Popular Woodworking 2000-12 № 119, страница 14
Flexner on Finishing
The Basics of Coloring Wood
The keys to understanding finishes.
So you've completed your project and
now you want to color it so it matches another object, a color chip or a vision you have in your head. Achieving this match can be one of the most difficult tasks in wood finishing, but before you get into the actual mixing of colors, it helps to understand what's possible and know the "tools" you have at your disposal.
Any color can be matched, but not any wood. You have to pay attention to how the wood or woods you're finishing compare to the sample you're trying to match.
There are four large categories of woods: softwoods such as pine and fir; tight-grained hardwoods such as maple, birch and cherry; medium-grained hardwoods such as walnut and mahogany; and coarsegrained hardwoods such as oak and ash.
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 two different categories has its limitations because of the large differences in grain and figure. You should take these limitations into account when you're choosing the wood for your 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 they differ besides the obvious variances in color.
• Type of colorant: 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. Dye is better at changing the color of wood without muddying it — especially dense woods such as maple. Some stains contain only dye, some contain only pigment, and some contain both.
• Amount of colorant: Stains differ in the ratio of colorant (pigment and dye) to liquid (thinner and binder). The higher the ratio of colorant in the first coat you apply, the
darker the stain will make the wood. You can control how dark you color the wood in one application of stain by adding pigment or dye to increase the ratio or by thinning to decrease the ratio.
• Type of binder: Most stains contain a binder, which seals the pigment or dye into the wood or onto its surface. Binders are oil, alkyd, oil/alkyd or water-base finish. The biggest difference among binders is drying time — oil dries slowly, alkyd and water base dry rapidly. But also important is water-base stain's characteristic of raising wood grain. Some dye stains, usually identified as "non-grain-raising" (or NGR), "water-soluble," or "alcohol-soluble" don't contain a binder.
If a stain contains a binder, every coat after the first remains on top of the wood; it doesn't go into the wood. Pigment in these stains obscures the wood if some is left on the surface. Dye in these stains is fairly transparent. Dye without a binder continues to add color into the wood and darken it more with each coat.
The same stain was applied to the left side of each of these woods -from the top down:oak, pine, mahogany, maple.Yet each still looks like the wood it is.There are limitations in what you can accomplish making one wood look like another.
If you apply a pigment or dye stain over a sealed surface and leave it, the stain is called a toner or shading stain.
• Thickness: Most stains come in liquid form for fast and easy application, but some are thick gels. Gel stains are useful for reducing blotching on woods such as pine and cherry, because gels don't penetrate into the wood.
Just as with liquid stains, the color in a gel stain can be adjusted by adding pigment to darken or tweak its color, or by adding a clear gel finish to lighten its color.
Gel stains are usually labeled as such, but manufacturers rarely provide much information about the type or amount of colorant or binder. To a large degree, you have to experiment and learn by trial and error, and this is the primary reason many people find staining so problematic.
The basic way to apply a stain is to wipe, brush or spray a wet coat onto the wood, continued on page 26
24 Popular Woodworking December 1000