China Clay for Paint Industry:
China clays are not generally used to the extent it deserves in paint industry. This is mainly due to its great oil absorption characteristics and on account of the clay becoming rather transparent when ground in oil. The average specific gravity of china clay or kaolin is 2.25, and a gallon of pulverized dry clay packed will not weigh over 6 1/2 to 6 3/4 pounds. It requires 30 pounds, or nearly 4 gallons of linseed oil to mix 70 pounds dry china clay to a stiff paste, while 55 pounds of oil and 45 pounds of clay will be about the right consistency to be spread with a brush.
Wherever whiting agent is barred out as an extender for heavy pigments for the reason that the presence of carbonate of lime makes the paint subject to disintegration from contact with sulphur gases, or that the alkalinity of whiting agent affects the color, china clay or kaolin will be the best pigment to replace it. It is really a better suspender for heavy pigments than the ordinary grades of whiting agent and only their higher costs, and the fact that it is so great an oil absorber, are against its more extended use.
To be Contd…
