Popular Woodworking 2006-11 № 158, страница 64

Flexner on Finishing

Making Sense of Dyes

Don't allow the packaging to cause you confusion.

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.

Understanding Dye

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

by Bob Flexner

Bob is the author of "Understanding Wood Finishing" and a contributing editor to Popular Woodworking. In 2007, he'll be teaching three finishing classes at the Marc Adams School of Woodworking.

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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.

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The two types of dye discussed in this article, in three types of packaging, are (left to right) concentrated liquid NGR, methanol-thinned liquid NGR and four containers of water-soluble powders.

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Popular Woodworking November 2006