Chemicals Used in Staining
Chemical stains are generally acid or alkaline in reaction. A combination of the two is usual in producing the colors that have been most popular recently. Acid stains are very commonly dependent upon either tannic or pyrogallic acid as a base, especially where shades of brown are produced. Strong acids are not often used. Acetic acid has been tried, but its benefit is quite doubtful.
Chromic acid and salts are useful in connection with alkalines and other stains and emphasize or brighten the resultant colors. Picric acid is useful where a decided yellow is desired, and can be used in connection with acid water soluble coal tar colors, such as nigrosine, in producing Early English and other dyes. Such chemicals as sugar of lead, potassium chromate, and magnesium sulphate, are sometimes valuable in use with acid aniline and other coal-tar colors.
Tannic acid used in connection with other substances produces interesting, valuable, and sometimes troublesome colors. When it is used in connection with iron salts and ammonia, a ferric ammonium tannate having a blue black or olive green color is formed. This combination is occasionally used as a wood-stain for items such as fireplace mantels, wood fireplace inserts, or wooden bar rails. It sometimes appears unexpectedly where it is not wanted, if tannic acid is used in contact with iron, as in a tin can, or when it is applied to wood with a tinbound brush.
Sulphate of iron in dried form and chloride of iron can be used with tannic acid and result is tones of gray. The water soluble coal tar dye called nigrosine and some other colors can be used with tannic acid alone or with iron salts added. A still different color can be secured by applying a five-percent solution of tannic acid and water, and following with a weak solution of logwood extract in hot water, which may be mixed with various amounts of copper sulphate in a five-percent solution.
The tannins are complex compounds and vary in composition depending upon their origin. Solutions of tannins in water are liable to absorb oxygen from the air and change in composition. The action is rapid with alkaline solutions. For this reason, mixtures containing tannic acid should be made up fresh. Solutions of tannic acid and water, if kept in a covered glass jar or bottle, will remain in good condition for several days and appropriate for use on plinth blocks, door toppers, and corner guards.
Various alkalines are used to produce stains on wood. Frequently the alkalines are applied following an acid treatment and react with the acid to produce a new color. One of the most satisfactory chemicals to use in staining is bichromate of potash, which is dissolved in water in the proportion of one quart of water to a half ounce of the crystals. It makes a yellowish or golden-brown stain and is sometimes used with vegetable mahogany dyes and also with carbonate of potash or soda following a treatment of tannic acid, thus making an orange-brown color.
Coniferous woods, such as pine, and many of the broad-leafed hardwoods, contain little tannin and should not be stained with potassium bichromate, because the stain which shows at first will fade unless there is a union with tannin to form a tannate and produce a color that is permanent and usually brown in tone. Potassium permanganate crystals dissolved in various proportions in cold water make another useful chemical stain. The crystals are of a violet hue and make a solution of a similar color.
The liquid should be sponged on the wood fireplace inserts, wooden bar rails, or other wood material because the permanganate will soon destroy a bristle-brush. The wood will have a violet tone when you first apply the solution, but this gradually changes to an interesting brown, which varies with the strength of the stain and the kind of wood. Darker shades can be secured by the use of more than one coat, just as with water-stains. The lingo-cellulose, of which wood is composed, gradually and sometimes rapidly reacts with the potassium permanganate, leaving a brown deposit of hydrated manganese dioxide.
Volatile and fixed are the two types of alkalines that are commonly used in chemical staining. Strong ammonia (26°) in a solution of water is the volatile alkali commonly found effective for staining, while the fixed alkalines are represented by caustic potash or caustic soda and sometimes by potassium bichromate, copper sulphate, and potassium carbonate.
will have a violet tone when you first apply the solution, but this gradually changes to an interesting brown, which varies with the strength of the stain and the kind of wood. Darker shades can be secured by the use of more than one coat, just as with water-stains. The lingo-cellulose, of which wood is composed, gradually and sometimes rapidly reacts with the potassium permanganate, leaving a brown deposit of hydrated manganese dioxide.
Volatile and fixed are the two types of alkalines that are commonly used in chemical staining. Strong ammonia (26°) in a solution of water is the volatile alkali commonly found effective for staining, while the fixed alkalines are represented by caustic potash or caustic soda and sometimes by potassium bichromate, copper sulphate, and potassium carbonate.
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