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Coloring Finishing And Painting Wood
The powder form, very commonly used for textiledyes and wood-stains, is the most difficult to dissolve. The different classes of dyestuffs, and the individual colors in the groups, vary greatly in their solubility.
121. Water-Soluble Colors.—Dyestuffs of the usual solubility, when being prepared as wood-stains, are generally dissolved in the proportion of about 3 to 31/4 ounces of powder to the gallon of soft water. Some of the dye-powders of low solubility are used in wood-stains in the proportion of one ounce, or even less, to the gallon of water. Dyes for wood are, however, very strong in color, and often as much as six ounces of color in powder form are mixed with one gallon of water in order to secure the proper strength.
Dealers in dyes for wood-stains usually give instructions as to the amount of powder that should be used in the solvents, which are also named, as water, alcohol, benzol, turpentine, and others. It should be remembered, how ever, that straining a dye-mixture thru a cloth of fine mesh is generally advantageous, because this process removes specks and any undissolved powder that may settle to the bottom after the solution becomes cold.
The acid coal-tar dyes which are very often used in staining high-grade furniture are usually very soluble, which is also generally true of alcohol-soluble powders. The oil-soluble colors are often harder to dissolve. Hard water when used in dyeing textiles is generally acidulated slightly with acetic acid, using only enough acid in the bath to give an acid reaction with litmus paper. It is, however, preferable in some cases to add a small amount of sulphuric acid to the water instead of acetic acid. This hint on the use of acid with acid dyes in dyeing textiles may prove advantageous to wood-finishers in preparing acid water-soluble dyes for staining wood.
Water containing iron compounds should not be used in dye-baths or stains without first making tests, because chemical reactions of this metal or its salts are liable to change the dye-mixture itself in such a way that modified or duller colors may result. Salts of iron with alkali mordants were used as dyes by many ancient peoples, and are still of service in improved forms.
Most dyes, especially acid coal-tar dyes, are most satisfactorily dissolved by using boiling soft water.9 The mixing should be done in vessels of glass, earthenware, or copper, but never in containers of tin, if acid is to be added to the solution, or if the dye itself has an acid reaction, because the iron which forms the body of all tin-plated sheetmetal may change the dye itself.
122. Spirit-Stains.—Basic dyes are usually soluble in either water or alcohol. If water is used many basic dyes, such as Malachite Green and Methyl Violet, should be mixed with a small quantity of cold water slightly acidulated with acetic acid, and after stirring well, the thin paste formed can be added to boiling soft water.
