A natural phosphorous- containing protein found in milk. Casein is composed of the following major amino acids: glutamic acid (20.2%), proline (13.2%), aspartic acid (6.1%), leucine (9.0%), lysine (6.7%), valine (7.2%), tyrosine (5.5%), isoleucine (6.0%) and phenylalanine (5.1%) with no measurable amounts of hydroxyproline (Mills and White 1994). It has been used as a glue and binder since earliest recorded periods. Casein curds form naturally as milk sours, but it is also precipitated by adding dilute hydrochloric acid to hot skim milk. The curds are collected, washed and dried to form a white to yellowish powder. The dried casein is insoluble in water and alcohol but is soluble in carbonates and other alkaline solutions. For use, casein is soaked overnight in a solution with a weak alkali (ammonium carbonate, borax or lime) to form a clear, viscous solution. Solutions of casein are used as adhesives and as paint binders and architectural paints. The paint film is brittle but very hard-wearing. It was popular in the late 19th century for stencilling on walls as it dries quickly and has the required matt finish. Furthermore, since it is instantly soluble and does not form a thick layer, elaborate schemes could be built up with four or five overlaid stencil shapes. Casein paints are now sold in powder form or ready-prepared. See also : casein paint. Synonyms: caseinate; whey glue; Casco Glue; milk acid powder; kasein; ammonium casein; borax casein; lime-casein; Lactilith; Galalith; Erinoid; Kyloid; causeum. Trench (2000); Museum of Fine Arts, Boston (2000). [J. Cassar, R. de Angelis]