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Coloring Finishing And Painting Wood
Often chemical staining depends upon the changing of coloring-matter already in the wood to a new or different color, because of a chemical reaction, rather than to the application of a dye or pigment. Woods differ greatly in their chemical composition, consequently they react very differently to chemical treatment.
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. Often chemical staining depends upon the changing of coloring-matter already in the wood to a new or different color, because of a chemical reaction, rather than to the application of a dye or pigment. Woods differ greatly in their chemical composition, consequently they react very differently to chemical treatment.
39. Waning Popularity of Chemical Stains.—Oak, which a few years ago was so much used for furniture, has partly been replaced by black walnut and other woods which are not with our present knowledge so easily stained by chemical processes. Another reason for the decline of chemical staining is that a uniform tone cannot usually be secured on an article of furniture, even when made of oak which is one of the best woods for this kind of staining. This unevenness is due to the fact that sap-wood is not changed to a tone to match heart-wood, and boards from different trees do not take equal amounts of color.
Considerable "doctoring" of spots and streaks was a common aftermath of chemical staining. Some factories gradually came to the practice of giving a light chemical stain, following this treatment with a water-soluble or other coal-tar dye coating to even up the color and produce a flat uniform tone. The hardest blow of all to chemical stains has come from the great improvements in coal-tar dyes that arc, in some of their forms, as permanent as any stains. These synthetic dyes are very convenient to use, and last, but not least, they can be found in almost any color, shade, and tint desired.
Much of the "period furniture" of the present day, which has to a considerable extent displaced the oak "mission furniture" of a few years ago, is made of black walnut ; and this wood is finished in various ways, as in a natural color, given a light or weak stain, two-toned or duo-toned with light and dark effects of the same color, or even poly-chromed in part, with the remainder left in a natural finish.
