The hardest of the varnish resins is the Zan zibar copal, which comes in small flat pieces, having a surface resembling gooseskin and hence is known as "gooseskin" copal. Next come the Sierra Leone, the Gaboon, and the Angola copals, all of which, like the Zanzibar, are fossil resins found in Africa.
The copal chiefly used by American varnish manufacturers is the kauri copal, found in New Zealand and named from the kauri tree, of which it is a fossil product. Great forests of the kauri trees still grow in the islands, and some of the lumps of fossil resin are found deep in the ground beneath these trees, but by far the larger part is found in portions of the island where no kauri trees have existed within the memory of man.
The kauri tree is probably the most slow growing plant known. A sapling planted by the government in Auckland was still a sapling a hundred years later, and some of the great trees in the forests now standing were undoubt edly in existence long before the pyramids of Egypt were built. As in the case of many other trees, a resinous substance exudes from the kauri tree, chiefly at the junction of the main branches with the trunk and under the forks of some of the large branches. It is almost im possible to realize how slowly this lump of gum grows. Not less than a hundred years would be required for the formation of a lump the size of a man's head. Fossil lumps are found occa sionally which weigh a hundred pounds or even more, to produce which ages must have elapsed.
The fossil gum has come from trees that cen turies or perhaps thousands of years ago either perished of old age or from which branches were torn off by storms, carrying with them the lumps of gum that clung to them. The wood de cayed and became a part of the soil, but the gum remained covered with the earth, and grew harder as centuries passed, until it has become exactly what the varnish makers of to-day need. The gum diggers are mostly outcasts of society, both men and women, who have failed to earn a living in other occupations and have turned to gum digging as a last resort. The earth is prodded with a long spear of peculiar shape to detect lumps of gum which are often concealed several feet below the surface, and the experi enced digger can detect by the feeling of the object struck whether it is the desired gum or merely a stone or piece of charred wood from some forest fire of ages past. More than two
million dollars worth of gum thus collected is shipped from New Zealand every year, the greater part of it coming to New York; and although the exhaustion of the supply has fre quently been predicted, it still seems to be suf ficient for a long time to come. Varnish made from the kauri copal is not as durable as that made from the African copals, and does not equal it in other respects.
Manila and Borneo copals are also much used in varnish making, but are inferior to the kauri, being much softer. The West India and South American copals are little used in the United States, and are soft and of inferior quality.
Common rosin, or colophony, is the residue remaining in the still after the spirits of tur pentine have been distilled from the crude tur pentine. This latter is the sap of the long-leafed pine of the South Atlantic states. It is probable that the crude turpentine is chemically decom posed in the still, and is broken up into two parts—spirits of turpentine, and rosin.
Rosin is much used in varnish making. The addition of a small percentage to an oil-resin varnish of the better grade will often make it ready for use earlier than it would be by a simple aging process. The addition of not more than from three to five per cent of rosin to a copal varnish cannot necessarily be regarded as an adulteration. When it is added in larger quan tities, as it frequently is, it is done solely for the purpose of reducing the cost of the varnish. When added in large quantities, it is injurious to the varnish, causing it to crack. The cheap varnishes used in the factories where low-priced furniture is made are almost entirely made from rosin, and such varnish will crack and peel in a manner that is very disheartening. The same result may be expected when rosin varnish is employed for finishing the woodwork of a house. The varnish will soon begin to lose its luster, and before long will crack and peel, leaving a surface that is almost impossible to finish over satisfactorily. Lightness of color is obtained by sorting the lumps of gum for their color be fore they are melted. Extra pale varnish com mands a high price. Its use is necessary when finishing such woods as white holly or when mix ing white enamels; but for ordinary work, where extreme lightness of color is no object, there is no advantage in using an extra light varnish.