THE TECHNICS OF CASEIN PAINTING. 67 



and it will also bear additions of ground marble, cement and 

 earthy pigments. 



New cement plaster, or such as exhibits fine cracks, 

 moisture or efflorescent salts, is best washed over with dilute 

 hydrochloric or sulphuric acid (1 part of acid to 8 to 10 of 

 water), and after a short time has elapsed wiped with a rag 

 and left to dry. A preliminary coating of caoutchouc butter, 

 Kesserl's fluoride paint, diluted blood, etc., is also advisable. 



For indoor use the ground should be impregnated with 

 alum, 1 part of which is dissolved in 5 of hot water and then 

 diluted with 10 parts more. This soaking, however, is only 

 needed for walls that have so far been coated with lime paint 

 or distemper. Gerhardt's paint soap is also recommended for 

 the same purpose, its antiseptic properties and power of 

 rendering animal matter insoluble fitting it for use on 

 articles where fungoid growth is feared. The penetration 

 of this preparation into the ground increases the durability 

 of the casein paint, especially if the alum impregnation and 

 Gerhardt's soap treatment be combined. 



Joints, cracks or holes in brick or woodwork must be 

 filled up with undiluted casein paint ; but large fissures are 

 best stopped with casein putty (c[.v.) 



If there are any damp places in the plaster, and it is 

 desired to prevent them showing through, they should be 

 impregnated with a thin solution of shellac before the paint 

 is applied. Certain impregnating varnishes are also sold for 

 the same purpose. 



Metals, such as zinc, copper and iron, may be painted 

 with quick-drying casein paints without any preparation, 

 provided the surface is clear and not covered with a film of 

 oxide. Should this, however, be present in the form, say of 

 iron rust, it must be removed, for instance by washing with 

 caustic soda and petroleum. 



Finally, in the case of surfaces that are to be decorated, 



