed flesh side of the binding’s original
leather. Strips of thin polyester must be inserted at
every point of possible contact. After the work has
dried overnight and the necessary paring/sanding
of the edges completed, the flaps are glued or pasted
down. For the sides, one may use paste; for the spine,
a paste and ethyl vinyl acetate/polyvinyl acetate (EVA/
PVA) mixture, say, 10% EVA for a durable and flexible
bond is recommended. The object is to use an
adhesive with the right working characteristics applied
in a controlled way.
21.2.8 Offsetting
To control the amount of adhesive used, apply it
evenly to a slip of polyester which is then inserted
under the flap. The flap is pressed gently onto the
adhesive, the polyester removed, and the flap pressed
firmly onto the board. The spine and detached components
can be pressed onto a film of adhesive applied
to the surface of a (lithographic) paring stone. Of
course, a brush may be used but the offsetting technique
does reduce the need to lift and flex the leather
flap. An artist’s fan brush is also a popular tool for this
purpose. Again, the adhesive must be allowed to dry
completely before removing the facing. Fragments of
grain remaining on the facing tissue are accurately cut
from the tissue; the lacunae glued, and the fragment
replaced. Some workers have used animal glue/
gelatine (12%) for reattaching the grain layer to its substrate
and as a local consolidant. A traditional bookbinding
adhesive is thin animal glue to which a small
quantity of paste is added to slow the drying time.
After final cosmetic retouching with dye or watercolour,
the repaired cover is given a sparing application
of leather dressing. The late Dr Ron Reed gives a
number of suitable recipes in his famous book (Reed,
1972). Because the wax/oil, British Museum-type
dressing interferes with the facing process, application
was discontinued in the Long Room project, although
a recipe was given in the booklet documenting that
work (Cains and Swift, 1988).
21.2.9 Board attachment
The joint tacket method of board attachment was
first published in 1988 (Cains and Swift, 1988), the
year of an important conference held at Corpus
Christi College, Cambridge (Cains, 1994), and is
one of several repair methods designed in the TCD
workshop or in collaboration with colleagues.
Bernard Middleton was probably the first to illustrate
a method for adding multiple threads to the
existing cord or thong sewing supports to create a new
slip (Middleton, 1972). This approach represents
a family of methods using new thread or strands of
cord lightly glued to the original supports and then
secured by oversewing or resewing all along at several
points down the spine. The new fibre should not
be attached by oversewing directly to the original
stations without the assurance that plenty of residual
strength still remains in the original system.
21.2.10 Helical oversewing
Text blocks that are intact and unbroken but with
cords or vegetable-tanned leather thongs totally
degraded can be resewn in situ onto new supports.
After lining the cleaned-off spine with pasted Japanese
paper and thin fabric, centres of the sections are
marked with slips of paper and new endbands sewn
on as best practice recommends to provide slips as
228 Conservation of leather and related materials
board attachment points. The original endband cores
can be drilled and oversewn onto the text block.
New supports are lightly glued to the original stations
and oversewn onto the spine through random but
regularly spaced intervals through the selected centre,
or sewn all along for several gatherings at the joints
and at intervals between. Oversewing is achieved by
piercing the centre fold from inside and following the
awl point with needle and thread back into the fold
and exiting to the spine at the other side of the support.
A centre, four or more gatherings down, is
opened and the process repeated, creating a neat spiral
of thread that embraces the original sewing threads,
the linings, and the new supports.
The more usual approach is related to Middleton’s
method and has been illustrated in the postprint of
the Corpus Christi Conference (Cains, 1994: 129,
Figure 8). For large volumes, a substantial slip needs
to be made of multiple threads. These are sewn
around the original supports and through the centres
of several sections at spaced intervals to distribute the
load, starting at the lowest section. As one moves
toward the joint, the lower threads are embraced to
form a slip. In the illustrated example noted above,
the slip has been passed through the first original
lacing tunnel and then returned to the joint, divided
and then tacketed over itself with the ends fanned
out. To reinforce the first and last fold, a loose guard
of slunk parchment or tough handmade paper may
be inserted before sewing.
21.2.11 The joint tacket
The joint tacket system is also illustrated in the same
publication (Cains, 1994), but is not described in
as much detail as the variation of this technique
published by Robert Espinosa and Pamela Barrios
(Espinosa and Barrios, 1991). The joint tacket was
the product of a moment’s improvisation to deal
with a book urgently needed for an exhibition. The
original method was to drill a tunnel at the base of
each saw kerf of the recessed sewing; the drill angled
to exit at a point about 10mm below and through
the leather of the spine – or, more usually, having
removed the spine leather, through the new lining.
A threading hook is formed by grinding a slot in
one side of the eye of a needle, which is then inserting
into a pin vice (to be discussed later). The hook
is inserted from the spine to the joint, and about a
foot of thread is passed through, forming a loop at
the spine. (The reverse of this threading direction is
considered better ‘engineering’ by my colleagues.)
The two ends of the thread are passed through the
loop and the hitch tightened. The geometry of the
board attachment system was devised with conscious
reference to eighth century binding practice.
When drilling the bifurcated lacing tunnels in the
board, it is preferable to drill from the pastedown
side. Mark the centre of the lacing station at the
joint edge of the pastedown, then mark the centres
of the two angled tunnels in relation to it, and drill
from that side to the board joint edge. Drilling this
way ensures a more symmetrical triangle will result.
The threads are hooked through the tunnels and the
ends wound together two or three times and tightened
to form a tacket. Espinosa suggests a square, or
reef knot.
The threads are cut off leaving a short length on
each side of the tacket (or knot) which are frayed
out, pasted down, and boned or lightly hammered
after drying. The tacket form of twisted thread gives
a flatter profile than a knot, but if a totally level
result is required, a ‘V’ channel may be cut between
the two tunnels following Carolingian practice.
21.2.12 Drills
Modern twist drills are often too short in relation to
the gauge needed for our work, and can be brittle
or tend to clog. The chuck of the flexible-shaft drill
should be of the collet type; even the smallest of the
Jacobs key chucks is too bulky for many jobs requiring
acutely angled holes. The Foredom Electric
Company (16 Stony Hill Road, Bethel, CT 06801,
USA, tel. 01-203-792-8622; http://www.foredom.
com/) offers a splendid range of tools, footcontrolled
motors and handpieces.
21.2.13 Making the needle drill bit
Traditional flat drill bits are easily made from bookbinder’s
needles or other sources of hardened carbon
steel wire (such as balance staff and pivot wire for
clock making). We use wire in 0.9, 1.2 and 1.6mm
diameters in 7.6cm (3 inch) lengths which is cut
down to the length required.
The point of the needle is cut off with wire nippers
and again at the base of the eye; the cutting
edge is formed at this, the widest point of the needle
below the eye. Secure the needle in a pin vice.
The famous L.S. Starrett Company (1993) no. 240
series range is recommended with collet chuck
capacity of 0 –1.4mm (A) and 0.64 –1.9mm (B).
A bench-mounted ‘hobby’ grinder with 15.2cm
(6 inch) diameter wheel can be used, but great care
must be taken to avoid blueing (softening) the carbon
steel of the needle. When grinding with this
Conservation of leather bookbindings: a mosaic of contemporary techniques 229
machine, hold the needle to the wheel for a second
and then remove it for a few seconds to air cool
without changing the position of the hand (a sort of
pivoting action), and repeat until a hollow ground
bevel has been made on one side. Turn the needle
180 degrees and repeat, being careful to ensure the
symmetry of the ground edges. The drill point is
ground with a few light touches of the grindstone
or formed on a fine (Norton India) oil stone. The
drill point should be central and the two bevelled
cutting-edge angles equal. Inspect with a linen glass
(lupe) to check the symmetry and angles compared
to Figure 21.1 given here.
21.3 Leather Conservation –
bookbinding leather consolidants
Glen Ruzicka, Paula Zyats, Sarah Reidell and
Olivia Primanis
21.3.1 Introduction
The repair of books and leather bookbindings is
unlike that of stationary leather objects. Books are
functioning structures, and, as such, conservation
treatment in most libraries and archives must respond
to physical demands for access to the text. Repairs
made to an original binding are typically required to
be flexible and strong. The joints of the book covers
must hinge properly, and move easily, while still
effectively attaching the text to the covers. Spines
must be mobile. The materials used in book conservation
must be long lasting and flexible. The use of
stiff fill materials, such as coloured waxes, is impractical
if the volume is to be used.
The challenge of conserving both the form and
function of leather-bound books is daunting. As
leather deteriorates, it becomes powdery and loses
flexibility. This is especially typical of nineteenth
and twentieth century vegetable-tanned leather
used to cover books because of the types of tannins
and acidic chemical processes employed to stabilize
the animal skins. Often there is ample justification
to simply house a deteriorated book in a polyester
jacket and a box, and, if severely deteriorated, to
rebind it preserving the original binding. But, if it
is repaired with the intention that the book is to be
used, conservators must address the powdery leather
and detached book covers and spines.
21.3.2 ENVIRONMENT Leather Project
The ENVIRONMENT Leather Project (Larsen et al.,
1996) developed a helpful procedure for determining
whether a leather binding should be treated
with a consolidant. This procedure offers a practical
method for characterizing the deterioration of leather
by comparing a sample with images of four increasingly
desiccated leather samples. Figure 21.2(a)
recreates the Project’s fibre samples portraying the
fibres in a new leather sample as thick and long.
Figures 21.2(b)–21.2(d) depict leather fibres in increasing
intervals of deterioration, reduced in length and
width, until eventually degrading to a powder. The
ease or difficulty with which the few discrete fibres
can be teased from the leather cover for examination
also aids in assessing their condition.
21.3.3 Consolidants
As part of the repair process, book conservators can
treat deteriorated leather bindings with the application
of a consolidant. Solvents in dressings affect surface
finishes by wetting, swelling, and deforming the
leather, as well as dissolving or dislocating the original
tannage components (McCrady and Raphael,
1983). The effect of consolidants is most apparent in
changes that sometimes occur to the optical characteristics
and flexibility of bookbinding leathers.
Nevertheless, the application of a consolidant has
become a practical response to the immediate problem
presented by powdery leather.
Traditionally, leathers were treated using oil dressings
to maintain their surfaces and keep them flexible.
However, it has been shown that excess oil added
to aged leather replaces the chemically bound moisture
content of leather, actually causing further desiccation
in the fibres (Hallebeek and Soest, 1981). Not
only does oil dressing impede further conservation
treatment, but it has been shown to weaken leather
(McCrady and Raphael, 1983). Because of this,
many book conservators sought alternatives to traditional
leather dressings.
In the last 25 years, the most widely used consolidant
for deteriorated leather (‘red-rot’) has been Klucel
G (hydroxypropylcellulose). Klucel G is prepared as
a 1–2% solution in ethanol or isopropyl alcohol.
230 Conservation of leather and related materials
Figure 21.1 The flat drill.
Conservation of leather bookbindings: a mosaic of contemporary techniques 231
(a) (b)
(c) (d)
Figure 21.2(a–d) Fibre samples at the various levels of deterioration (4 ϫ magnification).
Applied directly to deteriorated leather, Klucel G
is usually immediately effective in consolidating the
powdery leather dust with minor change in
the appearance of the leather. In 1984, following the
Foundation of the American Institute for Conservation
(FAIC) Leather Conservation Intensive held in
Harpers Ferry, West Virginia, book conservators
became aware of the limitations of Klucel G (Haines,
1985). According to Pieter Hallebeek (Central
Research Laboratory for Objects of Art and Science,
Amsterdam), the film formed by Klucel G is known
to break down in the presence of sulphuric acid, a
by-product of leather deterioration. A 1991 Journal of
the International Institute for Conservation entry by the
Canadian Conservation Institute (CCI) referenced in
Hein (1997) states that both Paraloid B72 and Klucel
G-F have high stress values and should only be used
on semi-rigid materials because stress fractures easily
form. In light of this and other research (Haines,
2002), concern about the flexibility of Klucel G over
time prompted conservators at the Conservation
Center for Art and Historic Artifacts (CCAHA) in
Philadelphia to search for alternative coatings.
Limited research in leather surface treatments to
date has failed to provide clear guidance in selecting
an appropriate treatment. In the 1980s, a new coating
introduced by the Leather Conservation Centre
(University College Campus, Boughton Green Road,
Northampton, NN2 7AN, England; tel. 01604
719766), SC6000, seemed promising. SC6000, an
acrylic polymer and wax emulsion dressing, imparted
some strength and protection to the leather’s surface.
In practice, however, it was found that SC6000
did not sufficiently penetrate the grain layer of the
skin. The comparatively strong wax and acrylic film
that formed on the grain surface of deteriorated leather
caused the grain layer to split from the corium. The
finish of the original SC6000 was not only too
strong for weakened skins, but also imparted an
unwanted shine to the leather.
Conservators at the CCAHA experimented with
a mixture that would improve the penetration of
SC6000. Equal parts (1:1:1) of SC6000, Klucel G in a
2% ethanol solution, and ethanol blended together
proved to be a practical solution. The SC6000/Klucel
mixture proved effective even on very deteriorated
leathers and satisfactorily penetrated the grain of the
leather. An advantage of this mixture is that both the
strength of the coating is diluted and the shiny finish
toned down. Not only is the new strength more
appropriate for aged bindings, but the gentle sheen
looks more presentable. The SC6000/Klucel mixture
was affectionately dubbed the ‘red-rot cocktail’.
Because powdery, deteriorated leather is the endpoint
of acid hydrolysis, it is irreversible. Treatment
can only try to halt its further progress and reinforce
or support the damaged structure ( Jackman, 1982).
Protecting the leather from air pollutants, which
increase the hydrolysis reaction, can slow the process.
The wax component of the SC6000/Klucel mixture
does provide a level of protection for the leather. In
less severe cases of red rot a mild humidification of
the affected leather through a light application of
methyl cellulose in water, or even thin paste, adds
moisture and some flexibility to the skin. A coating of
the lightweight SC6000/Klucel mixture applied to
the humidified leather helps retain the added moisture,
as well as provides a fairly durable surface. The
coating does not penetrate into the skin appreciably,
unlike oil dressings, which can cause further desiccation
of leather (Zyats, 1996). It has been demonstrated
that the SC6000/Klucel G mixture holds up well in
recent research on coatings for leather (Haines, 2002).
The light sheen of the SC6000/Klucel mixture,
combined with the protection afforded by the wax
and acrylic in the emulsion, also works very well to
coat acrylic-toned paper repairs used on damaged
leather bindings. Paper repairs, if left untreated,
generally have fragile surfaces and can become
nappy with use. The SC6000/Klucel mixture effectively
prevents this sort of abrasion, while the sheen
of the finish visually integrates the paper repair with
the original surface.
In general, the SC6000/Klucel mixture has been a
very useful consolidant in the conservation treatment
of fragile and aged leathers. The mixture can also be
used successfully as a surface treatment for new leather
and paper repairs, including those applied to parchment
bindings and documents. Using the SC6000/
Klucel mixture on added materials has become an
integral part of CCAHA repair procedures.
21.4 Solvent-set book repair tissue
Alan Puglia and Priscilla Anderson
Solvent-set book repair tissue is an experimental
treatment under development at Harvard University
Library. The technique uses prepared Japanese paper
that is colour toned and coated with acrylic adhesive.
The dry acrylic adhesive is reactivated with nonaqueous
solvents of relatively low toxicity, such
as ethanol and isopropanol. The technique was
developed for batch treatments of leather-bound,
special collection materials and is a variation of
232 Conservation of leather and related materials
Etherington’s Japanese paper hinge repair (see 21.5
below). The potential advantages of solvent-set book
repair tissue include: quick application; strength and
stability of the repair materials; ease in matching
repair tissue to binding substrate; and reversibility of
the adhesive. Also, a solvent-based adhesive is less
likely to darken or more seriously damage aged
leather as is common with water-based adhesives.
Acrylic adhesives as a general class retain some
reversibility with either organic solvents or heat.
Lascaux 498 HV (Lascaux Colours & Restauro, Alois
K. Diethelm AG Farbenfabrik, Zürichstrasse 42,
CH-8306 Brüttisellen, Switzerland; tel. ϩ41-1-807
41 41; http://www.lascaux.ch/english/restauro/
index.html) is currently used in the painting conservation
field for lining original canvases to new support
linings. Accelerated ageing and testing of
Lascaux 498 HV indicates that although the adhesive
does yellow somewhat, it does retain solubility
(Duffy, 1989). Nonetheless, the use of this adhesive
in this application should be considered experimental
since its interaction with leather has not
been tested.
21.4.1 Preparation of the repair tissue
The tissue selected for this technique should be a
strong, long-fibred, 100% kozo paper. It should be
reasonably transparent so the colour of the volume’s
leather will show through the finished repair. A
paper that has proven successful is KTLG from the
University of Iowa’s Center for the Book Paper
Facility (100 Oakdale Campus #M109 OH, Iowa
City, IA 52242-5000, USA; tel. ϩ1-319-335-4410;
http://www.uiowa.edu/ϳctrbook/), a smoothfinished
kozo tissue about 0.05mm in thickness.
The tissue is toned with thinned liquid acrylic
paints to lightly tint the tissue resulting in a highly
translucent material. It is only necessary to match the
general colour family of the leathers, not to exactly
replicate the hue and saturation.
Spread a thin, even layer of the Lascaux 498HV
adhesive onto polyester film by squeegeeing through
a screen. If the resulting layer is too thick, reduce it
by offsetting the adhesive onto another sheet of
polyester film, or use a finer screen. A thin coat on
a repair tissue is more flexible, conforms more closely
to the leather surface, and is less likely to cause weak
leather to delaminate than a thicker coating.
Lightly mist both the tissue and the fresh adhesive
layer with water. Slowly drop the tissue onto the
adhesive, avoiding wrinkles and bubbles. Surface
tension between the two wet surfaces encourages
full contact; pressing is not necessary. Allow the tissue
and adhesive to air dry completely. The dried
tissue may be left on the polyester film for convenient
cutting and handling. If bubbles do occur, use a
warm (not hot) tacking iron on the dried tissue to
join it to the underlying adhesive layer.
21.4.2 Leather consolidation
As mentioned above by Cains, consolidation of
deteriorated leather may be required to prepare the
surface to accept and hold a sound repair. As an
alternative to Klucel G, one part Lascaux 498 HV
adhesive dissolved in six parts isopropanol yields a
clear, slightly viscous solution that may work well as a
consolidant. Preliminary experiments indicate that the
Lascaux solution requires only one coat to consolidate
most leathers, it leaves the leather flexible, and it provides
a strong bond with the repair tissue. Though the
use of Lascaux as a consolidant is experimental, its
favourable working properties encourage continued
research into the use of acrylics as consolidants.
21.4.3 Repair technique
Cut and shape a repair strip from the dried tissue with
a scalpel and peel it off the polyester film support.
Reactivate the adhesive film by brushing the adhesive
side with either alcohol or the diluted acrylic adhesive,
working on a non-absorbent surface. Place the
repair tissue over the damaged area. If the repair is
over a joint, gently lift the board immediately after
applying the tissue to locate the natural crease line of
the joint. The adhesive has sufficient slip to allow rapid
adjustments to the placement of the strip, and then sets
in under two minutes. After drying overnight, any lifting
areas are easily touched up with a warm tacking
iron. Additional toning with acrylics or watercolours,
and/or surface finishing as described by Etherington
may be undertaken if necessary.
21.4.4 Reversing solvent-set tissue repairs
Removing tissue applied with acrylic adhesives over
weak, damaged leather should be approached with
care. Lascaux 498 HV can be softened with alcohols
and/or heat. Brush small amounts of solvent to one
edge of a repair and slowly lift and work back the
repair from the leather. Alternatively, a heated
microspatula can be used to lift the repair.
21.4.5 Conclusion
Solvent-set book repair tissue has been used successfully
to rejoin detached boards, to reinforce split
Conservation of leather bookbindings: a mosaic of contemporary techniques 233
joints and breaks in the spine, and to rebuild end caps.
It is well suited for quick repairs and batch treatments.
It is also useful for more complex treatments
and may be combined with other repair methods,
such as tacketing, when rejoining detached boards
of larger volumes. The technique should be considered
experimental until suitable testing of leathers
treated with acrylic adhesives can be performed.
21.5 Split joints on leather bindings
Don Etherington
Faced with the problem of determining the best use
of the conservation dollar, preservation administrators
are always looking for ways to minimize the
labour-intensive procedures that have prevailed over
the last 50 years. While working at the Library of
Congress, I was instrumental in developing the concept
of ‘phased preservation’, a technique that protected,
rehoused, and supported material en masse
with, at times, some minimal treatment.
In pursuing this philosophy over the last 20 years, I
developed various techniques that have been adopted
extensively throughout the United States. The latest
technique is the use of Japanese paper for reattaching
or supporting weakened joints of leather bindings,
particularly of nineteenth and twentieth century vintage,
on books no larger than 25.4cm (10 inches) high
and 3.8cm (1.5 inches) thick (Etherington, 1995).
The procedure is relatively simple and particularly
effective on books that have a tight spine that
would generally require skilled expertise and extensive
time to repair. Anyone who has contemplated
rebacking a tight spine, especially on a thin book
with raised bands, will appreciate the problems associated
with this type of work.
Many research library special collections have large
groups of nineteenth and twentieth century bindings
bound by French and English trade houses with
detached boards or weakened joints, both inside and
out. This is caused by the choice of poor-quality
leather at the outset and the trade practice of paring
leather very thin for ease in working and to satisfy
aesthetic tastes. Usually, the spine itself is intact and
the sides of the boards are in good condition; it is
only at the joint that the damage is apparent.
To alleviate the time-consuming practice of lifting
the leather spine and the leather from the sides of the
boards, a Japanese paper strip is placed over the joint
that extends slightly over the spine and the boards.
Another strip of Japanese paper serves to strengthen
the inside joint. The paper used for the outside is a
very strong, solid-dyed paper with good tear strength;
for the inside, natural-coloured Japanese paper is used
to sympathetically match the endpapers or textblock.
If it is necessary to match the original colour of the
leather cover, some dyeing of the coloured paper
may also be attempted.
Ideally, the dyed paper as produced by the manufacturer
can be used, as there are currently some 35
or so colours available. The strips of Japanese paper
for the inside are attached to the text block before
attempting the outside repair. This is to make
allowance for the ease of opening at the joint. The
other portion of the inside hinge will be attached to
the board at a later stage.
A strip of Japanese dyed paper is cut to size using a
technique that produces a slightly feathered edge. An
expeditious approach is to use a sharpened bone folder
dipped in the standing water used to prevent PVA
brushes from drying out. This mixture gives a welldefined
line for tearing the paper strips. The strip is
generally no more than 6.3mm (1/4 inch) to 7.9mm
(5/16 inches) in width, and extends about 12.7mm
(0.5 inches) beyond the length of the boards.
The boards are placed in position on the book
and a weight is placed on top. Paste or a mixture of
rice starch paste and Jade 403 (or similar PVA) is
used to attach the strip across the joint, rubbing
down lightly with the palm of the hand so the paper
sinks into the undulations of the damaged leather
and across the edges of the raised bands. The feathered
edge of the strip blends into the leather nicely.
Let dry for an hour and then turn in the strip at the
head and the tail. In most instances, I turn it down
only to the height of the square of the board and then
cut off the repair paper near the edge of the endpaper.
If a leather binding exhibits red rot, treat the leather
with Klucel G (as described by Cains in 21.2). This
treatment is necessary, as books with friable red rot
will reject the Japanese paper strip.
The Japanese paper is now attached to the inside
of the board. This attachment can either be over the
original endpapers or slid beneath them. I generally
let the structure of the book indicate what is possible.
Obviously, attachment under the original endpapers
(both the free-fly end and the board paper) is
the more sophisticated method. In general, if the
need to lift the inside board paper is purely cosmetic,
the added cost should be evaluated carefully.
After the book has been repaired, the leather and
the repair strip are given a light surface coating consisting
of a 1:1 mixture of Klucel G and SC6000
(Klucel G is a leather consolidant produced by the
Hercules Chemical Company and is obtainable from
the usual conservation supply houses; SC6000 is a
234 Conservation of leather and related materials
plasticized acrylic polymer and is available through
the Leather Conservation Centre, England). The
paper repair is thus sealed, and a satin finish is
obtained. If a higher shine is desired, a second, light
application of pure SC6000 is appropriate, followed
by a light buffing with a soft cloth. If the book is
valuable and heavily gold tooled on the spine, an
option for improving the aesthetic finish of the repair
is to remove areas of the strip that may be covering
tooling, and lifting the edge of original leather labels
so the Japanese paper can be slipped underneath.
For books that are broken only at the joints, the
rationale for making repairs with a strong Japanese
paper instead of a pared strip of leather comes down to
one word: ‘strength’. The application of two strips of
Japanese paper, one outside and one inside, tends to
create a strong board attachment to the spine, and is
a method that results in minimal intervention to the
original binding. The technique normally takes
about an hour.
21.6 A variation on the Japanese paper
hinge – adding a cloth inner hinge
Bill Minter
While the reattachment of leather-covered boards
with Japanese paper has been shown to be strong,
there are times when it may prove inadequate. A
variation of this practice is to attach a cloth inner
hinge in a technique similar to one presented by
David Brock at the AIC Book and Paper Group
meeting in Albuquerque, New Mexico, in 1991.
The boards can be prepared in the usual manner, as
described by Etherington (in 21.5). However, prior
to attaching the board, the pastedown should be lifted
to accept a cloth inner hinge that will be sewn to the
text block. A strip of unbleached cotton muslin, cut
on the bias, is adhered to the shoulder. Instead of positioning
the cut edge at the top of the shoulder, in this
variation the cut edge is positioned at the bottom of
the shoulder with the free cloth extending upward.
This cloth is then mechanically secured by sewing
in a unique manner with a so-called linen-thread
‘staple’. Holes are stabbed (or drilled, as described by
Cains in 21.2) through the cloth, through the shoulder,
and through the leather in the following manner.
Two holes, about 5mm apart, should be stabbed in
the least obtrusive location, such as along raised bands,
avoiding any gold tooling. While stabbing, use a piece
of rubber or plastic to support the leather, thereby
eliminating the possibility of chipping the spine
leather where the needle stabs through. Use as many
pairs of holes as are needed for the book, and stab two
additional pairs of holes near the head and tail. A piece
of linen thread is passed through the pair of holes with
the ends on the outside of the spine, and both ends are
cut to about 20mm. Secure the thread inside the
shoulder on the cloth with a dab of adhesive. All pairs
of holes are ‘stapled’ in the same manner.
Now, cut the ends to about 4mm, fray out/fan out,
and paste the tails to the leather. Fold the cloth along
the shoulder and attach the board with the Japanese
paper as described by Etherington. (Note: I prefer to
use an undyed 100% kozo fibre Japanese paper because
some dyed papers contain unstable groundwood
pulp.) When the boards are secured with the Japanese
paper, the cloth inner hinge can be inserted under the
pastedown and finished in the usual manner. This
cloth hinge can be hidden with a strip of Japanese
paper. While retouching the Japanese paper on the
outside, those frayed-out pieces of thread can also be
retouched.
21.7 Split-hinge board reattachment
David Brock
The following is a technique I have been using at
Stanford University for the past several years to
reattach the boards of leather-covered, tightbacked
books sewn on raised bands (Brock, 2001). It involves
lifting the spine leather, board leather, and pastedowns
at the head and tail only.
The steps are as follows:
1. At the head and tail spine panels, make a cut
through the leather near the base of the band,
going from shoulder to shoulder.
2. Lift the spine panels.
3. Pastewash the spine to remove any deteriorated
spine linings and adhesive.
4. Paste a light Japanese paper lining onto the
spine.
5. When the Japanese paper lining is dry, secure
loose or broken endbands with thread.
6. Depending upon the size of the book, weight of
the boards, and movement of the spine, adhere
one or two cotton or airplane linen linings with
PVA. The cloth should be cut on the bias and
extend 12.7 to 25.4mm (0.5 to 1 inch) beyond
the shoulders, and go from near the base of the
band to the end of the spine. If the spine has
endbands, extend the cloth onto the endbands to
help anchor them a little more securely to the
textblock. It is important to work the PVA well
into the cloth, as the strength of this mend
Conservation of leather bookbindings: a mosaic of contemporary techniques 235
depends, in part, upon a strong bond between
the cloth and the text spine. The cloth can be
dampened slightly during bonding to achieve
greater adhesion.
7. Determine now if further spine linings are needed
to support the spine when the book is opened.
8. Lift the leather and pastedowns of the boards at
the head and tail.
9. If only one cloth lining has been used, cut the
extensions in half (see Figure 21.3).
10. Fray out the edges of the extensions.
11. Place the boards in position on the book. If one
spine lining has been used, adhere the outer half
of the extensions to the boards with PVA, going
underneath the lifted leather. When using two
spine linings, adhere the whole extension (see
Figure 21.4). Allow to dry.
