40 CASEIN. 



paint, as already stated. Excellent paints are also made of 

 blood albumen and similar substances ; and in some cases, 

 glue, mucilage, dextrin, glutin, or starch, in admixture with 

 salts ; insoluble compounds being thereby formed. 



The paints with a basis of casein have proved to be best, 

 and have the most extensive use. They are made from 

 commercial casein powder, which readily dissolves in suitable 

 proportions of caustic lime, ammonia, or salts of same that 

 easily liberate these bases. When blood or blood albumen is 

 used, the one must first be well dried and the other finely 

 ground, in order that they may form a good bind with caus- 

 tic lime. Glue also must be ground, and the mass may 

 be treated with potassium bichromate, tannin, alum, etc., to 

 make it insoluble on exposure to light. Glutin must be 

 allowed to rot, and then be dried, ground and mixed with a 

 certain proportion of alkali for use. 



In preparing all these powdered paints, which are to be 

 made up into a wash with cold or hot water or milk of lime, 

 the main point is to adjust the proportions of casein, starch, 

 glue, glutin and other albuminoids so as to properly fix the 

 pigment and the material used as loading, or for shading the 

 colours. An insuffieisnt quantity of the medium would lower 

 the durability of the paint below the limit expected of it, 

 and it would not stand the action of rain, snow, etc., but 

 wipe off with the hand, or brush off. 



On the other hand, an excess of medium would make the 

 paint streaky and liable to crack and peel off. Now, as the 

 loading materials used require very different quantities of 

 binding constituents to fix them properly, this circumstance 

 must be borne in mind. The same applies to the body 

 colours, which require a larger or smaller quantity of bind- 

 ing ingredients, according as they are specifically heavier or 

 lighter. These pigments should be able to retain their colour 

 when used in mixtures containing caustic lime, alkalies, or 



