Study of the soil biodegradation on vegetable-tanned and chrome-tanned leathers - a tool for
                             characterising of archaeological leather


                                       Gabriela Vyskočilová


Many remains of ancient clothing, footwear and utensils made from leather have been found in
archaeological sites throughout the world. The appropriate conservation treatment for these
artefacts, in order to protect their integrity and scientific value, requires the understanding of
leather structure as well as it’s deterioration under burial medium, wet or dry conditions.
Historical leather and parchment were subject of international research projects (STEP,
Environmnet, I.D.A.P) but any complex research was dedicated to archaeological leathers although
that is very often and mainly very sensitive material with susceptibility for wrong handling. In
case of archaeological leathers (contrary to historical leather and parchment), mechanisms of
degradation have not been researched yet and almost none studies were published.

Wide range of methods (generally used for analysis of historical leather and parchment) have been
employed to assess degradation processes and changes occurring in buried archaeological leather.

Infrared spectroscopy (FTIR) is widely used for historical collagen-based materials investigation,
enabling the detection of conformational changes of collagen on deterioration, as well as the
identification of materials added during the manufacturing process or formed on ageing. Thermal
methods as DSC, TG or MHT are used for determination of hydrothermal stability and evaluation of
decay collagen substrate.

Mechanical testing is done for comparison of strength and elongation changes influenced by
degradation processes. Chemical analysis (e.g. determination of extractible substances, total ash
or nitrogen content etc.) is generally used in leather industry for evaluation of the leather
quality. Determination of pH is used for asses of free acids as progress of acid hydrolysis in
collagen substrate. Stereomicroscopy and SEM is used for observing of the morphological changes.
EDX was used for determination of the elements adsorbed from soil.

The aim of the study is to bring some new knowledge about mechanisms of leather biodegradation
ongoing in soil environment and find useful methods for evaluation of degradation level of
archaeological leathers in conservation practice. In contrary to leathers from the air environment
which are influenced by pollutants, temperature and relative humidity fluctuation, archaeological
leathers are influenced mainly by (micro)biocenosis


References:

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2)      Larsen, R. and C. European, ENVIRONMENT Leather Project : deterioration and conservation of
vegetable tanned leather. 1996, København: Royal Danish Academy of Fine Arts, School of
Conservation.

3)      Larsen, R., et al., Improved damage assessment of parchment (IDAP) : assessment, data
collection and sharing of knowledge. 2007, [Luxembourg]: European Commission, Directorate-General
for Research, Directorate I--Environment.

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