12. Open the boards and glue (PVA) the remaining
extensions to the boards, going underneath the
lifted pastedowns. When dry, readhere the paste-
downs.
13. Before gluing down the lifted leather, adhere a
wet-torn strip of Japanese paper over the cloth
showing in the joint. I usually use a heavyweight
Uda. This strip should begin slightly underneath
the lifted board leather and extend a little way
onto the spine. This will hide the weave of the
cloth and add strength to the joint. Colour the
Japanese paper to match the leather with artist’s
acrylics mixed in a little methyl cellulose. Mixing
the acrylics in methyl cellulose slows down their
quick drying time and makes their application
easier.
14. Re-adhere the lifted board leather and spine
panels.
15. Open the boards and paste a strip of suitableweight
Japanese paper in the hinge area, running
from head to tail and from the base of the
shoulder to the top of the board. This adds to the
strength of the attachment and gives a neater
appearance to the inside of the covers. The narrow
line of paper that shows in the joint when the
boards are closed can be coloured with the acrylic
paint/methyl cellulose mixture to match the
leather.
16. If the joint edges of the spine panels at the head
and tail are visually distracting, a narrow strip
of Japanese paper can be adhered just over the
edges and then coloured to match the leather.
This method has been successful on board
reattachments for both large and small books, with a
few variations required depending upon the weight
and size of the book. While this technique doesn’t
entirely replace leather rebacking in my conservation
work, I use it much more often than traditional
rebacking.
21.8 Board slotting – a machinesupported
book conservation
method
Friederike Zimmern
21.8.1 Introduction
Board slotting is a very useful approach for repairing
leather bindings, especially for nineteenth century
hollow backs. It also works well for tight back
236 Conservation of leather and related materials
Head
and
tail
Goes
under
leather
Goes
under
pastedown
Cotton or
airplane linen
Figure 21.3 Single spine lining.
Head
and
tail
Goes
under
leather
Goes
under
pastedown
Cotton or
airplane linen
Figure 21.4 Double spine lining.
bindings, even those with raised bands, if the original
spine can be effectively removed.
Board slotting was conceptualized by Christopher
Clarkson in the late 1970s while working at the
Library of Congress and later perfected while
working at West Dean College (Clarkson, 1992).
Consequently, the method was established at the
Bodleian Library in Oxford in 1994 under the
guidance of Edward Adcock (Simpson, 1994b).
After working at the Bodleian Library in 1996, I
was able to improve the method by designing and
constructing a new board slotting machine in
co-operation with an engineering company. This
project was conducted in 1998 as a senior thesis at
the Book and Paper Conservation Program at the
Academy of Art and Design in Stuttgart, Germany
(Zimmern, 1999).
21.8.2 The method
The board slotting technique is divided into three
steps:
1. Treatment of text block
2. Treatment of boards
3. Reattachment of text block and boards.
21.8.3 Treatment of the text block
The first step is to detach the original spine, if it has
not become separated already, and to remove damaged
or loose spine linings. Paste a piece of prewashed
cotton fabric to the spine of the text block
that is cut the length of the spine and overlaps either
shoulder by approximately 2.5cm. The cotton lining
can be mechanically secured to the spine by
sewing through the first and last sections. Any loose
sections are reinforced by catching them up with
the sewing thread. Next, a hollow tube cut to the
height of the boards can be pasted to the spine.
Paste a second lining of appropriately dyed cotton
fabric to the hollow tube. Turn in this fabric at
head and tail of the hollow and allow it to dry. After
drying, paste the two fabrics together at their flaps
(see Figure 21.5). If no hollow is used, turn in the
second fabric at head and tail, and paste only the
overlapping parts to the flaps of the first fabric. As a
result of the pasting, two tongues will emerge that
are taped down temporarily to a thin cardstock
insert to remain flat following drying. The flaps
should be well dried, preferable overnight, so they
become stiff enough to insert into the slots in the
boards.
The question as to whether or not a hollow is
necessary has to be answered individually, book by
book, and depends upon how the book opens. If the
spine construction is very weak, a spine lining and/or
hollow may be appropriate; conversely, if the spine is
quite tight, no additional spine linings or hollows
should be used. However, a very light hollow can be
made from thin Japanese paper that will be helpful in
adjusting the new spine lining later on. If there is a
piece missing from the original spine, a cardstock fill
can be positioned under the second fabric on top of
the hollow.
21.8.4 Treatment of boards
A milling machine is needed to create the slot in the
spine edge of the board in preparation for insertion of
the new material. The depth of the slot, which can
be between 5 and 8mm deep, is dependent upon the
size and the strength of the boards. The slot, which is
cut at an angle, only extends the height of the boards
so the head or tail edges of the cover remain undamaged.
The cutting begins almost directly underneath
the original board leather and extends to the middle
of the board thickness. The angle ensures the boards’
function will not change and the book will open well
after the repair is completed. The precise degree of
this angle depends upon the board thickness and is
easily calculated from the thickness of the board and
the depth of the slot (see Figure 21.6 ).
21.8.5 Reattachment of text block and
boards
The pasted cotton tongue is used to reconnect the
text block and cover. Stiffened by the paste, the
tongue is cut to the respective depth of the slot.
The slot in the board can be opened a bit with a
spatula to make insertion of the tongue easier. With
a syringe, starch paste is fed into the opening and
smoothed. Old book boards absorb quite a bit of paste
Conservation of leather bookbindings: a mosaic of contemporary techniques 237
Spine
Text
block
Paste
Tongue
Figure 21.5 Schematic diagram of the text block. The
covers are taken off and a cotton fabric is pasted onto the
spine. A second cotton fabric is worked over the first, but
pasted together only at their flaps to form a tongue.
so an adequate amount must be injected. The tongue
is then placed into the slot with the help of a spatula.
The book is pressed carefully and left to dry. Finally,
the original spine is cleaned of old spine linings and
attached to the new cotton spine (as described by
Cains in Section 21.2) (see Figure 21.7).
21.8.6 The board slotting machine
Board slotting requires a machine. Christopher
Clarkson’s first prototype was a commercially available
milling machine that required a few adjustments to be
adapted to board slotting. This concept worked well,
but the setup was laborious, making the whole system
relatively complicated and time consuming in practice.
Part of my project was to develop a machine that
would streamline the method. In collaboration with
the engineering firm Becker Preservotec (now ZFB –
Zentrum Fur Bucherhaltung GmbH, Mommsenstr. 7,
D-04329, Leipzig, Germany; tel. ϩ49-341-25989-0;
http://www.zfb.com), a board slotting machine that
met this objective was developed. In contrast to the
machine in use at Oxford, the present model is simpler
to handle and therefore saves preparation time (see
Figures 21.8 and 21.9).
21.8.7 Scientific analyses
The board slotting method, as with any other type
of conservation treatment, is only as good as its
repair material. Therefore, the newly inserted materials
required testing for their strength and stability.
21.8.7.1 Fold endurance test
The fabric inserted into the board slot is required
to flex at the joint each time the book is opened.
For this reason, the fabric should possess very good
flexible strength. Consequently, fold endurance
tests were carried out with linen and cotton fabrics.
The following three materials were tested: Aerolinen
155g/m2
, Aerocotton 145g/m2
(Samuel Lamont &
Sons Limited, Ballymena, North Ireland), and
Aerocotton 100g/m2
(Friebe Luftfahrt-Bedarf
GmbH, Mannheim, Germany). Three samples of
each material were tested with the grain direction of
the fabric parallel to the folding. Each material was
tested until the fabric tore, and the average of the
three samples was taken. The test machine was an
apparatus manufactured by the firm Louis Schopper
of Leipzig, and was designed to bend materials 180
degrees under tension. This approach is a nonstandard
methodology, but the data are useful for
comparing the folding characteristics of the three
materials with the other.
238 Conservation of leather and related materials
Slot
Board
Figure 21.6 Schematic diagram of a slotted book board.
The slot starts close to the leather and continues to the
middle of the board’s thickness. Its depth can vary between
5 and 8mm. The angle depends upon the board’s thickness.
Spine Text block
Board
Board
Tongue
Figure 21.7 Schematic diagram of a book treated with
the board slotting method. The boards are reattached by
pasting the fabric into the slot.
Figure 21.8 The milling machine Emco FB-2, used for
the board slotting technique by the Bodleian Library.
21.8.7.1.1 Results
Aerolinen 155g/m2
16 000 folds
Aerocotton 145g/m2
90 000 folds
Aerocotton 100g/m2
71 500 folds
The results show cotton has significantly better folding
strength than linen, and even the thinner cotton
fabric proved much stronger than the linen. Though
linen has better tear resistance and tensile strength
than cotton, linen fibres are inflexible and break
much earlier than cotton fibres. Fold tests against the
grain direction reduced the number of folds of each
material by at least one third. No tests were carried
out with the fibres diagonal to the folding movement.
21.8.7.2 Tensile strength test
A second parameter to be tested was the strength of
the adhesive within the slot. Three different types of
adhesives were tested: polyvinyl acetate, gelatine,
and wheat starch paste. Under specially designed
conditions, each adhesive was used with fabric samples
that were subsequently pulled out of their board
slots. This testing was done at the Institut fuer
Textilchemie, Denkendorf, and conducted according
to German standard ‘DIN 53857’. Three samples
of each adhesive underwent this test and the
average was taken of the resultant data.
21.8.7.2.1 Results
Polyvinyl acetate 24.8kg
Gelatine 22.7kg
Wheat starch paste 19.5kg
These results demonstrated that PVA and gelatine
were slightly stronger than paste. Nevertheless,
wheat starch paste exhibited sufficient adhesive
power to hold the fabric inside the slot, even when
used in conjunction with heavy books. Because of
its open (e.g. drying) time and well-known permanence,
paste emerged as the preferred adhesive.
21.8.8 Dyeing with reactive dyes
The first lining of cotton fabric shows inside the
book once the repair is completed, so it should
Conservation of leather bookbindings: a mosaic of contemporary techniques 239
Figure 21.9 The board slotting machine developed by Becker Preservotec in cooperation with the Academy of Art
and Design, Stuttgart.
240 Conservation of leather and related materials
Figure 21.10(a & b) Detail image of two books treated with the board slotting method by the author. (Ioh. Pomtow
(ed.) (1885). Poetae Lyrici Graeci Minores, vols 1 and 2.)
blend with the colour of the pastedowns and flyleaves.
Cotton fabric normally has a cream colour
that provides a sympathetic match for most flyleaves.
The second fabric lining is visible in the
outer joints and should therefore match the original
colour of the book cover. This is always a difficult
task to achieve because spine and board coverings
tend to fade differently due to their dissimilar
exposures to light. Therefore, a dyeing procedure
with reactive dyes was adapted from the Bodleian
Library (Simpson, 1994a) and modified slightly
(Zimmern, 1999). Lightfastness tests were used and
the dyeing procedure found to be acceptable. Still,
the dyeing procedure proves to be very time consuming,
and it would be advantageous if a commercial
firm could be identified willing to produce a
good, standard cotton fabric (like Aerocotton) and
dye it in several tones with light- and water-stable
dyes (Figure 21.10).
21.8.9 Conclusions
In contrast to other methods, board slotting has the
following advantages:
1. Gilding and decoration on the cover as well as on
the board edges are not affected by the process.
2. Original leather parts on the boards and the pastedowns
are not damaged.
3. The method is applicable for degraded leather
because the leather itself requires no manipulation.
4. In contrast to manual board slotting, slotting
with the machine is much more exact and even.
While slotting with the machine, parts of the
cardboard cover are removed preventing the slot
from swelling due to the newly inserted fabric.
As a result, one can say that the board slotting method
is fast, economical, and able to return books to a
durable and usable condition without changing the
integrity of the object. With experience, it becomes
apparent that board slotting does not change the
appearance of the book significantly, and can be effectively
combined with other methods, such as Japanese
paper hinge repair for small books, as described by
Etherington, Minter and Brock (21.5, 21.6 and 21.7
above respectively).
The board slotting method enriches the already
well-known possibilities for reattaching book boards.
It is hoped that it will be used more in the future.
21.8.10 Acknowledgements
Without the help of many people, this project
would not have been possible. Sincere thanks are
due to: Prof. Dr G. Banik, Ing. E. Becker,
Dr A. Blüher, Ing. H. Dallmann, Ing. H-P. Gaibler,
Prof. Dr G. Hardtmann, B. Hassel, Dr J. Migl,
D-E. Petersen, Dr V. Trost, Prof. Dr J. Szirmai
and Dr W. Wächter.
21.9 A variation on the board slotting
machine
Bill Minter
There is a very nice hand tool from FEIN Power
Tools, Inc., USA (1030 Alcon Street, Pittsburgh, PA
Conservation of leather bookbindings: a mosaic of contemporary techniques 241
Figure 21.11 Minter’s mounted FEIN MultiMaster with oscillating saw blade for board slotting is advanced by hand
to create a slot in the edge of the binderboard which is clamped in the jig.
15220, USA; tel. 01-412-922-8886; http://www.
feinus.com/) that can be adapted to board slotting.
The beauty of this tool is that it is very safe to operate.
The FEIN MultiMaster tool (MSXE 636-2) oscillates
a saw blade in such a manner that it will cut and
slot binderboard, but will not cut human skin. The
tool is mounted on a platform and advanced by hand
into and along the edge of the board while it is secured
in a fixture (Figures 21.11 and 21.12).
A variation on this idea also employing the FEIN
MultiMaster was subsequently developed by Manfred
Mayer from the University Library of Graz, Austria,
demonstrating the suitability of this tool for building
an affordable board slotting machine.
References
Brock, D. (2001) Board Reattachment. Abbey Newsletter,
24 (April, no. 6), 93.
Cains, A. (1981) Preparation of the Book for Conservation
and Repair. New Bookbinder, 1, 11–25.
Cains, A. (1992) A Facing Method for Leather, Paper and
Membrane. In Conference Papers, Manchester 1992
(S. Fairbrass, ed.), pp. 152–157. Institute of Paper
Conservation.
Cains, A. (1994) In-situ Treatment of Manuscripts
and Printed Books in Trinity College, Dublin.
In Conservation and Preservation in Small Libraries
(N. Hadgraft and K. Swift, eds), pp. 127–131. Parker
Library Publications.
Cains, A. (2000) The Long Room Survey of Sixteenthand
Seventeenth-century Books of the First Collections.
In Essays on the History of Trinity College Library Dublin
(A. Walsh and V. Kinane, eds), pp. 53–71. Dublin:
Four Courts Press.
Cains, A. and Swift, K. (1988) Preserving our Printed
Heritage. Trinity College Library.
Clarkson, C. (1992) Board Slotting – A New Technique
for Re-attaching Bookboards. In Conference Papers
Manchester 1992 (S. Fairbrass, ed.), pp. 158–164.
Institute of Paper Conservation.
Duffy, M.C. (1989) A Study of Acrylic Dispersions Used
in the Treatment of Paintings. Journal of the American
Institute for Conservation, 28(2), 67–77.
Espinosa, R. and Barrios, P. (1991) Joint Tacketing; A
Method of Board Reattachment. Book and Paper Group
Annual, 10, 78–83.
Etherington, D. (1995) Japanese Paper Hinge Repair for
Loose Boards on Leather Books. Abbey Newsletter,
25(3), 48– 49.
Haines, B. (1985) Bookbinding Leather Conservation. In
Recent Advances in Leather Conservation: Proceedings of
a Refresher Course Sponsored by FAIC, June 1984.
Foundation of the American Institute for Conservation
of Historic and Artistic Works.
Haines, B. (2002) Surface Coatings for Binding Leathers.
Northampton: Leather Conservation Centre.
Hallebeek, P. and Soest, H.A.B. van (1981) Conservation
of Caskets and Furniture Covered with Leather. In
ICOM Committee for Conservation, 6th triennial meeting,
Ottawa, 21–25 September 1981: preprints (vol. 4), p. 2.
International Council of Museums.
242 Conservation of leather and related materials
Figure 21.12 Mayer’s mounted FEIN MultiMaster for board slotting from the University Library of Graz, Austria.
Hein, J. (1997) Leather Treatment Procedures: An
Excerpt from an Annotated Leather Bibliography.
Leather Conservation News, 13(2), 2.
Hercules Incorporated (1979) Hercules KlucelS,
Hydroxypropyl Cellulose, Chemical and Physical Properties.
Hercules Incorporated [Hercules Plaza, 1313 North
Market Street, Wilmington, DE 19894-0001, USA;
tel. (302) 594-5000; http://www.herc.com/].
Jackman, J. (1982) Leather Conservation: A Current Survey.
Northampton: Leather Conservation Centre.
Larsen, R., Vest, M., Poulsen, D.V. and Kejser, U.B.
(1996) Fibre Assessment. In ENVIRONMENT Leather
Project: Deterioration and Conservation of Vegetable Tanned
Leather (R. Larsen, ed.), pp. 113–120. Royal Danish
Academy of Fine Arts, School of Conservation.
McCrady, E. and Raphael, T. (1983) Leather Dressing: To
Dress or Not to Dress. Leather Conservation News, 2
(December), 2.
Middleton, B. (1972) Restoration of Leather Bindings.
American Library Association.
O’Sullivan, W. (1992) Binding Memories of Trinity
Library. In Decantations: A Tribute to Maurice Craig
(A. Bernelle, ed.), pp. 168–176. Dublin: Lilliput Press.
Reed, R. (1972) Ancient Skins, Parchments and Leathers.
London: Seminar Press.
Simpson, E. (1994a) Dying Aerolinen and Aerocotton
with Reactive Dyes. Paper Conservation News, 71, 7–9.
Simpson, E. (1994b) Setting up a Board Slotting
Programme. Paper Conservator, 18, 77–89.
L.S. Starrett Company (1993) Catalogue no. 28. Third
edition. The L.S. Starrett Company [121 Crescent
Street, Athol, MA 01331, USA; tel. 01-978-249-3551;
http://www.starrett.com/].
Zimmern, F. (1999) Board Slotting. Eine
Maschinenunterstützte Buchrestaurierungsmethode. Deutsches
Bibliotheksinstitut, Dbi-Materialien, 184.
Zyats, P. (1996) The Effects of Coatings or Dressings on
Degraded Bookbinding Leather. Graduate student project.
Winterthur/University of Delaware Program in
Conservation.
Conservation of leather bookbindings: a mosaic of contemporary techniques 243
22.1 Introduction
22.1.1 The archaeological context
It is a paradox that leather survives under extreme
conditions and that desiccated and waterlogged
contexts both provide excellent conditions for salvage.
Preserved organic objects reveal much about
the past, not least because the majority of cultural
artefacts were (and still are) made from organic
materials. The survival of a representative selection
of such ancient material is unusual, and where it
occurs it illuminates a culture in a special way. Ätzi,
the Bronze-age ice-man discovered in the Tyrolean
Alps in 1991, possessed a range of garments and
utensils that revealed a sophisticated use of different
skins (Spindler, 1994).
The infrequency of such preservation may lead to
misinterpretation; skin products from the Pharaonic
period have given the ancient Egyptians an undeserved
reputation for excellent leather technology
(Driel-Murray, 2000). Extant evidence which is
common in some cultures but rarely found in
others (perhaps more sophisticated) may thus distort
our cultural perspective. The balance can be redressed
by the identification, preservation and interpretation
of organic remains, including leather, even
(perhaps especially) if these are fragmentary and
incomplete. Detailed investigation and conservation
is both possible and rewarding.
Methods used in the retrieval and treatment of
archaeological finds are designed to protect the
integrity of the remains, however insubstantial, in
order to preserve their scientific value. The process,
starting with on-site retrieval and recording, progresses
to research and conservation, but as conservators
have an input at each of these stages this
chapter sets out to explain their involvement and
show what they aim to achieve.
22.1.2 Leather technology and
material culture
Methods of skin preparation and ways of working
leather, or applying it on composite objects, normally
follow cultural traditions which are influenced
by availability of materials and by the character
of the local economy. Study and analysis of evidence
of materials, methods and traditions in archaeological
leatherwork not only helps to indicate its probable
origin and date but can also contribute significantly
towards a better understanding of the culture and
economic background from which it comes. The
manner in which leather was originally processed is
an important line of enquiry.
22.1.2.1 Tannage
Hardwearing vegetable-tanned leathers, fine alumtawed
skins, oil-tanned and untreated skins all have
their place in developing societies depending on
geographical location and technological progress,
rather than date. All of these types might survive dry
burial and/or peat bogs, but only vegetable-tanned
leathers commonly survive wet anaerobic deposits
of a more general nature. For this reason collections
of archaeological leather from European sites are
strongly biased towards those prepared by vegetable
tanning. Recent analyses show that tannage can be
identified, or sometimes inferred, when evidence is
handled sensitively (Groenman-van Waateringe et al.,
1999; Driel-Murray, 2002; Mould et al., 2003). The
identification of material evidence for tanning from
archaeological remains is hampered by problems,
244
22
The conservation of archaeological leather
E. Cameron, J. Spriggs and B. Wills
The conservation of archaeological leather 245
some of which are pointed out by Cameron (2000),
Mould et al. (2003) and Wills (2002).
22.1.2.2 Currying
Currying, which involves the working of oils into
the grain surface of vegetable-tanned leather and the
paring down of hides to a standard thickness, rarely
leaves any evidence (but see Mould et al., 2003).
Consequently we know little of the history of currying
or of the relationship between early tanners
and curriers in England or elsewhere.
22.1.2.3 Leatherworking
Apart from the half-moon knife and diamond-shaped
awl few hand tools of medieval or earlier date are
exclusive to leather workshops. Many, such as traditional
hog’s bristle sewing needles, may have been
of organic materials that do not normally survive
burial. Since the character of leatherworking can
vary widely between different cultures all kinds of
observations relating to technique, levels of craftsmanship
and artistic skill are useful for typological
classification. This extends to the embellishment of
leather in various ways such as tooling, embroidery,
gilding or the attachment of decorative fittings.
Obscure methods used for moulding and hardening
leather (so-called cuir bouilli) for the production
of medieval armour as well as other items of a
more domestic nature continue to arouse curiosity
(Cameron, 2000; Dobson, 2003).
22.1.2.4 Leather dyes and pigments
Dyes and pigments do not often survive burial but
examples include two sheaths with red pigment from
London (Cowgill et al., 1987: MOL cat. Nos 479
and 487), dyed leather from Kerma, ancient Nubia
(Wills, 2002) and a red-painted girdle from York
(Mould et al., 2003: cat. no 15872).
22.1.2.5 Environmental and social questions
When leather is found in large quantities, typically in
Europe from waterlogged medieval urban contexts,
there are opportunities to analyse the social setting by
linking artefact studies with other forms of environmental
evidence. Patterns of animal husbandry such
as seasonal or age-related butchery and connections
with the urban food supply can be revealed through
bone evidence (McGregor, 1998). In studying leather
it is sometimes possible to identify species, animal age
(approximately) and to observe its general condition
while variability in the leather assemblage may answer
questions relating to standards, quality control and
industrial organization. Large collections of shoes can
also be used for population studies, including statistical
analyses of foot sizes and evidence for foot defects.
Even the frequency of cobbling, the term for patching
and repairing worn items to extend their useful
life, can offer fascinating insights into social habits and
practice.
22.2 Wet leather
22.2.1 Condition
The condition of excavated leather is due to a combination
of pre- and post-depositional factors, such
as method of manufacture, in-use wear and tear, and
extent of decay during burial. Other factors, such as
imperfect tanning, and the animal species and body
area that the leather derived from, are also important.
For these reasons, leather is found in all states
of preservation, but if it survives at all, it should be
possible to preserve it intact.
Apart from splits, tears and other types of physical
damage, a curious type of degradation regularly
encountered in waterlogged leather is that of delamination
where the leather falls apart into two separate
layers. This condition, widely reported to affect
archaeological leather of all periods, sites, object types
and animal species, has sometimes been blamed on
poor tannage, but is more likely to be the result of
partial degradation at a point of weakness of the collagen
fibre weave in the leather structure (Spriggs,
2003; Ganiaris et al., 1982).
Waterlogged leather is typically almost black in
colour having become saturated with humic matter
from the burial medium and the products of reactions
between ferrous ions and tannins. Leather from
marine environments can be found in a variety of
paler brown colours. Leather which has been heavily
compacted in the ground becomes ingrained with
silt, clay and other materials which obscure the surface
and can be difficult to remove. Iron salts and
encrustations can also disfigure surfaces, and marine
concretions from shipwreck sites can become so
firmly attached to leather as to obscure the true form
and nature of objects ( Jenssen, 1987).
The occasional finds of bog bodies, both in the
UK and Denmark, demonstrate that raw hide can
survive in wet contexts although in these cases the
human skins are thought to have been preserved by
more than one factor. These include partial tanning
in the tannin-rich bog deposits, the bacteriocidal
properties of low pH, and the crosslinking of
246 Conservation of leather and related materials
collagen fibres in skin by sphagnan (a tanning agent
found in sphagnum moss and its peat derivatives)
(Painter, 1991; Turner and Scaife, 1995).
22.2.2 Preserving wet leather before
treatment
22.2.2.1 Storage
To avoid irreversible shrinkage and embrittlement
caused by uncontrolled drying, wet archaeological
leather requires wet storage from the moment of its
discovery. Leather finds, still dirty from the ground,
can be double wrapped in polythene with a little
water, and stored in plastic boxes or tubs with airtight
lids (Spriggs, 1980; Watkinson and Neale, 1998).
These boxes should themselves be stored in cool
(1–5°C), dark conditions. Unless the leather is due
for conservation soon after discovery, the boxes must
be checked every month or so, to ensure that their
contents are still wet, and free of fungal growth.
Opinions are divided on the use of fungicides. While
Edwards and Mould (1995) advocate the disposal of
leather left untreated after six months, broad-spectrum
fungicides such as Panacide and Adesol are employed
to good effect in many institutions, given adequate
safety and disposal procedures. Cold, but not frozen,
storage may also be recommended to maintain less
degraded leather in good condition until it can be
treated. The use of waterproof and fade-proof
labelling for wet-packed materials is essential – Tyvek
(spun-bonded polythene) labels with solvent-based
waterproof markers proving the most adaptable ( Jones
et al., 1980). Marine leather should be desalinated by
passing it through changes of fresh water soon after
discovery, the rate of salt removal being monitored
with conductivity or chloride meters until all trace is
removed (Pearson, 1987).
Leather should be handled as little as possible in
the wet state owing to its fragility and the weight of
attached soil. Composite objects, such as complete
shoes, require support on a lightweight base of some
waterproof material, such as Correx (fluted plastic)
board to prevent the various elements falling apart.
Most leather will originally have been made up into
the finished object by stitching with flax or hemp
thread, which may have degraded or disappeared
altogether.
22.2.2.2 Washing and recording
Most waterlogged leather is physically sound enough
to be washed manually using a gentle stream of
running water and soft brushes. Very fragile objects,
which could be damaged even by gentle brushing,
are sometimes cleaned ultrasonically (in a laboratory),
supported on fine plastic mesh.
Leather is often bagged on site in context groups
and after cleaning it is sorted into categories such as
objects and object parts; offcuts and leather production
debris; and featureless scraps. The advantages of
recording leather before treatment are threefold –
security against loss of identification, a basic visual
record of the collection, and measurements (against
which shrinkage that might occur during treatment
can be checked). The commonest method is to trace
around the wet leather in pencil onto plastic drafting
film. By tracing around the object again with red
crayon after treatment any shrinkage can be calculated
as a function of either dimensional or area change
(Ibbs, 1990). Condition and technological detail may
be added to the tracings using pencil and coloured
crayons, following a series of conventions (Goubitz,
1984; Spriggs, 1987). These drawings can serve as a
quick visual way of auditing the collections and their
condition. Many small but important and interesting
details may be observed during the cleaning and
drawing of wet leather and simple drawings are often
the best way of recording them (Figure 22.1). Radiography
can be useful for recording composite leather
objects, such as hobnailed Roman shoe and sandal
soles, and also for examining leather with mineral
concretions from marine contexts (Spriggs, 1987).
22.2.2.3 Assessment
Leather is assessed before treatment and the assessment
report acts as a permanent record. The purpose
of an assessment is:
(a) To make a list of the collection and provide a basic
record of what the collection contains in terms of
range of object types and manufacturing waste.
(b) To evaluate the importance of the collection in
terms of its information potential and therefore
research value.
(c) To record its general condition, the range of
preservation and to identify any particular
pathologies.
(d) To identify the resources (time, equipment,
materials) required to carry out conservation
work and future collections’ care needs.
22.2.2.4 Selection
Waterlogged leather is not found so often that the
application of a selection and disposal procedure
need be applied and so there is normally a presumption
that all preserved leather be kept. On the very
rare occasions that extremely large assemblages of
leather have been found, the decision has occasionally
been taken not to treat the waste pieces of hide
from shoe-making and shoe-mending, but such
decisions are normally made in consultation with a
leather specialist and museum curator.
