Seven Types of StainPosted on June 3rd, 2010 By Bob Flexner No comments
We use the term “stain” to identify a colorant we apply to wood to change its color. But stains are not equal. Besides the obvious differences in color, there are at least seven categories of commercial stains that each apply and color differently. If you really want to have control over staining, you need to understand the differences and how to identify and choose each type.
Oil stains are the most widely available and the type of stain most people think of when they think of stain. These are the easiest to use because the linseed oil (sometimes a mixture of linseed oil and varnish) binder allows plenty of time to remove the excess before the stain dries—even on large projects.
You can identify oil stains by their thinning and clean-up solvent: mineral spirits (paint thinner). Most manufacturers list it as “petroleum distillate.” Some brands use the more technical (and user unfriendly) name: “aliphatic hydrocarbon.”
Though some oil stains contain only pigment, many contain pigment and dye and some contain only dye. The type of colorant used doesn’t seem to make a lot of difference in the way the stain looks on the wood, however, because of the impact of the binder. (This goes for all stains with a binder included.)
Choose an oil stain to apply under any finish except water base, and in all cases where you don’t need any of the special characteristics offered by other stains. Allow overnight drying in a warm room before applying a finish.
Varnish stains resemble oil stains in every way but one. Varnish stains use only varnish (sometimes polyurethane varnish) as the binder, so varnish stains dry hard while oil stains don’t. Therefore, a varnish stain can be brushed on wood and left to dry without wiping while excess oil stain has to be wiped off or the finish applied on top may chip or peel.
Think of a varnish stain as alkyd paint with less colorant added.
Fortunately, most manufacturers label their varnish stains to distinguish them from oil stains because varnish stains use the same thinner as oil stains: mineral spirits. If you aren’t sure whether a stain is varnish or oil, put a puddle of stain on top of the can or on another non-porous surface and see if it dries hard after several days in a warm room. Thick oil stains never harden.
Varnish stains are more difficult to use than oil stains because there’s less time to wipe off excess. Brushing and leaving the excess usually leaves prominent brush marks that stand out because they’re colored.
Choose a varnish stain to overcoat an already stained and finished surface that is dull or scuffed, or if you’re wiping off excess on a small project.
Water-based stains use water-based finish as the binder and replace most of the organic thinner with water. So these stains pollute less, are less irritating to be around, and are easier to clean up than oil or varnish stains.
You can identify water-based stains by their thinning and clean-up solvent, which is water.
Water-based stains are usually the best stain to use under water-based finishes because these finishes don’t bond well over oil or varnish stains unless you give them a week or longer to thoroughly dry. Unfortunately, water-based stains are more difficult to use because they raise the grain of the wood, and they dry fast.
Sanding off raised grain inevitably leads to sanding through color in places. To avoid this, raise the grain and sand it off before applying the stain, or bury the raised grain.
To raise the grain first, wet the wood with a wet cloth. Let the wood dry overnight or at least for a few hours in a warm, dry room. Then sand off the roughness and apply the stain. To bury raised grain, simply apply the first coat of finish over the stain and raised grain, then sand smooth.
Overcoming fast drying is more difficult. You can add a slow evaporating solvent (usually propylene glycol) provided by some manufacturers, or you can add lacquer retarder. But adding either reduces the color intensity of the stain and defeats the main purpose of using water-based products in the first place—to reduce exposure to solvents.
A better method is to divide your project into smaller parts and apply and wipe off the stain on each before going to the next. You can also have a second person follow you, quickly wiping off the excess.
Choose a water-based stain for use under a water-based finish.
Most gel stains are oil-based, so they thin and clean up with mineral spirits. They are identifiable by their thickness, which is similar to mayonnaise. This makes them rather messy to apply, but gel stains solve the single biggest problem in wood finishing—blotching on pine.
