The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California

Coloring Finishing And Painting Wood

Then, too, articles can be moved and carefully handled much sooner than with the slow-setting type of varnishes. It is difficult to generalize, however, because the speed in drying of synthetic varnishes at present varies widely; some of the most rapid types, even, almost equal the rapidity of lacquer, tho this is not usual. Varnish manufacturers have discovered that the dry-speed of synthetic-resin varnishes can be varied considerably by selecting certain types of synthetic resins, and can be decreased by use of the modified type of synthetics which may contain fossil resins, ester-gum, or limed rosin. There are other factors that enter into quick drying, such as the type of thinner that is used, the vehicle or drying-oils selected, and their heat treatments. Turpen tine is less used in the new varnishes and has been replaced by cheaper mineral thinners which vary quite widely in their time of evaporation. The thinners actually used are usually petroleum products, such as mineral spirits.

Several factors have already been mentioned in connection with the drying of synthetic varnishes. Such varnishes do not dry by the rather simple processes of evaporation and oxidation, as is the case with fossil-resin varnishes. New and additional factors enter the drying process when synthetic resins and China-wood oil are used. The new factors are called polymerization and jellation. The drying, in case of synthetic-resin varnishes, quickly takes place on the surface. A protective coating of rather hard varnish is quickly formed on the outside, but there is not a corresponding rate of hardening thruout the entire thickness of the film.

Driers may also affect the rate of drying of synthetic varnishes. In general, the four-hour varnishes do not really need drier, and very little is used. More drier should not usually be added in order to speed up the setting and drying of varnish coatings because too much drier may upset the balance of ingredients in the varnish mixture. In the past, when unusual speed with fossil or ester-gum varnishes was desired, more drier was used and the amount of drying-oil was reduced. These changes are not needed when synthetic gums are chosen for varnish manufacture. The driers commonly used have usually been salts of cobalt, manganese, zinc, and lead. Some new types of driers known as "Naphthenates" and "Oilsolates" are now being employed to some extent. The chief purpose of driers is to accelerate the oxidation process thru the taking up of oxygen from the varnish drying-oils, which are really fatty organic acids. Large quantities of driers in varnish tend to cause brittleness of films and to reduce their resistance to alkalies.

333. Qualities of Varnishes.—Various tests and standards have been demanded by interested agencies, such as the Federal Government, several states, large cities, and by varnish buyers. These requirements have much in common tho they are not standardized.