Popular Woodworking 2006-06 № 155, страница 93

Varnish Stain

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 Stain

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.

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

Choose a water-based stain for use under a water-based finish.

Gel Stain

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

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.

—BF

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.

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