MATERIALS INFORMATION and TECHNICAL RESOURCES
for ARTISTS - Adhesives and Sizes
A “size” is a material that is applied to a support (wood, fabric, etc.) to
effectively seal the surface and serve as a barrier layer between the support and the
paint and ground layers. Certain materials used as size will help to prevent Support
Induced Discoloration (SID), a phenomenon that occurs when water-soluble
impurities in the support migrate up through the ground and paint layers. A layer of
size reduces the absorbency of the support, but size should not be applied too
thickly. Too thick an application can lead to problems of delamination. It is best to
use either a sponge or a brush and apply an even, thin solution that effectively
penetrates the surface of the support. Sizing both the back and front of wooden
supports will help mitigate warping of the panel. It is generally best to also size the
sides of the panel. This is even more important if the support will remain unframed
or is of lesser quality wood. Fabric supports, whether adhered to a rigid panel or
mounted onto a stretcher, tend to shrink once properly sized. This is especially true
when an animal glue size is used. Sizing reduces the absorbency of the fibers
(preventing “strikethrough” or mediums/solvents from seeping through to the back
of the support), protects the canvas from the acidity of certain materials (e.g. drying
oils, alkyds), and creates a taut, planar surface suitable for painting.
Table (courtesy of Golden Artist Colors, Inc.) summarizing results obtained using various sizes in
combination with linseed oil grounds and canvas supports.
PROTEINACEOUS SIZES AND GLUES
Animal glues are produced from a wide range of animal tissues (e.g. hides, bones,
etc.). Rabbit skin glue (RSG) is a term that is sometimes used as a descriptor for all
animal glue products, so RSG is not always derived from rabbits but may come from
other animals such as goats, sheep, and most commonly cows. Isinglass is glue
derived from the bladders of sturgeon fish. It is used as a size for handmade papers
and by art conservators in their work. Other fish derived glues are also available,
some of them in liquid form. These are generally best avoided as they often contain
other ingredients, Gelatin, another term associated with animal glue, generally
refers to grades that are more refined. Gelatin is available in sheets, shards, pellets,
or powders. Grocery store food gelatin tends to be weaker than other grades of
gelatin. Animal glues can be dissolved in hot water and applied as a warm, liquid
solution. Most animal glues will gel at room temperature. (Animal glues can also be
applied in cold, soft gelled form with a spatula or palette knife, although this is
generally not suggested).
If animal glues are to be used as a sizing material, artists should consider the
following:
 Glues respond readily to changes in temperature and relative humidity.
Animal glues will shrink as the humidity drops and swell and soften when the
humidity rises. These changes can lead to delamination and/or flaking of the
overlying ground and paint layers and to planar deformations in the support.
 Animal glue size should be used with a rigid support (or a canvas adhered to a
rigid support) as the rigidity mitigates the expansion and contraction of the
size layer.
 Glues tend to form fairly rigid and brittle films and should not be applied too
thickly to supports. 2-3 coats of dilute size are preferable to one thick layer of
glue. Instructions provided by the manufacturer for glue-size preparation
procedures should be followed.
 The surface of the support should be sanded after each coat of glue size with
the exception of the final coat.
 Animal glue sizes are not recommended for use with acrylic ground/paint
systems. They are compatible with glue-based grounds (e.g. true gesso, chalk)
and oil and/or alkyd paint systems.
 Although rabbit skin/animal glue possesses hygroscopic properties, many
artists continue to use this traditional material as a size and/or adhesive. If
you choose to use animal glue to adhere your canvas to a wooden support, the
following steps are recommended:
Prepare your animal glue following the directions on the package.
Brush a generous, even coat of glue onto the panel’s surface. You may
allow this coat to dry before continuing with the process or proceed
immediately. Immerse the canvas into the glue, wringing the fabric to
remove any excess. Position the fabric onto the panel. Use a
brayer/bone folder to eliminate any air bubbles, working from the
center outwards to the edges. If you have decided to keep excess
fabric along the outer edges, fold them over and attach to the backside
of the panel (or affix them later). Immediately apply a coat of glue to
the reverse of the panel (NOTE: It is not advised to leave a coat of
animal glue exposed to the environment. Subsequent layers of
priming and paint need to be applied to the reverse in order to avoid
warping, mimicking the same layering used on the front of the panel).
