Milk protein based, it is used as a binder in colors for paintings, as an adhesive, and also as a binder for gesso when preparing grounds for painting. When mixed with water and dry pigments, it makes an excellent paint. The base is a yellow powder that is made by drying the curd of skim milk. It was first widely used in the 19th century, and some historians think it was used earlier by painters and sculptors of early civilizations. It is known that a glue from curd was used by Egyptians, Greeks, Romans and Hebrews, and it is mentioned as an adhesive in 11th-century manuscripts. However as a binder in paint it is not referenced earlier than the 18th century. More recently it has has been very popular for commercial illustration until acrylics became highly developed. American artists who have used casein include Hans Hofmann Paul Cadmus, Oscar Bluemner, Yasuo Kuniyoshi, Emil Bisttram and Fairfield Porter. Source: Ralph Mayer, "A Dictionary of Art Terms and Techniques"; AskART Biographies <br><br>A natural protein obtained from cow&#39;s milk. Produces a flat, water-resistant film.<br><br>A water-soluble protein found in milk that is used as a binder for creating casein paints. Casein is sometimes used as an underpainting for oil or acrylic painting.