Page:Popular Science Monthly Volume 92.djvu/420

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��Popular Science Monthly

��been grown in the northwestern States, in Canada and in India for many years. A new and important source of supply is Argentina, in South America. The flax- seed is crushed and then heated to a tem- perature of about 160 degrees. It is pressed in large hydraulic- presses and yields from 26% to 34';o of linseed oil. This oil is set- tled or filtered, and then treat- ed chemically to remove cer- tain mucilag- inous matter, called "foots," before it is ready for the varnish maker.

China Con- tributes a Won- derful Oil

China wood- oil is another large factor in varnish making, is the product the "Tung nut," a nut growing in China. The nut has a soft shell and a meat similar in appearance to the Brazil nut. The shells are removed, then the nuts are crushed, heated and pressed in the most primitive way to produce the oil which is shipped to this country for varnish making. The oil has peculiar waterproof qualities not common to lin- seed oil.

Turpentine is the product of the long- leaf pine tree, grown in the Southern States of this country. The sap of this tree is collected and distilled. The dis- tillation produces turpentine and resin. Rosin is also used in the manufacture of the cheaper varnishes and after it has undergone certain treatment it becomes

���Varnish kettles. A coke fire heats them. The gum is melted, then oil is added

Varnish makers experiment many years to get better mixtures. This is a brush test

��fit for use in varnishes of better quality. All of the raw materials are brought together in the varnish factory and care- fully tested and graded for purity, color and other characteristics.

How the Varnish Is Made

The varnish itself is made by melting a quantity of gum in a cov- ered copper or aluminum ket- tle, over a fire. Coke is the fuel usually em- ployed. The varnish maker knows when the gum is suf- ficiently melt- ed, by the way it runs oflf the end of his stir- ring rod. The kettle is re- moved from the fire, and the oil, which may or may not have been previously heated, is added to the melted gum. The cover is removed and the kettle re- turned to the fire. The mixture is then cooked at a de- termined tempera- ture until it has a certain viscosity or "body." The ket- tle is cooled down to a temperature at which it is safe to add the thinners. The next step is the aging of the varnish. Certain varnishes attain their perfect condition only after long months of standing in tanks, where a slow blending- process goes on. This aging gives to the varnish properties that make it last. The varnish has to pass rigid tests for "body" or viscosity, for color, and for dry- ing quality also brushing and flowing tests before it is ready for the market.

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