Aniline Wood Dye, Coal Tar Dyes

¶ The extensive use and increasing importance of dye stains and tinting colors which are derived from coal tar make it desirable to present here a brief description of them.

¶ The word aniline is being used rather broadly in the paint trade to designate all coal tar colors, whereas many of the colors are not anilines. Many, however, are very closely related to anilines, being coal tar dye derivatives. A great many of the colors commonly used are anilines.

¶ The aniline and other coal tar dye stains are made from the light, middle and heavy oils which are cooked out of coal. By various fractional distillations over two thousand colors have been. made available for textile dyes, tinting colors, stain colors and many other coloring uses. About ninety-five per cent or more of the colors now used for water stains are secured from the coal tar dye sources. One phase of the marvelous accomplishments of chemistry is indicated by the very numerous products which this science has been able to produce from coal. Note these on the picture.

Picture 2. Indicating Some of the Numerous and Varied Products Which the Modern Chemist Takes out of the Common Black Tar Boiled out of Soft Coal. The Colored Dye Stuffs Alone are numbered by Thousands.

¶ The first artificial coal tar dyes, called mauve and magenta, were made by Perkins from coal in 1865. From that beginning a tremendous development has taken place. Now all dyestuffs are of artificial coal tar origin with but few exceptions. Even natural indigo and madder lakes have been displaced by coal tar indigo and madder lake. The many lake color pigments used by the old time carriage and auto painter are nearly all made today under the same names but from coal tar dyes.

¶ In the paint industry we hear most about aniline colors, alizarine reds, nigrosine black, para reds, chinolin, toluidine red and eosine, but there are a great many others. The coal tar dyes come to the painter in many forms as stains and tinting colors as well as in ready prepared paints. The stains are marketed in dry powder form soluble in water or alcohol, benzine, benzole, oil, etc. They are designated as water-soluble, spirit-soluble and oil-soluble colors. The factory-made stains are largely, but not entirely, made with coal tar dyes. Many of the tinting colors which are of earth pigment origin are toned and brightened up with coal tar dyes. The coal tar dyes resulting from the chemical processes direct are very finely divided pigments as to texture and have very little hiding power or opacity. They do have exceptionally great tinting strength, however, and are precipitated in the chemical process upon inert base pigments like barytes.

¶ The coal tar colors are broadly classified as acid colors, basic colors, spirit colors, oil colors and direct colors. The acid colors are water soluble and can be mixed with acids or reacting chemicals. They interest the furniture industry mostly and all who use water stains. The direct colors can be mixed with the acid colors. The basic, spirit and oil colors are never mixed with acid or direct colors.

¶ The colors of the coal tar group represent aU degrees of permanency in strong light and direct sunlight. The cosine red coal tar group includes colors which are quite fugitive, fading too soon to have a wide range of utility. Magenta (mauve) is quite fugitive but enjoys rather extensive use among artists and decorators for its own peculiar color quality. The alizarine reds are permanent in strong light but not in direct sunlight, nor to the degree that earth colors are permanent. Toluidine red is strictly permanent in strong light and to a remarkable degree. It does not bleed. Its cost is rather high, however. Rose lake and rose pink are of the amaranth coal tar group and are only fairly permanent but quite extensively used. Vermilionette, an eo-sine coal tar color, fades too readily in sunlight to have great utility. Harrison red, also a coal tar color, is bright in hue and fairly permanent. Geranium lake is another eosine color which is rather fugitive and fades too much in strong light.

¶ Some of the coal tar colors which fade too soon in strong light prove much more permanent when covered with varnish, shellac or wax. The coal tar colors which are absolutely soluble in both water and alcohol are not as a rule fast to strong light.

¶ Most coal tar reds are stable chemically and cause no unfavorable reactions when mixed with other colors, pigments and liquids and when used in undercoats. One of the reds, however, has caused a great deal of trouble in years past, para red. It is soluble in oil and has been extensively used in the past for making bright red paints for farm machinery and for making red mahogany stains. A great deal of this stain was used on birch and maple doors and interior trim for houses. When these surfaces are refinished with paint or enamel the stain "bleeds" through many coats, giving a pink tint to white and light colors. Para reds are now made which do not bleed. The bleeding reds should never have been sold as stains. Sometimes a coat or two of shellac will stop the bleeding. This is especially true if the old finish is stripped off and washed up thoroughly with alcohol to remove as much of the stain as possible. In extreme cases, however, nothing short of a coat of black paint, flat, or a coat of aluminum bronze, or both, will seal up these bleeding reds.

¶ Stain is simply a mixture of coloring matter in a liquid. There is a limit to the amount of coloring matter each liquid will dissolve per gallon. When that limit is reached the stain solution becomes cloudy, or may precipitate coloring matter which settles to the bottom of the pot, or it may do both. So when a clear, color-saturated stain does not produce a color on wood which is dark enough in one or two applications, allowing each to dry, don't overload the liquid with more coloring matter. It is better to find some other stain to do the job alone or as a first coat over which the other stain is used. Often two or more stains mixed together will give the color wanted. If it is convenient to use a stain quite hot it is satisfactory to make a supersaturated solution without having a cloudy stain or one from which the coloring matter crystalizes and precipitates to the bottom of the pot.

¶ Heat increases the solubility of colors of the coal tar class, but if you use hot water, benzine, turpentine, alcohol, mineral spirits, etc. for the liquid in order to dissolve more coloring matter and secure a darker color and greater penetration of the stain into the wood, the stain should be kept hot while being brushed on to the wood. If the stain becomes chilled the aniline coloring matter will precipitate gradually as the stain gets colder. The first hot stain applied will be darker than the later applications of colder mixture.

¶ In cold weather if aniline or other coal tar water stain gets chilled the coloring matter will slowly crystallize and settle to the bottom of the pot and the stain, will then be lighter in color. It should be heated to re-dissolve the color. Alcohol spirit stains are affected by cold to a much less degree than water stains. Oil stains are not so affected. Nigrosine black is more completely soluble than some others like the orange and other light colors.

¶ When water soluble aniline and other coal tar colors are dissolved in hot water and, upon cooling to 70 degrees, precipitate color which settles to the bottom of the pot a super-saturated solution has been made. More coloring matter has been dissolved by the heat than the water can carry at a lower temperature. The remedy is to add more hot water.

¶ In manufacturing processes where large quantities of small articles like toys are stained by dipping them, into a super-saturated solution of stain the stain is kept hot to the boiling point by a steam jet or coil in the tanks.

¶ Coal tar colors are usually sold in dry powder form, although factory-prepared stains include these dissolved in water, spirit and oil and sold by the gallon. The dry stain colors are concentrated as to coloring matter and their great strength makes it necessary to use only a very little with each gallon of water to make a strong stain. An ounce or two to the gallon is often enough, depending upon what particular color you are mixing and how dark a stain is wanted. The dry stain is sold by the ounce and pound.

¶ Where hot water is not available on the job it is better to buy the stain in liquid form of standard colors. The dry form costs less per gallon, however, and permits the mixing and blending of colors to suit the needs in matching.

¶ The dry stain powders are often composed of fine and coarse particles. The finer particles settle to the bottom when the packages are subject to vibration or jarring. Care should be taken to see that the dry powder in a package is well mixed before using. The stain will not work right otherwise. It is also important to keep dry stain powders in a dry place and sealed up tightly in the cans. They will absorb moisture from a damp atmosphere. Deterioration will result.

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