Blotching is uneven coloring caused by varying densities and resin deposits in the wood and is the only problem that can’t be fixed by stripping and starting over. The only ways to remove blotching are to sand it out, which is very time consuming, or paint the wood, which is seldom a desired solution.
So gel stains serve a very important role in wood finishing. And they are much more predictable and easy to use (only one product to apply) than applying a wood conditioner or washcoat before staining, which is the method most often suggested.
Choose a gel stain especially when staining pine, but also when staining other blotch-prone woods if you want to reduce the blotching.
Lacquer stains use very fast drying binders and solvents. Professional finishers love these stains because the finish can be applied within 15 minutes or so, and the stain can be added to lacquer to make a “toner” for adjusting color between coats of finish. It’s probably this use that has given these stains their name because they don’t use lacquer as the binder. They use a very fast drying varnish—a short-oil varnish.
You can identify lacquer stains by their strong, pungent odor caused by the solvents, which usually include xylene and various ketones. These should be listed on the cans.
Lacquer stains are difficult to use because of their very fast drying. Professionals usually work in pairs, with one person spraying the stain and the other following right behind wiping off the excess.
Choose a lacquer stain if you want to reduce the time between staining and finishing and are working together with someone else or are staining small surfaces. Also choose a lacquer stain if you want to add a colorant to lacquer.
Water-Soluble Dye Stain
Water-soluble dyes are sold in powder form, which makes them easy to identify. These dyes are also referred to as “aniline” dyes and were developed in the late nineteenth century for use on textiles and then adapted for wood. They were very popular in the furniture industry until the 1950s when metal-complex dyes were developed, and they continue to be popular with amateur and small-shop woodworkers because of their richness, wide choice of colors and ease of use.
To make a liquid dye from the powder, simply dissolve it in water. The ratio of one ounce of powder in one quart of water usually makes a standard color, but you can dissolve more or less powder to create a more or less intense color. The hotter the water the more powder you can dissolve. Use distilled water if there’s so much metal residue in your tap water that it affects the color.
The dye has an infinite shelf life in both powder and liquid forms.
Water-soluble dyes have two great advantages and one disadvantage when compared to the stains above.
One advantage is that the dye doesn’t obscure the wood no matter how dark you get it. A black dye, for example, can ebonize wood without completely hiding the figure.
Also, because there’s no binder in the dye, you can darken or lighten or change the color right on the wood even after the dye has totally dried. Apply more dye to darken the color. Wipe with a wet or damp cloth to lighten the color. Apply a different colored dye to change the color.
The problem with dye is that it fades in UV light, which means sunlight and fluorescent light. You may not want to use a dye if your project will be subjected to one of these light sources.
Two related but more seldom used dyes are alcohol-soluble and oil-soluble powder dyes. Alcohol-soluble dyes are sometimes used by touch-up specialists in combination with shellac to take advantage of the fast drying characteristic, and oil-soluble dyes are sometimes added to oil stains.
Choose a water-soluble dye if you want deeper or more even coloring than can be achieved with stains that contain a binder, or you want more control of the color after you apply the stain to the wood.
Metal-Complex (Metalized) Dye Stain
A weakness of dye is that it fades fairly quickly in UV light, so a more fade-resistant dye was developed in the 1950s called “metal-complex,” or “metalized” dye. This dye still fades, just not as rapidly.
Metalized dyes are usually available thinned with acetone (methanol was once used) and ready to use. These dyes are labeled “non-grain-raising” or “NGR” and are very popular in industry and in shops that spray their stains. The dye can be sprayed directly on the wood to act as a stain, and it dries very rapidly so finish can be applied within minutes. The dye can also be added to lacquer and sprayed as a toner.
Metalized dyes are also available in concentrated liquid form for you to thin with water, alcohol, acetone or lacquer thinner. Using water provides more time for application, of course, but introduces grain raising.
Choose a metalized dye stain if you want a deeper or more even coloring than can be achieved with pigment. Choose also if you want to reduce the time between staining and finishing or add a dye colorant to lacquer.