Casein paint, derived from milk, is a fast-drying, water-soluble medium used by artists. It generally has a glue-like consistency, but can be thinned with water to the degree that ...
http://en.wikipedia.org/wiki/Casein_paint

Casein (from Latin caseus "cheese") is the predominant phosphoprotein (?S1, ?S2, ?, ?) that accounts for nearly 80% of proteins in milk and cheese.
http://en.wikipedia.org/wiki/Casein

casein (k?`s?n), well-defined group of proteins found in milk, constituting about 80% of the proteins in cow's milk, but only 40% in human milk.
http://encyclopedia2.thefreedictionary.com/casein+paint

Shiva Casein Paint 39% off. Natural Casein based water paints from Shiva from Art Supply.Com in Chicago
http://www.artsupply.com/richeson/casein.htm

casein. Main protein of milk, from which it can be separated by the action of acid, the enzyme rennin, or bacteria (souring); it is also the main protein in cheese.
http://encyclopedia.farlex.com/casein+paint