For allow for adequate drying, stand the panel on its edge or lean
against a wall.
Older artist manuals suggest the addition of alum to harden animal glues and make
them less water soluble. This is no longer recommended as it tends to make the glue
overly brittle. Weak solutions of formaldehyde were also applied to tan the glue.
Artists should strictly avoid formaldehyde is it has been shown to be a significant
health hazard.
ACRYLIC-BASED ADHESIVES AND SIZES
There are several types of acrylic-based resins that can be used as sizes and
adhesives. Methods of application and aging properties vary widely depending on
the type of acrylic polymer(s), the presence of additives, and whether the acrylic
resin is delivered in an aqueous or solvent-based solution.
NOTE: “Dispersion” and “Emulsion” are terms that refer to mixtures of things that
are not normally compatible and/or miscible. These terms are often used by art
supply companies as product descriptors. A dispersion (e.g. ketchup, ink) is simply
a slurry of small, solid particles suspended in a primary vehicle. There are two
categories of emulsions: oil-in-water (o/w) emulsions (e.g. mayonnaise,
moisturizers) and water-in-oil (w/o) emulsions (e.g. sunscreen).
Acrylic-Based Resins are available in a wide array of pre-dissolved solvent
solutions, as dry resins, and as commercially available fixatives. Artists should be
aware that the most of these products available today have yet to be tested for their
long-term aging properties (e.g. propensity for yellowing, darkening, difficulty to
remove over time, etc.). For absorbent panel supports, artists may consider sealing
the surface (taking care not to apply a layer that is too thick) with certain acrylicbased
resins. Paraloid B-72 can be dissolved in aromatic solvents (or combinations
of ethanol and aromatic solvents) and applied thinly to absorbent rigid supports.
Thin applications of MSA varnish may also be used to seal rigid supports. Note that
these materials will remain soluble to solvents so it is probably best to avoid
applying a subsequent layer that contains mineral spirits and/or turpentine (e.g. oil
grounds). If acrylic-based resins are used as a sealant/size, they should only be used
for absorbent rigid supports (not flexible supports) and are best used in
combination with aqueous-based grounds (e.g. acrylic).
Acrylic Polymer Dispersions come in two forms: fluid acrylic dispersions which
are composed of finely distributed particles of resin suspended in water (these
dispersions often appear “milky white” but clarify with drying) and gelled acrylic
dispersions which are fluid dispersions with additional thickeners. As the water
evaporates from a dispersion, the solid particles move closer together forming a
continuous, transparent or semi-transparent film. Certain acrylic dispersions when
delivered in dilute aqueous solutions have good penetration and wetting properties.
They dry fairly quickly and do not have to be mixed with toxic solvents.
When using an acrylic polymer dispersion as a sizing material, artists should
consider the following:
 Conduct their own experiments as it can be difficult to identify the exact
components and chemical composition of these products. Keep records of the
date purchased as well as the manufacturer.
 Check with the manufacturer to see if extensive product testing has been
performed to evaluate its suitability as a size and/or adhesive. Many
manufacturers offer acrylic dispersion mediums that are acceptable as sizes.
One, Golden’s Specialty Acrylic Polymers (GAC) line, has been extensively
tested as a size for both acrylic and oil paintings. GAC 200 can be applied as is
(if one chooses to dilute it for improved workability, it should not be diluted
further than 20-25%). GAC 400 can be used instead of rabbit skin glue to
stiffen a canvas and a coat of GAC 100 applied atop GAC 400 can help to
provide a barrier against oil penetration. It is essential that GAC products
used as sizing material be allowed to dry at 70 F/21 C before ground and
paint layers are applied. MSA varnishes can also be used as a size for sealing
panels as long as it is not applied too thickly.
