Rigid Supports Part I
Originally published at MITRA (Materials Information and Technical Resources for Artists) from the University of Delaware here:
(A most updated version found in this section:Resources)
MATERIALS INFORMATION and TECHNICAL RESOURCES for ARTISTS**
Rigid Supports
There are pros and cons to all solid and flexible supports. Generally speaking, an ideal support will be able to withstand fluctuations in RH and temperature, possess an adequate level of absorbency and/or tooth, remain planar and resist warping, and not become brittle or fragile with age.
One drawback often associated with flexible supports is that they are more susceptible to being damaged by physical impact (e.g. tears, impact cracks, punctures, etc.) Flexible supports made from cellulose like cotton and linen are more likely to respond to changes in the environment, giving rise to draws in the corners, an overall loss of tension, and other planar deformations. Such damages can lead to both short and long term condition issues and can affect the stability of the paint and ground layers. Because of these issues, artists are highly encouraged to affix protective backing boards to the reverse of their paintings. This helps to prevent physical impacts from the reverse and help to buffer and slow the fabric’s response to changes in humidity.
Rigid supports made from hygroscopic materials like wood are less likely to withstand physical damage but will still react to changes in the environment (e.g. warping, cracking, etc.) which can adversely affect the ground and paint layers.
There are steps that artists can take to mitigate some of these problems. One method is to adhere a fabric support over the face of the rigid panel. The fabric can serve as a less brittle interlayer which may stop the crack or split from telegraphing from the support to the ground and paint layers should the rigid support exhibit warping and/or cracking. Rigid supports can also be cradled or braced, particularly if they are large in size, to counteract possible warping or other types of planar deformations.
RIGID SUPPORTS
Many different solid support materials are available to artists. These materials include wood, metal, and modern composite materials. As there are pros and cons associated with any choice of solid support, artists should keep in mind the size, ground, and paint layers that will be applied when selecting and preparing their substrates. The following is information about a number of types of solid supports that are currently available to artists. Additional information on historical and contemporary practices relating to rigid supports is available in the section containing online resources and references.
Solid Wood Panels
For centuries painters have used hardwoods (from deciduous trees and narrow-leaved evergreens) and semi-hardwoods (partially matured cuttings from deciduous trees) including oak, mahogany, chestnut, and poplar have been used as
supports. The long-term ageing properties of solid wood panels depend on the type and cut of wood. Sapwood is the outermost portion of a tree trunk (the living part of the tree), while heartwood is the trunk’s inner (dead) core. Heartwood is more suitable for use for painting supports as it shrinks and swells less than sapwood. All solid wood panels are susceptible to some degree of warping, shrinkage or expansion. This can be lessened by the selection of the more appropriate cuts of wood ( radial rather than tangential ), proper preparation (ageing and drying) of the wooden support, and the method of treatment (finishing both sides of the panel in a similar manner). Some types of wood are more likely to experience attacks by wood-boring insects. This should be taken into consideration when selecting and preparing a wooden support.
The stability of a wooden board is greatly influenced by where it was cut from the original tree trunk. Wood expands and contracts in the direction perpendicular to the grain direction. Wooden boards tend to be most stable when they are most similar on the front and back. Tangentially sawn planks are prone to planar deformations like warping, splitting, and cracking as these planks often contain both sapwood and heartwood and the number of grain lines are very different on the front as compared to the back. Radially sawn planks are generally more stable. When a panel support is comprised of multiple planks, the orientation of the wood grain has an effect on the stability of the panel. If the grain of adjoining planks is oriented perpendicular to one another, structural problems can arise when the support experiences environmental fluctuations. Therefore, if multiple planks are to be joined together, all of the planks should have the wood grain oriented in the same direction. Supports created from multiple planks can develop splits and cracks along the joins when subjected to adverse environmental conditions, and tension between the sections of the wood can result in cracking or splitting. Artists who work on a larger scale should keep this in mind when selecting and/or preparing wooden panel supports.