22.2.3 Past treatments
Old treatments for wet leather are rarely well documented
but are of interest to present-day conservators
faced with old collections that appear to be in
poor condition, actively degrading and in need of
retreatment (Williams et al., 1999). The progressive
introduction of conservation techniques is charted
here by following the development of leather conservation
at the York Archaeological Trust (YAT)
(Spriggs, 2003).
Large assemblages of archaeological leather, discovered
in the deep anoxic deposits that underlie
much of the modern city of York, have been systematically
conserved, studied and published over
the past 30 years by the York Archaeological Trust.
Its methods and materials have tended to mirror
techniques being employed at other laboratories,
both in the UK (Ganiaris et al., 1982) and in
Scandinavia (Peacock, 2001). The emergence of international
specialist research groups such as the ICOM
Conservation Committee Working Group on Waterlogged
Organic Archaeological Materials have
assisted in raising standards and creating collaborative
research projects.
22.2.3.1 Solvent dehydration techniques
Early treatments for waterlogged leather involved
the gradual replacement of water with oil, such as
castor oil. The first methods employed at YAT were
based on the staged replacement of water in the
leather with a solvent of a lower surface tension in
which various proprietary leather dressings might
also be dissolved. These treatments, developed from
contemporary published methods (Reed, 1972;
Waterer, 1972), were applied to several assemblages
of leather from York during the 1970s and the
results were considered successful at the time.
The practice at York was to pass the leather
through several baths of acetone until, by measuring
the density of the acetone with a floating hydrometer,
dehydration was judged complete. The leather
was then passed through a tank of proprietary
leather dressing, dissolved in an appropriate solvent,
such as mineral spirits (also known as white spirit)
and 1,1,1-trichloroethane (Genklene), both being
miscible with acetone. Of the dressings used, products
such as ‘Guildhall Leather Dressing’, ‘British
Museum Leather Dressing’ (BMLD) and ‘Pliantine’
were used, the latter becoming, for a while, the
favoured material at the YAT laboratories (Spriggs,
2003). These were all based on lanolin with varying
quantities of other wax or oil constituents in hexane
solvent. The dressings were applied both by immersion
and by subsequent brushing or wiping on, in
order to plump up the surfaces and improve the
rather dry appearance. Although some shrinkage
was always experienced with these treatments (typically
5–10% linear reduction), the properties of
texture, feel, flexibility and weight were all considered
satisfactory. However, there was a feeling of unease at
the time that the dressings being applied had been
formulated for use on historical and ethnographic
The conservation of archaeological leather 247
Figure 22.1 Technical drawings of cleaned waterlogged
leather are made before treatment as a permanent record of
the leather ‘as found’. (Courtesy York Archaeology Trust)
leathers, rather than archaeological leather. Only in
retrospect, many years later, have these treatments
been found to have had a seriously deleterious effect
on the objects (see below).
Another promising product was Bavon which
had been developed for use in the leather processing
industry as a lubricant and waterproofing agent
for chrome-tanned leathers. Based on a mix of alkylated
succinic acid and mineral oils it was available
in two forms: Bavon ASAK/ABP, the solvent-based
version, and Bavon ASAK 520S, its emulsified
form (Peacock, 2001). Tests of the water-based
treatment were unsatisfactory. Severe shrinkage and
embrittlement occurred, and a white deposit of
emulsified oils remained on the surface after freezedrying
which was very difficult to remove. However,
test results on the use of the solvent-based ABP version
were more promising (Rector, 1975), and a system
using Bavon ASAK/ABP was developed and
used extensively in York until the advent of freezedrying
(see below). This involved pre-treatment
with dilute hydrochloric acid or EDTA (to remove
silt and lime concretions and to improve colour) followed
by solvent dehydration and then immersion
for several days in dilute baths of Bavon ASAK/ABP
and lanolin. After removal from the bath pure
Bavon ABP was rubbed into the surface and the
leather was then set aside to dry in a fume cupboard
(Spriggs, 2003).
The quantities of leather being excavated in York
and elsewhere in the UK by the late 1970s, coupled
with mounting concerns about health and safety
and the cost of solvent-based treatments, led to
increased efforts to find alternatives which did not
involve the use of organic solvents.
22.2.3.2 Freeze-drying from glycerol and PEGs
A method of treating wet leather based on heated
baths of polyethylene glycol (PEG) was developed at
the British Museum (Muhlethaler, 1973). However,
owing to the necessity of providing heat, both to
keep the PEG molten and to drive off the water, the
leather tended to shrink and warp badly, and tests at
York resulted in the process being abandoned there
(Spriggs, 2003).
Reports of successful treatments involving vacuum
freeze-drying spurred conservators at YAT to
experiment for themselves (Organ, 1958; Sturge,
1973; Rosenquist, 1975). Early tests showed that
good results could be obtained with both glycerol
and the lower molecular weight PEGs, once the
optimum quantity of these materials had been
introduced into the leather. Based on these successes,
a freeze-drying unit was acquired in 1979,
making YAT one of the first archaeological laboratories
in the UK to use the technique on a routine
basis (Spriggs, 1981).
22.2.4 Present-day conservation treatments
If archaeological leather is allowed to dry naturally
from the wet state, contractile forces will cause it
to shrink dramatically and become stiff and hard, a
state which is difficult to reverse. The aim of any
stabilization treatment for wet leather is to render it
dry while preserving its size and shape, preferably by
doing as little to the leather as possible (minimal
intervention). The conservation process should also
aim to render the leather suitable for occasional
handling, study and storage in normal museum conditions
through improving its physical strength and
flexibility and its resistance to damage from environmental
fluctuations. Further work might involve
reshaping crushed pieces and other measures undertaken
to improve the appearance of important items
wanted for exhibition.
Freeze-drying is normally preceded by treatment
with a water soluble compound such as glycerol or
PEG 400. In this two-stage process, just enough
glycerol or PEG is used to give dimensional stability
during freeze-drying and also to ensure some flexibility
and cohesion to the leather structure. It also
acts as a cryoprotector as it protects the leather
structure from damage from ice-crystal formation
and expansion during rapid cooling prior to the
freeze-drying process.
In vacuum freeze-drying ice crystals in the frozen
product are encouraged to sublime at reduced pressure
by applying a vacuum. This drying overcomes
the natural forces of surface tension inherent to liquid
water, and can be made to happen quite rapidly
(Adams, 1994). Freeze-drying is quick and cost effective.
It allows batch treatment as opposed to each
piece being dealt with separately at every stage of
the treatment – a great boon if dealing with large
quantities (Figure 22.2). Non-vacuum freeze-drying
requires simpler equipment but can also give good
results although it is much slower (Storch, 1997).
The appearance of freeze-dried leather is dry and
fine detail of decoration, manufacture and wear is
well preserved and highly visible.
Glycerol and the lower molecular weight PEGs
act as cryoprotectors during freeze-drying, and as
lubricants and humectants afterwards. Further dressings,
such as PEG 1500, can be applied to the surface
248 Conservation of leather and related materials
The conservation of archaeological leather 249
for cosmetic purposes or as consolidants. Any
leather item that is fragile or likely to shed fibres
may require further consolidation in order to
strengthen it.
22.2.4.1 Reshaping and reconstruction
Leather reconstruction is a delicate and timeconsuming
business normally undertaken by conservators
for specific purposes, but as it requires much
direct handling of the leather the potential for causing
damage is high. Many leather items, mainly shoes,
have been reconstructed at York for various exhibitions
and on each occasion time spent in identifying
the best techniques and materials for joining,
lining, supporting, stitching and padding out
these objects produced fine results (Spriggs, 2003)
(Figure 22.3).
Large shoe components and other finds of sheet
leather, often recovered in a crushed, bent or creased
state, sometimes need to be reshaped. These can be
pressed between sheets of card or Correx board after
Figure 22.2 Preparing a load for accelerated freeze-drying: a temperature probe is being inserted into a sample
waterlogged leather piece. (Courtesy York Archaeology Trust)
250 Conservation of leather and related materials
the glycerol pre-treatment so that the new shape
becomes ‘set’ during freeze-drying.
Freeze-dried leather that has been pre-treated
with glycerol will accept adhesives readily and
reshaping is also possible by partial rehumidification.
One problem regularly encountered is that of
creases in the leather that, despite best endeavours,
persist through the treatment process. These can be
removed to an extent by applying gentle tension to
the leather after relaxing it in a high-humidity environment.
The possibility of rehumidifying, and so
relaxing, the leather structure is one of the advantages
of employing a hygroscopic lubricant such as
glycerol in the initial treatment (Peacock, 1983).
22.2.4.2 Marine leather
Once it has been desalinated, leather from marine
environments may normally be treated very similarly
to any other sort of waterlogged leather. However,
the leather may be disfigured with marine
concretions and iron staining which may need to
be removed. Mechanical techniques using scalpels,
modified engraving tools and dental descalers (applied
with great care) may be effective but chemical
cleaning techniques are often necessary too. Chelating
agents, mineral and organic acids as well as other
compounds have been used in the past ( Jenssen,
1987) but many of these have an unknown effect
on the leather, and some are very hazardous to
health. Other reagents, such sodium di-thionite and
ammonium citrate are used for iron-stain removal
and research has demonstrated their effectiveness
on marine leather prior to freeze-drying (Godfrey
et al., 2002).
22.2.4.3 Composites and special items
Leather objects incorporating metal fittings, such as
shoe and belt buckles, studs and harness attachments,
are frequently found on excavations. Conservation
treatments and storage environments for
leather and metals tend to be incompatible and
leather is normally given priority. At York it was felt
that the solvent-based treatments for leather would
not adversely affect metals, whereas the aqueous
PEG treatments were likely to be more cause for
concern, especially for iron. In a YAT survey of six
leather items with iron fittings, the iron on the three
that had received solvent-based treatments had survived
well. But the iron fittings on the three treated
with glycerol and freeze-dried showed signs of postconservation
corrosion damage. A further ten items
with copper alloy, tin and lead/tin alloy attachments
Figure 22.3 Freeze-dried and reconstructed leather footwear from the Coppergate excavations, York. (Courtesy
York Archaeology Trust)
The conservation of archaeological leather 251
had not suffered any obvious post-conservation corrosion
damage (Spriggs, 2003).
In archaeological deposits where Roman leatherwork
is preserved, the soles of carbatinae and other
hobnailed shoe and sandal types present a particular
conservation problem. The partial corrosion of the
hobnails may often impregnate and embrittle the
surrounding leather of the multi-layered sole structures,
often to the extent that they are liable to separate
and fragment and the hobnails lose their
positions during the cleaning process. X-radiography
of the sole units before cleaning will at least record
the original positions of the hobnails. After that,
only very careful support during handling, and
custom-made packaging after stabilization, will protect
the sole from disintegration (Spriggs, 1987).
The use of water soluble iron corrosion inhibitors,
such as Hostacor IT, are used at some centres for both
the temporary storage and water-based treatment of
leather/iron composites (Starling, 1987; Degrigny
et al., 2002). Variable levels of protection seem to be
obtained and a search to find the best inhibitor and
the optimum conditions for its use continues.
Raw hide and other non-vegetable-tanned hides
occasionally survive in waterlogged contexts. As an
example, a crumpled mass of skin complete with
hair was recovered from Viking levels at 16–22
Coppergate, York, in 1978. It was identified as being
calfskin and analysis of a fragment using infrared spectrophotometry
showed that it was heavily impregnated
with Stockholm tar (softwood resins), the
bactericidal properties of which may well explain its
survival. The hide required repeated immersions in a
chelating agent to release the folds, a process that was
only partially successful, followed by treatment with
PEG 1500 and freeze-drying (Spriggs, 2003). Most
of the recent finds of bog bodies have been preserved
using a similar system of PEG impregnation followed
by freeze-drying (e.g. Omar et al., 1989).
22.2.4.4 Comparisons of techniques
It is always instructive to compare the results of dissimilar
treatments to the same material. In York, a
recent examination of some of the pieces treated
with Bavon ASAK/ABP in the 1970s concluded
that the results were not inferior to the freeze-dried
product. Despite varying widely in condition
as-found, many pieces are still soft, pliable, dry in
feel and appearance, and a rich brown colour. There
has been no undue crumbling or fragmentation, and
the original packaging is unstained. Dimensional
shrinkage was between 3 and 10%.
Adverse comments have been made about the
freeze-drying of leather, both in terms of the unnecessary
complexity of the freeze-drying process and
equipment (Goubitz, 1997), and, more importantly
perhaps, concerning the condition and appearance of
the dried leather (Swann, 1997). Most archaeological
conservators, although convinced that freeze-drying
is the most reliable technique currently available for
treating waterlogged leather, would welcome new
developments in this field.
22.2.4.5 New approaches
Conservators are continually searching for more
effective treatments and substitutes for PEG 400 and
glycerol. A novel technique developed from medical
research and used to preserve histological specimens
is that of ‘plastination’ (Smith, 2003). This
method involves the dehydration of waterlogged
leather through baths of acetone, which is then
replaced with silicone oil (under vacuum). This oil
can be polymerized into a solid either by introducing
a catalyst vapour (under vacuum) or by applying
liquid catalyst to the skin surface. The treatments
are reported to give a dimensionally stable, flexible
and aesthetically pleasing result, but there are concerns
about the long-term stability of the polymer,
as well as the fact that it is not reversible (Baltazar
et al., 1996).
22.3 Dry leather
22.3.1 Condition
Dry-preserved leather is often found in, though not
exclusive to, hot and arid regions of the world.
Temperate regions also provide examples of protection
from moisture, such as Roman shoes from a
burial in Southfleet, Kent (British Museum registration
numbers PRB 1836, 0213.17–19). The shoes
were preserved inside a child’s stone coffin although
an associated textile was ‘reduced to tinder’
(Rashleigh, 1803; Walker, 1990). In good condition,
the purple colour, form and stitching, including gold
stitching, was largely intact (Figures 22.4 and 22.5).
Medieval and later shoes which have been concealed
in buildings also show an exceptional degree of
preservation. Leather in consistently dry burial conditions
has achieved a degree of stability within its
environment. Collagen, the principal component of
leather, is inflexible in the desiccated state; it is
unaffected by fungi, bacteria and hydrolysis, the major
252 Conservation of leather and related materials
Figure 22.4 Roman shoes from Kent, third century AD.
Figure 22.5 Detail of third century AD Roman shoes from Kent, showing reticulation and gold thread.
elements of decay (Cronyn, 1990). Desiccation allows
leather to keep some of its distinctive qualities; colour,
form, surface finish, tannins and, occasionally, flexibility.
Less ideal contexts result in a loss of elasticity
and fragmentation. Ancient desiccated leather may
be found in remarkably good condition, or, at the
other extreme, so brittle that it cannot be handled
without damage (Figure 22.6).
22.3.1.1 Deterioration
Change, however, does occur over time; much of
the water content (typically 15% for new leather) is
lost under desiccating conditions, leading to inflexibility
and permanent damage. ‘Leather’ that is lightly
cured (‘pseudo-tannages’ such as skins treated by
smoking, dressing with mineral earths, salt, animal
fats or oils) may survive better than vegetable tanned.
In general, relatively unaltered collagen survives
much better than highly modified skin or leather,
which are variable in their stability (Horie, 1990).
If skin is better preserved than leather in dry
archaeological and historical contexts, this may be
because of its physical as well as its chemical structure.
The compacted fibres of a dried skin allow less
interaction with the environment than in the more
open structure of leather. In effect, a smaller surface
area admits fewer pollutants.
Consistently dry environments, predictably, preserve
organic materials more successfully than intermittently
wet contexts such as those subject to rain,
ground water, or close contact with a decaying body
(Wills, 2001). High temperatures and RH cause
hydrolytic degradation resulting in shrinkage, fibre
collapse, embrittlement and cracking (Cronyn, 1990);
the more frequent the cycle of wetting and drying,
the greater the damage. Water dissolves tannins, which
when redeposited on the surface cause darkening and
hardening of the leather. Deteriorated leathers are
especially vulnerable, because the damaged fibres are
more susceptible to collapse.
Vegetable-tanned leathers absorb sulphur dioxide
and follow a path of acidic decay often called ‘red
rot’, where fibre scission leads to the leather disintegrating
ultimately to a reddish fibrous powder. This
pattern of decay is more common in late nineteenth
century and twentieth century leathers, but may
be found in more ancient leathers. To compare the
deterioration patterns of ancient leathers with those
of more recently naturally aged leathers, Larsen
analysed seven small samples of Egyptian, Nubian
and Coptic origin. Due to the small amount of
samples, only amino acid analysis and measurement
of hydrothermal stability were undertaken. In general,
the significant oxidative changes of the collagen
from the samples was found to follow the same
pattern and lie in the same range as the newer historical
leathers (Larsen, 1994, 1995). The Nubian
leather gelatinized completely on contact with water
at 20°C. Examination under the microscope of the
Egyptian leather showed that it had lost the fibre
structure, and was turned into a hard and amorphous
mass, like dry glue. This resembles the behaviour
of some samples of the ancient Roman and
Egyptian leathers at the British Museum, which
show gelatinization on wetting.
22.3.2 On-site retrieval
22.3.2.1 Planning for excavation
The retrieval of desiccated leather on excavation
can be a surprise, however well prepared the expedition.
Personal preparation is vital. Along with
The conservation of archaeological leather 253
Figure 22.6 Newly excavated post-Meroitic leather,
c.350 AD.
254 Conservation of leather and related materials
assembling the required materials and tools and
consulting the available literature, useful advice is to
be had from those with relevant personal experience.
Practical treatments should be considered and
tested, if possible, in advance of excavation. Consideration
(Schofield, 1996) should be given to:
(a) which materials, chemicals, solvents, packaging
or other facilities are obtainable locally;
(b) how the local climate and area affects planned
treatments and procedures;
(c) the destination of excavated material;
(d) the degree of conservation/restoration required.
22.3.2.2 Limitations on transport of solvents
and materials
Solvents and resins in solution may not be transported
by air, and alcohols will not be readily available
in countries under Sharia law. The limited
weight of tools and materials it is possible physically
to carry out to excavation (by air or otherwise)
encourages careful choice. It may be necessary to use
resins that serve more than one conservation purpose.
22.3.2.3 On site; initial procedures
On-site lifting procedures, as well as transport, storage
and handling, depend on the size and condition of the
object, its intimate association with another structure
(such as a body) and its condition (Cruickshank,
2001). When lifting fragmentary items, all pieces
should be kept in their original relationship as far as is
possible. Fragile items should be supported. Newly
excavated pieces, though apparently dry, will contain
some moisture. These should be kept initially in a
sealed container and allowed to dry slowly (or equilibrate
to local conditions) over a period of days.
Composite artefacts, e.g. a quiver containing
arrows, require particular care. The arrows may first
be removed singly so that these do not subsequently
damage the quiver itself when lifting. Each object
dictates its own approach; requiring an understanding
of construction, areas of weakness and the relationship
of different materials.
22.3.2.4 Handling
Protective gloves and a mask should be worn to
avoid contamination of (and also from) the material
at all times. This is of particular importance if DNA
analysis is planned. Some material is so fragile that
handling without further breakage is almost impossible.
This may dictate consolidation at an early stage
(see below).
22.3.2.5 Packing and transport
The mode of transport, destination and condition
of the roads will influence decisions on packing.
Fragile material may be supported in Plastozote
(polyethylene foam) cut-outs, each tailored to the
fragment shape, packed in Perspex boxes.
22.3.2.6 Storage
Dry leather is best stored in dry, even, cool conditions.
It should be boxed to protect from dust and
to buffer from temperature and RH fluctuations,
and padded/supported as necessary to avoid damage.
Good labelling is essential to protect from unnecessary
handling.
22.3.3 Recording procedures
Standard conventions in recording, assessment and
selection apply (see above). Initial cleaning, and
possibly stabilization, following the usual conservation
procedures, may be necessary before diagnostic
processes can proceed. Drawings and technical information
records are useful (Figure 22.7). Desiccated
leather may be examined and tested to identify and
record the following features (Wills, 2002):
(a) Tannage identification
(b) Surface features, hair and species ID
(c) Seams, structural and decorative elements,
impressions, etc.
(d) Colour
(e) Leatherworking tools
(f ) DNA analysis.
22.3.3.1 Presence of tannage
Ancient dry leather materials may carry evidence of
vegetable tannage or other skin preparation (Daniels,
1997; Thickett and Wills, 1996) even after millennia.
Two thirds of leather samples from a Nubian
cemetery site (Kerma Ancien and Kerma Classique,
c. 2500 BC– 1750 BC), for example, showed the presence
of vegetable tannage (Ryder, 1984).
22.3.3.2 Vegetable tannage test
A simple test for the presence of a vegetable tan is
based on the reaction of iron salts with tannins. A
2% freshly made solution of ferrous sulphate (FeSO4)
w/v in distilled water, applied to a small area gives a
blue–black stain if positive. The colour change is
irreversible, so this test should be carried out on a
hidden area. If the material is for study only, it may
The conservation of archaeological leather 255
Figure 22.7 Technical record of an early medieval Nubian sandal.
be done with a fine sable brush in situ on an object.
If for display, a few fibres may be removed to be
tested under magnification. As a further refinement,
the type of tannin may be identified by the application
of a drop of vanillin in alcohol, followed by a
drop of concentrated hydrochloric acid. A positive
result is bright red in colour, showing condensed
vegetable tannins. No reaction demonstrates a
hydrolysable tannin (Daniels, 1993). It should be
noted that the test results will not show on very dark
leathers, and that a positive result demonstrates the
presence of tannins, not necessarily tannage. Testing
a cross-section of leather is of greater value, showing
whether the tannin is superficial. If so, it may relate
to a vegetable colouring agent such as pomegranate
juice or madder. Care is required with very decayed
material, as water may rapidly convert aged skin to
gelatine, or, with acidic leather, activate residual sulphates
to create sulphuric acid.
Tannin tests carried out on some early medieval
Nubian (Welsby, 1998) leather samples in the British
Museum (Thickett and Wills, 1996) showed varying
results. Extracts were tested separately with ammonium
ferric sulphate solution for the presence of tannin,
and aluminon (the triammonium salt of
aurintricarboxylic acid) solution for the alum. Thin
caprine leather gave some positive results for vegetable
tan, and the thicker thongs (more likely to be
raw hide or simply tanned) gave a range of results,
including positive for the presence of alum. It should
be noted that any possible background contamination
with alum had not been taken into account, so
these results should be interpreted with discretion.
22.3.3.3 Surface features and cross-section
Information is revealed by examination under magnification
of the grain pattern, presence of hairs, decoration,
tooling, evidence of wear, deposits, staining
and abrasion. Species identification is often possible.
A cross-section of the skin gives further diagnostic
detail. If hair remains, fibre analysis is possible. The
presence or absence of a woolly winter coat may
indicate the season of death (Ryder, 1987). The
256 Conservation of leather and related materials
thickness of the leather is of interest, giving some
indication of the species and age of the animal if
intact, and leatherworking techniques if split.
22.3.3.4 Seams, structural and decorative elements,
impressions
The range of features (type of seam, stitching, perforations,
nails, knots, bindings, etc.) is recorded in
a systematic manner (Goubitz, 1984; Spriggs, 1987).
Seams stitched when wet are recognizable by distortion
created by the pull of the thread.
Materials adjacent to the leather may leave interpretable
impressions. In examples of excavated Kerma
leather, where no textile remained, the indentations
of a plain-weave textile were evident. Weave analysis
was possible; four pieces of leather revealed thread
counts varying from 10 to 12 threads by 12 to 14
threads per 10mm2
(Welsby, 2001).
22.3.3.5 Colour
Colour may be natural, applied pigment, dye, or the
result of decay. Dye and pigment analysis techniques
might be accessed and adapted from textile analysis
protocols (Smith, 2000).
22.3.3.6 Leatherworking tools
The methods of cutting, stitching and finishing give
clues to the tools used. This may become significant
if the tools themselves have not been found.
22.3.4 Present-day treatments
22.3.4.1 Considerations prior to conservation
treatment
The end purpose (study or display) and the end place
(storage/display in the country of origin or elsewhere)
will affect the type of treatment. This should
be discussed and methods considered early in the
project. Samples should of course be taken before
treatments begin to safeguard the future potential for
analysis. Desiccated leather is, however, occasionally
found in such good condition that intervention is
neither necessary nor desirable (Volken, 2001).
22.3.4.2 Cleaning
Conservation training is needed to understand and
apply treatments successfully, and this includes
apparently straightforward cleaning techniques. The
standard range of non-aqueous cleaning treatments
(dry brushing, vacuuming, Wishab sacrificial rubber,
chemical sponges, etc.) should be tested and applied
as appropriate.
22.3.4.3 To flex or not to flex
It may be helpful to consider here the arguments for
and against ‘restoring’ suppleness to leather. Most
ancient dry leather has lost flexibility. Archaeological
leather on display or in storage is static; it need not
be supple. Methods of introducing permanent flexibility
into old leather have sometimes limited the
object’s lifespan, and dressings and leather softeners
can be damaging (see below). Temporary pliancy is,
however, useful when reshaping a three-dimensional
object (Wills, 2000), and such methods will be considered
more fully below.
22.3.4.4 Dressings
The above paragraph leads to discussion of another
misconception; the ‘feeding’ of leather. It is not
hungry, and does not need food. Dressings lubricate
working leather structures such as harness, but can
be damaging to aged leather. Dry leather pieces
treated with glycerine and thymol in the Louvre in
the 1980s had, when re-examined, turned from red
to black (Montembault, 2001).
Leather dressings damage in the following ways
(Raphael, 1993):
(a) darken many lighter colour leathers
(b) encourage mould and biological attack
(c) form fatty spews over the surface
(d) oxidize over time to stiffen the material
(e) wick into surrounding materials
(f ) soften original finishes and decoration
(g) cause dust to accumulate
(h) impede future conservation treatments
(i) contaminate the material for future scientific
analysis
to which may be added:
( j) provide a route of ingress for contaminants and
catalysts for further decay.
22.3.4.5 Consolidation as a first-aid measure on site
Consolidation is sometimes necessary to strengthen a
fragile object in situ on site. It allows lifting and subsequent
safe transport, handling, recording and reconstruction
of an item that might otherwise be lost or
damaged. Further treatment may well be necessary. If
first-aid consolidation is required, it becomes particularly
important to remember to take samples for
analysis before treatment.
The conservation of archaeological leather 257
22.3.4.6 Consolidation: a range of resins
The ideal leather consolidant has not yet been
found. Conservation standards require such a material
to confer resilience, strength, stability, flexibility,
reversibility, and retain colour and surface qualities.
Resins currently or recently used in dry leather consolidation
include those based on acrylic resins such
as Paraloid B72, Paraloid F10, Pliantex; those based
on cellulose such as Cellugel, Klucel G, and others
such as a polyvinyl butyryl (Mowital B30H). A wider
range of potential consolidants has been explored in
the past, including gelatine, polyurethanes, polyvinyl
acetate emulsions, epoxy resins and a polyvinyl
acetate/ethylene copolymer (Vinamul 3252).
Though many of the above resins are useful in
specific areas, new materials are still sought for conservation
treatments in the studio and on excavation.
Cyclododecan ( Jagers and Hangleitner, 1995;
Hilby, 1997), a temporary consolidant of fragile
material, is worth investigation for use on site.
Some conservators have found it beneficial to treat
dry leather as wet; to rehydrate it and then treat as
waterlogged (Volken, 2001). This applies only to
robust and recently excavated material.
22.3.4.7 Consolidation in hot climates
Dry leather from hot, arid sites, and which remains
stored or displayed in the country of origin, is subject
to the potentially damaging extremes of that climate.
Conservation treatments should take this into account
and be modified to fit those challenging conditions
(Wills, 2001). The more familiar conservation materials
used in temperate climates (such as Paraloid B72
which has a Tg of 40°C) may have to be rejected in
favour of those stable at higher temperatures with a
higher glass transition temperature (Tg).
22.3.4.8 Reshaping
Reshaping is sometimes required to help comprehend
a three-dimensional object. It is a delicate and subtle
process, not to be undertaken without appropriate
knowledge and experience. Robust, newly excavated
leather items may be most pliable immediately after
excavation, and so are best reshaped gently as soon as
possible. Others, too fragile to manipulate, require
padding to stabilize their present shape. Reshaping
may also be done off-site, back in a conservation studio,
or later still in the case of long-stored material.
Misshapen organic objects often retain a memory
of their shape during their ‘working’ life. This assists
the process of recalling the original form, along
with cultural knowledge (Sully, 1992). Reshaping a
rigid, deformed leather item involves the (often temporary)
admission of a plasticizing agent such as moisture,
to the structure of the skin, causing it to swell.
The process may be carried out before or after consolidation
(Wills, 2000).
22.3.4.9 Repair, backing and reconstruction
Where it is necessary to make joins, a range of
acrylic and other conservation adhesives is available.
