Coloring Wood Overview
Coloring wood usually presents the biggest challenge in the wood finishing process because more can go wrong. By organizing and defining the major differences in the woods, the various types of products used to color wood and the application methods, you can see the big picture and get a better idea of all the choices you have. You will improve your chances for a successful result.
Any color can be matched, but not any wood. You have to pay attention to the characteristics of the wood you are coloring.
There are four large categories of woods: softwoods such as pine, cedar and fir; tight-grained hardwoods such as maple, birch, poplar and cherry; medium-grained hardwoods such as walnut, mahogany and teak; and coarse-grained hardwoods such as oak, ash and elm.
Within each of these categories, you can pretty successfully match any two woods using some combination of bleach and stain. But trying to match woods of different categories has its limitations because of the large differences in grain and figure. You should take these limitations into account when you are choosing a wood, or woods, for a project.
TYPES OF STAIN
The basic way to change a wood’s color is to apply stain. In choosing a stain, you need to take into account the four ways in which stains differ, besides the obvious variances in color, because they will affect the results you get.
There are two types of colorant used in stains: pigment and dye. Pigment is finely ground natural or synthetic earth. Dye is a chemical that dissolves in a liquid. Everything that settles to the bottom of a container is pigment, and all the color that remains in the liquid after the pigment has settled is dye.
Pigment is better at highlighting grain if the excess is wiped off, and at obscuring the wood if the excess is left in any thickness on the surface. Pigment is also much more fade resistant than dye. Dye is better at changing the color of wood without muddying it—especially dense woods such as birch and maple.
Some commercial stains contain only pigment, some contain only dye, and some contain both. Because manufacturers rarely provide this information, you have to test the stain yourself. Carefully open a can that has sat on a shelf long enough for all the pigment to settle and insert a light-colored stirring stick halfway down. If the stain colors the stick, the stain contains dye. Then insert the stick to the bottom of the can. If you can pull up some solid material, the stain contains pigment.
Choose a pigmented stain for areas that are exposed to direct sunlight and a dye stain when you want to add more color without muddying the wood.
Dye stains are also available dissolved in just a solvent (no binder), and these are most useful for getting light woods dark without obscuring the wood and for matching color. The two large categories of solvent dye stains are water-soluble and non-grain-raising (NGR). NGR stains are also called metalized or metal-complex stains.
Water-soluble dyes are available primarily through mail order. NGR dyes are available at paint stores and distributors that sell to the professional paint trade, and at most woodworking stores.
Amount of Colorant
Stains differ in the ratio of colorant (pigment and dye) to liquid (binder and thinner). The higher the ratio of colorant, the darker the stain will make the wood. Commercial stains vary in the amount of colorant they contain but no indication is given on the container. You’ll have to learn the differences by experience.
You can control how dark you color the wood in one application of stain by adding pigment or dye to increase the ratio of colorant to thinner or by thinning to decrease the ratio.
Type of Binder
Most commercial stains contain a binder, which seals the pigment or dye into the wood or onto its surface. Binders are oil, varnish, lacquer and water-based finish. The biggest difference among binders is drying time—oil and varnish dry slowly, lacquer and water-based dry rapidly.
Oil stains are the common mineral-spirits-clean-up wiping stains you find on the shelves of paint stores and home centers.
Varnish stains (including polyurethane-varnish stains) are more like thinned paint because they dry hard like paint so the excess can be left thick. But these stains contain less pigment than paint, so you can still see through to the wood. The most common use for these stains is to coat over an existing finish (usually woodwork, not furniture) that is scratched, nicked and dull from age.
Lacquer stains are actually very fast-drying alkyd-varnish stains that are commonly referred to as “lacquer” stains because they can be added to lacquer to make a toner. These stains are commonly used by professionals and are very effective in production situations because they dry fast enough so you can coat over with a finish within 15 minutes or so. Sometimes you can identify these stains by the description on the can or by the inclusion of fast-evaporating acetone, MEK, toluene or xylene solvents. But if the all-inclusive phrase “petroleum distillate” is the only solvent listed, you will have to learn by trial and error.
