CRUDE MINERAL PIGMENTS 323 



Asl)estos can hardly \)e classed as pi^nienl, altliou^h \viu>ii 

 used as a filler its white color lightens the color of the material 

 to which it is added. The chief use of asbestos in paint manu- 

 facture is to yield a so called n()ninflamma])le or fireproof paint. 

 The fibrous varieties of talc arc also used for this purpose. 

 Only a small proportion of the total production of asbestos 

 in the United States is utilized in paint manufacture. 



Both the natural mineral and the artifical product made 

 in the electric fu.rnace are used as a black pigment and in pen- 

 cils, crayons, and in stove polish. The color of the pigment 

 is a dull ]ilack and permanent, and on account of its resistance 

 to the action of the atmosphere, as wtII as that of ordinary 

 chemicals, it is of great value as the basis of a protective paint 

 for coating oxidizable metals, chiefly iron and steel. 



The purer grades of as})haltum are largely used as a basis 

 for the manufacture of a black varnish, and as a protective 

 paint for the interior of chlorine stills, bleaching powder cham- 

 bers, acid tanks, and like apparatus. Asphaltum is not acted 

 upon by ordinary chemicals, and for this reason it is invaluable 

 for protecting structures of iron, steel, and even wood, w^hich 

 would be rapidly destroyed by acid fumes unless coated with 

 some inert material. 



WTiiting, or Paris white, is composed of calcium carbon- 

 ate (CaCOa). Calcium carbonate occurs quite extensively in 

 nature, either in the cr>'stalline form, as the w^ell known min- 

 eral calcite, or calc spar, or in the compact form, such as marble 

 and limestone, or as the soft compact variet}' known as chalk. 

 It is produced artifically as a by-product of many chemical 

 operations. The whiting used in commerce is generally pre- 

 pared by grinding and levigating pure chalk, large deposits 

 of which occur, notably in England and France. The chief 

 use of whiting as a pigment is to modify the shade of other 

 pigments. It is also largely used as a basis for whitewash, 

 and when mixed mth from 15 to 18 per cent of Unseed oil it 

 forms putty. 