 Know that acrylic polymer dispersions tend to be more stable than animal
glue sizes. However, this does depend on the polymer and/or additives
present in the dispersion. Applicability depends upon the specific purpose.
 Apply acrylic-based sizes evenly to the back, front, and sides of wooden
supports to prevent uneven warping.
 Know that acrylic gel mediums can be used to adhere fabric or paper to a rigid
support (see “Rigid Supports” document). Avoid using Golden’s Soft Gel as a
size/sealant. If acrylic gel is used as both the adhesive and size, it is
recommended that an acrylic ground also be used (avoid using a traditional
glue ground).
VINYL-BASED ADHESIVES AND SIZES
The vinyl group is the ethylene molecule minus one hydrogen atom. Vinyl-based
sizes and adhesives encompass a wide range of compounds including polyvinyl
acetate (PVA or PVAC) and polyvinyl chloride (PVC). PVA resins are colorless,
thermoplastic resins prepared by the polymerization of vinyl acetate. PVA waterbased
dispersions are the main component in most household white glues (e.g.
Elmer’s Glue). They set through evaporation/absorption. As the water evaporates,
the resin particles move closer together forming a continuous film. PVA resins are
also present in some hot-melt adhesives, sealants, fabric finishes, and inks. While
PVA resins tend to be fairly water-resistant, they produce a somewhat porous film
and are inherently acidic unless they are buffered.
When using a vinyl-based polymer as a sizing material, artists should consider the
following:
 Conduct their own experiments as it can be difficult to identify the exact
components and chemical composition of these products. Keep records of the
date purchased as well as the manufacturer.
 Not use PVC polymers as sizing or adhesives as these products may contain
potentially hazardous plasticizers and problematic additives.
 Make sure that any PVA polymer used as a size and/or adhesive will have a
neutral pH (around 7) upon setting. Lineco pH Neutral adhesive and
Gamblin’s PVA size are examples of two PVA-based adhesives that have been
buffered to a neutral pH.
 Know that pH neutral PVA adhesives are more stable than animal glue sizes.
However, this stability is dependent upon the polymer and/or additives
present in the dispersion. Some consider acrylic dispersion sizes preferable to
PVA sizes. They tend to provide a greater degree of stiffness, are less porous,
and are more efficient at preventing support induced discoloration.
 Apply PVA-based sizes evenly to the back, front, and sides of wooden supports
to prevent uneven warping.
 Know that pH neutral PVA adhesives can be used to adhere fabric or paper to
a rigid support (see “Rigid Supports” document). If a pH neutral adhesive is
used as both the adhesive and size, traditional glue grounds should be
avoided.
BEVA 371 ADHESIVE AND BEVA GEL
BEVA 371 is a mixture of ethylene vinyl acetate copolymer, polycyclohexanone
resin, phthatate ester, and paraffin wax that has been dissolved in aromatic
hydrocarbon solvent(s). (The “B” in BEVA stands for Berger as the formulation was
developed by Gustav Berger). BEVA can be purchased as a solution, film, a waxy
solid, or a gel. It has been used by conservators since 1970.
BEVA 371 adhesive is a waxy solid that contains residual aromatic solvents. It is
prepared by diluting it with solvents, allowing the adhesive to dry, and then heating
it at a temperature of 65.6 degrees Celsius. BEVA Gel is an aqueous dispersion of
ethylene vinyl acetate and acrylic resins dissolved in a cellulosic material. As BEVA
Gel has a higher molecular weight than BEVA 371, a higher temperature (70-72
degrees C) is required to activate the resin. BEVA Film is BEVA 371 adhesive that
has been cast into a thin film on a silicone-coated sheet of Mylar.
When using BEVA 371 Adhesive/Film/Gel as an adhesive, artists should consider
the following:
 Exercise appropriate health and safety procedures. All BEVA products contain
a certain amount of aromatic hydrocarbon solvents and some require
additional solvents for dilution/preparation. The heat used to activate them
can cause residual solvents to off-gas. This is less of an issue with the BEVA
Gel.
