The decorators, who formerly used the better grades of glue and gelatine for their distemper and fresco material, have made progress in the use of casein, but they require far better material than the cold water paints described in the foregoing. While for ordinary painting the alkaline soluble casein is dissolved by the aid of the cheaper calcium hydrate, the decorator will use the water soluble casein and depend upon spirit of ammonia or solutions of borax, bicarbonate of soda or waterglass to effect the solution. For special purposes emulsions of wax or oil are sometimes added. There are certain precautions which the decorator must not be unmindful of and that is, when the surface is lime plaster, it should first be coated with diluted skimmed milk, while cracks or scaled parts must be filled up. Water stains or spaces previously whitewashed or kalsomined should be treated with alum size. For fresco painting the ground work must be especially well prepared. Every coat of plaster must be thoroughly dry before the next is applied so that not a trace of moisture can be present. The colors that are safe in use with casein in fresco and distemper painting are as follows: -
Yellow. - Cadmium yellow, French ocher, chrome ocher, chrome yellow, Dutch pink, raw sienna.
Green. - Oxide of chromium green, Guignet's green, ultramarine green, terra verte, Verona green, mineral green.
A varnish that many take for a substitute for linseed oil varnish is known as casein varnish, but it is an error to think that this solution of casein in water will take the place of oil varnish. These products, under whatever name they may appear in the market, are simply solutions of casein in liquid ammonia, borax or sodium bicarbonate, waterglass or caustic soda lye, to which are sometimes added emulsions of soap, rosin or wax, turpentine, etc., to make the so-called varnish dry more rapidly and more elastic. It is applied to surfaces where the natural color of the material is not to be changed by paint, as a cheap coating to give temporary protection, though some may believe that it will exclude moisture permanently. The cold water paints on the market that are sold in this country and in Europe under fanciful names number hundreds, not to say thousands, and it is astounding to see the claims put forth in the specifications for letters patent. This does not mean, that all the cold water paints consist of casein as the binder, the brands containing animal glue are also quite numerous, especially those sold in the American market.
The dry kalsomine paints that contain glue must be dissolved in boiling water, but they are nearly, if not entirely obsolete. It may interest some of our readers to learn that casein is being used as a fixative for insoluble dyes in calico printing. The casein is dissolved in lime water for this purpose and so used.
In conclusion we would point out that casein has obtained vast importance as a substitute for celluloid. While the latter is combustible in the extreme, casein does not readily take fire. The methods of manufacture are protected by a series of patents. Due to its high insulating properties, as also to the fact that it can be worked in the cold condition and formed into any shape after softening in hot water, its uses in this connection are almost unlimited.