CASEIN PAINTS. 43 



It is extremely important that they should all be very 

 finely powdered. The caustic lime, Ca(OH) 2 , is obtained 

 as -a fine white powder by slaking lumps of pure calcined 

 marble lime with one-third their own weight of water in 

 a porcelain vessel. The water and lime combine to form 

 calcium hydrate, with liberation of heat and a faint alkaline 

 smell. The resulting slaked lime should be kept in tightly 

 closed vessels or, preferably, used at once. 



With regard to making this preparation in different colours, 

 it should be noted that the mixing of the earthy pigments or 

 so-called lime-proof colours may take place either when the 

 paint is being made or else just before use (see instructions 

 later). The following pigments are fast to lime : Antimony 

 yellow, barium yellow, barium white, ivory black, chrome 

 green, chrome orange, colcothar, green earth, cadmium 

 yellow, cobalt blue, cobalt green, Mars brown, Naples 

 yellow, ochre, Paris black, satinober, Schweinfurt green, 

 Terra di Siena, ultramarine, umber, Vandyke brown, and 

 zinc white. If the pigments are added at the time of 

 manufacture, the weight of levigated chalk must be reduced 

 by that of the pigment used. For instance : 



Casein, soluble in alkali 10 parts. 



Caustic lime . . . .... 10 ,, 



Levigated chalk 40 ,, 



Ochre 40 



Borax as before ; ultramarine nil. 



When, by making a little of the mass up into paint, the 

 ingredients have been found to be thoroughly mixed, the pow- 

 der must be packed in tightly closed boxes, lined with paper. 

 In this way the article will keep indefinitely, in a dry place, 

 without losing any of its properties. 



Making this powder up into paint is a comparatively easy 

 matter, though a certain amount of care is necessary to en- 

 sure good results. The operation may be performed in any 

 vessel that is clean and free from grease, in the following 