To reinforce the joins, suitable backing materials
include Japanese kozo (mulberry fibre) papers and
non-woven polyester fabrics. Solvent reactivation of
adhesive films (or the adhesive-impregnated backing
material) often works well. To make fills, glass
microballoons and pastes derived from cellulose
fibres have been used. A displayable leather object
may additionally need mounting and support.
For a more extensive and detailed discussion of
the conservation of desiccated archaeological leather,
please refer to Wills (2002).
22.4 Mineralized leather
22.4.1 Condition
Metals such as iron and copper alloy corrode during
burial and the products of their corrosion dissolve in
the ground water. Iron readily forms insoluble complexes
with tannins, but leather buried in very close
proximity to corroding metals and saturated by the
water is also affected by the solute precipitating
within the skin structure (Turgoose, 1989). Minerals
most commonly encountered in leather are oxides
and phosphates of iron, and carbonates and chlorides
of copper. High mineral content in waterlogged
leather is indicated by metal staining and decreased
flexibility (Hovmand and Jones, 2001). In the course
of mineralization metal ions are precipitated either
inside collagen fibre bundles (replacement) or outside
them (cementation). Under certain conditions mineralization
is progressive and skin structures can first
undergo cementation followed by a second stage
during which the fibre structures themselves are
replaced. This does not noticeably retard the
hydrolysis and dissolution of the protein element, but
mineralized skin or leather sometimes survives burial
when unaffected parts of the same object, further
from the source of metal ions, does not. Completely
mineralized leather is rigid, crumbly and ochre
coloured with no visible organic content, yet some
features of its original structure may still be preserved
(Figures 22.8 and 22.9). This type of evidence is
258 Conservation of leather and related materials
Figure 22.8 Detail of a mineralized decorated knife sheath (seventh to eighth centuries AD). Grave 5352, St Mary’s
Stadium, Southampton, UK. (Courtesy of Institute of Archaeology, Oxford)
Figure 22.9 Scanning electron micrograph of mineralized collagen fibres from a knife sheath (sixth to seventh
centuries AD). Grave 4269, Buttermarket, Ipswich, UK.
The conservation of archaeological leather 259
prone to physical damage through poor handling,
abrasion and inadequate conditions of storage.
22.4.2 On-site retrieval
Completely mineralized leather is most often found
in aerated acidic conditions which promote the corrosion
of metals. The existence of mineralized leather
may, however, be disguised beneath bulky corrosion
products so it is best practice to retrieve finds complete
with adhering deposits. Small items such as
knives and sheaths up to 200mm in length can usually
be lifted straight into a box, but larger or complex
finds require support from beneath and at the sides to
prevent collapse. One advantage of this approach is
that transient evidence at the edges is held in position
until it can be examined and recorded in a more controlled
setting. Different ways of lifting fragile finds
are described by Watkinson and Neal (1998).
Totally mineralized organic remains do not normally
undergo change following excavation but they
are at risk if the metal with which they are associated
undergoes fresh corrosion or if they are not protected
from physical damage, including unnecessary handling.
Both are avoided by using standard packaging
regimes (Watkinson and Neal, 1998). Iron that has not
totally oxidized before excavation and is not subject to
environmental control afterwards can be expected to
corrode afresh. If left unchecked the gradual disintegration
of the metallic element is likely to cause
remains of mineralized leather to fall away.
For those involved in on-site retrieval it will be
essential to the specialist to know the orientation of
finds in the ground, such as which way up, and the
spatial relationship of finds groups. In some cases the
specialist should be invited on site.
22.4.3 Recording
The extent of mineralized deposits within soil blocks,
or around metal objects, can be recorded by radiography,
a standard procedure in the recording and
assessment of finds. X-rays can reveal multi-layered
constructions, such as the scabbards of swords, and
the existence of straps or rivets before any cleaning
takes place.
It is likely that a limited amount of soil removal
may then be necessary in order accurately to identify
the organic materials present and to assess their
condition. A picture will gradually emerge of the
research value of the remains and the required level
of recording. When they are seen at magnifications
of ϫ25 or even ϫ1000, details of skin structures
preserved in mineralized leather vary in quality
according to the circumstances of their original
formation and subsequent history. The make-up of
the mineral compounds and their sequential deposition
can reproduce structures in fine and precise
detail, or not at all as the case may be. The characterization
of mineralized organic materials in general
is specialist work. On significant finds and when
more than one type of material is present (such as
wood, textile and leather) some of the cleaning as
well as the recording should be completed by the
specialist concerned to ensure that nothing important
is overlooked or removed.
Features indicative of skin or leather can be preserved
in mineralized remains to such a degree that its
identity, even to species, may be obvious. Grain
patterns and hair shafts may be recognized as well as
evidence of craft work such as stitching and tooling
(Filmer-Sankey and Pestell, 2001: pl. XXXVI,
XXXVIII, XXXIX). However, if the grain surface
has been lost underlying deposits can be searched
(using microscopy and scanning electron microscopy)
for evidence that the remains represent a skin product
of some kind (Cameron and Edwards, 2003).
Mineralized leather tends to be regarded as
unpromising material for organic analyses (such as
for DNA, tannins or dyes), but the same may not be
true of partially mineralized leather.
22.4.4 Treatment
Partially mineralized leather most commonly comes
from anaerobic waterlogged contexts and feels
inflexible and crystalline and attempts to flex it can
result in cracking. Following excavation there is
a danger that the mineral content may undergo
volume change through oxidation and that this
could result in distortion of its surviving connective
tissue and further chemical breakdown through
changes of pH. Methods of reducing mineral content
by using sequestering agents, and important
considerations in deciding whether to do so, are
discussed by Ganiaris et al. (1982) and Hovmand
and Jones (2001).
Completely mineralized leather, being generally
friable and brittle, is normally found in aerobic
deposits and is already oxidized. However, it often
gives the impression of extreme weakness, and fear
of it crumbling away normally initiates a strong
desire to consolidate. For research purposes this
is discouraged because it prevents further examination
or sampling for analysis. Arguments for consolidation,
to allow transport, display and handling,
260 Conservation of leather and related materials
have to be balanced against its negative impact on
research value.
22.5 Long-term storage of
archaeological leather
22.5.1 Storage requirements
22.5.1.1 Storage of dried and desiccated leather
Dry leather is best stored in moderately dry, even,
cool conditions; it is generally content in the compromise
environment that suits both metals and organics
(c.16°C and 40%RH). The use of glycerol or PEG
400 (both hygroscopic) in the freeze-drying treatment
of wet leathers makes this all the more necessary.
Optimum environmental conditions for the storage
and display of partially mineralized leather depends
on the proportional balance between organic and
mineral and on the relative importance assigned to
each. Cool, dry environments to minimize chemical
change are likely to be beneficial, especially as so
many mineralized leathers contain metallic elements,
such as iron hobnails in the soles of Roman shoes,
which tend to corrode if levels of relative humidity
rise above 20%. Oxygen scavengers such as RP
System (MGC) in sealed containers or packages are
useful for storing combinations of materials with
differing RH requirements.
22.5.1.2 General points on storage
(a) box to protect from light, dust and to buffer
from temperature and RH fluctuations
(b) pack in suitable containers, padding as necessary
to support fragile material
(c) good labelling essential to protect from unnecessary
handling and inadvertent disposal
(d) regular monitoring of conditions
(e) set and check pest traps
(f ) regular condition surveys (e.g. Sully and SuensonTaylor,
1998).
22.5.2 Condition assessments of
treated leather
Condition audits on collections are a core function
of good collections care, and it will be found necessary
sooner or later to repack old collections of conserved
leather to bring them up to modern standards
(Edwards and Mould, 1995). A risk assessment
should be undertaken under Health and Safety
Executive regulations (2000) and appropriate safety
precautions taken when handling items showing
signs of past mould growth, and to protect against
dust inhalation. Collections condition surveys are a
means of assessing the effectiveness of packaging and
storage conditions, as well as the success of the conservation
treatment. Published surveys of leather
collections at York (Spriggs, 2003), the University
of Trondheim (Peacock, 2001), and the Museum of
London (Sully and Suenson-Taylor, 1996) used
rather different survey techniques, yet each recognized
that the conditions under which the collections
were being kept needed to be improved in a
number of ways. At York it was noted that much of
the leather appeared to be inherently fragile, and
required better packaging to prevent fragmentation.
The widespread effect of biodeterioration (mould
growth) was ascribed to high humidity in storage
areas and overcrowded boxes. Finally, the leather
that had been treated before 1976, using the early
solvent and dressing-based treatments, was moist
and sticking to its packaging.
22.5.3 Old collections/retreatments
A surprising amount of dry archaeological leather,
of varying ages and in different states of preservation,
is to be found in museums and stores. This
ranges from material that had always been dry, to
that which was once wet or waterlogged. Old conservation
and excavation records, where these exist,
are helpful when re-evaluating these collections.
The leather itself may show evidence of past interference
such as dressings or repairs. Early conservation
reference works give clues to possible old
treatments if no records are found. The Conservation
of Antiquities and Works of Art (Plenderleith and
Werner, 1956) and A Guide to the Conservation and
Restoration of Objects Made Wholly or in Part of Leather
(Waterer, 1972) are of value. Any subsequent conservation
treatments undertaken must take into
account earlier treatments.
22.6 Purpose of treatment: a call
for clarity
The conservation of archaeological leather would
benefit if we defined more clearly the two functions
of an object after excavation. Its first function is as a
resource for the information it carries; the second
is as a displayable object. In its first role, as an object
of research, its keepers are hedged about with
restraints which limit its chemical contamination
and protect its physical integrity. In effect, while its
potential is assessed, records made, specialist opinions
sought and samples taken the environment is
adapted to the requirements of the material. It may
not be possible, or convenient, to maintain this situation
indefinitely and a point may be reached
when the object must be adapted to suit the environments
of museum stores and galleries. This
change of status, marking the transition of an object
from its first to second functions, is in many respects
a one-way process in that conservation treatments at
this level are designed around permanency and
exhibitions. Sometimes this involves treatments that
can never be completely reversed. Most archaeological
leather in museum collections has already passed
through this second stage because it has been freezedried,
consolidated or treated in some other way.
Conservators in the future need to be respectful of
the research potential of freshly excavated leather
and appreciative of its visual impact on display. The
two functions require different types of conservation
skills and treatments, performed in the correct order,
but in doing so the various needs of the researcher
and museum curator can be met equally.
22.7 Conclusion
Leather is an extraordinary material because it carries
its entire history, including that of the original
animal, in its structure and on its surface. It has a
technological richness that few fully appreciate, with
unexplored zones waiting to be researched, such as
the history of the development of vegetable tanning
in Europe and the Near East, and an evaluation of
archaeological skin and leather as a resource for
genetic studies through DNA analysis (Wayne et al.,
1999). Among archaeological finds, where so much
that endures is of metal or ceramic, the discovery of
organic materials is both exciting and demanding,
especially when evidence of craft or industry also
emerges from the same context. No one can predict
where and when leather will be found but organized
retrieval followed by sympathetic handling and
treatment will affect the quality of the published
results and broaden our view of past cultures.
References
Adams, G. (1994) Freeze-drying – Art or Science? In
A Celebration of Wood (Spriggs, J., ed.), pp. 49–54
Wetlands Archaeological Research Project 8.
Baltazar, V., Lyons, W. and Murray, A. (1996) Plastination
as a Consolidation Technique for Archaeological
Bone, Waterlogged Leather and Waterlogged Wood.
In Twenty Second Annual Association of Graduate
Programs in Art Conservation Student Conference Papers
Queen’s University, pp. 4 –10. Ontario.
Cameron, E. (2000) Sheaths and Scabbards in England
AD400 –1100. Oxford: British Archaeological Reports,
British Series 301.
Cameron, E. and Edwards, G. (2004) Evidence of Leather
on Finds from Anglo-Saxon Cemeteries at St Stephen’s
Lane/Buttermarket, Ipswich, Suffolk 1987–88 and Boss
Hall, Ipswich 1990. Portsmouth: English Heritage
Centre for Archaeology Report 23/2004.
Cowgill, J., Neergaard, M. de and Griffiths, N. (1987)
Knives and Scabbards: Medieval Finds from Excavations in
London. Museum of London.
Cronyn, J. (1990) The Elements of Archaeological
Conservation. London: Routledge.
Cruickshank, P. (2001) Leather Shrouds … a Rare Find in
Jordan. In Leather Wet and Dry: Current Treatments in the
Conservation of Waterlogged and Desiccated Archaeological
Leather (B. Wills, ed.), pp. 63–70. London: Archetype.
Daniels, V. (1993) Evaluation of a Test for Tannins in Leather.
British Museum Department of Conservation Internal
Report no. CA 1993/2.
Daniels, V. (1997) Analysis of Excavated Leather Samples
from Kerma. British Museum Department of
Conservation Internal Report no. CA 1997/48.
Degrigny, C., Baron, G., Christodoulou, P., Tran, K. and
Hiron, X. (2002) Conservation of a Collection of
Waterlogged Composite Rifles Dating from the 17th
Century Recovered from the Brescou II Marine Site.
In Proceedings of the 8th ICOM Group on Wet Organic
Archaeological Materials Conference (P. Hoffman, J. Spriggs,
T. Grant, C. Cook, and A., Recht, eds), pp. 399– 412.
Stockholm (Bremerhaven).
Dobson, C. (2003) As Tough as Old Boots? A Study of
Hardened Leather Armour, Part 1: Techniques of
Manufacture, pp. 55–77. Art and Arms Florence, City
of the Medici, Conference Proceedings May 30th–June 1st
2003.
Driel-Murray, van C. (2000) Leather and Skin Products.
In Ancient Egyptian Materials and Technology
(P.T. Nicholson and I. Shaw, eds), pp. 299–319.
Cambridge: Cambridge University Press.
Driel-Murray, van C. (2002) Ancient Skin Processing and
the Impact of Rome on Tanning Technology. In Le
Travail du Cuir de la Préhistoire à nos Jours (F. AudoinRouzeau,
and S. Beyries, eds), pp. 251–265. Antibes:
APDCA.
Edwards, G. and Mould, Q. (1995) Guidelines for the
Care of Waterlogged Archaeological Leather. English
Heritage Scientific and Technical Publication,
Guideline 4.
Filmer-Sankey, W. and Pestell, T. (2001) Snape AngloSaxon
Cemetery: Excavations and Surveys 1824–1992.
East Anglian Archaeology Report 95.
The conservation of archaeological leather 261
262 Conservation of leather and related materials
Ganiaris, H., Keene, S. and Starling, K. (1982) A Comparison
of Some Treatments for Excavated Leather.
The Conservator, 6, 12–24.
Godfrey, I., Kasi, K. and Richards, V. (2002) Iron Removal
from Waterlogged Leather and Rope Recovered from
Shipwreck Sites. In Proceedings of the 8th ICOM Group
on Wet Organic Archaeological Materials Conference
(P. Hoffman, J. Spriggs, T. Grant, C. Cook, and
A. Recht, eds), pp. 439–467. Stockholm (Bremerhaven).
Goubitz, O. (1984) The Drawing and Registration of
Archaeological Footwear. Studies in Conservation, 29,
187–196.
Goubitz, O. (1997) What is Wrong with Freeze-drying?
In ICOM Working Group on the Treatment of and Research
into Leather, in Particular of Ethnographic Objects
(P. Hallebeek, ed.), pp. 36 –37. ICOM interim meeting,
Amsterdam, April 1995. Paris: ICOM.
Groenman-van Waateringe, W., Kilian, M. and Londen,
H. van (1999) The Curing of Hides and Skins in
European Prehistory. Antiquity, 73, 884 –890.
Health and Safety Executive (2000) Management of
Health and Safety at Work. In Management of Health and
Safety at Work Regulation 1999. Approved Code of Practice
and Guidance L21. HSE Books.
Hilby, G. (1997) Cyclododecan, a Volatile Binding
Medium. Restauro, 2, 96 –103.
Horie, C. (1990) Deterioration of Skin in Museum Collections.
Polymer Degradation and Stability, 29, 109–133.
Hovmand, I. and Jones, J. (2001) Experimental Work on
the Mineral Content of Archaeological Leather. In
Leather Wet and Dry (B. Wills, ed.), pp. 27–36. London:
Archetype.
Ibbs, B. (1990) Shrinkage Calculations. Conservation
News, 41, 7.
Jagers, E. and Hangleitner, M. (1995) Flüchtige Bindemittel.
Zeitschrift für Kunsttechnologie und Konservierung, 2,
385–392. Worms.
Jenssen, V. (1987) Conservation of Wet Organic
Artefacts, Excluding Wood. In Conservation of Marine
Archaeological Objects (C. Pearson, ed.), pp. 122–163.
London: Butterworths.
Jones, A., Jones. J. and Spriggs, J. (1980) Results of a
Marker Trial. Conservation News, 11, 6 –7.
Larsen, R. (1994) Deterioration and Conservation of
Vegetable Tanned Leather. In STEP Leather Project.
Protection and Conservation of European Cultural Heritage
Research Report 1 (R. Larsen, ed.), pp. 165–179.
European Commission, Directorate-General for
Science, Research and Development, The Royal
Danish Academy of Fine Arts, School of Conservation,
Denmark.
Larsen, R. (1995) The Mechanisms of Deterioration. In
Fundamental Aspects of the Deterioration of Vegetable Tanned
Leathers, PhD thesis. The Royal Danish Academy of Fine
Arts, School of Conservation, Denmark.
McGregor, A. (1998) Hides, Horns and Bones. In Leather
and Fur: Aspects of Early Medieval Trade and Technology
(E. Cameron, ed.), pp. 11–26. London.
Montembault, V. (2001) Treatments of Archaeological
Leather in France. In Leather Wet and Dry: Current
Treatments in the Conservation of Waterlogged and
Desiccated Archaeological Leather (Wills, B. ed.), pp. 45–50.
London: Archetype.
Mould, Q., Carlisle, I. and Cameron, E. (2003) Leather
and Leather-working in Anglo-Scandinavian and Medieval
York. The Archaeology of York AY17/16. York: The
Council for British Archaeology, pp. 3227–3231.
Muhlethaler, B. (1973) Conservation of Waterlogged Wood
and Leather. Paris, pp. 25–72.
Omar, S., McCord, M. and Daniels, V. (1989) The
Conservation of Bog Bodies by Freeze-drying. Studies
in Conservation, 34(3), 101–109.
Organ, R. (1958) Carbowax and Other Materials in the
Treatment of Water-logged Palaeolithic Wood. Studies
in Conservation, 4, 96.
Painter, T. (1991a). Preservation in Peat. Chemistry and
Industry, 17 June, 421– 424.
Painter, T. (1991b). Lindow Man, Tollund Man and Other
Peat-bog Bodies: The Preservation and Antimicrobial
Action of Spagnan, a Reactive Glycuronoglycan with
Tanning and Sequestering Properties. Carbohydrate
Polymers, 15, 123–142.
Peacock, E. (1983) The Conservation and Restoration of
Some Anglo-Scandinavian Leather Shoes. The Conservator,
7, 18–23.
Peacock, E. (2001) Water-degraded Archaeological
Leather: An Overview of Treatments used at
Vitenskapsmuseum (Trondheim). In Leather Wet and
Dry: Current Treatments in the Conservation of Waterlogged
and Desiccated Archaeological Leather (B. Wills, ed.),
pp. 11–25. London: Archetype.
Pearson, C. (1987) Conservation of Marine Archaeological
Objects. London: Butterworths, p. 115.
Plenderleith, H.J. and Werner, A.E. (1956) The
Conservation of Antiquities and Works of Art. London:
Oxford University Press.
Raphael, T. (1993) The Care of Leather and Skin Products:
A Curatorial Guide. Leather Conservation News, 9, 1–15.
Rashleigh, P. (1803) Account of a Further Discovery of
Antiquities at Southfleet in Kent, in a Letter from the
Rev. Peter Rashleigh, Rector of that Place, to the Rt. Hon.
Sir Joseph Banks, Bart. K.B.P.R.S. and F.S.A. Archaeologia,
14, 221–223, pl. 38. London: Society of Antiquaries.
Rector, B. (1975) The Treatment of Waterlogged Leather
from Blackfriars, City of London. Transactions of the
Museums Assistants Group, 12, 33–37.
Reed, R. (1972) Ancient Skins, Parchments and Leathers,
p. 267. London: Seminar Press.
Rosenquist, A. (1975) Experiments on the Conservation
of Waterlogged Wood and Leather by Freeze-drying.
In Problems in the Conservation of Waterlogged Wood
(A. Oddy, ed.), pp. 9–23. National Maritime Museum
Monographs and Reports, 16.
Ryder, M. (1984) Skin, Hair and Cloth Remains from the
Ancient Kerma Civilisation of Northern Sudan. Journal
of Archaeological Science, 11, 477– 484.
The conservation of archaeological leather 263
Ryder, M. (1987) Sheepskin from Ancient Kerma, Nothern
Sudan. Oxford Journal of Archaeology, 6(3), 369–380.
Schofield, G. (1996) From Fjord to Wadi. Scottish Society
for Conservation and Restoration Journal, 7, 17–18.
Smith, A. (2000) Down Among the Molecules: Chemical
Analysis in the Study of Historical and Archaeological
Textiles. In Textiles Revealed; Object Lessons in Historic
Textile and Costume Research (M. Brooks, ed.),
pp. 149–150. London: Archetype.
Smith, W. (2003) Archaeological Conservation Using Polymers.
Texas Agriculture and Mining Anthropology Series 6.
Spindler, K. (1994) The Man in the Ice. London:
Weidenfeld & Nicolson.
Spriggs, J. (1980) The Recovery and Storage of Waterlogged
Material from York. The Conservator, 4, 19–24.
Spriggs, J. (1981) The Conservation of Timber Structures
at York – A Progress Report. In Proceedings of the ICOM
Waterlogged Wood Working Group Conference, Ottawa
(D. Grattan, and J. McCawley, eds), p. 149. Canadian
Conservation Institute.
Spriggs, J. (1987) Aspects of Leather Conservation at
York. In Recent Research in Archaeological Footwear
(D. Friendship-Taylor, J. Swann, and S. Thomas, eds),
pp. 43– 46 Association of Archaeological Illustrators
and Surveyors Technical Paper 8.
Spriggs, J. (2003) Conservation of the Leatherwork. In
Leather and Leather-working in Anglo-Scandinavian and
Medieval York (Q. Mould, I. Carlisle, and E. Cameron,
eds), pp. 3213–3221. The Archaeology of York
AY17/16.
Starling, K. (1987) The Conservation of Wet
Metal/Organic Composite Archaeological Artefacts at
the Museum of London. In Conservation of Wet Wood
and Metal (I. MacLeod, ed.), pp. 215–219. Proceedings
of the ICOM Waterlogged Wood Working Group
Conference, Freemantle.
Storch, P. (1997) Non-vacuum Freeze-dry Treatment of
Two Leather Objects. Leather Conservation News, 13/2,
15–17. Minnesota Historical Society/ICOM.
Sturge, J. (1973) The Conservation of Wet Leather, unpublished
dissertation for the Diploma in Conservation,
Institute of Archaeology, London.
Sully, D. (1992) Humidification: The Reshaping of
Leather, Skin and Gut Objects for Display. In The Conservation
of Leathercraft and Leather Objects (P. Hallebeek,
M. Kite, and C. Calnan, eds), pp. 50 –53. London:
ICOM Symposium.
Sully, D. and Suenson-Taylor, K. (1996) A Condition
Survey of Glycerol Treated Freeze-dried Leather in
Long-term Storage. In Archaeological Conservation and its
Consequences (A. Roy, and P. Smith, eds), pp. 177–181.
Preprints of the IIC Congress, Copenhagen.
Sully, D. and Suenson-Taylor, K. (1998) An Interventive
Study of Glycerol Treated Freeze-dried Leather.
In Conference Proceedings of the 7th ICOM Group on
Wet Organic Archaeological Materials (C. BonnotDeconne,
X. Hiron, and Q. Tran, eds), pp. 224 –231.
Grenoble.
Swann, J. (1997) Shoe Conservation: Freeze-drying
Problems? In ICOM Working Group on the Treatment of
and Research into Leather, in Particular of Ethnographic
Objects (P. Hallebeek, ed.), pp. 34 –35. Interim
Meeting, Amsterdam, April 1995. Paris: ICOM.
Thickett, D. and Wills, B. (1996) Report on First Season
Gabati Leather. British Museum Department of Conservation
Internal Report 96/15/O/8.
Turgoose, S. (1989) Corrosion and Structure: Modelling
the Preservation Mechanisms. In Evidence Preserved
in Corrosion Products: New Fields in Artefact Studies (R.
Janaway and B. Scott, eds), pp. 30 –32. United Kingdom
Institute for Conservation Occasional Paper 8.
Turner, R. and Scaife, R. (eds) (1995) Bog Bodies: New
Discoveries and New Perspectives. London: British
Museum.
Volken, M. (2001) Practical Approaches in the Treatment
of Archaeological Leather. In Leather Wet and Dry:
Current Treatments in the Conservation of Waterlogged
and Desiccated Archaeological Leather (B. Wills, ed.),
pp. 37– 44. London: Archetype.
Walker, S. (1990) Corpus Signorum Imperii Romani, Great
Britain II, Fascicule 2, pp. 57–58. Catalogue of Roman
Sarcophagi in the British Museum. British Museum
Publications.
Waterer, J. (1972) A Guide to the Conservation and
Restoration of Objects Made Wholly or in Part of Leather.
London: Bell.
Watkinson, D. and Neal, V. (1998) First Aid for Finds.
UKIC Archaeology Section and Rescue.
Wayne, R., Leonard, J. and Cooper, A. (1999) Full of
Sound and Fury: The Recent History of Ancient DNA.
Annual Review of Ecology, Evolution, and Systematics, 30,
457–477.
Welsby, D. (1998) Soba II: Renewed Excavations Within
the Metropolis of the Kingdom of Alwa. BIEA Memoir,
15, 182–185. London: British Museum Press.
Welsby, D. (2001) Life on the Desert Edge; Seven
Thousand Years of Settlement in the Northern
Dongola Reach, Sudan. Sudan Archaeological Research
Society, 7, London. 450 – 457.
Williams, E., Harnett, L., Bonnot-Diconne, C. and
Barthe, J. (1999) Castor Oil and PEG 400 Followed
by Freeze-drying: Re-assessing Treatment Methods
for Waterlogged Leather. Leather Conservation News,
15(2), 1–10.
Wills, B. (2000) A Review of the Conservation Treatment
of a Romano-Egyptian Cuirass and Helmet Made from
Crocodile Skin. The Conservator, 24, 80 –88.
Wills, B. (2001) Excavating Desiccated Leather: Conservation
Problems on Site and After. In Leather Wet
and Dry: Current Treatments in the Conservation of
Waterlogged and Desiccated Archaeological Leather (B. Wills,
ed.), pp. 51– 62. London: Archetype.
Wills, B. (2002) Windows into Ancient Nubian
Leatherwork. In Le Travail du Cuir de la Préhistoire à
nos Jours (F. Audoin-Rouzeau, and S. Beyries, eds),
pp. 41– 64. Antibes: APCDA.
This chapter offers a selection of case histories of treatments
which were undertaken to a variety of objects
at the Leather Conservation Centre, Northampton,
UK, during the ten years prior to publication of this
book. It is not intended that they be read as an instruction
manual of how to treat similar objects, but rather
to show what has been done to particular objects in
the circumstances which prevailed at the time.
To this end these case histories are published in
the form of conservation reports. It is intended that
they will provide examples of treatments which will
expand on the information given in Chapter 13.
The objects have come from a variety of sources
including museums, historic houses and private
clients. In some cases, where the objects belong to
private clients, they are still in regular use so treatments
have been chosen with this in mind. Recommendations
for aftercare have also been included in
cases where appropriate.
264
23
Case histories of treatments
Staff of the Leather Conservation Centre
Case histories of treatments 265
23.1 The Gold State Coach. 1762
The Royal Collection
LCC Ref: 359–95. Conservator: Theodore Sturge
Date: February 1996
23.1.1 Description
This is the coach that is used on the most important
royal occasions such as coronations. It was built in
1762 and has a leather roof. Originally the leather was
silvered and then lacquered with a crimson glaze
which was built up in five layers. The effect would
have been for it to glitter with a red gold colour in the
sun. Since its original decoration it has been repainted
seven times. The existing top coat consists of gold leaf
which has been varnished. On top of this there is a
laurel leaf decoration in a dark brown glaze which was
sealed with a further heavy varnish. In all, the leather
has had 45 layers of decorative finish applied to it, to
give a total of eight decorative surfaces. As a result, the
paint layer is about 1mm thick.
The paint was sectioned by Jo Darrah of
the Victoria and Albert Museum’s Conservation
Department. She has suggested the following
chronology for the decorative surfaces:
1. 1762 George III’s coronation – Crimson glaze
on silver leaf.
