PAINT PIGMENTS AND THEIR PROPERTIES 55 



for outside work. Lead pigments are never used with lithopone, 

 as lead sulphide results, giving a black appearance. Its char- 

 acteristic flocculent, non-crystalline nature is plainly evident 

 when examined under the microscope. 



Magnesium Silicate (Asbestine and Talcose). This pig- 

 ment comes in two forms: as asbestine and as talcose (talc, etc.). 

 The former is very fibrous in nature and is a very stable pigment 

 to use in the manufacture of paint, on account of its inert nature 

 and tendency to hold up heavier pigments, and prevent settling. 

 It also has the property of strengthening a paint coat in which 

 it is used. The talcose variety is very tabular in form. Both 



By Polarized Light By Transmitted Light 



Barium Sulphate (Barytes) 



varieties are transparent in oil, and very inert. They have a 

 gravity of about 2.7 and grind in about 32% of oil. 



Barium Sulphate (Barytes). By grinding the crude ore, 

 treating with acid to remove the iron, and finally washing, 

 floating, and drying, there is produced the commercial form of 

 this valuable pigment. It is used in large quantity as a base 

 upon which to precipitate colors, and also together with other 

 white pigments in the manufacture of ready-mixed paints. It 

 renders the paint coating more resistant to abrasion, and gives 

 to the paint certain very important brushing qualities. It is a 

 very stable pigment, not being materially affected by either acid 

 or alkali, and can be used with the most delicate colors. In 

 oil it is transparent and must be mixed with opaque pigments 