 BEVA Gel can be used in a similar manner as BEVA Film and BEVA Adhesive
but tends not to form as strong of a bond. This may not be an issue depending
on the weight and/or nature of the canvas support. It is reversible in water
which may counter indicate its use for some circumstances.
 Consider the following steps when adhering canvas to a rigid support (panel
supports should first be sealed):
Apply one to two even coats of dilute BEVA adhesive (thin cream
consistency) to the panel after cleaning the surface and two coats to
the reverse of the canvas (wear adequate protection as solvents are
required). If you are using BEVA film it is better to use two sheets of
film as opposed to one, although one sheet may be able to provide
enough adhesion. Place the film with the BEVA-side facing the panel
(or canvas if you are using two sheets) without removing the siliconecoated
Mylar and apply heat evenly using an iron (BEVA adhesive
requires a temperature of around 65.6 degrees Celsius to be reactivated).
Weight down the surface until the BEVA has cooled and
then carefully peel away the silicone-coated Mylar (NOTE: If you
attempt to remove the Mylar too soon you will pull up the BEVA). If
you are using two sheets, repeat this process with the other sheet of
BEVA film when applying to the reverse of the canvas support
(consider placing silicone-release paper/Mylar beneath the canvas
when applying heat, silicone side facing up). Then position your
canvas directly atop the BEVA film, place silicone-release paper/Mylar
(silicone side facing down) atop the canvas, and apply heat. If you are
using BEVA adhesive simply wait for the coats of BEVA to dry (in a
well ventilated space) and repeat the aforementioned step. If you
experience difficulties using BEVA film, try applying a coat of adhesive
to the back of the canvas or switch to the adhesive altogether.
OTHER TYPES OF SEALANTS
Although not traditionally thought of as sizing materials, shellac and
polyurethanes (both water-born and solvent-born) have been used to seal the
surface of wooden supports and decrease absorbency. Both prevent Support
Induced Discoloration (SID), a phenomenon that occurs when impurities in the
support migrate up through the ground and paint layers.
Shellac is obtained from raw shellac, a resinous material that is excreted by the
Laccifera lacca insect (native to both India and Thailand) and then chemically
refined or washed by hand to produce a variety of grades with varying color and
quality. Sticklac is the rawest form and still contains the red lac dye. Seedlac is
sticklac that has been repeatedly washed and strained of contaminants. It contains a
small amount of impurities that only further chemical refinement will remove. Dewaxed
shellac is seedlac from which the wax content has been removed, producing
flakes that have high water-resistance and transparency. Bleached shellac, often
considered to be the highest grade of shellac, is produced by removing both the wax
and the colored resin content from seedlac, resulting in a “blonde” or nearly
colorless product. Bleached shellac become more difficult to dissolve in ethanol the
older it is and those using it should choose only the freshest supply.
When using shellac or polyurethane as sealants, artists should consider the
following:
 Avoid using them with fabric or paper supports.
 Use them to seal wooden supports only if they are unable to use other
products (e.g. PVA, acrylics). Shellac and polyurethane are less than ideal
materials in terms of reversibility, brittleness and aging characteristics.
 Apply both of these materials as thinly as possible to the front, back, and sides
a wooden support. Applying a sealant coat that is too thick can lead to
delamination and flaking of the paint and ground layers. Two to three dilute
coats are usually sufficient. Additional coats may be needed if the support is
especially absorbent.
 Use solvent-born polyurethane in a well ventilated area and follow proper
health and safety procedures. Water-born polyurethanes are less toxic, but
create a less effective moisture barrier than solvent-born polyurethanes.
When a solvent-born polyurethane is used, a wooden support experiences
less planar deformation and/or warping.
