ho n you think of coloring wood, you probably think of staining first. Stains come in a wide variety of colors, and they're relatively easy to use. Stains add richness and depth to almost any wood. They allow you to make cheap, uninteresting woods like poplar and soft maple resemble higher-quality woods like walnut and mahogany. Stains are useful for evening out color variations between different boards, or between heart-wood and sapwood on the same board.
The most common stains available are made from pigment suspended in a liquid, such as oil. Pigment is a very finely-ground colored powder—the same solid material that gives color to paint. Some pigments are ground from colored earth, but more often, pigments arc synthetic. (There's another type of stain that's made from dve. For more information see mv article. "Aniline Dyes," in the Nov./Dec. 1988 /Hi'.)
When you stir up a container of pigment stain, the pigment particles are suspended in the liquid. The pigment does not dissolve. Left undisturbed for a period of time, the pigment is heavy enough to settle to the bottom of the stain container and will need to be stirred back into suspension before use.
The fact that pigment particles don't dissolve is sig nificant for three reasons. First, the pigment tends both to obscure the fine detail of the wood and at the same time give the wood the appearance of depth. Second, the pigment can only penetrate into spaces in the wood that are big enough to accommodate the particles (see sidebar). Third, the pigment might simply blow away or be brushed oft the surface if there weren't some glue-like binder in the stain to hold the pigment to the wood. More about this later.
Pigment stains obscure the wood in the same way that paint does, but to a lesser extent. The more pigment you leave on the surface (that is, the less stain you wipe off), the more the stain will perform like paint to cover the nuances of the wood's figure.
Even when you wipe off all the excess stain, some pigment lodges in the pores of the wood and makes the pores appear darker. When a finish is applied over the stain, the darkened pores give the wood the appearance of greater depth. You can control to what degree you want to obscure the wood or enhance its depth by varying the amount of excess stain you wipe off.
When you apply a pigment stain, the total amount of pigment that can be absorbed is reached very quickly. As long as you apply a good, wet coat of stain, you will achieve as dark a color as you can get with that stain. Leaving the stain on the wood longer or applying a second coat won't darken the color (see section on varnish-based stains). The pores of the wood will already be tilled with all the pigment they can hold. There are only three ways to get a darker color: I) use a darker or more heavily-pigmented stain to begin with. 2) don't wipe off all the excess stain (i.e., leave more pigment on the surface), 3) create artificial scratches with sandpaper so more pigment can lodge
Varnish stains—Manv stains currently on the mar-ket are made with alkyd- or polyurethane-resin varnish. These stains are usually sold as "varnish stains," or as stains that "stain-and-seal" or "stain-seal-and-finish" in one step. Like oil stains, they're thinned with mineral spirits or naptha.
These stains are, quite literally, thinned paint. If you apply a heavy coat of varnish stain without wiping off the excess, you can totally obscure the wood and the film will dry hard—just like paint.
Because varnish stains cover, or partially cover, the wood, they're especially useful for blending sapwood with hcartwood or blending boards of different shades. Additional coats of varnish stain, left thick on the wood, will darken the color but will also obscure the wood.
While they may be referred to as varnish stains, very few stains are made from straight varnish. Most contain a mixture of oil and varnish. The higher the percentage of oil, the easier the stain is to use. The higher the percentage of varnish, the more the stain will perform like paint and be difficult to wipe off.
There are three other stains that are based on oil or varnish—or a mixture of the two—that you're likely to see in stores: semi-transparent, penetrating, and gel.
Semi-transparent stains are stains which contain some dye along with the pigment. They have less tendency to obscure the wood than straight pigment stains, and they will do a belter job of coloring dense summer wood growth, because the dye penetrates everywhere the solvent does (see sidebar).
Penetrating stain has traditionally meant an oil-based dye stain containing no pigment at all. But I've come across some pigment stains called "penetrating" where the word is used to mean that the binder for the pigment is composed primarily of oil rather than varnish. Using the term in this way is confusing. If you find a stain which contains pigment, that stain can't legitimately be called a penetrating stain.
Gel stains can contain pigment, dye, oil. varnish or any combination thereof. "Gel" simply means that there are thickeners added to keep the stain from dripping or running.
If you choose to use a gel stain you should pay attention to what type of coloring material (pigment or dye) and what type of binder (oil or varnish) is used. These ingredients determine the degree of color penetration and the clarity or cover you will get. The gel only affects the working qualities.
Lacquer-based stains —Nitrocellulose lacquer-based stains are very popular in industry and with in the scratches and darken the wood.
The coarseness of the sandpaper you use for finish sanding has a significant effect on the way a surface accepts slain. Coarse-grit scratches make more room for pigment. Fine scratches make less room. But if the scratches are too coarse, they'll show up in the finished piece. Opinions vary, but I think 180- to 220-grit sandpaper gives the most pleasing results. Sand the entire surface to the same grit and remove tool scratches and pad-sander swirls, or they'll be highlighted by the stain. Always sand in the direction of the grain, if possible.
When you think of the pigment as dust-sized colored particles, it's easy to see that something is needed lo adhere these particles to the wood or they'll simply blow away. The "glue" used to hold the pigment color to the wood is called the binder, and there are several different kinds. It's important to understand what these different kinds of binders are, because it's the binders and their corresponding solvents that determine the characteristics of the stain.
Most binders can be classified as one of four types— or some combination thereof. The four most common types of binder used to stick pigment to the wood are oil, alkyd or polyurethane varnish, nitrocellulose lacquer, and waterborne acrylic resin.
Oil-based stains—Oil stains are the oldest, prob-ablv the most common, and definitely the easiest to use. Since these stains are most commonly wiped on and wiped off the wood, they are often called "wiping" stains. They are usually based on boiled linseed oil. which cures very slowly, giving you plenty of working time. Oil-based stains are thinned with mineral spirits or naptha.
There's no trick to applying oil-based stains. You simply cover all of the wood (or, if you're working on a particularly large surface, a section of the wood) with the stain, and, while it's still wet, wipe oft all of the excess. Pigment will remain everywhere there's a pore or scratch large enough to accept it. The oil will cure, binding the pigment to the wood. It makes no difference how you apply the stain. You can wipe, brush, or spray it on the wood, or you can dip the wood into the slain. I usually wipe it on with a soaked cloth or sponge.
Oil-based stains are not meant to be left thick on the wood. Linseed oil never hardens thoroughly, and, if left on in any thickness, will wrinkle when it cures. With oil-based stains, it's always best to wipe off all
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