2. 1789 George III’s recovery – Crimson glaze on
pink ochre.
3. 1820 George IV’s coronation – Red glaze on
white.
4. 1830 William IV’s coronation – Red glaze on
dark red.
5. 1837 Victoria’s coronation – Red glaze on red.
6. 1862 Albert, the Prince Consort’s death. – Black.
7. 1887 Victoria’s Golden Jubilee – Red glaze on
crimson.
8. 1901 Edward VII’s coronation – Gold leaf, heavy
varnish.
23.1.2 The problems and the options
Following a very hot summer, cracks in the roof
became significantly worse. A major split had opened
up in the front quadrant where the leather had given
way. There was a smaller split in the rear quadrant. In
addition, there were numerous small cracks in the
surface where the underlying leather was starting to
break down as the weakened fibres pulled apart.
There was some loss of paint associated with these
cracks and splits.
There were two treatment options. One was to
dismantle the roof of the coach and to replace the
leather with new. This would have involved more
than just taking off the original leather. All the decorative
gold cherubs, etc. would have had to have
been removed to give access to the edges and the
fixing points. This would have been very complex
and time consuming. Instead, it was decided to
repair the existing roof.
23.1.3 Treatment
The surface was cleaned with mineral spirits. It was
further cleaned later as part of the consolidation
procedure (see below).
The leather had been stretched over a timber roof
structure but was not attached with adhesive. As a
result, it was possible to insert a patch of polyester
sail cloth behind the larger of the splits (Figure 23.1).
This fabric was chosen because it has good dimensional
stability, resistance to rot, and would not
allow the adhesive to penetrate from one side to the
other. This was important because, if at all possible,
the leather and its patch should not become attached
to the timber underneath. If it had, it would have
restrained further movement. This could have led to
undesirable stresses should there be further changes
to the storage conditions, even if these were fairly
modest. The edges of the split had lifted slightly so
the leather was humidified by laying Aquatex, a
semi-permeable membrane, over the painted surface.
Wet blotting paper was then laid over this.
There were sufficient cracks in the adjacent paint
work to allow the water vapour which passed
through the membrane to relax the leather into its
correct plane. While the leather was still humid,
Vinamul 3254 was inserted between it and the sailcloth
and sandbags were laid on top to hold it in
place as it dried. Vinamul 3254, an ethylene vinyl
acetate copolymer emulsion, was chosen for its
toughness and relative fluidity, which allowed it to
be easily inserted into the rather tight gap between
the sailcloth and leather. The smaller
split proved too tight to treat in this way and was
simply filled, along with the other gaps, as described
below.
The cracks in the paint work were consolidated
with a 5% solution of Paraloid B72 in toluene. This
was flooded into the cracks and the surplus was
cleaned away with swabs moistened with toluene.
This had an additional useful effect in that the overall
paint surface was further cleaned. The aim was
not only to consolidate the cracks and the loose
266 Conservation of leather and related materials
Figure 23.1 Major split in roof and cracks in the paint surface. The sailcloth has been inserted.
Figure 23.2 Filling the split with Beva 371 and a heated spatula.
Case histories of treatments 267
paint, but also the underlying leather. In the areas
under the cracks, the leather fibres were starting to
pull apart and it was hoped that the Paraloid resin
would bond them together, reducing the extent of
the splitting.
The gaps left where the edges of the two larger
splits did not come together completely, the larger
cracks, and the areas where the paint had been lost,
were filled with solid Beva 371. The Beva was made
up using flake metal powders so that the colour was
similar to that of the gold finish. It was applied with
a heated spatula (Figures 23.2 and 23.3).
The inpainting of the fills and the final varnishing
of the whole roof were carried out by Royal
Mews staff. The varnish filled the cracks further,
and probably increased the roof ’s resistance to
water, should it ever be used for a state occasion on
a wet day.
Figure 23.3 The finished repair. Inpainting still to be carried out.
268 Conservation of leather and related materials
23.2 Dog Whip – believed to be
eighteenth century
Private collection
LCC Ref: 354–95. Conservator: Theodore Sturge
Date: September 1995
23.2.1 Description
This dog whip comes from a church in Chesterfield
where it was used to chase dogs out before services.
It has a wooden handle with a leather grip and a raw
hide thong. The thong is attached to the handle
with a raw hide loop bound to the wood with cord.
The thong, although distorted, was intact, but
the loop attaching it to the handle had broken. The
wood was broken under the grip and the end was
missing. The leather grip had dropped off and there
was evidence of past woodworm damage, but this
was old and inactive (Figure 23.4).
The whip was not actively deteriorating, but
there was a risk that loose sections would be lost. In
addition it was not in a fit state to display. As a result
of these needs the work was more akin to restoration
than to conservation.
23.2.2 Treatment
The length of the missing wood was estimated and a
new section was made in pine (Figure 23.5). The
break in the original wood was sealed with a coat the
Vinamul 3254 (EVA vinyl acetate copolymer dispersion
adhesive). This gave a soluble layer which could
be broken down in future should removal be necessary.
The break was very uneven so it was filled with
Ronseal wood filler, a polyester-based filler. The filler
also acted as an adhesive between the old and the new
wood. The new wood was toned down to match the
original with wood stain and water colours.
The broken raw hide loop at the top was replaced
with new raw hide. The cord binding was replaced
as the original was found to be too weak to use
again (Figure 23.6). The new cord binding and raw
hide were toned down with Winsor and Newton
watercolours.
The leather grip was humidified to allow reshaping.
Water was introduced by wrapping Aquatex, a
semi-permeable membrane on fabric, round the
leather and then putting wet paper towel around
this. Water vapour, but not liquid water, penetrated
the membrane and relaxed the leather. The leather
was reattached using a three to one mixture of Lascaux
dispersions 498HV and 360HV (thermoplastic
butyl methacrylate copolymer dispersions thickened
with acrylic butyl ester). The adhesive was applied
at either end, with the centre section left free. The
grip was given a final light finish with British Museum
Leather Dressing (lanolin, beeswax and cedar wood
oil in hexane).
The raw hide thong was humidified and straightened
(Figure 23.7).
Case histories of treatments 269
Figure 23.5 New timber spliced onto handle.
Figure 23.4 Before conservation.
270 Conservation of leather and related materials
Figure 23.6 Replacing the broken raw hide loop on the tip.
Figure 23.7 The finished whip.
Case histories of treatments 271
23.3 Fire Bucket
Private collection
LCC Ref: 549–99. Conservator: Theodore
Sturge
Date: August 1999
23.3.1 Description
This fire bucket was made for the Westminster
Insurance Company, and probably dates from the
eighteenth century. It bears the date 1717 but this
relates to the foundation of the insurance company
rather than to its manufacture. It is 29cm high and
28cm in diameter across the top.
The main body of the bucket is made from two
substantial pieces of vegetable-tanned hide. The sides
are made from a single piece with a vertical sewn
seam, and the base from a separate piece, also sewn.
The rim is reinforced with a half round timber lath
over which leather has been moulded and then
sewn. Two leather loops, which pass down the outside
of the top edge and behind the lath, are sewn to
the main body. These contain iron rings which, in
turn, hold the handle. The interior of the bucket is
coated with pitch and the outside painted black.
The painted crest of the company is on the front, as
is the date 1717.
The bucket was in poor condition (Figure 23.8).
Almost half of the lath was missing. Part of the
leather covering for the lath was hanging off, and
about half was missing. Adjacent to this, there was a
hole in the main body of the bucket and about
100cm2
of leather was missing. The handle itself
was made with multiple pieces of leather sewn
together. This was intact but some of the stitching
had broken down. The loops of leather attaching
the iron rings for the handle to the bucket were in a
fragmentary state and had lost their strength.
23.3.2 Treatment
The whole bucket was surface cleaned with Wishab
sponges followed by damp swabs. The crest was
cleaned with isopropyl alcohol. As with all painted
surfaces, great care needed to be taken when cleaning
with solvents and careful testing was vital. Some
fire buckets, but not this one, are decorated with
transfers rather than paint. If this is the case, it is
likely that very little cleaning will be possible.
The leather adjacent to the area of loss was consolidated
to give a sound surface to enable the repair
to be attached. A 10% solution of Paraloid B67 in
white spirits was chosen as a high level of flexibility
was not needed, and the high glass transition temperature
of this acrylic resin ensured that it did not
have a tacky surface. The same solution was used to
consolidate the paint adjacent to the lost leather and
the pitch on the interior.
The missing section of wooden lath on the rim
was rebuilt using laminated balsa wood. The layers
were shaped using a violin maker’s bending iron and
bonded together with the Lascaux acrylic dispersion
498HV. The laminated balsa was then shaped to the
correct profile (Figure 23.9). Balsa worked well as it
was easy to bend and cut to shape and the laminated
structure was quite strong compared with balsa
wood on its own. Once the lath was in place, the
loose leather was reattached with more of the
Lascaux adhesive. The missing sections of leather in
the main body of the bucket were filled with solid
Beva 371 to which pigment had been added. This
was built up and bonded to the original using a
heated spatula (Figure 23.10). The original plan was
to use vegetable-tanned hide but it proved impossible
to mould it satisfactorily and cut to fit it to the
complex shape. The exposed lath was covered with
new vegetable-tanned calfskin (Figure 23.11). The
lath and surrounding leather were covered in cling
film to keep them dry while the new leather was
thoroughly wetted and moulded around the lath.
When dry, the new leather held its shape and was
trimmed to size and bonded into place with the
Figure 23.8 Before conservation.
272 Conservation of leather and related materials
Figure 23.9 The new section of lath for the rim built up in balsa wood.
Figure 23.10 Building up the missing section with solid Beva 371 and a heated spatula.
Case histories of treatments 273
Lascaux dispersion. The original had a very heavy
layer of paint on it and when the new leather was
painted to match the grain texture showed through.
The thick paint on the original was therefore replicated
by working solid Beva into the surface of the
new leather with a heated spatula. The Beva fill was
then painted to match the original using artists’
quality acrylic paints with a final coat of gum arabic
toned with Winsor and Newton watercolours to
give a suitable glazed finish.
The weak sections of the handle were reinforced
by inserting new vegetable-tanned calf between the
layers and then replacing the missing stitching using
the original holes.
The bucket was to go into an environment where
it was likely to be handled by untrained staff so it
was very likely that it would be lifted by its handle.
The original disintegrating loops used to hold the
handle to the main body were so damaged that it
was felt a satisfactory, strong repair was impossible.
As a result they were replaced using new leather
stitched into place through the original holes.
Although the work was not for a museum, the
owner still asked for a minimum level of intervention
consistent with the handling demands of the
object. Full inpainting of the missing areas of the
crest was therefore not carried out. Instead, only a
minimum consistent with making the image readable
was done. This was carried out with Winsor
and Newton watercolours.
The exterior of the bucket was lightly finished with
Renaissance micro-crystalline wax polish and the handle
was lightly dressed with Pliantine (Figure 23.12).
Figure 23.12 The finished bucket.
Figure 23.11 New calfskin moulded to fit the rim.
274 Conservation of leather and related materials
23.4 Fireman’s Helmet
Private collection
LCC Ref: 549–99. Conservator: Theodore Sturge
Date: August 1999
23.4.1 Description
This early helmet, one of four, is probably eighteenth
century. It is made from degrained, vegetable-tanned
cattle hide, except for the hatband which is vegetabletanned
sheepskin.
The main shell has been moulded in two halves
and then sewn together. The joint was thickened to
increase its strength, with a rope-like material. The
wide brim was sewn into place. Inside there was a
label, apparently giving the name of the owner.
Each hat had a different name.
The main body of the helmet was in good
condition, but the brim was in poor condition
(Figure 23.13). Its pH was 2.5, and it was suffering
from severe red rot. Diluting the test solution ten
times gave a pH of 3.5, indicating that damaging
strong acids were present. The hatband was also suffering
from red rot.
23.4.2 Treatment
Initially, the whole hat was cleaned with a soft brush
and a vacuum cleaner. Further cleaning was carried
out with Wishab sponges. These soft sponges crumble
with the dirt sticking to the fragments which are
brushed and vacuumed away. However, they need
to be used with care, as on a fragile surface they can
cause damage and remove flakes.
The red rot on the rim and hatband was treated
with a 1% solution of aluminium alkoxide in mineral
spirits. The leather was saturated and then the excess
was blotted off with paper towels. This latter process
is important, as if there is an excess left on, an insoluble
white deposit can remain on the surface. This is
very difficult to remove once it forms. After treatment
the pH had increased to 3.8, well above the
figure of 3.0 usually regarded as the pH below which
leather is unstable.
The fragile rim was consolidated with a 3% solution
of Pliantex, a flexible acrylic resin, in toluene.
Although this consolidated the body of the leather,
it did not hold the flakes in place. These were
reattached by inserting an acrylic dispersion, Lascaux
498HV and 360HV in a 3:1 mixture, under each
loose flake, and then pressing them into place.
Because it is in the form of a dispersion rather than
a solution, the adhesive does not soak into the
leather. As a result, it holds the flakes well.
The hole in the rim was filled with new vegetabletanned
calfskin coloured with Sellaset dyes. This
was butt jointed to the original leather. As this was
not a strong join it was reinforced with suitably
coloured Stabiltex (polyester) fabric. Beva film was
used as an adhesive. This was first applied to the
Stabiltex, which was then cut to size and applied to
the join. The bond is made with an electric-heated
spatula. Stabiltex and Beva film were also applied
across the splits in the rim. Stabiltex was chosen for
its strength and relative transparency, which made a
discreet repair possible.
The areas on the rim where the grain surface had
been lost were coloured with Sellaset dyes. This was
applied locally with a brush to tone the damage in
with the surrounding colour. A final light finish was
applied to the entire helmet using Renaissance microcrystalline
wax polish (Figure 23.14).
Case histories of treatments 275
Figure 23.14 After conservation.
Figure 23.13 Before conservation.
276 Conservation of leather and related materials
23.5 Leather Lion
Private collection
LCC Ref: 397–96. Conservator: Ian Beaumont
Date: October 1996
23.5.1 Description
This lion was made by H.E. Jackman in 1950. It was
designed to sit on a mantelpiece or desk. The core
was a coarse white material, probably plaster of Paris.
This was reinforced with a steel wire armature. The
vegetable-tanned leather had then been moulded
over the core, presumably while wet. There were
some joins in the leather under the chin and around
the mane. The leather was a natural brown in colour.
The leather was, in general, in good condition. It
had been handled over the years, leaving a smooth
surface and some slight soiling. The main damage was
to the end of the tail where a section of the leather
and core were missing (Figure 23.15) and to the front
left paw which was also missing (Figure 23.16). There
was also some damage to the back left paw.
Figure 23.15 Before conservation, note damage to tail.
Figure 23.16 Before conservation, note missing front paw and damage to rear paw.
Case histories of treatments 277
Figure 23.18 After conservation.
Figure 23.17 Modelling a new core for the front paw.
278 Conservation of leather and related materials
Figure 23.19 After conservation.
23.5.2 Treatment
The missing sections of the core were built up with
Milliput, an epoxy putty (Figure 23.17). The surface
of the original plaster was friable so it was consolidated
with 5% Paraloid B72 in toluene to give a sound
surface for the Milliput to bond to. The Milliput was
chosen as it bonded well to the original core and it is
easy to model as it cures. The shape of the paw was
outlined on the base and this was used as a guide.
The areas where the leather was missing were
re-covered with new vegetable-tanned calfskin. When
wet, vegetable-tanned leathers usually mould well.
In this case, the leather used was very thin, 0.8mm,
and it took the impression of the underlying core
very well. It was even possible to work it into the
claws of the lion so that they showed on the front. It
is helpful to continue to work the leather as it dries.
When part dry it often reaches a stage where it is
almost ‘cheesy’ in consistency and it can be pushed
into shape with tools such as bone folders. Once
dry, the shape will be held.
The dry moulded leather was attached to the core
with a mixture of acrylic emulsion adhesives,
Lascaux 498HV and 360HV, in a 3:1 ratio.
The whole lion was lightly cleaned and polished
with Renaissance micro-crystalline wax polish. The
new sections were toned down by adding dry pigments
to the wax. This was applied only to the new
leather. Pigments in wax were chosen, rather than
dye, as it was a surface patination that was required
rather than an in-depth colouring of the leather
(Figures 23.18 and 23.19).
Case histories of treatments 279
23.6 Sedan Chair
Private collection
LCC Ref: 416–97. Conservators: Theodore Sturge
and Nina Frankenhauser
Date: July 2000
23.6.1 Description
This eighteenth century sedan chair was conventionally
constructed with a wooden frame, the outside of
which was covered in vegetable-tanned, black, patent
leather calfskin. The inside was covered with textiles.
It was approximately 170cm high, 81cm wide and
94cm deep (Figure 23.20).
The leather was attached with dome-headed
brass tacks arranged to give a simple decorative
border.
The windows, which could be lowered on braided
straps, were framed with a smooth finished gilt timber
subframe. Around the windows and along the
top, just beneath the roof, there was a carved gilt
wood trim.
The leather was chemically stable and reasonably
strong. The patent leather finish was in good
condition except for a few vertical lines on the
sides, apparently caused by a liquid running
down. However, it had split in a number of places
both on the flat sides and on the concave segments
of roof. There was some distortion associated with
the splits.
The gilt areas were in good condition except for
some fairly light soiling and some worn areas on the
highest points.
The textiles on the inside were heavily soiled
and one of the straps for lowering the window had
broken at the point where it joined the sash frame.
23.6.2 Repairs
The leather was repaired using three different techniques.
The method chosen for each repair depended
on two factors: the availability of access to the back
of the leather, and whether or not the leather was
flat, as on the vertical surfaces, or curved, as on the
roof. In addition, three different repair materials
were used, leather for larger repairs to flat areas,
Reemay for smaller ones on flat areas, and cast GRP
(Glass Reinforced Plastic/fibreglass) for the curved
areas on the roof. The only areas where there was
any access to the back of the leather without going
through the split were in those places where the
interior fabric had come away partially. This did not
give full access, but it did allow some unwanted
materials used during the repair work to be removed
when the work was finished.
Where there was access to the back, a card sandwich
was used. This was used with both leather and
Reemay as a repair material. The sandwich was made
up with stiff card on the outsides, two layers of silicone
release paper and the repair material in the middle.
A tracing of the split was made on Melinex and
this was used to pierce pairs of holes along the line of
the split. Loops of strong thread were passed through
the holes and tied loosely. The back piece of card, silicone
release paper and the repair material were
inserted through the split and then drawn up into
position using the threads. Adhesive was then inserted
between the repair material and the back of the
leather. This was a mixture of acrylic dispersions,
Lascaux 498HV and 360HV, in a 3:1 ratio and was
chosen as it does not grab quickly and thus allows
time for the repair to be manoeuvred into position.
Once the position was correct, the outer silicone
paper and card were slid into place down the thread
which was cut and then retied close to the leather.Figure 23.20 The chair, after treatment.
280 Conservation of leather and related materials
Wedges were then inserted in the loops to pull them
tight and hold the sandwich tightly together (Figure
23.21). Once dry, the thread was cut and pulled out
through the card. The card and silicone release paper
were removed from the front and back. In places
where the card on the inside would drop into an
inaccessible space, it was found helpful to tie a thread
to the corner prior to insertion and bring this out
through a suitable gap. This allowed the card to be
retrieved.
In areas where the card could not be readily
removed from the inside, a low pressure suction box
was used (Figures 23.22–23.24). This was simple in
construction. It was a sealed box with a perforated
steel face on one side. The box was connected to a
variable speed vacuum cleaner. The repair material,
usually leather, was slipped behind the split and held
in position with a thread brought out through the
split. Once the repair was in place, and the Lascaux
adhesive inserted, the low pressure box was placed
over the area being repaired. This sucked the original
leather onto its front face ensuring it was flat,
and the air being drawn through the split held the
repair onto the back of the leather. It was then left
under low suction to dry. There was a small risk that
adhesive would be drawn out onto the front face of
Figure 23.21 The repair sandwich held together with
wedges.
Figure 23.22 Low pressure suction box.
Case histories of treatments 281
the suction box. To avoid any risk of the leather
sticking to the metal, a sheet of Reemay was taped
over the perforated surface. The advantage of this
method was that no unneeded materials remained
on the back, so completely blind repairs were possible.
However, the system with card does ensure
that the patch is in good contact with the back.
Both hold the leather flat during the repair which
helps to ensure a minimum of distortion.
The roof required a radically different approach as
the leather was curved and there was no access to the
back (Figure 23.25). The varying curvature made a
low pressure box impracticable, and the card sandwich
will not work without a flat surface. A curved
repair piece was required which could be inserted.
Moulded leather was considered but it was not felt to
be stiff enough to hold against the underside. Instead,
a glass fibre reinforced polyester (GRP) repair piece
was made to fit each split. These were stiff enough to
be held in place, but slightly flexible, allowing them to
adjust slightly to fit. To obtain the correct shape, plaster
of Paris was cast onto an undamaged section of
roof with a similar curvature. While this was being
done, the surface of the leather was protected with
cling film. Fortunately, a second chair with an identical
framework and shape was in the workshop.
Although this too needed some roof repairs, it provided
an extra opportunity to cast plaster of Paris to
Figure 23.23 Damage before repair using low pressure suction box.
Figure 23.24 Damage after repair using low pressure suction box.
282 Conservation of leather and related materials
Figure 23.25 The roof, before treatment.
match damaged areas. The curvature was then
adjusted if necessary. The surface of the plaster was
waxed and the GRP was cast onto it using 1oz/sq.ft
(300g/m2
) chopped strand fibreglass mat and Trylon
SP701PA polyester lay-up resin. The resulting patch
was trimmed and degreased with acetone. The patch
had loops of strong thread passed through it on the
line of the split (Figure 23.26). These were used to
hold the patch in position by attaching them to elastic
bands suspended from the ceiling (Figure 23.27). This
held the patch securely against the back of the leather
while it was attached with the Lascaux acrylic
Figure 23.26 Positioning the GRP repairs with threads.
Case histories of treatments 283
mixture. Contact was improved by inserting wedges
and pressing the leather down with sandbags. There
was some distortion to the leather so it was humidified
by laying Aquatex covered with damp paper towel
over the distorted edges. This was done prior to the
application of adhesive but with the supporting GRP
in place.
23.6.3 Cleaning
The surface of the leather was cleaned with a cloth
and white spirits. No way was found to remove the
vertical runs. It was thought this might be blanching
from water and that it might be possible to reform
the surface with solvent. However, no suitable
solvent could be found for this, or to remove
the runs.
The carved gilt wood was lightly cleaned with a
50/50 mixture of water and white spirits emulsified
with 1% non-ionic detergent. This cleaned the surface
safely but care needs to be taken if water-based
cleaning is used on gold in case it is bonded to the
wood with a water soluble adhesive. As always,
cleaning tests are essential.
The fabric on the interior was cleaned with a soft
brush and a low powered vacuum cleaner. The
broken strap was repaired by adding new fabric which
was both sewn and adhered with the Lascaux mixture.
It was then reattached with the original nails.
Figure 23.27. The GRP patch held in place with
elastic bands. Also shows smaller patch prior to insertion.
Figure 23.28 The finished roof complete with Beva fills.
284 Conservation of leather and related materials
23.6.4 Gap filling and finishing
The two holes were filled with new vegetabletanned
calfskin dyed with Sellaset dyes. The larger
gaps in the splits were filled with pigmented solid
Beva 371 applied with a heated spatula (Figure 23.28).
Care was taken that it was melted right down into
the split to ensure a good bond. If the heating is too
superficial, a bond only forms on the top surface
and it can pull away. The fine gaps in the splits were
filled with Aquafil 945, an acrylic filler. This was
coloured, prior to application, with artists’ quality
acrylic paints. This filler dries by evaporation and
there is some shrinkage. As a result it is not suitable
for larger areas of damage.
The areas where the black finish had been lost
and the underlying brown was showing through
were inpainted with Sellaset dyes. The fills were
inpainted with Winsor and Newton watercolours.
The whole of the outside was polished with
National Trust furniture polish. No dressing was
applied as this could soften and damage the finish.
Case histories of treatments 285
Figure 23.29 Before conservation.
23.7 Jewellery Box
Private collection
LCC Ref: 593–00. Conservator: Theodore Sturge
Date: May 2000
23.7.1 Description
The outside of this box was covered with a red,
vegetable-tanned, sheepskin skiver. The top was
padded and slightly domed. Inside there was a liftout
tray. Both this and the inside of the top and bottom
of the box are lined with red velvet. The box is
20.4 ϫ 13.8 ϫ 9.5cm and is probably twentieth
century.
The red skiver was very thin, and over the top it
had split and pulled away with about 7cm2
missing.
In addition, the surface was scuffed and a strip of
adhesive tape had been fixed to the surface and then
pulled off. Both these had exposed the underlying
brown colour of the leather (Figure 23.29).
23.7.2 Treatment
There were two aspects to the treatment of the
leather: repairs to the splits and filling the gaps. The
principal problem was that the leather was very thin,
and any repair had to be light enough not to show
through. In addition, some of the splits ran along
the edge where the leather folded over the top and
down the side. The leather on the sides was very
well attached. To repair these areas, the leather
needed to be eased away from the wood so that a
repair material could be inserted behind it. Because
the leather was very thin and well attached to the
wood, there was a danger that the repair material
would show through on the outer surface. Leather
was felt to be too bulky so a fine Japanese tissue
paper was used for most of the work. Before use,
this was coloured with a dilute wash of artists’ quality
acrylic paint. This was matched approximately
to the colour of the leather, so that if a sliver showed
through a crack it would be unobtrusive. Had white
tissue paper been used it would have caught the
eye. To keep the thickness down an adhesive with
low bulk was needed. After testing to ensure that
the red colour of the leather would not be affected
by water, wheat starch paste was selected. If the two
surfaces to be joined are clean and reasonably
smooth, and both are of natural materials,
wheat starch paste can give a very strong bond. In
addition, most of its bulk is water so the adhesive
adds little to the overall thickness, and does not
stiffen it significantly either. The disadvantage of
wheat starch paste is that its high water content can
overwet the leather unless it is used very sparingly.
Because the top was curved by the padding, it
was not practical to repair all the splits with a single
piece of tissue paper. Instead, the splits were systematically
joined with smaller pieces until there was, in
effect, a single flap of leather. The gaps were then
filled. The leather had an unusual finish which it was
impossible to match. Initially, it was thought that
suitably coloured Japanese tissue paper would be
more appropriate than a non-matching leather
which could look obtrusive. However, in practice, a
fine, dyed, vegetable-tanned sheepskin skiver proved
a more appropriate choice. Patches of this were
placed on the back of the leather so that they filled
the gaps. These were attached with an acrylic emulsion
286 Conservation of leather and related materials
Figure 23.30 After conservation.
mix, Lascaux 498HV and 360HV, in a 3:1 ratio.
Finally, the resultant large flap of leather was secured
around the edges using leather or tissue paper, as
appropriate, to bridge the gap. Where necessary the
leather on the sides of the box was eased away, so
that the repair material could be inserted behind it.
The areas where the surface of the leather had
been lost, exposing the brown underneath, were
inpainted with a Sellaset dye mix. This was done with
a fine brush so that it was only applied to the damage.
If the dye solution spreads onto the sound surface it
often does not ‘take’ and ‘bronzing’, a visual effect
similar to oil on water, forms. This can be very difficult
to remove although isopropyl alcohol may be
effective. It can be difficult to match the colour exactly.
If the dye is too bright it will make the inpainting
obtrusive. It is better if it is a little duller in colour
than the original so that the eye is drawn to the original
rather than the inpainting.
A final finish of leather balm, a wax emulsion,
was applied to the outside (Figure 23.30).
Case histories of treatments 287
23.8 Dining Chairs
Private collection
LCC Ref: 539–99 and 521–98. Conservators: Ian
Beaumont and Theodore Sturge
Date: November 1999
23.8.1 Description
Three sets of chairs are discussed in this case study.
Their needs were very different, as were their treatments.
Two of the sets, both Victorian, belonged to
a single owner. One was in relatively poor condition
and it was to be used on a daily basis. The
owner was clear that these should be re-covered to
give a usable set of chairs. The second set was to be
used less regularly and although worn, conservation
was a viable long-term option. The third group
came from a larger set of late eighteenth century
chairs, the majority of which were in good condition.
However, four of the seat covers were worn and
split, and the underlying upholstery was in need of
attention. These chairs were to be used and a reasonably
robust repair was needed that would not
affect their overall appearance relative to the untreated
chairs in the set.
23.8.2 The set of eight chairs for
reupholstering
The original vegetable-tanned goatskin appeared to
be dark green. However, when the leather was
taken off the chairs, hidden unfaded areas were
found to be a dark royal blue. The panels on the
backs were embossed in gold with the family crest
and monogram. The leather was extensively split,
there were missing areas, self-adhesive tape had been
applied to the surface, and it had been overdressed
leaving it feeling damp and sticky (Figure 23.31).
