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Coloring Finishing And Painting Wood
A flatter, more even tone can be secured by brushing lengthwise, especially on open-grained or porous woods, because the bristles of the brush get down into the low places of the cell lumina or openings more satisfactorily when the stain is applied with the grain. Most stains must be rubbed or wiped off with some absorbent material, such as cotton-waste. It is often best to wipe off crosswise and to finish lengthwise. The crosswise wiping rubs the stain into the pores, and the lengthwise rubbing cleans off any excess and evens up the color.
37. Speed in Staining.—Speed in applying the coloring-liquid is fundamental to success with most stains. Speed secures uniform color and helps in preventing laps and streaks. The amount of speed required varies with the kinds of stain used, depending upon the rapidity of the evaporation of the solvents which hold the coloring-matter in solution. Spirit-stains containing alcohol evaporate with astonishing rapidity. Volatile oil-stains vary greatly in rapidity of drying; those containing gasoline evaporate almost instantly; while, if turpentine is used as a solvent, vaporization is much slower.
The manufacturers of the best volatile oil-stains in liquid form ordinarily use solvents, generally in a mixture, which will control the rapidity of drying and slow down the evaporation to practical workable limits. Pigment oil-stains usually contain a certain amount of some drying-oil, usually raw linseed-oil, and this makes them dry slowly. There is no difficulty in applying pigment oil-stains, as they dry very slowly—so slowly in fact, that no other finish should be placed over them for several days.
Chemical Stains
During the years just preceding the world war certain forms of chemical stain enjoyed quite a little popularity. White oak was a suitable material for the manufacture of mission furniture which was then in vogue, and this wood with its high tannic-acid content lent itself admirably to several chemical stains, the most satisfactory of which was produced by the ammonia fuming process. Other acid and alkaline stains were used with some success, and writers of that period predicted a great future for chemical stains. The most popular stains of the present day are the result of chemical discoveries, but they are synthetic dyes instead of true chemical stains in the sense that that term is usually used by the wood-finisher.
38. Definition of Chemical Stains.—In a scientific sense, chemical stains depend upon some chemical reaction in the wood resulting in the formation of new colored compounds. One of the chemicals is sometimes contained in the wood itself. In other cases one chemical may be applied to the surface of the wood and be absorbed or produce some chemical change. Later on, another chemical which may be in the form of a gas or liquid, may come in contact with the first and bring about a chemical change in the wood itself, thereby causing a change in color. True chemical staining, therefore, is the result of chemical action in the wood which produces a new color.
