PAINT PIGMENTS AND THEIR PROPERTIES 



51 



tendency to chalk, but this may be overcome by admixture 

 with other pigments such as zinc oxide and iron oxide. Lane 

 has found it to be very durable when admixed with lampblack. 

 Zinc Oxide. This extremely white and fine pigment is pre- 

 pared by the roasting and sublimation of franklinite, zincite, 

 and other zinc-bearing ores largely found in New Jersey. Its 

 purity approaches in most instances 99.5 or more. It has a 



View of Bag Room receiving Zinc Oxide 



specific gravity of 5.2. On account of its stability, whiteness, 

 and opacity, it is invaluable as a pigment when a constituent 

 in a combination formula. Its extreme hardness renders it less 

 resistant to temperature changes, when used alone. Under the 

 microscope the fineness and structure of the particles are clearly 

 evident. The French-process zinc oxide produced in America 

 by the sublimation and oxidation of spelter is the purest made, 

 and superior to imported grades which often contain ultra- 

 marine blue as a whitening agent. 



Zinc Lead White. This extremely fine pigment, consisting 

 of about equal parts of zinc oxide and lead sulphate, results 



