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Coloring Finishing And Painting Wood
A brief description of the types of varnish most commonly used by the wood-finisher follows:
191. Architectural Varnish.—This term is used to include varnishes that can be used satisfactorily for decorative work, and also on the interior and exterior of buildings.
192. Automobile Varnish.—Long-oil finishing-varnishes containing about 40 per cent of drying-oils, largely linseedoil, with hard gums, are used on automobiles and railway coaches.
193. Baking-Varnish.—Such varnishes have compositions which enable them to be dried by heat above normal, usually in ovens. They are intended for use over either wood or metal. Baking-varnishes are most frequently dipped or sprayed on art-metal objects, parts of automobiles, and fine machines, such as typewriters. Temperatures of from 90° to 220° F. are used in the drying-rooms and ovens.
Such varnishes contain more than the normal amount of drying-oil, but not more than 24 gallons to the 100 pounds of gum; and when baked on they produce a very elastic finnish that is usually durable and smooth. Rosin-varnishes, unless hardened rosin is used, will not stand baking at high temperatures, because rosin softens at about 154° F. (67.7° C). Most good baking-varnishes will stand a temperature of 160c F. for an hour. A hardened dammar-varnish will stand baking at 220° F. Congo and kauri varnishes are not injured by a temperature of 180° F. No oil-varnish will endure a temperature of 300° F. without turning yellow.
194. Coach-Varnish.—At present this term means an architectural varnish, but formerly it referred to a fine grade of carriage or railway-car varnish.
195. Exterior Varnish.—This name is given to oil-varnishes which are intended for outdoor use on doors, stores, and the exteriors of buildings. They are made to resist the elements of destruction under exposed conditions, and contain more than the usual amount of drying-oils.
196. Enamel-Varnishes.—Specially prepared varnishes are manufactured for use in enamels. Formerly, very white or transparent varnishes manufactured from dammar-gum as a resin were selected for use in white enamels, because such varnishes do not contain linseed-oil which may turn yellow with time. Enamel-varnishes, especially those made for use with white enamel, must be without color when new, and should not discolor with age. Dammar-varnishes are not durable, and are going out of use, because satisfactory, clear, and transparent oil-varnishes which are durable have been prepared recently for use in even the whitest enamels.
Varnishes intended to be used with white enamel are generally of the short-oil type, and are often made from properly treated rosin and pale magnesia linseed-oil. A better varnish for enamel manufacture, however, is a shortoil, pale, ester-gum compound.
