The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
Coloring Finishing And Painting Wood
1. Spirit-varnishes dry entirely by evaporation of the solvent. The most common types are: (a) shellac containing an alcohol solvent, and (b) dammar-varnish, which is made with a volatile oil such as turpentine or a turpentine substitute which is often petroleum spirits.
2. Fossil-gum, ester-gum, and limed-rosin varnishes dry in two ways: (a) by evaporation of the volatile thinner or solvents, and (b) thru the oxidation of the vehicle or dryingoils—generally consisting of specially treated boiled linseed-oil in the standard slow-drying varnishes. These are the old types of oil-varnishes which have been used for hundreds of years and were almost universally employed for permanent finishes until very recently.
3. The China-wood oil types of slow-drying varnishes are made from fossil gums, ester-gum or specially treated rosin. Such varnishes contain China-wood oil as the chief drying-oil of the varnish vehicle and dry: (a) partly by the evaporation of the thinner, (b) partly by oxidation of the drying-oil or oils, and finally (c) thru the polymerization of the China-wood oil which has peculiar drying characteristics that are different from those of linseed-oil previously used as the chief drying-oil in oil-varnishes.
4. The synthetic-resin and China-wood oil type of fourhour or quick-drying varnishes dries in three ways as follows: (a) thru evaporation of a volatile thinner, such as varnolene (a petroleum product) and xylol (a high-boiling coal-tar product); (b) thru a modified amount of oxidation; and (c) thru a new factor or reaction called polymerization or gelatinization of both the Chind-wood oil and the liquefied synthetic resins. These combined processes of setting and drying produce a speed in surface setting previously unknown and a considerable acceleration in complete hardening or drying of films made from such varnishes. Attention should be called to the fact that synthetic resins are chemically a product of reactions such as polymerization or condensation, and that the molecules are quite complex and of somewhat indefinite structure. Various factors used in manufacturing synthetic resins may change the final resin product, tho the materials from which the resins are made may be identical. The varnishes which are sold on the market as rapid-drying or four-hour varnishes are made entirely or largely from synthetic resins and contain considerable amounts of China-wood oil, which dries rapidly, partly by polymerization.
320. Spirit-Varnishes.—The old types of spirit and volatile oil-varnishes, such as shellac and dammar-varnish, are still used for numerous purposes. The reader is referred to Chapter XI in this book for detailed information. Spiritvarnishes are made cold or without great heat by dissolving the resin in its best solvent, such as grain alcohol for shellac, and turpentine or more commonly a turpentine substitute for dammar and mastic. Shellac substitutes, which are cheap, inferior finishes, also belong in this group if they contain alcohol as a solvent. Some of the new synthetic gums similar to those used in lacquers are also soluble in volatile oils, and varnishes from them belong in this group because they dry by evaporation.
