Oleo Resinous Varnishes
Information on the properties of oleo resinous varnishes and sources of resin.
Oleo-resinous varnishes are made by dissolving certain resins in linseed oil, with the aid of heat; and as one effect of the resinous resin is to thicken the oil, they are thinned with turpentine (or a substitute). The larger the proportion of resin, the quicker they are to dry, also the harder and more lustrous, but also the less elastic and durable. The best of these are more durable than the spirit varnishes. The dark-colored varnishes are less costly than the paler ones, because the clear, transparent resins are more rare and expensive; but they are just as good in everything but color, and for many purposes this is no objection, as where they are used over dark wood, or as an ingredient of paint (except pure white paint).
The resins used in varnish-making are of vegetable origin, and come from the warmer parts of the earth, mostly from Africa, the Philippine Islands, and from Brazil; though one important and valuable resin comes from New Zealand, which is outside the tropics. They have formed lumps on the trees, as spruce-gum is found on spruce trees in this country, but in larger pieces; but for the most part they are dug up from the earth, the trees which produce them having long ago fallen and decayed, and by being long buried in the earth the resin has become harder and more valuable. Fresh resins are, as a rule, too soft to make good varnish. They are of many different kinds, and are believed to have been produced by various hardwood trees.
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