Figure 23.31 Chair prior to reupholstery. Note the
extensive use of tape used for previous repairs.
Figure 23.32 The reupholstered chair.
288 Conservation of leather and related materials
23.8.2.1 Treatment
The chairs were stripped of their leather and existing
upholstery. The underlying upholstery was kept
and as much of it as possible was reused during the
subsequent reupholstery so that the shape and look
of the chairs would be retained.
The leather was replaced with vegetable-tanned
hair sheep dyed to match the original royal blue.
This was used in preference to goat as larger sizes
are more readily available. Its visual appearance and
strength are very similar to that of goat, and it is a
much more robust material than wool sheep. The
crest on the back was reproduced. One of the existing
crests was scanned and the artwork re-established
by hand. This was used to make an embossing plate.
To increase the durability of the gold embossing, it
was carried out using looseleaf gold rather than the
thinner gold film. This was more time consuming
and expensive, but the increased thickness should
ensure a longer life. The resultant chairs were suitable
for heavy use (Figure 23.32).
23.8.3 The set of eight chairs repaired
without removing the covers
The seats of these Victorian dining chairs were
upholstered in vegetable-tanned goatskin which had
faded from royal blue to green. The tops were
deeply buttoned with leather-covered buttons.
The condition of the chairs varied considerably.
Four of them had been treated on a previous occasion
by another workshop. There were no details of
this treatment available, but it included refinishing
with a green-pigmented surface coating. The damage
included splits, particularly on the front corners,
loss of leather associated with some of the splits,
splashes of paint and missing buttons. In addition,
there were flaps of loose grain surface and flakes
coming away. These were exposing the lighter colour
of the underlying corium (Figure 23.33).
At some time, the leather on all the chairs had
been given a heavy coat of wax polish. The webbing
underneath was also starting to break down on most
of the chairs.
23.8.3.1 Treatment
To ensure that the underlying upholstery was sound,
all the chairs had an additional layer of webbing
applied to the underside. This was placed over the top
of the existing webbing. In this way the seat was made
structurally sound but the original was not lost.
The splits were repaired with 0.5mm vegetabletanned
goatskin. This was dyed with Sellaset dyes,
and was used both to repair the splits and to fill any
gaps where the leather was missing. This was chosen
because it matched the original well, and it was still
strong when reduced to this thickness. Some
leathers, when reduced in thickness, lose their
strength as the longer, stronger, bundles of fibre on
the flesh side are removed. If the leather is too thick
or springy, it does not blend in so well and the repair
becomes cumbersome, may not bond well, and can
show through onto the front. The repairs were
bonded into place with Hewit Reversible PVA adhesive
M218. This was selected for its high tack which
assists in the positioning of awkward repairs. The
M218 adhesive was also slipped under the flaps and
flakes of loose grain surface so that they could be
pressed back into place.
Figure 23.33 Chair prior to repair without removal of
cover.
Case histories of treatments 289
The areas where the leather surface had been
scuffed or flakes had been lost were light in colour.
These were inpainted with Sellaset dyes to reduce
the visual impact of the damage. A final finish of
SC6000, an acrylic resin and wax mixture, was
applied to all the leather. This consolidated the surface,
re-established a finish in those areas where it
had been lost, and drew the overall appearance
together (Figure 23.34). SC6000 needs to be used
with care. The result can be overshiny or uneven, so
careful testing, as with all finishes, is essential. In
addition, it contains isopropyl alcohol which may
dissolve the existing finish.
23.8.4 The four chairs where the covers
were removed and conserved
These chairs were part of a large set. The leather on
the rest of the chairs, although worn, was still intact
and the requirement was for the conserved leather
to match the untreated seats. The vegetable-tanned
goatskin was heavily worn, and much of the red
surface finish was missing. There were also areas,
particularly on the corners, where the leather had
split and, in some areas, adjacent leather had been
lost. The leather was no longer strong enough to
stand being restretched onto the new upholstery
(Figures 23.35 and 23.36).
23.8.4.1 Treatment
The leather was carefully removed from the chairs.
The dome-headed nails attaching it were difficult to
remove without damaging either them or the
leather. A decision was made to sacrifice the nails to
protect the leather.
The back of the leather was cleaned with Wishab
sponges to give a clean surface for repair. Where
there were gaps these were filled with new vegetabletanned
goatskin applied to the back (Figure 23.37).
The new leather was initially dyed with Sellaset
dyes. The burgundy colour, and the finish, were
broken by lightly sanding the surface with fine glass
paper. It was further adjusted by applying a second,
darker dye on a cotton wool swab. These were
damp, rather than wet, and gave a mottled effect.
The splits where there was no loss were repaired
Figure 23.35 Chair prior to removing cover.
Figure 23.34 Chair after conservation.
290 Conservation of leather and related materials
Figure 23.37 The back during repair showing the leather repairs in the areas where the leather was missing and the
Cerex repairs to the splits.
Figure 23.36 Detail of damage prior to removal of cover.
Case histories of treatments 291
with localized patches of fine Cerex, a non-woven,
nylon fabric (Figure 23.37). The entire back of the
leather was then covered with more Cerex. Cerex is
quite soft and flexible and can be worked onto an
uneven surface. However, to aid application, it was
applied in large strips. These went over the whole
surface, including the leather and localized Cerex
repairs, and extended beyond the tacking edges
(Figure 23.38). This surplus was left in place to give
the upholsterer an edge to pull on. It was trimmed
off after the leather had been replaced on the seat.
Cerex was chosen in preference to Reemay or a
woven fabric, because of its softness and low bulk.
Both the patches and the full lining were applied
with a mixture of Lascaux acrylic dispersions, 498HV
and 360HV, in a 3:1 ratio. This was flexible, wetted
out the Cerex well and could be brushed out to a
thin layer. The lined leather was still soft and flexible
enough to be replaced on the chairs, but had
sufficient strength to withstand some use. The overall
appearance had not changed relative to the
untreated chairs in the set. Because the chairs had to
match the rest of the set, the worn surface was not
restored in any way. No dye was applied to the areas
where colour was lost and no surface finish or dressing
was added (Figure 23.39 and 23.40).
23.8.5 Overview
These three treatments were very different, but were
each legitimate in their own context. None of the
items belonged to a museum or was to be displayed
in an historic house. Instead, they all came from private
owners, and their needs were not the same.
Indeed, two of the sets came from a single owner and
her requirements varied. Unless they are in an environment
such as a museum, chairs usually need to be
functional, and the treatment should reflect this.
Although replacing the leather on chairs as a routine
treatment is to be discouraged, there are occasions
when it may be necessary, and a purist conservation
philosophy is inappropriate. Factors which need to
be considered include the rarity and value of the
chair, the use to which the chair is to be put, the
room setting in which it is to be used, and the viability
of preserving the existing leather. The cost of the
work may also be relevant. The cost of conservation
often exceeds that of re-covering, and may significantly
exceed the value of the chair itself. Where a
chair has been in a family for a long time, the value
of the object relative to the cost of conservation may
not be an issue. But if the chairs have been bought
recently, and there are no emotional ties, a more
pragmatic approach by the owner is likely.
Figure 23.38 The finished back with the full Cerex lining.
292 Conservation of leather and related materials
Figure 23.39 The finished chair.
Figure 23.40 Detail of repaired seat.
Case histories of treatments 293
23.9 Alum Tawed Gloves, having
belonged to Oliver Cromwell
Private collection
LCC Ref: 607.00. Conservator: Ian Beaumont
Date: March 2001
23.9.1 Description
The gloves date from the mid-to late seventeenth
century, and are made from alum-tawed lambskin,
the traditional glovemaking leather. The leather has
been stained a buff colour on the grain, leaving the
suede flesh side white. The gloves have been sewn
inside out and then turned right side out. The cuffs of
the gloves have been pierced to look like lace work.
This may have been done by hand but it is more
likely that the leather has been cut with a blade
shaped to the lace design. There are traces of an adhesive
on the turned face of the cuff. This would suggest
that there had been something bonded to it at some
time. Under the microscope the fibres of what could
have been a pink or blue textile could be seen. The
gloves measure 220mm in length and 95mm in
width.
23.9.2 Condition
While the general condition of the gloves was quite
good, they had sustained some damage (Figure 23.41).
Most of this was confined to the cuff area of the
gloves. This was associated with the very delicate
nature of the lace work.
The left-hand glove had a large area of the underside
of the lace work cuff missing. This also included
quite a large area of the glove itself, underneath the
turned cuff. There was also a small area missing
opposite this large missing area. There had been
some attempt in the past at repairing the damage
with a cotton thread that had been wound around
the leather lace work.
The right-hand glove was in better condition in
that it was complete. There were though many
breaks in the leather lace work.
The gloves were very flat having been stored in
the same position for a long time and in both cases
the cuffs were very misshapen.
Although the gloves were soiled this was dirt that
they had acquired during their useful life and not
while in storage.
23.9.3 Treatment
23.9.3.1 Removal of old repairs
It was necessary to remove previous restoration before
treatment could commence. The cotton thread was
removed from around the leather lace work and
where it had been stitched through the glove itself.
23.9.3.2 Reshaping
The leather was humidified in order that the gloves
could be reshaped. This was done using a Gore-Tex
membrane which allows water vapour to enter the
leather without exposing it to water droplets. The
lace work was repositioned and allowed to dry in
the correct position.
Figure 23.41 Gloves before treatment.
294 Conservation of leather and related materials
23.9.3.3 Repairs
The breaks in the lace work were repaired using very
small pieces of alum-tawed lambskin leather, which
had been skived down to a very fine substance. This
was bonded across the breaks with wheat starch
paste. After drying, the repairs were in painted with
Windsor and Newton watercolours (Figure 23.42).
The large missing area was replicated from a similar
piece of alum-tawed leather, which had been
dyed to match the original with Windsor and
Newton watercolours. This was also bonded into
place with wheat starch paste.
23.9.3.4 Second reshaping
The gloves were humidified a second time to allow
the cuffs to be turned and to re-establish their original
turn-back folds.
23.9.3.5 Mounts
Perspex mounts were made to support the gloves,
the fingers of which were filled with acid-free rolls
to keep them in a more natural shape. The mounts
are not just for display, they can and should be used
for handling and storage purposes (Figure 23.43).
23.9.4 Future care
On no account should any kind of leather dressing
be applied to the gloves. The leather is supple and in
good condition. They should not be handled unless
absolutely necessary. Should they need dusting this
should be carried out with a pony hair brush. They
should be kept in a stable environment and not
exposed either to high or to low humidities. High
humidity is especially dangerous as this can encourage
mould growth.
Figure 23.42 Replicated leather lace work being fitted into place.
Case histories of treatments 295
Figure 23.44 Detail of replicated leather area.
Figure 23.43 Finished and mounted gloves.
296 Conservation of leather and related materials
23.10 Court Gloves
Private collection
LCC Ref: 435–97. Conservator: Theodore Sturge
Date: August 1998
23.10.1 Description
There were two pairs of full length, white leather
gloves. They were probably mid-twentieth century.
One pair was finished with the grain side out and
the other was suede finished. There were buttons at
the wrist (Figure 23.45). On the inside were maker’s
marks in purple ink.
Both pairs of gloves were soiled. The grain-out
pair had a crease down either side and this was particularly
dirty. There were some small splits between the
fingers adjacent to the stitching, where the leather
had given way.
23.10.2 Treatment
These gloves may originally have been designed to
be washed. However, in gloves of this type the
leather has often aged to a point where this is no
longer safe. Examples have been seen where washing
has left them split, heavily distorted and beyond
rescue. However, non-polar solvents are usually
safe. If there are, as here, any maker’s marks present,
they must be tested very carefully to see if these will
run. In addition, the solubility of the buttons in the
cleaning solvent should be checked.
Most of the heavy soiling along the fold was
cleaned off with a soft pencil eraser. However, the
amount of cleaning that was possible was limited by
the fragility of the grain surface, which tended to lift
if too much work was done on it.
Both pairs were cleaned by immersing them in
odourless mineral spirits. This was chosen in
preference to white spirit because it does not have a
lingering smell as it dries. However, it is not as efficient
a solvent for some elements of the soiling as
white spirits, as it contains less aromatic hydrocarbons
and its effect was rather limited, especially on the
sueded pair. As a result, on this pair, white spirits was
used as well. This still did not clean very well and, as a
last resort, a small amount of non-ionic detergent was
added to the white spirits. The detergent is a concentrated
solution in water, so this added a small amount
of water. The polar water, combined with the detergent,
worked well and much of the dirt was removed.
It must, however, be stressed that the use of water in
this way bears a high risk and all concerned should be
aware that the object could be in jeopardy.
When white gloves like these are immersed in solvent
they become translucent and orange/yellow in
colour. Faults in the skin may become visible, and
imprints such as the purple maker’s mark show
through to the outside. In all cases where gloves such
as these have been cleaned in this way at the Leather
Conservation Centre, the opacity of the leather has
returned on drying, but again, a small test is advisable.
After cleaning, the gloves were dried flat. They
were laid on absorbent paper towel which drew
most of the solvent out of the leather. In the early
stages of drying the paper was changed frequently.
The splits were repaired with very fine white silk
fabric. This was pre-coated with a mixture of Lascaux
acrylic dispersions, 498HV and 360HV, in a 3:1
ratio. When this was dry, the patch was cut out with
the bias along the line most likely to be stretched.
The Lascaux can be used as a heat-sensitive adhesive.
In this case it was fixed into position on the inside
with an electric-heated spatula. A heat-sensitive adhesive
was used because it enabled the spread of the
adhesive to be controlled. It also gave a very rapid
bond. This made the rather awkward location inside
the gloves easier to work on as the repair could be
held in place for the short period while it cooled.
Figure 23.45 The grain-out gloves after treatment.
Case histories of treatments 297
Figure 23.46 The components for the mount made from Plastazote foam and a cable tie.
23.11 Mounting of a Collection of
Flying Helmets
Museum collection
LCC Ref: 793–03. Mounts made by Ian Beaumont
Date: September 2003
23.11.1 Description
A collection of military flying helmets and accessories
from the twentieth century collected from
British and foreign sources. These were made from
a variety of leather types. It was requested that after
conservation each be supplied with a storage mount.
These were to be inexpensive, interchangeable where
possible, chemically and physically stable and had
to provide adequate support to each object. Space
restrictions also had to be borne in mind.
The simple storage mounts were designed and
made from Plastazote foam as shown in Figures
23.46 –23.53.
23.11.2 Mount instructions
298 Conservation of leather and related materials
Figure 23.47 The Plastazote is cut to shape and size on a small hobby band saw. This is not essential and can be done
with a knife. The chamfered edge on the base is for aesthetic reasons but is not essential. The chamfered edge of the
main support softens the edge where it comes into contact with the helmet.
Figure 23.48 The mount is folded over and placed on the centre of the base so that the profile can be transferred
onto the base and the location hole cut out.
Case histories of treatments 299
Figure 23.50 The cable tie is threaded through the holes tightened and the excess tie cut off.
Figure 23.49 Two holes are punched through the mount near the base.
300 Conservation of leather and related materials
Figure 23.51 The mechanism is then pushed into the foam to hide it from view. The mount can then be pushed
into the base; this can be bonded if necessary.
Figure 23.52 The flying helmet can the be placed on the mount.
Case histories of treatments 301
Figure 23.53 The flying helmet on its completed mount.
302 Conservation of leather and related materials
23.12 Leather Components from
Panhard et Levassor Automobile. 1899
Museum collection
LCC Ref: 737–02. Conservator: Yvette Fletcher
Date: May 2003
23.12.1 Description
Leather components from a 1899 Panhard automobile,
including the hood, the rear seat assembly
with loose squab cushion and the fall from the front
seat. All the leather is black vegetable-tanned cattle
hide in various weights (Figure 23.54).
23.12.1.1 Hood
The hood is attached to a painted ferrous metal and
wooden frame, has a blue wool textile lining and
measures 950 ϫ 1160 ϫ 1350mm when erected.
The front edge is of heavy patent finished carriage
leather with brass beading. There is a loose flap on
Figure 23.54 View of Panhard with hood in place.
Case histories of treatments 303
the back of the hood, which is buckled into place
and can be rolled up out of the way with two leather
straps from the inside. There are also four buckles
around the edge of the back of the hood, and two
more inside each of the sides. There is a length of
black painted copper alloy at the junction between
the top of the hood and the back on the outside.
23.12.1.2 Rear seat
The seat assembly is on a wooden base with an iron
frame and a brass rail and trim. The seat back is
covered in leather front and back, and measures
695 ϫ 150mm. There is a trim around the edge of
the wooden portion of heavy patent-finished carriage
leather, bound in a finer leather, with a brass
beading around the middle.
The loose squab cushion, measuring 650 ϫ
365 ϫ 100mm, is of leather with a textile lining on
the base, and has leather piping and buttons in a
square 3 ϫ 5 arrangement. It has been reupholstered
in the past using foam, and the buttons were
possibly replaced at this time.
23.12.1.3 Seat fall
The fall from the front seat of the car is of leather
with a nailed top edge (associated metal work
not available) measuring 800 (min.)–845 (max.) ϫ
350mm. It was originally lined in black-coated textile
which has been removed and replaced with
black leather cloth.
23.12.1.4 Front seat
The front seat squab cushion is a modern leather
reproduction. The original leather upholstered back
of the seat is black leather with deep buttoning.
23.12.2 Condition
23.12.2.1 Hood
The hood leather had been heavily oiled, which may
affect the success of some of the treatments. Generally,
the hood was sound but dusty and dirty, with an area
of paint damage on the interior lower right-hand corner.
The leather had worn at the folds with small associated
tears, and there had been some loss of surface.
There were several large tears, one small tear at the
front of the hood and a few small holes. Two buckles
were missing from the hood back where the buckle
straps had broken, and the two studs on the exterior
back top edge (which the straps on the interior hook
onto to hold up the back flap) were missing. There
was a small sewn leather repair on the back flap of the
hood. One of the interior strap ends was also missing.
Where the leather was wrapped around the metal
frame, there had been some losses and shrinkage. The
lower edge of the hood flap was torn and there were
small losses where it attaches to the studs on the metal
frame. There were residues of metal polish around the
brass beading on the front edge. The wool textile lining
was in a generally good condition if a little dusty,
but was faded on what would be the top fold when
the hood is down.
23.12.2.2 Rear seat
The seat back was in good condition, with a little
cracking to the surface at the outside edges of the
upholstered front. The leather edging around the
wooden seat was somewhat cracked, as is the nature
of this type of coated leather. The front edge was
folding inwards a little. There was some wear at the
corners and the edges. Generally the edging leather
was in good condition, but had been disfigured by
Figure 23.56 Hood after conservation.Figure 23.55 Hood before conservation.
304 Conservation of leather and related materials
brass polish around the beading and wax polish in
the stitching.
The squab cushion was in very poor condition
(Figure 23.57). The foam upholstery, which was a relatively
recent inappropriate addition, had forced the
cushion apart and had caused the seams to fail. It had
also caused the leather to split alongside those seams
which were holding. The corners were in particularly
bad condition, with splits, losses and old repairs.
23.12.2.3 Seat fall
The seat fall was in a very fragile condition and had
also been heavily oiled, which may affect the success
of some of the treatments. There was a waxy residue
in the stitching. There were two large areas of
weakness in the leather with two associated holes,
and an old, stuck repair of a leather patch at the top
edge. The original stitching had failed in some
areas. The leather had torn along a length of the
stitching on the bottom right-hand corner. There
were tears and small losses along the nailed top edge.
23.12.2.4 Front seat
The back of the seat had several small splits and holes
and there were areas of surface loss on the leather.
The end (9–10cm) of one of the straps used to hold
the seat in place was missing. One buckle and strap was
found under the seat, the second was missing.
23.12.3 Treatment
It is understood that the original leather on the
automobile will be for museum display only, and
that a project is under way to make replica leather
components for use out of doors.
After testing to find suitable cleaning systems and
solvents, it was felt that Leather Groom (a foaming
proprietary leather cleaner and conditioner) was most
suitable and all the leather was cleaned to remove dust
and dirt, and some of the excess leather dressings.
23.12.3.1 Hood
1. The holes and tears were patched using an archival
quality, vegetable-tanned, calf leather which had
been dyed to match the original. These patches
were adhered using a reversible PVA adhesive. Any
small losses and the edges of larger repairs were
infilled using pigment-coloured Beva, a thermoplastic
wax/resin adhesive which was melted into
place using a heated spatula. There was no reason
to disturb the sewn leather patch in the back flap,
as this is perfectly sound and is part of the history
of the object.
2. The broken buckle straps were removed on the
back of the hood (for return to the museum)
and were replaced using two new buckles. As it
appeared that earlier replacement straps had been
sewn through the blue lining, the new buckles
were also stitched to the hood in this way, thereby
removing the necessity of unstitching the lining.
3. The holes in the bottom of the back flap where
it attaches to the studs on the frame were repaired
using the small patches of leather and the
pigment-coloured Beva. However, as it was felt
that these holes should not be used to attach the
hood to the lower metal bar, small loops of black
elastic were sewn to the hood lining to stretch
over the metal studs.
4. The brass polish deposits proved difficult to remove
from the leather on the front edge and it was felt
that any treatment used to effect complete removal
would be too invasive. The waxy/oily deposits
from the grain of the hood leather were removed
as much as possible by mechanical means.
5. The loss of surface was made less obtrusive using
leather dyes mixed to the correct colour.
6. The hood was given a light surface coating of
SC6000, an acrylic wax blend, to protect the
leather and improve its appearance.
7. The two side covers were cleaned and conserved
using the same treatments.
8. The lining was lightly vacuum cleaned to remove
surface dust.
9. The missing buckles and studs were replaced.
23.12.3.2 Rear seat
23.12.3.2.1 Back
Leather dyes mixed to the correct colour were used
to disguise any small cracks. A light surface coating
of SC6000 was applied to protect the leather.
Figure 23.57 Before conservation – inside of squab
cushion with metal sprung unit and padding.
Case histories of treatments 305
23.12.3.2.2 Leather edging
The brass polish deposits proved difficult to remove
from the leather edging and it was felt that any treatment
used to effect complete removal would be too
invasive.
23.12.3.2.3 Squab cushion (Figure 23.58)
1. The cushion was disassembled and the inside
lightly vacuum cleaned.
2. The sides were lined with archival quality,
vegetable-tanned, calf leather which had been
dyed to match the original. This lining was first
sewn in using pre-existing holes and then adhered
using a reversible PVA adhesive.
3. Missing edging was replaced were it was possible
to do so without causing further damage to the
original.
4. Any areas of loss were then filled using a pigmentcoloured
Beva and leather dyes were painted on
areas of surface loss to improve the appearance.
5. The bottom of the hessian lining surrounding
the spring box had been stamped with a large
maker’s mark. This area had several areas of
loss and in order to conserve the maker’s mark
for the future, it was felt that a new lining was
necessary. Therefore the original was unstitched
and a new piece of hessian inserted under the
original. The areas of loss were couched to the
new lining and the opening was also stitched
with couch stitching, using a polyester thread.
The original lining had been stitched using large
stitches which went under the metal bar and
which increased the tension of the covering. As
the lining is fragile, it was felt that this tensioning
would cause further damage and therefore was
not replaced.
6. The cushion was reassembled. A felt pad which did
not appear to be original and which had caused
a great deal of tension on the leather covering
was not refitted (but has been returned to the
museum). A small amount of horse hair was tucked
around the sides. The bottom hessian backing was
restitched using the original stitching holes.
7. The whole surface was given a light coating of
SC6000 to protect the leather and to improve its
appearance.
23.12.3.3 Seat fall
1. It was not felt necessary to remove the leather
cloth lining, as this is causing no active damage to
the skirt. Although it is a later addition, it is part
of the history of the object.
2. The two sides were unstitched and the seat fall
was relined using lightweight spun-bonded polyester
(Reemay). Because Reemay is spun bonded
rather than woven, it has no nap or grain and it
can move with the leather’s own dimensional
changes without imposing any of its own on the
leather. The Reemay was adhered using a 3:1
mix of Lascaux acrylic adhesives 498HV and
360HV. The sides were resewn using the preexisting
stitching holes.
3. The nailed edge was also strip lined with Reemay.
4. Any losses were infilled using pigment-coloured
Beva, a thermoplastic wax/resin adhesive which
was melted into place using a heated spatula. The
tear at the stitching was similarly repaired. The
areas of surface loss were painted with colourmatched
leather dyes.
5. The seat fall was given a light surface coating of
SC6000 to protect the leather and improve its
appearance.
6. The seat fall was then reattached to the car using
the existing holes.
23.12.3.4 Front seat
1. The front seat squab cushion is a modern leather
reproduction and is in good condition. However,
the bottom hessian cover was torn and therefore
this was replaced, being sewn into place using the
original stitching holes.
2. A button was missing from the seat, and this was
replaced.
3. The back of the seat had some small splits and
holes and this was patched using archival quality,
vegetable-tanned, calf leather which had been
dyed to match the original. These patches were
adhered using a reversible PVA adhesive.
4. The areas of surface loss were painted with
colour-matched leather dyes.
5. The seat was given a light surface coating of
SC6000 to protect the leather and improve its
appearance.
Figure 23.58. After conservation – squab cushion.
306 Conservation of leather and related materials
6. On the broken strap, a strip of matching leather,
shaped and hole punched using the second strap
as a template, was fixed to the broken end of the
original strap using a reversible PBA adhesive.
7. The found buckle strap was refitted. A second
buckle strap was made and fitted.
23.12.4 Future care
The leather should be lightly dusted using a lint-free
cloth as necessary. No dressings or cleaners should
be used.
The original holes in the lower edge of the hood
should not be used to fix the hood to the metal bar.
Elastic loops have been fitted for this purpose. If
possible, the buckles should not be undone.
The hood should be kept in an open position at
all times.
The seat apron should be moved with care. It is
understood that the apron has to be lifted to gain
access when the car is used (approximately 12 times
per year) and this has been taken into account when
selecting the treatment. However, the apron is fragile
and unnecessary usage should be avoided.
The rear squab seat was in a very fragile state and
although it has been lined and repaired carefully, it
would be preferable if the seat was not used for
seating.
Case histories of treatments 307
Figure 23.59 Before treatment.
23.13 Altar Frontal. 1756
Private collection
LCC Ref: 404–96. Conservator: Ian Beaumont
Date: May 1998
23.13.1 Description
This altar frontal from Little Malvern Court,
Worcestershire, is made in traditional gilt leather.
The geometric design is picked out with black lines
and a translucent red glaze and the background is an
off white paint. It is the same design as that in the
Marble Dining Room at Ham House, Richmond
upon Thames, but the colours are different. The
leather at Ham House was probably made by John
Hutton in 1756. The Ham House leather is a wallhanging,
and only has the geometric pattern, but
this altar frontal has an oval central motif added. The
overall size is 153.5 ϫ 83.5cm. and it was attached
with tacks to a timber frame made from 6 ϫ 1.6cm
battens. The paint surface and the silver leaf were in
generally good condition except for some surface
soiling, scuffing and scratching. The central motif
appeared to have been varnished at some time. This
was rather uneven. It is possible that this motif had
been repainted at some time.
The leather itself, although chemically stable with
no signs of red rot, was badly damaged. There were
several major splits and substantial sections had torn
away along the tacking edge (Figures 23.59 and
23.60). There was considerable distortion associated
with the tears and some shrinkage. In the centre
of the bottom edge the torn leather had been
reattached to the timber frame, probably with animal
glue.
23.13.2 Treatment
The leather was removed from the frame by removing
the tacks and releasing the adhesive on the bottom
edge. The leather was laid out flat on a table and
humidified by laying Aquatex, a semi-permeable
membrane, over the leather with a layer of damp
blotting paper over the top. This allowed water
vapour, but not liquid water, to penetrate the leather.
The leather relaxed and the edges of the splits came
back together. Gentle pressure was used to hold it flat
but care was needed because the paint was quite hard
and brittle, and had caused localized distortion. It had
pulled the leather out of shape along the lines of the
design so that there was a series of slight domes in the
surface. These were not removed as it was feared that
flattening them could crush the paint.
308 Conservation of leather and related materials
Figure 23.60 Detail before treatment.
Once the splits were lined up they were held in
place with localised facings of Japanese tissue paper
and wheat starch paste applied to the front (Figure
23.61). Wheat starch was chosen because it could be
very easily removed at a later stage, and the tissue
paper was used because it had little bulk and was
unlikely to leave an impression. In addition the torn
edges of the paper feathered off without a hard edge.
The splits were repaired from the back with
Reemay, a non-woven polyester fabric, and an acrylic
dispersion mixture, Lascaux 498HV and 360HV, in
a 3:1 ratio (Figure 23.62). The Reemay was chosen
because it has a similar structure to the leather, does
not impose a weave, and the repair is not too bulky.