Water-based stains also dry fast, but depending on the wood, they may raise the grain. The easiest way to deal with raised grain is to “bury” it with a coat of finish and then sand level. If you try to sand the stain itself to level the raised grain, you’re likely to sand through in places.
NGR and water-soluble dye stains don’t contain a binder. With no binder, it’s often possible to remove some of the color or make it more even by wiping with a cloth dampened with the solvent for the dye even after the dye has fully dried.
Most stains come in liquid form for fast and easy application, but some are thick gels. Gel stains color the wood but don’t penetrate into it, so they are useful for reducing blotching, especially on softwoods such as pine.
Though gel stains are somewhat messy and inefficient to use, they are very predictable. If you don’t have the time, or are unable to master, the washcoat technique (see below) for dealing with blotchy woods, then you may find gel stains an acceptable substitute.
Just as with liquid stains, the color in a gel stain can be adjusted by adding pigment to darken or tweak the color, or by adding a clear gel finish to lighten the color.
Colorants can be applied to wood in at least four ways. It makes a big difference for the effect you get which way you use.
Apply and Wipe Off
The basic way to apply a stain is to wipe, brush or spray a wet coat onto the wood, then wipe off the excess before it dries. This will produce an even coloring as long as you have prepared the wood well and it isn’t naturally blotchy. If you’re not using a spray gun, then wiping a stain onto the wood using a soaked cloth or sponge is far more efficient than brushing a stain.
Apply the Stain and Leave It
Brushing and leaving would be the typical way you would apply a varnish stain.
You can also spray an entire surface and not wipe off to produce an even coloring, or you can limit the spray to parts (for example, just sapwood) to correct an uneven coloring in the wood or create special effects. It’s best to use NGR dye stains or fast-drying “lacquer” stains and to thin the stain with three-or-more parts thinner so you don’t leave lap marks. It’s better to build the color slowly than to try to achieve it in just one pass.
Commercial thinned stains for spraying and leaving are commonly called “spray/no-wipe” stains.
Partially seal or “washcoat” the wood
A washcoat is any finish, sanding sealer or white glue that is thinned to approximately ten percent solids so it seals the wood just enough to prevent deep stain penetration and the resulting blotching that occurs on some woods. (There’s no reason to use a washcoat on woods such as oak and ash that don’t blotch.)
Ten percent solids translates to about two parts mineral spirits to one part varnish or polyurethane, one-and-a-half parts lacquer thinner to one part lacquer and three-quarter-pound-cut shellac. You may be able to thin a water-based finish with two parts water, but if this causes beading problems, you will have to use a solvent supplied by the manufacturer or use a commercial water-based washcoat, usually labeled “wood conditioner.”
Slow-drying commercial washcoats, both varnish and water-based, that are labeled “wood conditioner” are designed for wipe or brush application. The directions on the cans usually produce poor results. You need to allow wood conditioners to dry thoroughly before applying stain for them to be effective.
Seal the Wood and Apply a Glaze
Use a sanding sealer or first coat of finish to seal the wood, then apply a glaze to accentuate recesses or create a special effect. Glaze is a pigmented stain thickened enough so it stays where you put it. Gel stain can be used quite effectively.
You can use rags, brushes or specialized glazing tools to manipulate the glaze. Once you have the look you want, let the glaze dry, then coat over it to protect it from being scratched or rubbed off.
Seal the Wood and Apply a Toner (Shading Stain)
Use a sanding sealer or first coat of finish to seal the wood, then spray on a toner, also called a shading stain, to change the color of the wood or highlight parts of it. Toners and shading stains (the terms are often used interchangeably) are very useful for tweaking a color to an exact match.
Remember that a pigmented toner obscures wood while a dye toner doesn’t, and that over a sealed surface, toners and shading stains add color but don’t bring out the wood’s figure or highlight the grain.
Apply a coat of finish over the toner to protect it.
Any color effect can be produced with some combination of one or more of these types of products and application methods.
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