Making Sense of Dyes
When I opened my furniture making and restoration shop 30 years ago, there were two types of dye in wide use. I made great use of both, but for different situations.
These two types are still the most widely available and useful today, but packaging has introduced some confusion, so a discussion using brand names is warranted. Before launching into comparisons, however, I need to explain what I mean by “dye,” because packaging makes the understanding of this term confusing also.
There are two common colorants used to color wood: dye and pigment. The difference is simple. Dye is a colored chemical that dissolves in a liquid. Pigment is a solid substance (sometimes earth) ground into very small particles that suspend in a liquid. Dye is like coffee or tea; the color stays in solution. It doesn’t settle. Pigment is the colorant in paint; it settles and has to be stirred into suspension before using.
When you apply a solution of dye to wood, the color penetrates along with the liquid. Very dense woods such as maple and the dense areas of oak can be colored as dark as you want without muddying the wood.
When you apply a suspended pigment to wood, the pigment stays on the surface. Wipe off the excess stain and some pigment remains lodged in recesses created by the grain of the wood (think of the coarse grain of oak and how dark it gets) and sanding scratches. The coarser the sanding scratches the more pigment lodges and the darker the result.
Confusion about dye in stains is caused by the different ways it is packaged. Dye can be used together with just a solvent or it can be used, usually in combination with pigment, together with a solvent and a binder, as is typical in the cans of stain you buy at home centers. (See “Understanding Stains,” issue #155.)
The binder is a finish used to glue the pigment to the wood so the particles can’t be wiped off after the solvent evaporates. All oil, varnish and water-based stains contain a binder. Oil stains contain oil; varnish stains contain varnish; water-based stains contain water-based finish.
The stains at home centers usually contain both pigment and dye. Some contain only pigment. A few contain only dye. But they all work the same because of the included binder, and provide limited flexibility for controlling color.
You can thin the stain with the appropriate thinner (mineral spirits for oil and varnish stain, and water for water-based stain) to make the color lighter, or you can apply an extra coat or two after the stain has dried to make the color darker. But because each coat builds on top of the previous, each additional coat muddies the wood a little and can introduce a weakness in the film that might separate if knocked.
In contrast, dye in a solvent with no binder doesn’t build. Each additional coat simply dissolves into the previous coat making it darker and creating the same effect as if you had used a more intense dye color in the first place. Dyes in a solvent with no binder can create much deeper and richer colors in wood than dyes or pigments packaged with a binder.
Stains that contain only dye and a solvent (no binder) are called dyes or dye stains.
Dye has one big downside compared to pigment. Dye fades in sunlight and fluorescent light. So you shouldn’t use a stain that contains dye outside, and you should think carefully before using the stain on objects that will be placed near windows or in offices.
You can mix all brands of dye that thin with the same solvent. So as long as the dye is dissolved in water, for example, you don’t have to stay with one brand.
Apply a dye stain the same as oil, varnish and water-based stains. Apply a wet coat using any tool (rag, brush, paint roller, spray gun) and wipe off the excess, or most of the excess, before the stain dries. As long as you have prepared the wood well – that is, sanded out all the machine marks – and as long as the wood isn’t naturally prone to blotching, you will always get an even coloring.
Clearly, the evaporation rate of the solvent in the dye is critical for determining the time you have to remove the excess. Water-soluble dyes provide the most time. All other dyes are difficult to remove quickly enough.
Fortunately, dye stains are more forgiving than oil, varnish or water-based stains. A wet coat of dye tends to spread out and level better so streaks show less. With practice, you can usually wipe, brush, roll or spray a dye onto wood and it will spread well enough to produce an even coloring without wiping off the excess.
You can always get a second person to wipe right after you apply if you want to get the excess removed from a fast-drying dye.
Types of Dye
There are four types of dye – but you would rarely use two of them: powdered dyes that dissolve in alcohol and powdered dyes that dissolve in petroleum-distillate solvent (called “oil-soluble dyes”). Alcohol-soluble dyes are used primarily by people doing touch-up on furniture, and oil-soluble dyes are used primarily by manufacturers who add them to oil-based stains.
The two types of dye you will almost always use are powders that dissolve in water and dye already in liquid form. In fact, this is the easiest way to separate and identify them: water-soluble powders and liquids.
Water-soluble powdered dyes have the longest history for use on wood. These dyes (often called aniline dyes because the first dyes were made from aniline) were developed in the late 19th century for use in coloring textiles. By the end of the century, they were used in factories to color wood.
In the mid-20th century, ways were found to modify (by “metalizing”) the dyes so they are more fade-resistant. The emphasis is on “more” because these dyes still fade far more rapidly than pigment.
Metalized, or “metal-complex” dyes are almost always packaged in liquid form because they are usually dissolved in a solvent that isn’t widely available – glycol ether. The dissolved dye can then be thinned with water, alcohol or lacquer thinner (not mineral spirits or other petroleum distillates).
These liquid dyes are widely available to the professional finishing trade as “non-grain-raising” (NGR) stains. If you shop at woodworking stores or from catalogs, you may be familiar with this stain as Solarlux from the finish supplier Behlen.
NGR dyes sold to the professional trade are thinned quite substantially with methanol. They are ready to spray or add directly to any finish that thins with water, alcohol or lacquer thinner.
Throughout my woodworking and restoration career I’ve found these two types of dye (water-soluble and NGR) extremely useful. I’ve used the water-soluble dye powders to stain wood because these dyes provide enough “open time” for removing the excess and getting an even coloring, and they are easier to manipulate on the wood and available in many more useful wood-tone colors than NGR dyes.
I’ve added liquid NGR dyes to shellac and lacquer to make toners for tweaking the color on the wood when my staining didn’t give me exactly what I wanted. Good wood finishers and refinishers find toners extremely useful for matching colors.