When artists use wooden supports, they should:
Considering using well-seasoned hardwoods like mahogany, maple, or oak. Inspect the surface of the panel to ensure that no knots, cracks, or other deformations are present.
Use planks that are at least 2.5 cm (1”) thick, as thinner boards are more likely to suffer structural deformation.
Avoid semi-hardwoods and soft woods like poplar and pine when possible. If these woods are chosen, it is recommended that they be covered with a layer of canvas to prevent the transfer of splits and cracks from the support to the ground and paint layers. Larger format wooden supports comprised of multiple planks should also be covered with canvas (overall if possible or at least use canvas strips to cover joins/splits) to help prevent the transfer of splits and cracks from the support to the ground and paint layers.
Consider sizing (and possibly priming) both sides of the support in order to mitigate potential warping in the future. This procedure ensures that both sides of the panel will respond more similarly to environmental changes. Possible sizing materials to consider include neutral pH PVA, certain acrylic polymers (e.g. high quality acrylic dispersion mediums or gels), and varnish coatings (e.g. Regalrez 1094, MSA varnishes, etc.). Refined shellac and polyurethane coatings have also been used to effectively reduce the absorbency of the surface and to seal the wood but artists should take care not to apply these materials too thickly. Shellac and polyurethane are less than ideal materials in terms of reversibility, brittleness and aging characteristics.
Consider applying an even coat of neutral pH PVA adhesive or certain acrylic polymers (e.g. high quality acrylic dispersion mediums or gels)
when adhering canvas/paper to the surface of a panel following degreasing/cleaning of the surface. To adhere your canvas to a panel, the following steps are recommended:
Apply one even coat of PVA size or acrylic gel medium to the surface of the panel using a spatula or a brush. Lightly wet the reverse of the canvas (the side that will be adhered to the panel) with water to promote better adhesion. 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 another coat of PVA size or acrylic gel medium (stick to the same material you used previously) to the face of the canvas. Once the canvas has dried, apply a coat of PVA size or acrylic gel medium to the reverse of the panel to prevent potential warping.
Consider using BEVA 371 adhesive/film to adhere canvas to panel after the panel has been sealed. BEVA film (as opposed to the adhesive) will not penetrate the fabric support as readily as PVA adhesive and/or acrylic mediums might and the ability to re-activate the adhesive makes it far easier to eliminate any unwanted air-bubbles later on should they form during the process. To adhere your canvas to a panel, the following steps are recommended:
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 silicone-coated Mylar and apply heat evenly using an iron (BEVA adhesive requires a temperature of around 65.6 degrees Celsius to be re-activated). 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.
Consider using a temperature controlled vacuum table if you wish to adhere a completed painting onto a panel (in general this is not recommended). It may be possible to safely adhere your composition if it does not contain thickly built up paint, wax-based additives, or areas of strong impasto. Follow the instructions above but consider using a soft blotter paper over your silicone release paper/ Mylar to protect more delicate surfaces (you may also need to raise the temperature of your iron ever so slightly).
Although rabbit skin/animal glue possesses hygroscopic properties, many artists continue to use this traditional material as a size and/or adhesive. To adhere your canvas to a panel using animal glue, 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. Wearing nitrile gloves, immerse the canvas into the tepid glue (make sure that it is not so hot as to burn your hands), gently wring the fabric to remove excess glue. 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). Allow for adequate and even drying by standing the panel on its edge or leaning against a wall.
Provide additional auxiliary support to large format panels and panels that are less than ¾” thick by attaching a brace or cradle by gluing strips of wood around the outside edge of the back of the panel using the following steps:
Obtain 1” by 2” wooden boards (oak or maple are preferred) and cut them down to match the outer dimensions of the support (overall size will depend on what type of join is used for the corners). ■■■■and mitered tend to be the most common type of joins (consider using a 90 degree-corner clamp when making mitered corners), however lap joins are generally considered to be more structurally sound. Make sure that the wooden boards are perfectly aligned and flush with the outer edges by laying them on the reverse of the panel before gluing to the reverse (it can helpful to mark the position with a pencil). Use carpenter’s glue to adhere the wooden boards in place While the glue is drying, clamp/weight the boards to avoid creating any air bubbles. For large-scale supports artists may choose to construct horizontal and/or vertical crossbars although crossbars should NOT be glued directly to the reverse of the panel, only fixed to the outer boards of the cradle using glue and/or hardware.
