Page:Popular Science Monthly Volume 90.djvu/610

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��Popular Science Monthly

��Below : On the right is a barrel filled with dry pigment. The barrel on the left contains the same pigment after it has been milled with the requisite amount of linseed oil. Conden- sation reduces the volume

���Menhaden fish are not used for food. They are steamed and pressed to extract their oil, which is used in making paint

��dressed stone. The paint conies from the mill very smooth, and finely ground. It is allowed to flow into large tanks holding sometimes a thousand gallons or more, where it is thinned with oil, turpentine and drier. Tinting colors are added if a colored paint is desired.

Linseed oil forms the liquid part of most paints. When brushed out, it takes up oxygen from the air and becomes solid, forming a rubber-like substance which is very waterproof. When pigments are added to the oil, the same thing happens, but the dried oil is made stronger and the surface to which it is applied is colored, according to the colors of the pigments used. Oil squeezed from menhaden fish is used in some special kinds of paint. Oil from the nuts of the Chinese wood-oil tree is very useful for making highly waterproof paints. It has been used by the Chinese for many centuries to smear their junks and river boats. Oils expressed from ��the soya bean, cottonseed and corn germs are used to some minor extent in the paint industry.

Turpentine is produced by distilling the resin that comes from pine trees and is used in paint to make it spread easily, to aid it in drying and to help it penetrate deeply into the grain of wood, thus securing a good bond. Mineral spirits obtained by distil- ling petroleum is used for the same purpose.

��Varnish Is Made from Prehistoric Tree-Oozings Paints which dry with a gloss are called enamels.

���Filling cans with the prepared varnish and paints from a battery of storage vats in one of the great paint factories

��high luster or These are made from zinc oxide ground in varnish. Varnish is produced from fossil resins such as copal, kauri, etc. These resins, whici origina 11 flowed froi trees, hav< been deposit^ ed for centur-^ i e s in t h earth. They' are mined in Africa and NewZealand, and are found in big lumps.

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