PAINT PIGMENTS AND THEIR PROPERTIES 53 



from the reduction, volatilization and subsequent oxidation of 

 sulphur-bearing lead and zinc ores. It has a specific gravity of 

 4.4. Its slightly yellowish tint bars it from being used alone 

 very extensively, but when mixed with white lead, zinc oxide 

 and inert pigments, or used as a base for colored paints, it is of 

 considerable value. The magnification of the particles shows 



Asbestine Mine at Easton, Pa. 



the peculiar way in which the pigment agglomerates, and the 

 characteristics of a fine, uniform pigment. 



Lithopone. Lithopone, probably the whitest of pigments, 

 results from the double decomposition of zinc sulphate and 

 barium sulphide, thereby forming a molecular combination of 

 zinc sulphide and barium sulphate. The peculiar property which 

 it possesses, of darkening under the actinic rays of the sun, 

 makes it essential that it be combined with other, more stable 

 pigments to prolong its life when exposed to weather. Litho- 

 pone contains approximately 70% barium sulphate, 25 to 

 28% zinc sulphide, and as high as 5% of zinc oxide. Its 

 specific gravity is about 4.25. It is excellently suited for 

 interior use in the manufacture of enamels and wall finishes. 

 When properly mixed with other pigments, such as zinc oxide 

 and calcium carbonate, fair results are obtained as a pigment 



