SUNDRY APPLICATIONS OF CASEIN. 



153 



in contact with a priming containing lead, it follows that 

 they will undergo an entire change, often in a few years 

 turning brown and even quite black. Hence, even when an 

 artist carefully avoids the use of lead pigments, in order to 

 increase the life of his work, his precautions are of no avail 

 should he unhappily use canvas that has been primed with 

 a composition containing lead varnish. 



For this reason the use of casein for priming offers a 

 series of noteworthy advantages ; and it is especially indicated 

 where the risk of cracking comes into consideration. A can- 



PIG. 11. Werner and Pfleiderer's Kneader and Mixer with Heated Trough. 



vas prepared with casein is more durable and comparatively 

 cheaper than one primed with linseed varnish, and only a 

 little dearer than when distemper is used in priming. 



Casein soluble in alkali or in water may be used, the latter 

 being preferable because prepared on a manufacturing scale. 

 The casein powder is dissolved in the following manner : 



Thirty parts of clean water are heated in a pan to about 

 176 F. and then poured into the kneading and mixing 

 machine shown in Fig. 11, which is fitted with an arrange- 

 ment for heating the trough. The stirrers having been 



