Stretched Supports
|
|
Stretched Supports(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987) By the Renaissance, fabric was widely used as a support for painting and had almost replaced the wooden panel. Panels are heavy and the paintings on them are easily damaged. A bumped panel can send ripples through the surface, weakening the bond between the ground and the support. Fabric stretched over a frame resolved the two major problems of weight and elasticity. The time-tested practical approach to painting on a fabric support, such as canvas, is to stretch it across a frame, stretcher bars, or a panel. Paintings particularly oils-that are completed on unstretched fabrics and later stretched, form tiny, almost invisible, cracks in the paint film, which eventually become larger. Therefore, unstretched artwork should remain unstretched and stretched work is best left alone. Of all the possible fabric supports, canvas is the best choice because of its long history of durability. The term "canvas" is derived from canabis, also known as hemp, which, with flax, was the first fiber used to produce sailcloth. "Canvas" now includes jute, which is used to make burlap, and cotton. Of these three, cotton and flax, or linen, are the most popular. There are several ways to classify canvas. For the artist,. the most important information involves the ounces per square yard and the thread count. This information, however, is sometimes difficult to obtain. Ounces per square yard will tell how heavy the canvas is. Threads per square inch will tell how dense the canvas is. Canvas that is less than seven ounces per square yard with a thread count of less than fifty threads per square inch is too lightweight for use as a support for painting. It will not be sufficiently strong to resist tearing and the spaces between the threads will be too large to fill adequately during sizing. As long as the canvas is heavier than seven ounces with a tighter weave than fifty threads, your choice can be based more on appearance and feel than technical specifications. Linen has been found in Stone Age remains and in the tombs of ancient Egypt and has proven its durability. The linen wrappings from Egyptian mummies are still flexible today. The source of linen fibers is the flax plant, whose fibers are stronger than any other natural fiber and range in length from 10 to 36 inches. Linen fibers are round, not flat like cotton, which gives linen fabrics their irregular texture. Chemically, the fibers are 70 to 80 percent cellulose and contain the same oil that is found in the plant's seeds and that is used in linseed oil. The natural content of linseed oil preserves the fibers and keeps them flexible. On the other hand, it was long ago discovered that paintings using linseed oil on unsized linen rotted quickly, because the fibers can stand only so much linseed oil. When linseed oil dries it becomes acidic and will attack the cellulose. Today, the problem of acidity is greater, because of the acidic air pollutants, which can also attack the cellulose of linen. Bleached linens should not be used as a support for painting because the bleaching process severely weakens the fibers. The ropelike quality of the linen fibers produces an irregular texture which is especially ideal for figurative painting because of the sense of depth it gives to the surface. Unfortunately, linen is more difficult to stretch than cotton canvas, for it has a tendency to sag after the first attempt, thus requiring tightening. In addition, linen is often two to three times more expensive than cotton and is difficult to obtain in weights greater than seven ounces with thread counts greater than fifty. Although a thin linen canvas is stronger than a thin cotton canvas, artists should nevertheless use linen heavier than seven ounces per yard and denser than fifty threads per inch, with as few knots as possible. Today, the best grades of linen are produced in Belgium. Yet, few artists can afford an eight- to ten-ounce, tight-weave Belgian linen in widths larger than 54 inches, let alone find it. At the present time, most of the affordable linen is imported from Southeast Asia. The quality and consistency is not as good, but it is adequate. Cotton, like wood and linen, has been in use since prehistoric times, particularly in the Orient. The best cotton comes from the east coast of the United States; the second best is from Egypt. Cotton fiber is almost pure cellulose and is easily affected by acid and bleach. Therefore only unbleached cotton fabrics should be used as supports for paintings, and they should be sized before oil painting to protect against acidity. There are several negative aspects of using cotton as a support for painting. For figurative painting, cotton has a less interesting texture than linen. It is also less strong than linen, for its fibers are shorter, ranging from 5/16 to about 1 1/2 inches in length. Cotton fabrics derive their strength more from the process of twisting the yam during manufacturing than from the weight or thickness. A well-twisted yarn can be stronger than two yams of the same thickness that are not twisted. But, it is very difficult for most people to perceive this quality by casual inspection. What you can look for to give you an indication of the quality is the "trash" content. Trash is the waste recovered from the processing of the cotton bolls and, to cut expense, a small amount is often added back into the cotton as a filler. If too much trash is used, the strength of the fabric will suffer. An indication of the amount of trash in a fabric is the brown specks, called moats, which come from the seeds and husks of the cotton boll. The fewer moats you see, the less trash and the better the quality of the canvas. Lack of strength in a cotton canvas can be overcome by selecting a heavier weight and a tighter weave. Eight ounces per square yard should be a minimum. Most professional painters use a ten- to twelve-ounce canvas with a weave so tight that few if any holes can be seen when the fabric is held up to the light. Cotton is not as permanent as linen because it lacks linen's natural oil content. Cotton fabrics are basically unprotected cellulose, which is easily attacked by acidity. The exposure to the acidity from air pollution and ultraviolet light over several decades will substantially weaken a cotton canvas. This can be somewhat compensated for through proper sizing with acrylic mediums. Commercially Prepared Canvas is an alternative for those painters who do not wish to prepare a painting support themselves. Preparing a traditional glue-sized, lead-primed, linen canvas requires skill as well as effort, and a prepared canvas is often the only sane option. Manufacturers of prepared canvas refer to their products as "primed" canvas because they are ready for use without further preparation. This is not an accurate use of the term "primed," but it has been adopted because of convenience. It is simply easier to say "double-primed linen," for example, than "linen with a hide-glue size and a lead white, oil ground." Unfortunately, this use of the term "prime" has carried over to common artists' vocabulary, occasionally leading to incoherent discussions of various products and methods used in the preparation of canvas for painting. In this discussion of prepared canvas, the commercial descriptions of products are used, but please do not confuse them with the proper use of the term "primed." There are four basic varieties of prepared canvas available in most artists' materials stores. They are acrylic-gesso-primed cotton, acrylic-gesso-primed linen, glue-sized single-primed linen, and glue-sized double-primed linen. All of them can be used as supports for oil paintings. Acrylic or vinyl paints, however, may only be used on the acrylic-gesso-primed canvases, which conforms to the rule of not using a water-based paint over an oil-based surface. "Single-primed" and "double-primed" refer to the number of coats of lead paint that have been applied. The more coats, the smoother the surface, the stiffer the canvas, and the greater difficulty in stretching it. "Double-primed" is less flexible than "single," which makes its permanency more questionable. Commercially prepared primed canvas comes in several forms: rolls, panels, pads, and stretched. The rolls are generally of 6-yard lengths with widths ranging from 45 to 84 inches. Most are made from eight-ounce canvases, although different weights and weaves are common. There are differences in quality, but they are, in most cases, not related to permanency, and choice should therefore be based mainly on cost and personal taste. The only caution to be taken in your selection is the weight, or strength, of the canvas. Remember that the larger the painting, the heavier the canvas should be. Preprimed and stretched canvases are often of a quality too poor for professional work, and are normally reserved for studies or experimentation. The better grades are considered by many to be minimally acceptable in sizes up to 24"x30". Beyond this size, substantial reinforcement is often required. Canvas pads and canvas panels are not suitable for truly professional work. Stretching Canvas(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987)
|
Number of Visits to this site since Feb.18, 2008
Questions regarding materials and the
creative process will be considered a request for a consult and
|