It will also take up the shape of the uneven surface.
The adhesive was applied to the leather and the
Reemay, then they were brought together and the
Reemay stippled gently into place. It was then covered
with silicone release paper of the type known as parchment
paper for cooking, and blotting paper. This was
held in place and in shape with sandbags. The blotting
paper takes the water away from the adhesive,
speeding the drying of the adhesive and reducing the
wetting of the leather. In the early stages of drying it
needs to be changed frequently.
The original plan was to line the leather completely
with Reemay. The intention was to considerably
increase the strength of the entire object to
protect it against future damage. However, once
work started, the potential fragility of the paint layer
suggested that this might present too high a risk.
Application of adhesive introduces water which
leads to expansion then contraction of the leather,
and the stippling of the adhesive into the Reemay
would also apply stresses. While this risk was acceptable
for the areas which had to be repaired, it was
deemed unacceptable for those areas where it was
not essential. Once the repairs were dry, the facing
was removed with a small amount of moisture. At
this point it was found that the wheat starch paste
had pulled at the paint surface and some of the fine
lacquer on the surface was starting to lift. This did
not cause significant long-term problems, but it did
suggest that wheat starch paste should be used with
caution in future. An alternative, which has been
used elsewhere, is to apply small patches on the back
along the join to hold it in place, and then apply the
full repair, incorporating the small repair patches.
However, this does not hold it as well as a continuous
strip of facing along the front of the split.
The entire frontal was strip lined with new
vegetable-tanned calfskin which had been retanned
with 1% aluminium to improve its longevity
(Figure 23.63). This was chosen in preference to
Reemay because it gives a more robust edge to
reattach to the wooden frame. Reemay combined with
leather is very strong, but on its own it can distort
and pull out of shape. Because the altar frontal had
shrunk slightly the edges were not going to go quite
back into place. As a result, the reattachment was,
Case histories of treatments 309
Figure 23.62 Reemay repairs.
Figure 23.61 Japanese tissue paper facing along split.
310 Conservation of leather and related materials
on at least part of the edge, through the strip lining
rather than the original leather so the extra strength
of a leather strip lining was needed. Before the
leather was replaced, the frame was loose lined with
a black polyester fabric. This gave the back a tidy
appearance, and also gave some support to the
leather in case it should receive knocks in the future.
The paint surface was given a light overall clean
with a soft brush and a vacuum cleaner. The central
motif, which had been revarnished, had this layer of
varnish reduced, but not fully removed, with isopropyl
alcohol (Figure 23.64). This reduced the visual
impact of the extra varnish. Isopropyl alcohol is a
polar solvent. The yellow varnish over the silver on
gilt leather is usually soluble in polar solvents and as a
general rule they should be avoided. If they are used
extreme care must be taken, along with very careful
testing. The solvent can penetrate right through an
overlying paint layer and dissolve the varnish underneath,
at which point, the paint starts to move about
on a bed of liquid varnish.
Gap filling was carried out in three ways. Around
the edges there were areas where the leather had
shrunk and the strip lining was showing. The strip
lining was on the back surface of the original and was
thus set back. It also had an inappropriate surface
appearance. New vegetable-tanned calfskin with a
more suitable grain structure was skived down so that
it was very slightly thinner than the original leather,
and it was then dyed with Sellaset dyes to an unobtrusive
colour. This was then used as an inlay in the
missing areas (Figure 23.65). The larger gaps, where
the leather had split, were filled with solid Beva 371
applied with a heated spatula. The fine cracks along
splits were filled with a filler based on Encryl E, an
acrylic dispersion. The basic recipe for this is 85%
Encryl E, 9% wax FF, 1% thickener A and 5% glass
microspheres, all by weight. This is white but pigments
can be added. It is somewhat fluid and tends to
shrink, and is improved by adding extra microspheres.
It needs to be pressed well into the cracks
with a spatula. Because it sets by evaporation it tends
to shrink so it is only suitable for very fine cracks.
Inpainting on the Beva, acrylic fills and areas of
loss on the paint layer was carried out with Winsor
and Newton artists’ quality watercolours, which
were selected from those which are known to be
resistant to fading (Figures 23.66 and 23.67).
No varnish or other finishing material was applied
to the painted surface. As far as could be ascertained,
nothing had been applied since the leather had been
made. The exception to this was the central motif
which had been varnished. The paint surface was
fragile but sound, so nothing was needed to consolidate
it. Cleaning had not affected the surface and the
colour was still saturated, so a varnish was not needed
to re-establish the appearance. A varnish would have
brightened the finish and provided some protection.
Figure 23.63 The finished repairs complete with the strip lining. Note the distortion caused by the painted pattern
in the left half.
Case histories of treatments 311
Figure 23.64 Cleaning.
Figure 23.65 Inlay around the edge.
312 Conservation of leather and related materials
However, old varnishes applied for these reasons in
the past are now discoloured and proving problematic.
They are very difficult, or impossible to remove
because the solvents required usually dissolve the
original yellow varnish which had been applied over
the silver. Although it is believed that the varnishes in
use now will be readily removable in the future, we
cannot be certain, so caution is desirable.
Figure 23.66 Major split in Figure 23.60 after treatment.
Figure 23.67 The finished frontal.
Case histories of treatments 313
23.14 Gilt Leather Screen
Historic house
LCC Ref: 594 –00. Conservator: Ian Beaumont
Date: May 1998
23.14.1 Description
This six-fold chinoiserie screen is probably English
and dates from the late seventeenth or early eighteenth
century (Figure 23.68). It was covered with
gilt leather which had been made in the traditional
manner. The embossed cover strips were gilt leather
too. Unusually, these were found on the back of the
joins between the folds, as well as on the front.
There had been some previous restoration work
carried out on the screen. This included lining
with a fine fabric and the insertion of wooden panels
in the back of the framework. This afforded considerable
protection to the leather but added significantly
to the weight. The painted surface was generally in
good condition, but there were 11 substantial splits.
The leather had been reattached to the frames with
tacks. Many of these passed through the fabric lining
alone and this had torn, allowing the edge to pull
away. This may have been caused by the screen being
stored at some time in a dry environment. If screens
get too dry the leather can become very tight and
damage is possible. The cover strips were in very
poor condition. They had severe red rot and had lost
most of their strength (Figure 23.69).
23.14.2 Treatment
To allow the damage to be worked on, the individual
folds were separated out. When the cover strips
were removed they fell apart. The leather on four of
the folds was removed completely, while on the
other two it was retained in position. The decision
to remove only some of the leather was based on the
level of repair needed. By taking it right off, it was
possible to bring the edges of the major splits back
together. It also made carrying out the repairs easier.
Figure 23.68 The screen after treatment.
314 Conservation of leather and related materials
The earlier lining was still securely bonded to the
leather. Where the leather had torn, the fabric had
split along the same line. Rather than remove the
lining, the leather and old lining were treated as a
single layer. The splits were repaired with Reemay, a
non-woven polyester fabric, and an acrylic dispersion
adhesive, a mixture of Lascaux 498HV and
360HV in a 3:1 ratio. The Reemay and leather were
held flat with sandbags as the adhesive dried. The
edges were strip lined with Reemay and the Lascaux
mix to give a secure edge to reattach to the frames.
This was done with stainless steel staples rather than
tacks as they are less likely to split the wood and are
easier to remove should this be necessary.
The fine cracks left where the splits had been
brought back together were filled with Aquafil 945,
an acrylic-based filler. This is white, so the correct
colour was obtained by adding artists’ quality acrylic
paints. These were used in preference to dry pigments
because they mixed in more readily. The larger
gaps were filled with pigmented solid Beva 371
applied with an electric-heated spatula.
The inpainting was carried out with Winsor and
Newton artists’ quality watercolours chosen from
those with good stability when exposed to light.
The cover strips were no longer viable for regular
use. They could have been conserved for static display
of the screen in a museum, but they were too fragile
for the flexing and knocks involved with active use.
New cover strips were made to imitate the gilt leather.
For this a goatskin with a silver-coloured finish was
used as a base material. Initially, the silver layer was
wiped over with swabs of toluene. This took some of
the surface off and gave an aged appearance. Winsor
and Newton acrylic gloss varnish was used as a new
surface finish. To give the golden colour Winsor and
Newton calligraphy inks were added along with a
small amount of black Winsor and Newton artists’
quality watercolour. Fumed silica was added to reduce
the gloss. The original cover strips were embossed, but
replicating this would have required the production of
an embossing die. This would have added considerably
to the cost and could not be justified (Figure 23.70).
Figure 23.70 Detail. After treatment, complete with
new cover strips.
Figure 23.69 Detail. Before treatment.
Case histories of treatments 315
23.15 Gilt Leather Wall Hangings,
Levens Hall
Historic house
LCC Ref: 591–99. Conservators: Theodore Sturge,
Ian Beaumont, Ruth Rodriquez and Elise Blouet
Date: March 2000
23.15.1 Description
This leather is on the main staircase of Levens Hall,
Cumbria. There are 60 individual panels of gilt
leather mounted on three sides of the staircase. The
full-sized pieces are approximately 61 ϫ 73cm
(Figure 23.71).
There are two designs on the staircase. The first,
running up the bottom flight of stairs and on the
mid landing, dates from the first decade of the eighteenth
century and was probably manufactured in
the southern Netherlands or France. The other
design, alongside the upper flight of stairs, was probably
produced in the Netherlands in the second
quarter of the eighteenth century.
The individual pieces of leather were originally
sewn together, and were probably hung up in a similar
way to a tapestry. During conservation, stitch holes
and the remains of thread were found (Figure 23.72).
The leather pieces are now mounted separately onto
softwood subframes to which they were attached with
close-nailed tacks. The individual panels thus formed
are then fitted into an oak framework to give a panelled
effect.
The leather appears to have been remounted in its
present position in 1838. This date was written on
the plaster behind the leather (Figure 23.73) and an
inscription, in pencil, on the softwood subframe for
panel 56 reads ‘John Bolton aged 17 1838 son of
John Bolton of Levens Park Joiner 1838’. This is
one of the earliest examples of this type of reuse and
remounting.
The leather had been rather crudely revarnished,
possibly in 1838 when it was installed in this location.
This has now yellowed. The decorative surface
was in good condition except for some relatively
minor scuffs, cracks and scratches. The leather was
in a stable state with no sign of red rot, but there
was considerable physical damage with splits and
holes and associated distortion. However, very little
of the leather was actually missing.
Some parts of the walls had been affected by
damp. This had been cured but it had led to rot in
some of the wood. The oak framework had been
weakened but was still intact and usable with care.
A number of the softwood subframes on which the
leather was directly mounted were completely rotten
and had to be replaced. The leather was unaffected.
Figure 23.71 The conserved leather on the stairs.
316 Conservation of leather and related materials
23.15.2 Treatment
The method of installing the leather in the oak framework
varied. On two of the walls, the leather, on its
subframes, had been installed as the oak framework
was assembled. As a result it could not be removed
from the front. On the third wall, the oak beading
holding the leather in place was pinned in place from
the front allowing easy removal. However, the damage
caused to the plaster by the damp in the past
needed further attention, so the oak framework, complete
with the leather, was taken down by unscrewing
it from the wall. All those sections of leather which
needed treatment were then removed from the oak.
There were a large number of old patches on the
back of the leather (Figure 23.74). Many of these
appeared to relate to faults in the leather during its
original preparation prior to it being made into gilt
leather. Others appeared to have been applied later,
probably in 1838, at the time the leather was
mounted in the oak framework. A few of these
were made with fragments of gilt leather. Most of
the old repairs were sound, but a small number were
coming away. These were reattached as necessary as
the other repairs were carried out.
There were three levels of treatment needed
to repair the splits in the leather. The most badly
damaged leather, Figure 23.75, was removed from
the subframes, Figure 23.76, and given a full lining.
In less serious cases a strip lining was sufficient,
while the least damaged had localized repairs
applied without removing it from the subframes.
Where necessary, the gilt leather was relaxed with
moisture vapour to allow it to be reshaped. Where
the leather had been removed from the subframes this
was carried out by placing the leather in a chamber
with an ultrasonic humidifier. Once humid, it was
placed between boards to reshape it. Where localized
humidification was needed for leather still on its
subframe, Aquatex, a semi-permeable membrane,
Figure 23.73 Inscription on wall behind the leather.
Figure 23.72 The remains of the original stitching dating back prior to the leather’s reuse in 1838.
Figure 23.74 Old leather patches on the back and a
more recent repair with timber.
Case histories of treatments 317
was placed over the leather and then damp blotting
paper was laid over this. This allowed the water
vapour to pass into the leather, but the liquid water
was kept away by the membrane.
The new repairs were almost all carried out using
Reemay, a non-woven polyester fabric available in a
variety of thicknesses. The Reemay was chosen for a
number of reasons. As a non-woven fabric it does
not have a weave and structure of its own which it
imposes onto an object. It is also quite thin. This was
a distinct advantage over, say, leather or polyester sailcloth,
because once the leather was put back onto its
subframes it had to fit back into the rebates in the oak
framework. It was quite a tight fit, and had the
increase in thickness been substantial, this would have
led to significant problems. The Reemay also worked
well with the adhesive used, an acrylic dispersion
mixture of Lascaux 498HV and 360HV in a 3:1 ratio.
It wetted out well and went into good contact with
the leather. Reemay also comes on a roll so its use is
easy and, being thin, it can be joined by overlapping
the edges without any special treatment of the cut
edge to feather it off. Its only significant disadvantage
is that on its own it is not very strong. When the
repaired leather was replaced on the subframes there
was no problem if the staples could be put through
the leather and the Reemay, but if there was not
enough leather the staples went through the
Reemay alone. This led to two problems. If the staples
were put in with too much force, they could
cut the Reemay, and if the leather was too tight, the
Reemay could distort and pull away from the staples.
A number of solutions to this were explored.
All involved increasing the strength along the tacking
edge with a secondary strip lining. The following
were tried: a fine polyester sailcloth, leather, anFigure 23.75 A badly split section of leather.
Figure 23.76 The leather in Figure 23.75 removed from its frame.
318 Conservation of leather and related materials
extra layer of the thin Reemay and a thicker
Reemay. Although the increase in strength was
greatest with the sailcloth and leather, these were
relatively bulky and more likely to cause problems
when putting the leather back in the oak frame.
The addition of a layer of a heavier Reemay gave a
significant increase in strength without too much
bulk. It was also easy to apply as it was fully compatible
with the thinner Reemay. Provided care was
taken not to split it as the staples were inserted, it
provided the best all-round alternative.
The most badly damaged leather had distorted,
and on these pieces the major splits did not always
lie comfortably in their correct alignment. It was
necessary to hold them in position during treatment.
Two methods were used. First, Japanese tissue
paper was applied to the front of the leather with
wheat starch paste. This was applied as a strip along
the split. There were two potential problems with
this. The moisture in the wheat starch paste could
be absorbed by the leather, leading to localized
expansion, which threw the joint out of line, and it
was slow to dry. After the repair was complete, the
facing was removed with a small amount of moisture.
The alternative method again used Japanese
tissue paper, but in this case it was attached with
Beva film to the back of the leather. Small patches,
to form links between the two sides of the split,
were applied with a heated spatula along the line of
the join (Figure 23.77). These had the advantage
that they were quick to apply and did not involve
water, so there was no distortion. The disadvantage
was that it did not hold the whole join completely
in line in the same way as a facing on the front.
When the lining was applied these patches were
retained and incorporated into it.
The Lascaux adhesive was used for all the repairs,
including the linings, and reattaching the loose earlier
leather repairs. It was applied with a brush to both the
back of the leather and to the Reemay (Figure 23.78).
Figure 23.78 Applying adhesive to the leather and the
Reemay.
Figure 23.77 Patches of Japanese tissue paper along the join to hold it in place as the lining is applied. The Reemay
has been applied over them.
Case histories of treatments 319
Figure 23.79 Stippling the Reemay into place.
The two were then brought together and the Reemay
stippled into place (Figure 23.79). The excess adhesive
could be removed by laying paper towels over the wet
Reemay, and then rolling lightly with a paint roller
(Figure 23.80). This is not essential but the result is
neater and aesthetically more pleasing. In the case of a
full lining, the additional strip lining of thicker
Reemay was applied while the adhesive from the first
layer was still wet. Silicone release paper was then
placed over the adhesive and, in case any has come
through the splits, under the leather. This was covered
with layers of blotting paper to absorb the moisture,
and a board was placed on top to keep everything flat.
The blotting paper absorbs the water and in the initial
stages of drying it needs to be changed frequently
along with the silicone release paper. Once the adhesive
is dry enough to hold the Reemay on the leather
during careful handling, the leather can be turned
over and any excess that has come through splits and
holes onto the front can be cleaned away.
The use of water-based adhesives needs to be
approached with care. There are times when the
distortion they produce cannot be controlled and the
result is unsatisfactory. In this case the Reemay was
able to accommodate the changes in size of the leather
during treatment, and by drying under gentle pressure
a good, undistorted, result was obtained. Caution is
needed when pressure is used, as it can lead to a flattening
of the original moulding of the leather.
Where the damage was less serious, localized
repairs were carried out, again mainly with Reemay.
If necessary, short sections of the tacked edges
were freed so that, say, a corner could be repaired.
Some of the very small holes were repaired with
vegetable-tanned calfskin which had been retanned
with 1% aluminium to increase its longevity. The
small patches were cut to size and the edges skived
away to give a smooth join with the original. These
repairs were similar in style to those applied during
the production of the leather and, in some cases,
replaced these where they had been lost.
Once the leather had been repaired, it was cleaned.
Removal of the yellowed overvarnish was not an economic
proposition. Instead, a method of surface cleaning
was needed that would remove soiling engrained
in the surface while, if possible, leaving a good surface.
The presence of the original yellow varnish over
the silver ruled out polar solvents as this would have
been dissolved. Non-polar solvents on their own had
little effect, as did moisture. However, in this case,
320 Conservation of leather and related materials
Figure 23.81 Cleaning with a cloth.
Figure 23.80 Removing excess adhesive with paper towel and a roller.
Case histories of treatments 321
tests showed that a 1:1 mixture of water and white
spirits with 1% non-ionic detergent added worked
well. This was applied with soft cloths rather than
cotton wool swabs (Figure 23.81 and 23.82). This was
for two reasons. By using a cloth, the problem of the
cotton wool snagging on the surface was avoided.
This can lead to numerous fragments of cotton wool
being caught on the surface and these are time consuming
to remove. In addition, the work was in the
nature of a general clean of the surface rather than an
in-depth, detailed, cleaning as might be used when
removing old varnish from an easel painting. There
was old wax on the surface and the dirt was inbedded
in this. The cleaning removed much of this. After
cleaning, the surface was buffed gently with a clean,
dry, cloth. This brought a light sheen, probably associated
with the remains of the wax on the surface.
The end result was a good, but not spectacular,
improvement to the finish.
The very fine cracks where the leather had split
were filled with Aquafil 945, a flexible, acrylic,
resin-based filler to which a small amount of pigment
had been added. The larger cracks and gaps
were filled with pigmented, solid Beva 371 applied
with an electric-heated spatula (Figure 23.83).
Where appropriate, this was modelled to match the
moulding of the leather.
An ideal filler for leather has yet to be found.
The solid Beva 371 is a compromise. It is tough and
flexible and sticks reasonably well. However, it can
pull away from the edges of the filled area and its
texture is not ideal. Careful application to ensure
that it melts right down into the gap and bonds at
the lower levels, rather than just at the surface,
helps. A number of methods can be used to improve
the surface. If it is cleaned with a solvent such as
xylene, this will cut the surface back to leave a less
shiny finish. Another possibility is to take a piece of
silicone release paper, screw it up and flatten it several
times to give it a finish similar to that of the
grain surface of leather. If this is laid over the fill and
worked over with a heated spatula, this ‘craquelure’
is transferred to fill and the surface may be substantially
improved.
The fills were initially painted with a mica-based,
gold, artists’ quality acrylic paint. This was then
overpainted with Winsor and Newton watercolours.
Scratches and other damage to the leather were
also inpainted with watercolours. Where necessary,
gum arabic was added to increase the gloss. The
watercolours were carefully chosen from those
known to be light stable (Figures 23.84 –23.86).
A final surface finish was not needed as the cleaning
had left it with a good surface.
When the leather was put back onto the walls,
some of the new plaster work that had to be replaced
because of the damp penetration was not completely
dry. This raised the humidity behind the leather and
Figure 23.82 A half cleaned section.
322 Conservation of leather and related materials
Figure 23.83 Gap filling with Beva 371 and a heated spatula.
Figure 23.84 The back of the finished section.
Case histories of treatments 323
Figure 23.85 The front of the finished section.
Figure 23.86 The back of a completed section of panelling showing two full linings and smaller repairs.
324 Conservation of leather and related materials
some of it became slack. Those panels which were
untreated or fully lined responded evenly, but those
where the repairs were localized reacted unevenly,
and an outline of the repair was, in a few places,
visible. Ideally the reinstatement of the leather
would have been delayed a few weeks but the hall
was about to reopen to the public for the summer.
Instead, some of the leather was left out of the panelling
to let the air circulate. When the house was
revisited some months later, the walls had dried out
and the leather had settled down to its correct tension.
Although, in this case, there was no long-term problem,
it did highlight a potential pitfall. Localized
repairs and strip linings may create a piece of leather
which will respond unevenly to changes in relative
humidity and the result can be distracting. However,
the possible problems with this need to be balanced
against the more intrusive treatment of a full lining.
Case histories of treatments 325
23.16 Phillip Webb Settle. 1860–65
Private collection
LCC Ref: 262–93. Conservators: Aline Angus,
Theodore Sturge and Aki Arponen
Date: January 1994
23.16.1 Description
This settle was designed by Philip Webb and was
probably made around 1860–65. It was owned by
William Morris. The settle, made in ebonized wood,
had a curved canopy and it was the leather panels
on this upper section which were treated. The
settle is 204cm high, 199cm long and 54cm deep
(Figure 23.87).
The lower half of the canopy had three large vertical
panels of leather 42cm high ϫ 59cm wide.
These had been painted with large flowers and the
background was stamped with small circles. This
leather was in quite good condition with a pH of
3.5, indicating chemical stability. The punching had
cut into the surface and there was some associated
lifting and loss of the surface.
The upper curved part had six smaller panels of
leather 45cm ϫ 59cm. These were of gilt leather, and
instead of the large pattern on the lower panels, the
design consisted of rows of squares with an alternating
tile-like pattern. One of the designs had a circular
motif while the other had a symmetrical, stylized, leaf
design. This leather was in very poor condition. It had
a pH of 2.8 and had deteriorated to a point where it
had little strength. In the areas where the condition
was poorest, the paint surface was very fragile and
there was a significant amount of loss. The leather in
these areas was brittle and distorted. There had been
some previous work carried out which included some
repainting of the gold and a small amount of adhesive.
The leather sections were attached to the timber
with dome-headed nails around the edge of each
piece. It was also attached with adhesive. As a result,
the leather had to be treated in situ on the timber.
23.16.2 Treatment
The upper, gilt leather panels were too fragile to
clean without consolidation. Prior to consolidation
and cleaning, the solubility of the decorative surface
was tested to ensure that the solvents used would
not affect it. The decorative layer, and to an extent
the underlying leather, was consolidated with 1%
Pliantex, a flexible acrylic resin, in toluene. This was
Figure 23.87 The settle in Kelmscott Manor.
326 Conservation of leather and related materials
also applied to the lower panels, but after cleaning.
All the leather was cleaned with mineral spirits. This
was chosen because the paint, varnish, and Pliantex
were all unaffected by it. The only adverse affect of
the cleaning was that the overpainting on some of
the gilt leather became more visible. This overpaint
was not removed as there were no solvents which
would remove it without affecting the underlying
original paint and varnish.
The loose leather was laid back down onto the
underlying timber. It was humidified by laying
Aquatex, a semi-permeable membrane, over the surface
and then covering this with damp blotting paper
and light boards (Figure 23.88). The very brittle gilt
leather did not lie down very well. It relaxed partially,
but did not go completely flat. Resin based adhesives
proved unsatisfactory, but wheat starch paste was
found to be viable. The paste has a high water content
and this was used to further relax the leather during
the reattachment. The paste was worked to a very
smooth consistency, and sufficient water was added
to allow it to pass through a syringe. It was injected
behind the damage and any space was filled (Figure
23.89). This brought the paste into intimate contact
with the back of the leather. Some of the water was
absorbed by the leather which became soft. As the
leather was pressed carefully into place the excess
paste was extruded and removed (Figure 23.90). The
leather finished up in very good contact with the
wood and an excellent bond formed (Figure 23.91
and 23.92). Good contact is essential as wheat starch
paste is not a gap filling adhesive. When the leather is
in a very poor state, as this was, wheat starch paste can
lead to a significant darkening. In this case there was
some slight darkening, but most of it was hidden by
the paint layer and that which was visible was deemed
to be an acceptable price to pay for securing the
leather. Some alternatives were considered. The most
obvious alternative was Beva 371. The gel could have
been injected into and behind the areas of damage,
allowed to dry and a bond could have been formed
with a heated spatula. This would probably have held
it together, but it would have left a significant bulk of
adhesive in the object. However, it would have been
impossible to remove in the future, should the need
arise, and would have severely restricted the options
for further work. The wheat starch paste too would
be impossible to remove from leather as weak as this,
but it would be less of a hindrance to further work.
There were some smaller areas on the lower panels
which needed to be secured. The wheat starch paste
was tried but the leather was unsuitable. When
an attempt was made to press it down into place,
the punched decorative circles started to lift away,
Figure 23.88 Humidification with Aquatex.
Case histories of treatments 327
Figure 23.89 Injecting wheat starch paste.
Figure 23.90 Excess paste being removed with gentle pressure.
328 Conservation of leather and related materials
exposing the underlying corium. The paste had to be
carefully withdrawn and an alternative sought. It
proved impossible to find an adhesive which could be
introduced in the same way as the paste but without
disrupting the surface. Instead, the edges of all the
loose areas were secured by inserting a very small
amount of adhesive underneath. This ensured that
there was nothing lifting which could be caught and
damaged during, for example, dusting. A 3:1 mixture
of the acrylic dispersions Lascaux 498HV and
360HV was used instead of the paste.
On the upper gilt leather panels the golden yellow
varnish over the silver (or possibly tin) had, in
part, flaked away. This gave a distracting speckled
appearance to the surface. This was inpainted with
artists’ quality Winsor and Newton watercolours.
These were carefully selected from those known to
be resistant to fading. This gave a consistent appearance.
No attempt was made to repaint the design
where this had been lost. This was unnecessary for
the interpretation of the object, and the areas of loss
did not distract from the overall appearance.
When the above work was finished, the decorative
surfaces were still quite fragile and vulnerable.
A final coat of 2% Pliantex in toluene was applied to
consolidate it further and to fix the inpainting.
Figure 23.91. Detail before treatment.
Figure 23.92. Detail after treatment.
Case histories of treatments 329
23.17 Gilt Leather Wall Hangings at
Groote Schuur, Cape Town
Historic house
LCC Ref: 842–04. Conservators: Ian Beaumont,
Yvette A. Fletcher and Roy Thomson
Date: March 2004
23.17.1 Description
Groote Schuur (Big Barn) (Figure 23.100) was purchased
by Cecil Rhodes in the late nineteenth century
and rebuilt following a disastrous fire in the
early twentieth century. For many years it was Cape
Town’s official Presidential Residence. Both sections
of the main reception room are decorated with a
frieze of gilt leather. Just over half of the leather
panels are of original seventeenth-century manufacture.
The remainder are late nineteenth-century
replications.
23.17.1.1 Seventeenth century gilt leather wall panels
Eleven wall panels of embossed gilt leather, probably
made in the Low Countries in the late seventeenth
century. The leather is vegetable-tanned calfskin and
the intricate design of fruit and flower swags and garlands
with ribbons, birds, apes and other fauna was
applied in the traditional manner.
23.17.1.2 Nineteenth century gilt leather panel
One panel of embossed gilt leather made to the
same design as the seventeenth century panels.
23.17.2 Condition
23.17.2.1 Seventeenth century gilt leather wall panels
The panels had been removed from the north and
west wall corner as there had been severe damp
problems at this corner (Figure 23.93). The backs of
the panels had large quantities of paint and plaster
attached to them. Underneath this layer were remains
of a contact adhesive and animal glue (Figure 23.94).
Many of the panels had original patches on the reverse,
often used to cover holes or thin/weak areas. Some
of the panels showed evidence of previous treatments
and repairs, such as patching, overpainting and
nail holes where they had been fixed to the wall.
A panel from the west wall had a block of wood
attached to it. Three panels from the north wall had
significant areas of loss of leather.
Many of the panels had splits and holes. This was
particularly evident at the edges where they had
shrunk and torn away from the nailing which had
been used to fix them to the wall (Figure 23.95).
