THEORY AND PRACTICE OF PAINT MAKING 99 



found for the chemically inert pigments with rod-like or hair- 

 like structure, to strengthen the film, just as the steel rods and 

 iron mesh are used to reinforce concrete in structural work - 

 a suggestion which, since the first publication of the address, has 

 been widely accepted as a practical aid in the manufacture of 

 good paints." 



Use of Inert Pigments. There seems to be no reasonable 

 doubt as to the efficiency of a small amount of inert pigments 

 in paint, and the writer has often compared the manufacture of 

 paint of the above type to the making of various alloys wherein 

 zinc, copper, and other metals are added to gold in order to make 

 a product possessed of greater durability, etc. 



Batteries of Color Grinding Mills 



There has been considerable inquiry as to just what is meant 

 by the statement that " a moderate percentage of inert pig- 

 ments, combined with properly adjusted mixtures of white lead 

 and zinc oxide, have given wonderful service in all the tests." 

 The writer has been asked to define what " moderate " means. 

 A " moderate percentage of inert pigments " should be defined 

 as that amount of natural crystalline pigments that will, when 

 mixed with white lead and zinc oxide, not materially detract 

 from the hiding power of white lead and zinc oxide. It is possi- 

 ble to mix a certain percentage of these crystalline pigments 

 with white lead and zinc oxide, and, by thorough grinding, incor- 

 porate them in such a manner that the mixture will show nearly 

 as good a hiding power as the straight white lead and zinc oxide. 



