Article: Understanding The Different Stains
In this article we will discuss the many different types of stains available to the furniture refinisher, and their uses. Gel Stain, Oil Based Stain, Water Based Stain, Varnish Stain, Lacquer Stain, NGR Stain, Dyes & Pigments. We'll help you understand the differences.
There are many types of stain. Each type of stain handles and colors in its own unique way. To have full control of the coloring process, you need to understand how stains differ and what each does best.
Stains, with so many to choose from, where do you even begin?
For most stains the best application method is to apply a wet coat of stain using a rag, brush, stain pad or spray gun and wipe off the excess before it dries. But if it were only that easy. Where do we start? With so many stains to choose from, which stain is the best choice for your project?
Go to any home center and you will probably be offered a choice of four types of stain: oil, varnish, water-based and gel (though the shelf arrangement and labeling of these stains rarely makes this clear).
Go instead to a paint store that caters to the professional painting and finishing trades and you will likely find lacquer stains and NGR (non-grain-raising) dye stains in addition to all or at least some of the stains available at home centers.
Shop at a woodworkers store or from a catalog that caters to woodworkers, and to many of the stains already mentioned you can add water-soluble dyes and sometimes alcohol- and oil-soluble dyes.
Instead of buying any of these products to color wood, you could use natural stains such as the juice from walnut husks (boiled in water) or berries, or even coffee or tea. Or you could use a chemical such as lye, ammonia or potassium dichromate. (Natural stains fade rapidly; chemicals offer limited colors and are dangerous to use and difficult to control.)
You could also use a shading stain, toner or glaze to stain wood, though each of these is designed to be applied in between coats of finish. (I'm not going to discuss these products, or natural or chemical stains here.)
There are many types of stain. In this regard stains are like saws. (There are also many saws: table, band, jig, scroll, radial-arm, miter, sabre, hand, etc.) Each cuts wood just as all stains color wood.
Each saw performs some cuts better than others; likewise, each type of stain handles and colors in its own unique way. To have full control of the coloring process, you need to understand how stains differ and what each does best.
Oil stains are the most widely available and are the type most people think of when they think of stain. These are the easiest to use because the linseed oil base or binder (sometimes a mixture of linseed oil and varnish) 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. Minwax uses the more technical (and user unfriendly) name: aliphatic hydrocarbon.
Unfortunately, oil stains are often referred to as pigment stain or wiping stain and this introduces confusion.
Though some oil stains contain only pigment, most contain pigment and dye, and many contain only dye. Moreover, many varnish, water-based, gel and lacquer stains contain only pigment, and these are rarely referred to as pigment stains.
Oil stains can be wiped, of course, but so can all stains especially if the project is small. So technically, all stains can be wiping stains and the term loses its usefulness.
Choose an oil stain to apply under any finish except water based, and in all cases where you don't need any of the special characteristics offered by other stains.
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 whereas 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 is less time to wipe off the excess. Brushing and leaving the excess usually leaves prominent colored brush marks.
Traditionally, varnish stains were used most often to overcoat already stained and finished furniture, and woodwork that had become dull or scuffed. Because the stain hardens well, it didn't require a topcoat of finish in these situations and the brush marks were disguised by the already existing color.
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: water.
Water-based stains are usually best 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. 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, and then sand smooth.
Overcoming the quick drying time 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 purpose of using water-based products 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.
Most gel stains are oil- or varnish-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 in the wood and is the only problem that can't be fixed by stripping and starting over. The only way to remove blotching is 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 before staining. Choose a gel stain when staining pine or similar soft woods.
Lacquer stains use very fast-drying binders and solvents. Professional finishers often choose these types of stains because the finish can be applied within approximately 30 minutes, and the stain can be added to lacquer to make a toner for adjusting color between coats of finish.
You can identify lacquer stains by the strong, pungent odor caused by solvents such as xylene and various ketones, which will 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 are spraying and want to reduce the time between staining and finishing, or if you plan to add a colorant to your lacquer.
NGR Dye Stain:
NGR stands for non-grain-raising and refers to a type of dye that's usually dissolved in very fast evaporating solvents. As with lacquer stains, NGR dyes are favorites with professional finishers because there is little waiting between staining and finishing and the stain can be added to lacquer to make a toner.
All NGR dyes are packaged in liquid form and most contain methanol and sometimes other toxic solvents. No pigment or binder is included. Some NGR dyes are packaged in concentrated form and can be thinned with water, alcohol or lacquer thinner. (If thinned with water, they perform closer to the water-soluble dyes discussed below.)
Choose an NGR dye stain if you want a deeper or more even coloring than can be achieved with pigment. Also choose NGR if you want to reduce the time between staining and finishing or add a dye colorant to lacquer to make a toner.
Water-, Alcohol- and Oil-soluble Dyes:
These dyes are packaged in powder form, which makes them easy to identify. You have to dissolve them in the proper solvent.
Of the three, the most useful is water-soluble dye because it provides more time for wiping off the excess and there's no exposure to irritating solvents. (Handle grain raising and fast drying the same as with water-based stains, described earlier.) Alcohol-soluble dye is sometimes used by touch-up specialists precisely because of its very fast drying. Oil-soluble dye is rarely used anymore (except in oil stains). It's been replaced by NGR dye.
Choose a water-soluble dye if you want deeper or more even coloring than can be achieved with pigment.
Pigment and Dye:
Pigment and dye are the two primary colorants used in stains (chemicals being the other).
Pigment is ground earth or colored synthetic particles sized to imitate earth. The particles have weight so they settle to the bottom of the can if not kept in suspension by stirring.
Dye is a chemical that dissolves in one or more specific liquids (different dyes dissolve in different liquids). So dye becomes a part of the liquid and doesn't settle out.
You can tell if a stain contains pigment, dye or both by inserting a stirring stick after the stain has sat undisturbed on a shelf for several days or weeks. Pigment will have settled to the bottom; dye will still be in solution.
Because pigment has size it can't penetrate into wood. But after you wipe off excess stain, some pigment remains in pores and sanding scratches that are larger than the size of the pigment particles. This explains why sanding to finer grits produces a lighter coloring: less pigment can lodge.
Because dye dissolves in a liquid, it has no size and penetrates along with the liquid. So dye colors wood more uniformly.
You can't endlessly darken wood with pigment unless you leave some to build on the surface (equivalent to painting). But dye can be applied in many coats to darken wood as much as you want without obscuring the wood or creating any build as long as there is no binder in the dye that would itself build.
Dyes that don't build are NGR, water-soluble, alcohol-soluble and oil-soluble. Oil, varnish, water-based, gel and lacquer stains with dye included to add build.
All dyes, whether dissolved in solvent or containing an added binder, fade in bright light, especially sunlight and fluorescent light. You should avoid the use of dyes if your project will be placed in these conditions.
When excess stain is wiped off, pigment lodges in pores and sanding scratches highlighting them (left) while dye penetrates everywhere along with the liquid and colors more evenly.
All types of stain can vary in color intensity depending on the ratio of colorant (pigment, dye or chemical) to liquid (oil, varnish, solvent, thinner, etc.). The higher the ratio of colorant to liquid, the darker the stain colors the wood. You can change the ratio in any stain by adding pigment, dye or thinner.
Sometimes you hear that you can make wood darker by leaving a stain on the surface longer before wiping off the excess. The explanation given is that the stain penetrates deeper. This is not true. What happens is that more thinner evaporates increasing the ratio of colorant to liquid.
The color intensity of a stain is determined by the ratio of colorant to liquid. A full-strength commercial oil stain darkens wood more (left) than the same stain thinned 50 percent with mineral spirits (right).