ADDITIONAL REFERENCES AND RESOURCES
General
Gamblin Colors - Sizes and Grounds https://www.gamblincolors.com/oil-
painting/sizes-and-grounds
Golden Artist Colors - Preparing a Canvas for Oil Painting
http://www.justpaint.org/preparing-a-canvas-for-oil-painting
Golden Artist Colors - Preparing a Painting Support
http://www.goldenpaints.com/technicalinfo_prepsupp
“Cold Temperatures Effects on Modern Paints used for Priming Flexible Supports”
by Christina Young and Eric Hagan in Preparation for Painting: The Artist's Choice
and Its Consequences, edited by Joyce H. Townsend, Tiarna Doherty, Gunnar
Heydenreich, and Jacqueline Ridge (London: Archetype, 2008).
https://www.researchgate.net/publication/228778940_Cold_temperature_effects_
of_modern_paints_used_for_priming_flexible_supports
Texas A&M University - Adhesives and Consolidants Used in Conservation -
http://nautarch.tamu.edu/CRL/conservationmanual/File2.htm
New York Studio School – Notes on Sizing and Priming
http://www.nyss.org/media/uploads/workshop_pdf/Stretching_Demo_Workshop_
1.pdf
”Sizes and Grounds” in The Painter's Handbook: Revised and Expanded by Mark
David Gottsegen (New York: Watson-Guptill, 2006), pp. 51-72.
Proteinaceous Sizes/Adhesives
Natural Pigments – Preparation of Picture Canvas
http://www.naturalpigments.com/art-supply-education/cat/sizes-
adhesives/post/preparation-canvas/
Natural Pigments – Preparing Collagen Glue
http://www.naturalpigments.com/art-supply-education/cat/sizes-
adhesives/post/glue-sizes-adhesive/
Natural Pigments – Sizing Paper and Gelatin Sizing
http://www.naturalpigments.com/art-supply-education/cat/sizes-
adhesives/post/sizing-paper-gelatin/
Determining the Acceptable Ranges of Relative Humidity and Temperature in Museums and
Galleries – Part 1 by Marion Mecklenburg (Washington DC: Smithsonian Conservation
Institute, 2007) pp.8-10
https://repository.si.edu/bitstream/handle/10088/7056/Mecklenburg-Part1-
RH.pdf?sequence=1&isAllowed=y
Determining the Acceptable Ranges of Relative Humidity and Temperature in
Museums and Galleries - Part 2 by Marion Mecklenburg (Washington DC:
Smithsonian Conservation Institute, 2007) pp.4-6
https://repository.si.edu/bitstream/handle/10088/7055/Mecklenburg-Part2-
Temp.pdf?sequence=1&isAllowed=y
Acrylic Polymer Dispersions
Golden Artist Colors - Special Purpose Mediums
http://www.goldenpaints.com/products/medium-gels-pastes/special-purpose-
mediums
Golden Artist Colors - GAC Specialty Polymers
http://www.justpaint.org/gac-specialty-polymers
CAMEO Materials Database – Paraloid B-72 http://cameo.mfa.org/wiki/Paraloid@_B-72
Lascaux- Acrylic Sizing
http://lascaux.ch/pdf/en/produkte/malhilfen/impraeg_grund/52304.02_impraegn
ierungen_.pdf
Shellac
CAMEO Materials Database – Shellac http://cameo.mfa.org/wiki/Shellac
Victoria and Albert Museum – Aging Properties of Shellac -
http://www.vam.ac.uk/content/journals/conservation-journal/issue-11/the-
ageing-and-stabilisation-of-shellac-varnish-resin-an-undergraduate-research-
project-at-imperial-college/
Natural Pigments – Shellac http://www.naturalpigments.com/art-supply-
education/shellac-use-art/
University of Oslo - Investigating Shellac: Documenting the Process, Defining the
Product by Juliane Derry
https://www.duo.uio.no/bitstream/handle/10852/34480/Derry-
Master.pdf?sequence=5
Vinyl Based Adhesives
CAMEO Materials Database - PVA http://cameo.mfa.org/wiki/Polyvinyl_acetate
Lineco - White Neutral PH Adhesive http://www.lineco.com/cart.php?m=product_list&c=1118
BEVA 371
CAMEO Materials Database - BEVA® 371 http://cameo.mfa.org/wiki/BEVA%C2%AE_371
Conservation Support Systems
http://www.conservationsupportsystems.com/product/show/beva-371-
solution/beva-adhesives