Plywood
Plywood is a laminated wood product that is prepared by adhering together layers of thin wood veneer (plies) with the grain of each layer positioned at right angles to the grain of the preceding layer. Some types of plywood are available with a lumber, or solid wood, core.
Diagram showing the alternating directional grain of a 5-ply, wooden support. Some types of plywood are also available with a solid wood core.
The cross-laminate structure of plywood – particularly if the plies are all of equal thickness–helps ensure that the support is less prone to planar deformation. Plywood can be made from a variety of soft and hard woods. The latter tends to be more dimensionally stable. In general, the more layers, the more dimensionally
stable the plywood support. Exterior-grade plywood has superior resistance to moisture, while interior-grade plywood has the smoothest surface finish.
Gatorfoam board or Gatorboard is not plywood. it is composed of extruded polystyrene foam bonded between two layers of wood-fiber veneer. It provides a very rigid surface, but the wood-fiber layers may respond to changes in the environment.
Plywood and especially Gatorboard panels are not considered sufficiently stable for permanent use. Artists may be able to mitigate some of the problems associated with these substrates by considering the following recommendations:
Inspect the surface of plywood to ensure that are no knots, cracks, or other deformations.
Choose maple, walnut, or mahogany plywood which are more durable and stable (birch plywood can also be used, but the grain has a tendency to transfer through to the ground and paint layers over time).
For larger works choose plywood that is at least ¾” thick as this exhibits adequate dimensional stability.
Plywood can and Gatorboard panels may benefit from adhering a fabric layer to the surface before priming. These panels should be stored flat.
Consider sizing (and possibly priming) both sides of the support in order to mitigate potential warping in the future. Possible sizing materials to consider include neutral pH PVA, certain acrylic polymers (e.g. high quality acrylic dispersion mediums or gels), and varnish coatings (e.g. Regalrez 1094, MSA varnishes, etc.). Refined shellac and polyurethane coatings have also been used to effectively reduce the absorbency of the surface and to seal the wood but artists should take care not to apply these materials too thickly. Shellac and polyurethane are less than ideal materials in terms of reversibility, brittleness and aging characteristics.
Consider applying an even coat of neutral pH PVA adhesive or certain acrylic polymers (e.g. high quality acrylic dispersion mediums or gels) when adhering canvas/paper to the surface of a panel following degreasing/cleaning of the surface. To adhere your canvas to a panel, the following steps are recommended:
Apply one even coat of PVA size or acrylic gel medium to the surface of the panel using a spatula or a brush. Lightly wet the reverse of the canvas (the side that will be adhered to the panel) with water to promote better adhesion. 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 another coat of PVA size or acrylic gel medium (stick to the same material you used previously) to the face of the canvas. Once the canvas has dried,
apply a coat of PVA size or acrylic gel medium to the reverse of the panel to prevent potential warping.
Consider using BEVA 371 adhesive/film to adhere canvas to panel after the panel has been sealed. BEVA film (as opposed to the adhesive) will not penetrate the fabric support as readily as PVA adhesive or acrylic mediums might and the ability to re-activate the adhesive with heat makes it far easier to later address any unwanted air-bubbles should they form during the procedure. To adhere your canvas to a panel, the following steps are recommended:
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 silicone-coated Mylar and apply heat evenly using an iron (BEVA adhesive requires a temperature of around 65.6 degrees Celsius to be re-activated). 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.
