Casein paint has been used since ancient Egyptian times as a form of tempera paint, and is still used today. Some of the qualities that artists value casein paint for is that unlike gouache, it dries to an even consistency making it ideal for murals. Also, visually it can resemble oil painting more than most other water based paints, and works well as an underpainting.
A quick way to make casein painting medium is to take some skim milk cottage cheese and first wash off any of the milky fluids. The lumps of casein left behind are then dissolved by adding, in a pot, water and some ammonia. The ammonia should be preferably in the form of ammonium carbonate. As the mixture is stirred while it warms it begins to froth and the lumps dissolve. Don't boil it, but just keep it simmering and stirred until the frothing stops. Cool the syrup down and this is the medium. It will keep in the refrigerator for about four days.
Santa Clara Pueblo artist Pablita Velarde created a series of over 70 paintings of everyday Native American life in New Mexico for Bandelier National Monument between 1937 and 1943, painted mostly on masonite using casein paints.
Casein was widely used by commercial illustrators as the material of choice until the late 1960s when, with the advent of acrylic paint, casein became less popular.