In general the paint surface was in good condition
with only minor losses.
23.17.2.2 Nineteenth century gilt leather panel
This panel had been unstitched and removed from
the wall for historical analysis. Some of the stitch
holes on this and the adjoining panels had perforated
leaving small splits along the stitch fold. The
bottom edge of the panel had tears where the panel
had shrunk and torn away from the nailing fixing it
to the wall. On the panel immediately above the
panel in question, the stitching joining it to the left
side (facing) panel was also broken.
At first sight the panel appeared in very good
condition, the back was clean and showed no evidence
of having been adhered to the wall, nor of
previous treatments/repairs. The painted surface
was overall in good condition with only minor
losses and flaking of paint. However, small losses
Figure 23.93 Wall after replastering ready for leather to
be rehung.
330 Conservation of leather and related materials
Figure 23.94 Back of panel 4 showing contact adhesive, paint and plaster.
Figure 23.95 Front of panel 4 before cleaning.
Case histories of treatments 331
were evident in the deeper areas of embossing and
this is consistent with a condition known as red rot
which is a result of acidic damage to certain vegetabletanned
leathers, particularly those of nineteenth
century origin. This weakening of the leather may
also be the reason that the stitching holes are breaking
through and the acidity could also be causing
the sewing thread to become fragile.
23.17.3 Conservation treatment
23.17.3.1 Seventeenth century gilt leather wall panels
The plaster and paint were scraped from the back of
the panels using a small metal spatula.
Various methods were considered to remove the
contact adhesive. A technique was required that would
not damage the leather or the painted surface in any
way. It was therefore decided to use toluene which
was brushed onto the contact adhesive through a
buffer of blotting paper, allowed to soak in for only
a few seconds (to prevent any potential damage) and
then the softened adhesive could be rubbed away
using a vinyl glove (Figure 23.96 ). In the absence of
a fume cupboard, it was most fortunate that this
work could be done in the open air.
The cleaned panels were then humidified using a
semi-permeable membrane and dampened blotting
paper. This method allows water vapour to transfer
into the fibre structure of the leather to soften it
without potentially damaging liquid water to come
into direct contact with the leather. The leather was
then flattened as far as possible under boards and
sandbags and allowed to dry.
Where edges joined to another panel, lengths
of archival quality vegetable-tanned calfskin were
adhered to the sides with an overlap to allow for
shrinkage and to facilitate joining the panels together.
The top and bottom edges of the panels were also
strip lined in this way to allow for fixing to the wall.
The lengths of leather were skived along the edges to
reduce the bulk and to prevent the edges from showing
through in the future. A water reversible PVA
adhesive was used to attach the strips.
Any holes and splits were repaired by attaching
patches of the archival quality calf leather to the
reverse with a water reversible PVA adhesive. Any
edges which were damaged were strip lined, again
using the archival quality leather (Figure 23.97). The
repairs were infilled using pigment-coloured Beva, a
thermoplastic wax/resin adhesive which was melted
into place using a heated spatula.
The panels were joined together in pairs (lower
and upper panels) using the strip lining and PVA
adhesive and these pairs were then fixed to the wall
using staples through the overlapping strips of
leather. Each pair of panels was fitted to the adjoining
panel in the same way (Figure 23.98).
Those areas that had been filled with Beva were
inpainted to match the leather and continuity of the
design. It was decided in consultation with the client
that the strips of leather should be painted to match
the background of the original panels but the design
need not be inpainted (Figure 23.99). Acrylic paints
were used for this purpose.
Finally, the panels were given a very light coating
of micro-crystalline wax.
23.17.3.2 Nineteenth century gilt leather panel
A length of archival quality vegetable-tanned calfskin
was adhered to the bottom edge of the panel with an
overlap of approximately 3cm. A water reversible
PVA adhesive was used to adhere the strip of leather.
The inside edges of the strip were skived to prevent
the edges of the leather from showing through the
panel in the future.
As there was broken stitching on the panel above
and, necessarily, those to the left side (facing) of
Figure 23.96 Cleaning backs of panels, out of doors.
332 Conservation of leather and related materials
Figure 23.98 Some panels back on wall.
Figure 23.97 Panels, cleaned and patched.
Case histories of treatments 333
Figure 23.99 Section of wall after completion.
Figure 23.100 Groote Schuur (Great Barn), built for Cecil Rhodes and for many years Cape Town’s official
Presidential residence.
both panels, a further strip of leather was attached in
the same way from top to bottom of these two panels.
The detached panel was stitched to the panels to
its right and above using the original stitch holes.
A waxed linen thread was used.
These two panels were then adhered to the strip
of leather using a water reversible PVA adhesive.
The bottom of the panel was fixed to the wall using
staples through the overlapping strip of leather.
Any new leather which was showing through was
painted to match the background or the existing
panels.
23.17.4 Future care
The seventeenth century panels are now in a stable
condition and should remain so provided care is
taken. As with all leather objects the panels are sensitive
to changes in humidity. The nineteenth century
leather is affected by red rot and its condition
should be monitored.
The leather will not require feeding or dressing.
Application of oils or fats to the decorated surface
will soften the paint and varnish surface causing
irreparable damage. An occasional light dusting with
a lint-free cloth, or soft brush should be sufficient.
This page intentionally left blank
Acids, role in deterioration, 52
acid hydrolysis, 38
Acrylics, 127
Adhesives, 108, 124, 126 –7
ethnographic objects, 189
freezing tests, 165
fur repairs, 160 –1
leather bookbindings, 228
parchment glue, 193
parchment repair, 217–20
See also Animal glue
Aldehyde tanning, 31
Altar frontal case history, 307–12
Alum tawed gloves, case history, 293–5
Aluminium alkoxide, 122
Aluminium tanning, 29
detection of aluminium, 59
Amino acids, 44 –7
deterioration mechanisms, 45–7
general characteristics, 44 –5
side chains, 45
Ammonia, 125
Animal glue, 108, 124, 127, 192
bone glue, 193
fish glue, 108, 192, 194
hide glue, 193
rabbit skin glue, 193
skin glues, 192
See also Adhesives
Aquatic skins, 173–8
conservation, 178
ethnographic objects, 175–8
fish skin preparation, 174
structure and identification, 174 –5
Aqueous cleaning, 125
Archaeological leather, 244 – 61
condition assessments of treated
leather, 260
dry leather, 251–7
condition, 251–3
consolidation, 257
on-site retrieval, 253– 4
present-day treatments, 256 –7
recording procedures, 254 – 6
reshaping, 257
mineralized leather, 257– 60
condition, 257
on-site retrieval, 259
recording, 259
treatment, 259– 60
old collections, 260
purpose of treatment, 260 –1
retreatments, 260
storage, 260
wet leather, 245
composites and special items,
250 –1
condition, 245– 6
freeze-drying, 248–9, 251
marine leather, 250
past treatments, 247–8
present-day treatments, 248–51
preservation before treatment,
246 –7
reshaping and reconstruction,
249–50
solvent dehydration techniques,
247–8
Australopithecus habilis, 66
Automobile components, case history,
302– 6
Autoxidation, 39– 40
Awl, 103
Back stitch, 110
Bating, 77
Bavon leather lubricants, 121, 122, 248,
251
Beating, fur-skins, 153
Bedacryl 122X, 122
Beva 371, 123, 127, 127–8
Bird skins, See Feathered skins
Birds, taxidermy techniques, 131–2
bind up, 131
problems, 132
soft stuff, 131
Bleaching, 80
Bloom, 24
Board slotting, See Leather
bookbindings
Boards, 109
Bone folder, 104
Bone glue, 193
Bookbindings, See Leather
bookbindings
Boot, 111
Bound edge, 112
Bound seam, 111
Box stitch, 110
Brain tanning, 31
British Long Term Storage Trials
(BLTST), 36 –7
British Museum Leather Dressing, 121,
129
Brooklyn seam, 111
Brosser (round) seam, 111
Butt stitch, 110
Butted edge, 111
Cable stitching, 110 –11
Calfskin, 14
Carbon monoxide, 40
Carriages, 120
Cars, 120
case history, 302– 6
Case histories:
altar frontal, 307–12
alum tawed gloves, 293–5
court gloves, 296
cuir bouilli, 98–101
dining chairs, 287–92
dog whip, 268–70
fire bucket, 271–3
fireman’s helmet, 274 –5
flying helmets, mounting, 297–301
gilt leather screen, 313–14
gilt leather wall hangings:
Groote Schuur, 329–33
Levens Hall, 315–24
gold state coach, 265–7
jewellery box, 285– 6
leather lion, 276 –8
Panhard et Levassor automobile,
302– 6
Philip Webb settle, 325–8
sedan chair, 279–84
Casting, 128
Cattle skin, 12–13
Chain stitch, 110
Chamois leather, oil tanning, 30 –1
Chrome tanning, 27–9, 80 –1
fur-skins, 152–3
history, 74
Clam, 105
Cleaning, 125
archaeological leather, 256
ethnographic objects, 187
furs, 160
parchment, 210 –11
Clearing, 80
Clicking knife, 104
Closed seam, 111
335
Index
Clothing, 117
Cold storage, furs, 167
Collagen, 4 –10
bonding between molecules, 6 –8
covalent intermolecular bonding,
7–8
salt links, 6 –7
bonding within molecule, 6
colloidal nature, 42
deterioration mechanisms, 43–7
amino acids, 44 –7
peptides, 43– 4
fibril structure, 8–9, 11
shrinkage temperature, 9–10
Compass, 104 –5
Condensed tannins, 25– 6, 75
detection of, 59
Connolly’s Leather Food, 121
Conservation, 113
aquatic skins, 178
bird skins, 181–2
carriages, 120
cars, 120
clothing, 117
cuir bouilli, 97–101
case study, 98–101
damage caused by old treatments,
98, 99–101
original treatments, 98
stability, 97–8
display versus storage, 114
exotic skins, 172
feathered skins, 181–2
finish, 115
furs, 159– 65
case histories, 161–5
cleaning, 160
repair methods, 160 –1
handling by the public, 114 –15
harness, 118–19
luggage, 117
objects in use, 113–14
preventive conservation, 115–16
environment, 115–16
pests, 116
storage and display, 116
saddles, 117–18
screens, 119–20
sedan chairs, 120
shoes, 117
treatment levels, 114
wall hangings, 119–20
See also Case histories; Conservation
treatments
Conservation treatments:
adhesives, 126 –7
archaeological leather, 260 –1
dry leather, 257–9
mineralized leather, 259
purpose of treatment, 260 –1
retreatments, 260
wet leather, 247–51
casting, 128
consolidation techniques, 128
dressings, 128–9
dry cleaning, 124
finishes, 128–9
humidification, 125– 6
moulding, 128
parchment, 209–20
past treatments, 121– 4
1982 Jamieson survey, 121–2
1995 survey, 122–3
2000 list, 123– 4
2003 Canadian Conservation
Institute (CCI) survey, 124
proprietary leather cleaners, 125
repair materials, 126
solvent cleaning, 125
surface infilling materials, 127–8
wet cleaning, 125
See also Case histories; Specific
treatments
Consolidation techniques, 128
archaeological leather, 256 –7
inks and pigments, 216 –17
leather bookbindings, 230 –2, 233
weak parchment, 215–16
Corner stitch, 110
Cortex, hair, 151
Court gloves, case history, 296
Craft guilds, 82–3, 142
Crease, 104
Crease iron, 106
Crocodile skin, 171
See also Exotic skins
Crosses, of fur, 157–8
Crust leathers, 75– 6
Cuir bouilli, 94 –101
changes undergone by leather in
process, 97
conservation, 97–101
case study, 98–101
damage caused by old treatments,
98, 99–101
original treatments, 98
stability, 97–8
leather moulding techniques, 94
origins of technique, 94 –7
Curriers, 86
Currying, 245
Cuticle, hair, 150 –1
Damage, See Deterioration
Decay, resistance to, 1
Deerskins, 15
Denaturation, 52
Detergent, 125
Deterioration:
agents of, 37– 43
acid hydrolysis, 38
heat, 41
metals and salts, 40 –1
oxidation, 38– 40
water, 41–3
archaeological leather, 253
determination of, 59– 60
fat content, 63– 4
moisture content, 63
pH, 61–2
pH difference, 62–3
shrinkage temperature, 60 –1
sulphate content, 63
furs, 159
mechanisms, 36 –54
acids, 52
collagen, 43–7
fats, oils and waxes, 51
perspiration, 52
shrinkage temperature as measure
of deterioration, 52–3
vegetable tannins, 47–50
parchment, 203–9
Dining chairs, case history, 287–92
Dirt, 116
Display, 116
ethnographic objects, 190
furs, 166 –7
parchment, 209
versus storage, 114
Dividers, 104 –5
Dog whip case history, 268–70
Double-sided tape, 108
Dressings, 115, 128–9
archaeological leather, 256
Drills, for leather bookbindings,
229–30
Dropping, fur-skin joining, 155– 6
Dry cleaning, 124
Dyeing, 81
feathers, 181
fur-skins, 148–9, 153– 4
killing, 154
mordanting, 154
leather bookbindings, 225
Dyestuffs, 75, 245
Edge shave, 105– 6
Ellagic acid, 48–9
Ellagitannins, 23
Environment, 115–16
Ethnographic objects, 184
conservation, 186 –90
adhesives, 189
cleaning, 187–8
condition, 187
cosmetic repairs and infills, 190
display, 190
mending, 189
mounts/internal supports, 188–9
poisons, health and safety issues,
186 –7
pre-treatment examination, 186
repair supports, 189
reshaping, 188
sewing, 189
storage, 190
construction techniques, 185
decoration, 185– 6
ethical aspects, 184
fish skins, 175–8
tanning methods, 185
uses, 184 –5
Ethylene glycol, 123
Ethylene vinyl acetate (EVA), 127
Excavation:
dry leather, 253– 4
mineralized leather, 257–9
Exotic skins, 170 –3
conservation, 172
history, 170
336 Index
skin preparation, 171
tanning and dressing, 170 –1
light fastness, 172
water resistance, 172
uses of, 170 –1
Faced edge, 111
Facteka A, 121–2
Fancy stitching, 110
Fatliquoring, 81
Fats:
deterioration assessment, 63
role in deterioration, 51
Feathered skins, 178–82
conservation problems, 181–2
processing, 178–81
‘Feeding’ leather, 63
FEIN MultiMaster tool, 241–2
Finish, in conservation process, 115,
128–9
Finishing:
fur-skins, 154
tanning process, 81
Fire bucket case history, 271–3
Fireman’s helmet case history, 274 –5
Fish, taxidermy methods, 135–7
problems, 136 –7
Fish glue, 108, 192, 194
Fish skin, 173– 4
conservation, 178
ethnographic objects, 175–8
preparation, 174
structure and identification,
174 –5
Fleshing:
fur-skins, 152
parchment manufacture, 198
Flying helmets, case history, 297–301
Foam, 109
Fold endurance test, leather
bookbindings, 238
Formaldehyde tanning, 31
Free radicals, 38–9
Freeze-drying, 248–9, 251
Freezing:
adhesive tests, 165
furs, 167
French seam, 111
Fuller’s earth, 123
Fumigation, parchment, 210
Furs:
care of, 166 –7
freezing, 167
pest monitoring, 167
pest treatment, 167
storage and display, 166 –7
conservation methods, 159– 65
case histories, 161–5
cleaning, 160
repair methods, 160 –1
crosses, 157–8
damage, 159
dyeing, 148-9, 153– 4
killing, 154
mordanting, 154
finishing, 154
hair/fur fibres, 149
morphology, 150 –1
history of use, 141– 6
fashionable furs and dates, 146 –7
skin processing and dyeing, 148–9
husbandry and harvesting, 145– 6
making into garments or accessories,
154 –7
dropping or stranding, 155– 6
sewing, 156 –7
skin on skin method, 155
plates, 157–8
pointing, 154
skin dressing, 151–3
beating, 153
chrome, 152–3
fleshing, 152
oiling, 153
pickling, 152
soaking, 152
unhairing, 152
species identification, 158–9
terminology, 148
Gallic acid, 48–9
Gallotannins, 23
Gelatine, 124, 128, 193– 4
parchment repair, 218
Gilt leather, 88–90
production technique, 89
publications, 90 –3
screen, case history, 313–14
wall hangings, case histories:
Groote Schuur, 329–33
Levens Hall, 315–24
Glass bristle brushes, 124
Glove, 111
Gloves, 117
case histories, 293– 6
Glue, See Adhesives
Glutaraldehyde tanning, 31
Glycerol, 248
Goatskins, 14
Gold state coach case history, 265–7
Goldbeaters’ skin, 195
parchment repair, 219
Groomstick, 124
Guilds, 82–3, 142
Gut membrane, 195
Hair fibres, 149
morphology, 150 –1
cortex, 151
cuticle, 150 –1
medulla, 151
Hammer, 105
Handling, by the public, 114 –15
Harness, 118–19
Head knife, 103– 4
Heat, role in leather deterioration, 41
Hide, 148
raw hide, 185
Hide glue, 193
Humidification, 125– 6
parchment, 211–15
Hydrolysable tannins, 23–5, 75
detection of, 59
Hydroxyproline, 5
Hysteresis, 42
Identification:
aquatic skins, 174 –5
furs, 158–9
Industrial revolution, 86
Infestations:
furs, 167
monitoring, 167
treatment, 167
parchment, 206, 208
mould, 210
Infilling, 127–8
ethnographic objects, 190
parchment, 218–19
Inks, 206 –8
consolidation, 216 –17
Inseam, 111
Invasol S, 123
Isinglass, 194
Isopropanol alcohol, 123
Japanese tissue paper, 126, 127, 234 –5
solvent-set book repair tissue, 232– 4
Jean seam, 111
Jewellery box case history, 285– 6
Joint tacket system, 229
Keratin, 149–50
Killing, fur-skins, 153– 4
Klucel G, 128, 226 –7, 230 –2
application, 227
Knives, 103– 4
Lapped/overlay, 111
Lascaux acrylics, 127, 128
Latex, 108
Leather:
definition, 3
gilt leather, 88–90
publications, 90 –3
moulding techniques, 94
See also Cuir bouilli
properties of, 1–3
fibre weave and movement, 20 –1
skin fibre structure influence, 19–20
See also Archaeological leather;
Collagen; Mammalian skin
structure
Leather bookbindings, 225– 42
binding solutions, 225–30
adhesives, 228
board attachment, 228
board treatment, 228
drills, 229–30
facing degraded leather, 227–8
helical oversewing, 228–9
joint tacket, 229
Klucel G, 226 –7
offsetting, 228
board slotting, 236 – 42
board slotting machine, 238
board treatment, 236
dyeing, 241
reattachment, 237–8
scientific analyses, 238–39
Index 337
Leather bookbindings (contd)
text block treatment, 237
variation on the board slotting
machine, 241
leather consolidants, 230 –2
STEP Leather Project, 230
solvent-set book repair tissue,
232– 4
split joints on leather bindings,
234 –5
adding a cloth inner hinge, 235
split-hinge board reattachment,
235–7
Leather Conservation Centre,
Northampton, UK, 37
Leather Groom, 125
Leather lion case history, 276 –8
Leatherworkers:
social status of, 82–7
social separation, 84 –7
trade guilds, 82–3
Leatherworking, 246
tools, 103–8, 256
Light:
role in deterioration, 39, 115–16
taxidermy specimen care, 137
Liming, 77
parchment manufacture, 198,
201–2
Lipids, autoxidation of, 39– 40
Lock stitch, 110
Luggage, 117
Mammalian skin structure, 12
calfskin, 14
deerskins, 15
directional run of fibres, 19
fibre structure influence on leather
properties, 19–20
goatskins, 14
grain surface patterns, 17
mature cattle skin, 12–13
pigskins, 15–17
sheepskins, 14 –15
suede surfaces, 19
variation with location in skin, 19
See also Collagen
Mammals, taxidermy techniques,
132–5
problems, 134 –5
Marine leather, 251
Medieval period:
fashionable furs, 146
tanning, 68–73
Medulla, hair, 151
Metals, role in leather deterioration,
40 –1
Microcrystalline wax, 125, 129
Mineral spirit, 125
Mineralized leather, 257– 60
condition, 257–9
on-site retrieval, 259
recording, 259
treatment, 259– 60
Moccasin, 111
Mock stitching, 110
Moisture content, 64
Mordanting, 154
Mould, parchment, 210
Moulding, 128
Mounts:
ethnographic objects, 188–9
flying helmets, case history, 297–301
N-methoxymethyl nylon, 124
National Trust Furniture Polish, 129
Neanderthal Man, 66
Needles, 107–8
Neoprene, 108
Neutralfat SSS, 122
Nineteenth century:
fashionable furs, 146
tanning, 73–7
Nitrogen dioxide, 40
Oak bark, 86
Oil tanning, 30 –1
Oils:
deterioration assessment, 63
fur-skin dressing, 153
role in deterioration, 51
Open (flat) seam, 111–12
Opodeldoc, 123
Overlay, 111
Oxazolidine tanning, 31
Oxidation, 38– 40
atmospheric pollutants, 40
autoxidation of lipids, 39– 40
free radicals, 38–9
light, 39
Ozone, 40
Panhard et Levassor automobile
components, case history,
302– 6
Papers, 109
Paraloid B67, 128
Paraloid B72, 127
Parchment, 2, 200
characteristics, 203–9
conservation treatments, 209–20
cleaning methods, 210 –11
consolidation of inks and
pigments, 216 –17
consolidation of weak parchment,
215–16
humidification and softening,
211–15
mould and fumigation, 210
repairs and supports, 217–20
deterioration, 203–9
display, 209
format, 208–9
manufacture of, 198–9, 200 –3
drying, 198–9
liming, 198, 201–2
soaking, 198
temporary preservation, 198
unhairing and fleshing, 198
storage, 209
use of, 200 –3
Parchment glue, 193
Paring knives, 104
Pelt, 148
Peptides, 43
formation in deteriorated leather,
43– 4
Perspiration, 52
Pests, 116
furs, 167
monitoring, 167
treatment, 167
parchment, 208
pH, 61
deterioration indication, 61–2
pH difference, 62–3
Philip Webb settle, case history, 325–8
Photolysis, 39
Photoxidation, 39
Pickling, 77–80
fur-skins, 152
in taxidermy, 131
Pigments, 206 –7, 245
consolidation, 216 –17
See also Dyeing
Pigskins, 15–17
Piped seam, 112
Pique, 112
Pithecanthropoids, 66
Plastination, 251
Plates, of fur, 157–8
Plexisol, 122
Pliancreme, 122
Pliantex, 122, 123, 128
Pliantine, 123, 129
Plumage, See Feathered skins
Pointing, fur-skins, 154
Poisons, ethnographic objects, 186 –7
Polar organic solvents, 125
Polyester sailcloth, 126
Polyethylene glycol (PEG), 248–9
PEG 400, 123, 249
Polyvinyl acetate (PVA), 108, 127
Post-medieval period, 68–73
Post-tanning, 81
Prehistoric times, 66 –8
Preparation, 109
Preservatives, taxidermy, 140
Pretanning, 77–80
Pricking iron, 107
Prix-seam, 112
Pseudo leathers, 1–2
Quilting, 110
Rabbit skin glue, 193
Race, 105
Raw hide, 185
Raw/cut edge, 112
Reinforcements, 108–9
Relative humidity, 42–3, 115
taxidermy specimen care, 137
Renaissance wax, 123
Repairs:
archaeological leather, 257
ethnographic objects, 189
338 Index
furs, 160 –1
parchment, 217–20
repair materials, 126
sedan chair case history, 279–84
solvent-set book repair tissue,
233
Reptile skin, See Exotic skins
Reshaping:
archaeological leather, 249–50, 257
ethnographic objects, 188
Revolving hole punch, 105
Rounding, 110
Rubber cement, 124
Rubber solution, 108
Saddle soap, 123, 128
Saddle stitch, 109–10
Saddles, 117–18
Sausage casings, 197
SC6000, 128, 129
Screens, 119–20
case history, 313–14
Seal skin, 144
Seams, 111–12
Sedan chairs, 120
case history, 279–84
Settle, case history, 325–8
Sewing, 109–10
ethnographic objects, 189
furs, 156 –7
leather bookbindings, 228–9
See also Stitching
Sheepskins, 14 –16
Shoes, 117
archaeological specimens, 250 –2
Shrinkage temperature, 2, 9–10,
22–3
as measure of deterioration, 52–3,
60 –1
determination of, 60 –1
Silked seam, 112
Silking, 219
Skin glues, 192–3
Skin on skin method, 155
Skin, See Aquatic skins; Feathered skins;
Mammalian skin structure
Skiving, 109
Skiving knives, 104
Smoke sponges, 124
Smoking, 185
Social status of leatherworkers, 82–7
Sodium carboxy methyl cellulose
(CMC), 127
Soluble nylon, 124
Solvent cleaning, 125
ethnographic objects, 188
furs, 160
limitations on solvent transport, 254
Solvent dehydration techniques, 247–8
Solvent-set book repair tissue, 232– 4
Spanish (gilt) leather, 88–90
Species identification:
aquatic skins, 173–8
furs, 158–9
Spiral bladed cylinder knives, 74
Splitting machine, 74
Spot tests, 59
Sprung seam, 112
Spun-bonded polyester, 126
Squirrel skins, 143
Starch pastes, 108
State coach case history, 265–7
Steel rule, 104
STEP project, 37, 44
Steramould, 128
Stitch marker, 106 –7
Stitching, 109–10
decorative machine stitching,
110 –11
decorative stitching, 110
machine stitching, 110
parchment repair, 217
See also Sewing
Stoddard solvent, 123, 125
Storage, 116
archaeological leather, 246, 254,
260
ethnographic objects, 190
furs, 166 –7
cold storage, 167
parchment, 209
taxidermy specimens, 137– 40
versus display, 114
Stranding, fur-skin joining, 155– 6
Stripping, 80
Strop, 104
Suede surfaces, 17
Sulphur compounds:
deterioration assessment, 63
role in deterioration, 51–2
sulphur dioxide, 40
Supports:
ethnographic objects, 188, 189
parchment, 217–20
Syntans, 32– 4, 80
auxiliary syntans, 32–3
combination or retanning syntan,
33
replacement syntans, 33– 4
Tanneries:
location of, 84 –5
See also Leatherworkers
Tanning, 22–34, 77–81, 245– 6
aldehyde tanning, 31
determination of tanning process,
58– 60
aluminium, 59
archaeological leather, 254 – 6
condensed tannins, 59
hydrolysable tannins, 59
vegetable tannins, 59
ethnographic skins, 185
exotic skins, 171–2
history of, 66 –77
medieval and post-medieval
periods, 68–73
nineteenth century, 73–7
prehistoric and classical times,
66 –8
importance of tanning industry,
82
mineral tanning, 27–31
aluminium(III) salts, 29
chromium(III) salts, 27–9, 74,
80 –1
titanium(IV) salts, 29–30
zirconium(IV) salts, 30
oil tanning, 30 –1
post-tanning, 81
pretanning, 77–80
stages, 77–81
syntans, 32– 4, 80
auxiliary syntans, 32–3
combination or retanning syntan,
33
replacement syntans, 33– 4
vegetable tanning, 23– 6, 80
deterioration mechanisms,
47–50
history, 68–74
Tanning drum, 74
Taxidermy, 130 – 40
birds, 131–2
bind up, 131
problems, 132
soft stuff, 131
care, 137– 40
light, 137
relative humidity, 137
storage, 137– 40
temperature, 137
fish, 135–7
problems, 136 –7
mammals, 132–5
problems, 134 –5
preservatives, 140
terms, 131
Temperature, 115
taxidermy specimen care, 137
See also Shrinkage temperature
Tensile strength test, leather
bookbindings, 239
Thonging, 110
Thread, 108
Titanium tanning, 29–30
Toluene, 125
Tools, leathermaking, 103–8
Top stitching, 110
Trade guilds, 82–3, 142
Turned over edge, 112
Turned seam, 112
Unhairing:
fur-skins, 152
parchment manufacture, 198
Varnishes, 115
Vegetable tanning, 23– 6, 80
antioxidant ability of tannins, 47
detection of vegetable tannins, 59
archaeological leather, 254 –5
deterioration mechanisms,
47–50
history, 68–75
Vellum, 2
Vulpex, 122, 123
Index 339
Wadding, 109
Wall hangings, 119–20
case histories:
Groote Schuur, 329–33
Levens Hall, 315–24
Water:
types of in leather, 41–2
water activity, 42
Waterlogged leather, See Archaeological
leather
Waxes, role in deterioration, 51
Webb, Philip, settle case history, 325–8
Wet cleaning, 125
Wheat starch paste, 127
White spirit, 123, 125
Worshipful Company of Skinners of
London, 142
Woven fabric materials, 109
Xeroradiographic imaging, 99
Zirconium tanning, 30
340 Index