Casein Paints

Casein powder is not soluble in water, but dissolves easily when ammonia is added. When treated with certain chemicals [for example, spraying the finished coating with a 4 percent formaldehyde solution], it equals egg tempera in water resistance.

Paints made by grinding pigments in casein solutions are used for permanent painting in the gouache manner and also in mural [p. 155] painting in the fresco manner [see Mural Painting/Secco, page 184]. Their use to replace oil paints for large easel pictures has no precedent; it is a twentieth-century development. But approval as a permanent technique has been fairly universal. Cautious painters will confine the use to rigid panels; their ultimate permanence on canvas is doubtful. Casein solutions are also used as tempera ingredients; they emulsify readily with waxes, resins, and the vegetable oils; but the last named are not to be recommended since all mixtures of casein and linseed oil become quite yellow on aging. Most authorities agree that casein is inferior to glue as a sizing material and binder for grounds because of its tendency to become brittle with age; many find it less manipulative than the gum-arabic type of watercolor or gouache paint. [pp. 154-155]

Typical Recipe for Dissolving Casein - Allow 1 ounce of casein powder to soak in 6 fluid ounces of water overnight, then dissolve it by adding clear ammonia water, drop by drop with stirring, until the solution is as thick as honey and free from lumps or clots. For use as a paint binder add the preservative [1/8 to 1/4 teaspoonful of sodium orthophenyl phenate (Dowicide A)] and thin to desired consistency with about 6 fluid ounces of water. For use in gesso, start with 4 ounces of casein, 24 fluid ounces of water, use 3/4 teaspoon Dowicide A, and dilute with about 3 quarts of water. This should bind 4 pounds of chalk or whiting to a satisfactory gesso. Casein gesso is used like glue gesso but in much thinner coats.

There is also a form of casein powder called monoammonium caseinate or soluble casein, which may be dissolved by warming it in water without adding ammonia. Sometimes this material loses its ammonia content on aging; then it requires the addition of ammonia, the same as with the regular casein.

Casein is widely employed in industrial products, among which there are a few of interest to the artist. Casein glue, sold as a prepared powder to be mixed with water, is a very powerful adhesive for joining wood. Recipes for the use of adhesives made form curd date back to the eleventh or twelfth century. [p. 155]