(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987)
A ground is a stable, absorbent surface to which the paint can permanently adhere. All grounds are composed of gypsum (chalk) and adhesive. A good ground must have durability and a resistance to cracking.
The permanence of the finished artwork depends on the structural integrity of the support as well as the ground, both of which bear the same relationship to a painting as that of a foundation to the house built on it. No one would buy a house without having the foundation inspected, yet most artwork is collected solely on surface appearance. Many painters will take great pains to select the highest-quality paints and media to create the best possible surface appearance, yet are incredibly careless in the selection of a proper ground or support. Many artists assume, for example, that acrylic gesso can be applied to anything to make it safe to paint on. Acrylic gesso, however, should not be applied to tempered fiberboard, because the fiberboard is oil-impregnated and prevents proper bonding of the ground, leading the ground to detach itself as the board ages. Just as much care needs to be taken for what is below the surface as for what is applied on top of it.
In the past, grounds were tinted with lampblack, umber, or green earth to hide the yellowing effect of the linseed oil as it aged. The Holbein Company produces several tinted foundation whites for those who wish to duplicate the look of older painting styles.
Grounds for Paper. Acrylic gesso, which makes an excellent ground for paper, is often too thick to be easily applied directly to a paper support, yet thinning it only with water can result in a brittle ground. Acrylic gesso is made with as little binder as possible so that it will be an absorbent ground to receive paint. If it is further diluted and then placed on a highly absorbent support, such as an unsized paper, there may not be enough binder remaining in the ground to keep it flexible. Therefore, it is best to dilute the gesso with a mixture of half an acrylic polymer medium and half water, and apply two or more coats. Using the fifty-fifty mixture will replace what binder may be absorbed or washed away. It is not necessary, but it is helpful, to size the paper support before applying a ground. If a glue-sized paper with a lead white ground is desired it may be applied as it is for canvas.
Grounds for Canvas. Lead carbonate ground into linseed oil is the oldest substance still in use as a ground for oil painting. It is traditionally applied to a hide-glue-sized support, but it can just as well be placed over a support sized with polymer emulsion. Lead grounds are highly reflective and have been nicknamed silver white. They are also durable and very elastic. To maintain its flexibility, an oil ground must contain only linseed oil as its vehicle and it therefore has the disadvantage of tending to yellow.
Great care should be taken when handling a lead ground because of its toxicity. Another caution about using lead white is that air pollutants can react with unprotected lead white pigment and blackening can occur. A final protective varnish over the painting will prevent this. Nevertheless, if correctly used, lead carbonate is still one of the best options for a ground.
Today, many whites are ground only for mixing with colors and contain such oil vehicles as safflower oil, because they do not yellow as much as linseed oil. These mixing whites are not nearly as flexible and therefore not as safe for use as grounds. The term “foundation white” is often used by manufacturers to indicate that it is made to be used as a ground for painting.
The first coat of an oil ground should be applied thinly with a palette knife and worked into the surface texture. The second coat should cover the surface. Lead oil paint dries quickly, but a minimum of ten days should be allowed for the lead paints to cure before painting begins. The Fredrix Artist Canvas Company states that it ages its lead ground canvas several weeks before shipping or applying a second coat. To accommodate the impatient artist, fast-drying alkyd primers, consisting of titanium white in an alkyd resin, have recently been developed. A second coat can often be applied within three hours and will be ready for painting in twenty-four hours. Many traditionalists favor lead grounds and feel that there is little difference between alkyd primers and the use of acrylic gesso. They argue that a lead white ground supplies more than just a white surface to paint on; it also provides a naturalness to the eye that cannot be synthesized.
Gesso-which means “chalk” or “gypsum” in Italian-traditionally refers to recipes of chalk and glue for ground on rigid supports. Today, acrylic polymer emulsion gesso is so commonly used as the painting ground that it has taken the term “gesso” for itself and the original gesso is now usually referred to as powdered, or dry, gesso. Acrylic polymer emulsion gesso has not so much replaced the traditional gesso formula used on a rigid support as the hide glue and lead white ground combination used on canvas. Since the polymer of the acrylic polymer emulsion gesso can size a support as well as form a painting ground, it can be applied directly to canvas without any additional preparation. However, most painters find acrylic polymer gesso too thick to apply easily and choose to dilute it first. A very smooth surface can be achieved by first applying two coats and then sanding, and then repeating this several times until the surface is as smooth as vellum tracing paper.
Grounds for Wood or Wood Particle Panels. Only a few fastidious painters still use the traditional gesso ground of chalk (gypsum) and hide glue to size rigid supports. Polymer emulsion gesso is now the ground of choice, although the original gesso grounds are superior in absorbency and in their ability to be polished. Polymer gessos can also be polished, but not to the same degree. Modern ready-mixed commercial versions of traditional gesso often have titanium white added to increase coverage and add brilliance. This kind of gesso is supposed to be used only on rigid supports, but there is one notable exception to this rule. Over the centuries, Tibetan scroll painters have developed a technique to use this normally brittle ground on a flexible support. A thin layer of a white chalk and glue is applied to a stretched, glue-sized linen that is similar in weight to a bed sheet. The gesso surface is polished under compression first with a damp smooth rock, about the size of a small potato, and then with a small, very smooth, dry stone. This otherwise brittle ground is made flexible by the thinness of the glue and gesso layers, the application of the minimum amount of glue and size needed to create a safe ground, and the compression of the ground during polishing. This process has permitted scroll painters to create works that can be carefully, but safely, rolled and unrolled for centuries.
Whether a traditional gesso formulation or a modern polymer gesso is used to produce a ground on a wood support, it should first be sealed with a wood sealer to preserve the wood and protect the ground from any tree sap. After that, the methods of applying a polymer gesso ground to a wood support are the same as those for canvas. The preparation of a traditional gesso ground involves the same recipe for making a hide-glue size for canvas, except gypsum is added along with the glue before it is cooked (for a hide-glue recipe, see page 143). For every part of glue added to the water, two parts of gypsum are also added. After it is cooked and applied, the surface may be sanded and polished with a smooth stone or a silk cloth. Liquitex offers a convenient ready-mix called Gesso Ground Dry Mixture, which has detailed instructions for its use and how to mix it with a 10 percent hide-glue solution.
Traditional gessoed panels are often far more absorbent than those produced with a polymer gesso, and the surface often has to be primed before painting is begun.
Grounds for Metal. Metal is nonabsorbent and is a difficult surface to apply paint to. Only oil-based paints will bond permanently to the surface. Metal does not require a ground to receive paint, but it is often best to prime the surface first. This will help to keep the paint from sliding over the surface when it is being applied.