Consider using a temperature controlled vacuum table if you wish to adhere a completed painting onto a panel (in general this is not recommended). It may be possible to safely adhere your composition if it does not contain thickly built up paint, wax-based additives, or areas of strong impasto. Follow the instructions above but consider using a soft blotter paper over your silicone release paper/ Mylar to protect more delicate surfaces (you may also need to raise the temperature of your iron ever so slightly).
Although rabbit skin/animal glue possesses hygroscopic properties, many artists continue to use this traditional material as a size and/or adhesive. To adhere your canvas to a panel using animal glue, 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. Wearing nitrile gloves, immerse the canvas into the tepid glue (make sure that it is not so hot as to burn your hands), gently wring the fabric to remove excess glue. 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). Allow for adequate and even drying by standing the panel on its edge or leaning against a wall.
Provide additional auxiliary support to large format panels and panels that are less than ¾” thick by attaching a brace or cradle by gluing strips of wood around the outside edge of the back of the panel using the following steps:
Obtain 1” by 2” wooden boards (oak or maple are preferred) and cut them down to match the outer dimensions of the support (overall size will depend on what type of join is used for the corners). But and mitered tend to be the most common type of joins (consider using a 90 degree-corner clamp when making mitered corners), however lap joins are generally considered to be more structurally sound. Make sure that the wooden boards are perfectly aligned and flush with the outer edges by laying them on the reverse of the panel before gluing to the reverse (it can helpful to mark the position with a pencil). Use carpenter’s glue to adhere the wooden boards in place While the glue is drying, clamp/weight the boards to avoid creating any air bubbles. For large-scale supports artists may choose to construct horizontal and/or vertical crossbars although crossbars should NOT be glued directly to the reverse of the panel, only fixed to the outer boards of the cradle using glue and/or hardware.
Hardboards, Fiberboards, etc.
The terms “hardboard” and “fiberboard” are often used interchangeably despite the fact that they are different products. The major difference between hardboards such as fiberboard panels like Medium Density Fiberboard and High Density Fiberboard (e.g. Masonite) is the way in which they are manufactured.
Hardboard panels are generally created through a wet/dry process which relies on naturally present cellulosic lignin in the wood to cement the fibers together. Tempered hardboards are impregnated with an oily or resinous substance making them darker in color (untempered hardboards are usually a light brown color) and more resistant to moisture and mechanical damage (and therefore subsequent warping, raising of fibers, etc.) than untempered hardboard. Support- induced discoloration (SID) will occur if the oily or resinous material migrates through the size or sealant and stains the ground and/or paint layers. Masonite, one of the most commonly manufactured hardboards, first began to be used for artistic purposes in the late 1920s
Fiberboard panels are created through a dry process that relies on chemical agents like urea-formaldehyde to bind the wood fibers together. High Density Fiberboard (HDF) is superior to Medium Density Fiberboard (MDF) as it has significantly higher internal bond strength and is less susceptible to moisture damage. However, HDF is still prone to planar deformation. Proper sealing or sizing and ground application can mitigate this problem.
Clayboards are high-density fiberboards that have been coated with a layer rich in clay (kaolin). Because the clay layer serves as a stable ground, clayboards are not prone to support-induced discoloration (SID). Ampersand Art Supply is a major distributor of clayboards (and other solid supports for artists).
The advantages of these boards over wood are that they are available in large sheets, have no grain (i.e., no directional movement), and are not as sensitive to climatic changes or attack by wood-boring insects. Large sheets do tend to warp and twist and corners can become bent, compressed, or expanded. Untempered hardboards should not be used if long-term preservation is a concern. Untempered hardboard was once preferred over tempered due to the earlier use of substantial amounts of oil incorporated into the earlier tempering formulations which could make them inappropriate as a surface to receive water-containing grounds. High-quality hardboards purchased from respected suppliers do not suffer from this defect.
When artists choose to use these supports, they should:
Degrease the surface with denatured alcohol before applying layers of size, ground, and/or paint. Without this preparation, ground layers may not adhere to the smooth side of these supports because of surface resides such as paraffin wax that may be left during the manufacturing process.
