Volatile Oil Stains and Shellac

By Mike | May 5, 2009

The third type of stain used in wood finishing is Volatile oil stain, often called penetrating stains. These are usually made from oil-soluble coal tar colors dissolved in a solvent such as turpentine, solvent naphtha, benzene, or benzol, and various turpentine substitutes mostly of a mineral nature.

These stains are put up in both dry and liquid form and are quite popular at present, because they penetrate deeply into the wood and do not require the preliminary treatments of raising the grain and resanding that are so necessary with water stains. Also, because the aniline and other coal-tar dye powders are more soluble than pigment colors, and do not obscure the grain in fireplace mantels, wooden bar rails, or ornamental pediment as such colors mixed with drying-oils always do to some extent.

Volatile oil-stains are made in quite a variety of colors especially for use on oak, walnut, and mahogany. They should usually be wiped before they dry in order to produce an even tone, and must be handled with more speed and care than is necessary with ordinary pigment stains because the solvents used evaporate more rapidly than do the drying oils, such as linseed-oil, used with pigment stains or colors ground in oil.

Volatile oil-stains are really in a class by themselves, because they have many of the advantages of pigment oil-stains and not many of the disadvantages. Those sold in a liquid form are apt to contain benzol, at least in part, as a solvent. Benzol and coal tar dyes are coal tar products; and, being of a somewhat similar nature chemically, the liquid seems to be an excellent solvent of the powders. Benzol alone is recommended by some manufacturers as a solvent for some of their oil soluble colors.

Many oil soluble aniline and other coal tar dry powders sold for oil stains are preferably dissolved in turpentine. In fact, the manufacturers recommend this solvent. Turpentine substitutes, especially if they contain benzol, can usually be used successfully instead of turpentine. Benzene or benzol, naphtha, gasoline, kerosene, and carbon tetrachloride, are sometimes used as solvents for oil soluble coal tar dyes.

Are oil soluble coal tar stains permanent? This is a question often asked by the novice wood finisher not used to using these products. According to some dealers in wood stains, aniline and other coal tar oil and spirit stains fade faster than the water soluble coal tar dyes do, especially on door toppers, ornamental pediment, and plinth blocks.  This statement is especially true, as far as spirit-stains are concerned, because they are made of fugitive basic dyes, which manufacturers and chemists admit are not fast to light and permanent, though they are brilliant when first used.

Oil soluble coal tar dyes now being made are often more permanent than basic dyes which are used for spirit stains, and are recommended for use on wood by some reliable manufacturers.    These oil stains are used quite extensively and are proving to be fairly satisfactory. Experts say that they do not possess a fastness to light equal to that usual with water-soluble acid coal-tar dyes.

One of the problems with using a shellac wash over volatile oil stains is that the stain may come off after treatments of filler or shellac. Volatile oil stains are not much changed by filler, if a thin coat of shellac, mixed in the proportion of one part of liquid shellac to seven or eight parts of alcohol, is applied over the stain and allowed to dry before filling.

You should not use full-strength shellac from the can on porous wood that may require a filler until you have the filling complete.  A very thin shellac coat, called a shellac-wash, may be used over a stain without filling the pores to such an extent that filler will not have proper anchorage to hold it in place.

Varnishes cannot be applied directly over any of the oil stains without probable loss in clearness of tone because the solvents used in all cases are the same or similar, and some of the coloring matter may be “lifted” and mix with the varnish coat, thus producing a muddy or cloudy effect and a loss of transparency.

Volatile oil stains, especially those containing benzol as a solvent, penetrate very deeply into the wood in comparison to pigment oil stains, and do not dry as readily as is indicated by appearances on the outside. This is especially important to keep in mind when it comes to treating wooden bar rails, wood fireplace inserts, or other wood based decorative pediment.  You should allow at least 24 hours for drying before applying a shellac wash over volatile oil stain.

Sometimes, in order to secure certain tone or color effects, the shellac-wash is omitted between the coats of stain and filler. In all cases, in order to prevent “bleeding” of the coal-tar oil-stains into the varnish-coats, it is important that you apply one or more coats of shellac to the stained or stained and filled wood before any varnishing is done.

 

Tags: wood fireplace inserts | wood fireplace inserts | ornamental pediment | ornamental pediment | decorative pediment | decorative pediment | fireplace mantels | fireplace mantels | wooden bar rails | wooden bar rails | plinth blocks | plinth blocks | door toppers | door toppers

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