Unstretched Supports
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Unstretched Supports(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987) Wood is the oldest unstretched support, and examples of its use date back to 2900 B.C. in Egypt. During the Renaissance, oak was the wood of choice, followed in popularity by pine and then poplar. Wooden supports were panels made from boards joined together at the edges. Today, even if you chose to duplicate these panels and had the carpentry skills and knowledge of woods necessary to produce them, you would have great difficulty finding properly cured hardwood milled in the correct manner. Panels that are built up from boards joined side to side have the drawbacks of being heavy and having a tendency to develop a washboard effect on the surface of improperly prepared panels. Today's unstretched supports include canvas, paper, plywood, fiberboard, particle board, and metal. Plywood is available in two types. One has a solid wood core and a wood veneer on both sides. The other, which is most often used as a support for painting because of its availability and lower cost, consists of several veneers of wood glued with the grain at right angles to each other. The veneers of wood are produced by rotary cutting; a whole log is cut on a giant lathe by rotating it against a blade, shaving off layers. In all veneer plywood the inner layers are of a cheaper grade and are thicker than the veneer. The outer veneer can range from a construction grade to that of a fine-quality hardwood. A hardwood surface veneer plywood with one good side that is at least -1/4-inch thick is sufficiently warp-resistant for use as a support. Plywood is actually stronger than its equivalent in wooden planks and less subject to shrinkage and warpage. The problem with using plywood as a support for artwork is that the glue that bonds the plies can fail. In addition, a washboard effect can develop in a painting because the veneer is cut in a rotary fashion and then flattened and joined edge to edge to cover the large surface. In general, wood does not expand or shrink equally in all directions and, because of this, not only can this washboard effect appear but the entire board, no matter how thick, can warp. Gluing 1" X 2" strips of wood to the back of the plywood and sealing both sides with a wood sealer can help to prevent this. Sealing plywood also helps to reduce the tendency of the grain (the correct term for what most people call grain is actually "figure") to swell when such waterborne materials as acrylic gesso are applied. Most commercial wood sealers are oil-based so that they themselves will not swell the grain (figure) of the wood during application. Yet this does not present a problem for the subsequent application of acrylic emulsion paints or grounds because sealers work by soaking into the wood rather than sitting on top of it; they do not prevent paint or ground from also soaking in and establishing a firm mechanical bond. This appears to be one of the few exceptions to the rule of never applying a waterborne paint over an oil-based material. The surface should be lightly sanded after the sealer has dried and before the application of the size or ground. This increases the surface tooth for better adhesion. Fiberboard, commonly called by its trade name, Masonite, is made of ground wood chips, which include bark, that have been broken into fibers with the aid of steam and pressure. The fibers are glued together and formed into a sheet using the lignin content of the wood (lignin is the natural adhesive that holds a tree together) and some synthetic resin adhesive. Wax, rosin, paraffin, and a preservative are often used as additives to control moisture content and to resist attack from mildew and rot. A hardwood fiberboard, commonly referred to as tempered fiberboard, is produced by treating fiberboard with heat and impregnating it with oil. Tempered fiberboard is dark brown and has two smooth sides. Untempered fiberboard is chestnut brown and has only one smooth side. Fiberboard is dense, hard, durable, and does not warp or bend easily. Its thickness ranges from '/e to ' inch; '/a-inch is most commonly used as a support. Sheet sizes can be found up to 4' x 16'. Only untempered fiberboard should be used as a support. Tempered fiberboard is unsuitable because the oil impregnation does not allow for a secure ground. Fiberboard supports of 24"x36" and larger should be reinforced by gluing a framework of 1" x2" wood strips, made of either basswood or mahogany, to the back, as would be done for a framed panel. Particle Board, which is made from byproducts of milled lumber, began to be manufactured during the 1940s after synthetic resin glues were developed. Particle board, an inexpensive alternative to plywood, is formed by mixing wood chips and sawdust with a water repellent and a preservative and then gluing them together. Particle board looks like a wooden version of meatloaf, and when it is made wet it develops a similar texture because the wood chips swell and rise above the surface. Consequently, it is necessary to seal particle board with a wood sealer prior to preparation for painting. It also has no internal structure and tends to sag, particularly when it is exposed to moisture, unless it is sealed and reinforced with wood strips on the back. Particle board comes in the same sizes and thicknesses as plywood. A minimum thickness of 34 inch is best for use as a support for painting. Particle board is heavy, however, and the edges tend to crumble, which does not make it the best choice for a support. It has also been found to give off hazardous formaldehyde vapors. The only reason particle board still remains in use is because it is inexpensive. Metal was not used as a support for large paintings until the 1970s. In ancient times, metals were rare and too expensive to be used as a support for painting, except in the case of miniatures. Since metal is heavy, only thin metal sheets could be used and they were often too flexible. Copper was commonly used for miniatures until the development of aluminum, which was first used commercially in 1886. It was not a practical alternative until the introduction, in the 1970s, of aluminum honeycomb support panels, which were originally used by conservators for relining canvases. Frank Stella was the first major contemporary artist to use this material to produce sculptural paintings. Aluminum honeycomb support panels have a honeycomb aluminum core with a cell size of 3/8 inch and thickness of 9/16 inch covered on both sides with a skin of aluminum alloy that is 0.025-inch thick. The skin and honeycomb are bonded together with heat and pressure-cured epoxy. Some manufacturers, such as the Process Materials Corporation, supply the panels with a redwood edge. The overall thickness is 5/8 inch. There is no standard size because the panels are custom made. They are extremely expensive; a 40"X60" panel costs several hundred dollars.
The main advantage of this material is that it does not warp, is very strong and lightweight, and resists sagging. Unlike copper, which reacts with the linseed oil in oil paint and turns green, aluminum is relatively inert. However, an aluminum surface that is polished is not as good a support as a surface that is sanded or slightly oxidized. Although all metal supports can be painted on without sizing or ground, the surface of aluminum must be completely covered with paint or protected with a varnish. If this is not done, the moisture in the air will react with the aluminum and will result in corrosion. Unstretched Canvas has been successfully used as a support, but it has never quite caught on. Ed Moses, the founder of nonrigid, unstretched artwork, developed a means of impregnating paper or fabric art with an acrylic polymer medium to give it strength and durability. This process basically involves coating both sides of the material with a pure acrylic polymer (made by the Rohm and Haas Company), or any other acrylic polymer medium. The wet, coated material is then spread out on a sheet of glass to dry. When it is dry it can be carefully peeled off the glass. Collages can be made by adding coated dry material to the coated wet material on glass and, when dry, can be removed as one piece. The surface, although slick, will accept thin layers of acrylic or oil paint. Unstretched canvas can also be primed with acrylic gesso and then painted over with acrylic paints. However, uneven surfaces, shrinkage, and how to hang, display, and store unstretched artworks make this type of support problematic. A traditional hide-glue sizing and lead white priming should not be attempted on unstretched supports because of the potential for cracking. Paper painting supports should, in general, be heavyweight and have a high cotton content, like 300 lb., 100 percent cotton watercolor paper or 100 percent cotton museum board, both of which are durable and sufficiently absorbent to be adequately sized and primed for oil or acrylic painting. Wood-pulp papers or boards can be used if they are first thoroughly coated with an acrylic polymer medium on both sides. However, these are still not considered as safe for fine artwork as cotton papers and boards. Lightweight papers as well as print papers can be used, but they are best avoided until after experimentation with heavy paper and board. With rare exceptions, when using paper or board as a support the finished painting must still be framed behind glass, like any other paper artwork for proper protection. (Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987)
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