Gently sand the face of the panel with fine sandpaper (e.g. 220 grit) to provide a slight mechanical tooth but be careful to not overly roughen the surface and unevenly expose the wood fibers. This can lead to irregular swelling of the substrate (particularly when water-based sizes, sealants and/or priming/ground are applied).
Consider sizing (and possibly priming) both sides of the support in order to mitigate potential warping in the future. Possible sizing materials to consider include neutral pH PVA, certain acrylic polymers (e.g. high quality acrylic dispersion mediums or gels), and varnish coatings (e.g. Regalrez 1094, MSA varnish, etc.). Refined shellac and polyurethane coatings have also been used to effectively reduce the absorbency of the surface and to seal the wood but artists should take care not to apply these materials too thickly. Shellac and polyurethane are less than ideal materials in terms of reversibility, brittleness and aging characteristics.
Consider applying an even coat of neutral pH PVA adhesive or certain acrylic polymers (e.g. high quality acrylic dispersion mediums or gels) when adhering canvas/paper to the surface of a panel following degreasing/cleaning of the surface. To adhere your canvas to a panel, the following steps are recommended:
Apply one even coat of PVA size or acrylic gel medium to the surface of the panel using a spatula or a brush. Lightly wet the reverse of the canvas (the side that will be adhered to the panel) with water to promote better adhesion. 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 another coat of PVA size or acrylic gel medium (stick to the same material you used previously) to the face of the canvas. Once the canvas has dried, apply a coat of PVA size or acrylic gel medium to the reverse of the panel to prevent potential warping.
Consider using BEVA 371 adhesive/film to adhere canvas to panel after the panel has been sealed. BEVA film (as opposed to the adhesive) will not penetrate the fabric support as readily as PVA adhesive or acrylic mediums might and the ability to re-activate the adhesive with heat makes it far easier to later address any unwanted air-bubbles should they form during the procedure. To adhere your canvas to a panel, the following steps are recommended:
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 silicone-coated Mylar and apply heat evenly using an iron (BEVA adhesive requires a temperature of around 65.6 degrees Celsius to be re-activated). 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.
Consider using a temperature controlled vacuum table if you wish to adhere a completed painting onto a panel (in general this is not recommended). It may be possible to safely adhere your composition if it does not contain thickly built up paint, wax-based additives, or areas of strong impasto. Follow the instructions above but consider using a soft blotter paper over your silicone release paper/ Mylar to protect more delicate surfaces (you may also need to raise the temperature of your iron ever so slightly).
Although rabbit skin/animal glue possesses hygroscopic properties, many artists continue to use this traditional material as a size and/or adhesive. To adhere your canvas to a panel using animal glue, 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. Wearing nitrile gloves, immerse the canvas into the tepid glue (make sure that it is not so hot as to burn your hands), gently wring the fabric to remove excess glue. 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). Allow for adequate and even drying by standing the panel on its edge or leaning against a wall.
Provide additional auxiliary support to large format panels and panels that are less than ¾” thick by attaching a brace or cradle by gluing strips of wood around the outside edge of the back of the panel using the following steps:
Obtain 1” by 2” wooden boards (oak or maple are preferred) and cut them down to match the outer dimensions of the support (overall size will depend on what type of join is used for the corners). But and mitered tend to be the most common type of joins (consider using a 90 degree-corner clamp when making mitered corners), however lap joins are generally considered to be more structurally sound. Make sure that the wooden boards are perfectly aligned and flush with the outer edges by laying them on the reverse of the panel before gluing to the reverse (it can helpful to mark the position with a pencil). Use carpenter’s glue to adhere the wooden boards in place While the glue is drying, clamp/weight the boards to avoid creating any air bubbles. For large-scale supports artists may choose to construct horizontal and/or vertical crossbars although crossbars should NOT be glued directly to the reverse of the panel, only fixed to the outer boards of the cradle using glue and/or hardware.
(Continued in Part II)