Oil Based Varnish

¶ These are solutions of gum resins such as amber, Zanzibar, kauri, pontianak, Sierra Leone and gums in fixed oils, usually vegetable oils like linseed and china wood (tung) oil, produced with the aid of heat. They contain small amounts of metallic salts like manganese, red lead, litharge, etc., to facilitate drying, and also volatile liquids like turpentine, mineral spirits, etc., to make the solution sufficiently fluid for brushing. Other vegetable oils like soya bean oil, nut oils, sunflower seed oil, poppy seed oil, etc., and fish or menhaden oil are also used to get certain qualities in special purpose varnishes.

¶ Amber gum is considered the best varnish gum because it is very hard and resists moisture well, but amber gum varnish is dark in color. Zanzibar and kauri gums are the next best because the varnishes made from them are very hard and durable,kauri is the most used. Of course the quality of varnish depends upon many things in addition to the gum used; the formula and skillful use of it are equally important. It is well to note also that the varnishes made with a small proportion of oil are harder and more lustrous, but they are less elastic and less durable. Varnishes containing large proportions of oil, called long-oil varnishes, are more elastic and more durable than others, even though they do not take so high a gloss or polish. Spar varnish is a good example of the long-oil class. Dark colored varnishes are fully equal to the light colored varnishes, except as to color, and they are cheaper because clear, transparent light colored varnish gums are rare and consequently more expensive than dark gums.

¶ As with other materials varnishes of many grades are made. The high quality and more expensive grades are more transparent and more serviceable. There are medium grades and cheap grades made for cheap jobs. It is easy enough to test the quality of these oil varnishes. Simply coat a board with the varnish, about two coats are needed for a fair test. Let the varnish dry thoroughly. Then soak a sponge in water, squeeze out some of the water and place the sponge on top of the varnished board over night. If the varnish is of high quality it will be clear, bright and glossy in the morning ; such varnish is durable and a good representative of its class. But if the varnish turns white it means that it has absorbed the water from the sponge and if it remains white the water has dissolved part of the varnish. Varnish of this kind is not good enough for use on interior wood trim of buildings or on furniture.

¶ The oil or oleo-resinous varnishes are the most important group and include spar varnish, interior varnishes, floor varnish, gear varnish, rubbing varnish and color varnish. This group of varnishes is also re-classified, according to the proportion of oils to gums, as long-oil, medium-oil and short-oil varnishes. The short-oil varnishes are made -with a proportion of about 4 to 6 gallons of oil to 100 pounds of gum. In this class are the furniture, rubbing, piano and polishing varnishes. They are very hard when dry, have a high gloss and dry quickly. They are not as desirable as the medium-oil and long-oil varnishes, if used for the same purposes, but may be extremely durable when used for the purposes for which they are designed.

¶ The medium-oil varnishes are made with from 12 to 30 gallons of oil to 100 pounds of gums. They are the interior and architectural varnishes such as cabinet and floor varnishes. These are hard, have good gloss and are durable to a considerable degree.

¶ The long-oil varnishes were originally designed for exterior surfaces, and of course durability is the principal requirement for this class. In this group are included the spar varnishes, carriage, wagon, automobile, coach and agricultural implement varnishes. Spar varnish is particularly made to resist the action of water and salt, moist air. From 25 to 50 gallons of oil are used with each 100 pounds of gums in the production of the long-oil varnishes. A good exterior spar varnish contains about 36 gallons of oil to 100 pounds of kauri gum. Good floor varnish contains about 30 gallons of oil to 100 pounds of gum. A good interior varnish contains about 8 to 15 gallons of oil to 100 pounds of gum.

¶ In addition to these three groups of varnishes which are more or less clearly denned as to composition and qualities, there are many which are in between these made by mixing and blending the principal varnishes. In this manner many degrees of hardness, elasticity, gloss and durability are secured to fit many purposes, chiefly in the many industries manufacturing merchandise. Then there are many special purpose varnishes made for such purposes as grinding colors, enamels, flat paints, enamel undercoats, etc., called grinding varnishes. We have, too, the baking varnishes which contain little or no metallic salts driers, depending upon high temperatures to dry the coatings,the patent-leather varnishes, lithographic varnishes, etc.

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