Stains and Dyes

Wood has been stained with coloring agents of all descriptions for nearly as long as people have been working with wood. It comes naturally in a nearly endless variety of colors and textures, but many highly prized species are also difficult to obtain, and costly.

As a result, it is often desirable to alter the appearance of a more common wood to make it look like a more valuable or exotic species. Sometimes, color is used to enhance the natural properties of the wood, making the color and texture of the wood more apparent. And sometimes, a stain is used to mimic the appearance of aged wood, or to blend new construction into preexisting cabinetry. For all of these purposes, finishers have their choice of just two basic ways to color wood: stains and dyes.

A stain is very much like a transparent paint: it consists of a pigment (finely ground particles of solid color) suspended in a solvent with a varnish resin binder, which "glues" the particles to the surface. Since they use opaque particles deposited onto the wood's surface, stains tend to obscure the wood grain like a thin coat of paint, and multiple coats could result in an opaque color. Also, since the stain will be left thicker in tiny depressions in the wood's surface, such as pores or sanding scratches, stains are great for highlighting the texture of the wood.

A dye uses a mixture of dissolved chemicals to achieve its color, and these bond chemically with the wood fibers. Since the coloring takes place on the molecular level, there is little or no highlighting of surface texture or blotching of the wood grain like solid pigment particles do - whatever the dye touches, it colors evenly. Dyes have much less tendency to highlight scratches, pores, or end grain because the intensity of color is controlled mainly by the concentration of the chemical solution, not by how thick a coat of it is applied, although repeated coats can have the effect of concentrating the dye on the wood, giving a slightly darker color. Finally, dyes do not have a varnish base like stains, so a dye can usually be un-done easily by bleaching it out, since there is no sealer protecting the color.

These differences allow the finisher to achieve a great array of different effects by using dyes and stains in combination. For example, if it is desirable to finish curly mahogany in a medium-dark color while "popping" the grain, a thinned black dye could be applied to increase the contrast of the curly grain. After a light sanding, a golden amber dye would be applied to heighten the "popping" effect, then a sealer. Finally, a dark brown glazing stain, or gel stain, would be applied to achieve the final color and highlight the pores of the mahogany.

Some coloring products use dyes and stains mixed together to achieve more consistent results on different woods. Some topcoats even have dyes and stains mixed into them, intended for "one-step stain and topcoat" finishing, however after several coats of these products, the grain of the wood is often obscured and few users are happy with the results. A better choice is to use separate color and clearcoat.

Safety First!
Safety in the workshop is YOUR RESPONSIBILITY alone; I make no warranty as to the safety of any technique or tool shown or described on this site. Before beginning any project, you must understand woodshop safety, know how to safely operate any machinery that is to be used in the project, and understand the safe use and any potential safety hazards involved in the use of all materials to be used in the project. See the General Safety Notice and the Chemical Safety Note for additional information.

Pigment Stains:

General Characteristics: since pigment is composed of solid particles of color ground to a fine powder, it is non-transparent (opaque), but also tends to be lightfast (fade-resistant). Stains color by the action of pigment being adsorbed onto the fine texture of the wood's surface, so they do a great job of highlighting the wood's natural texture. On the other hand, any "extra texture," such as sanding scratches, tearout, crushed wood, or even end grain will tend to pick up more color, resulting in streaking or blotching. An artificial lack of fine texture, the result of sealing the wood (leftover varnish when stripping, or glue spots when building or repairing furniture), will result in a "hole" in the stained color. Stains tend not to penetrate into the wood, but rather sit on the surface. Also, due to the varnish binder that "glues" the pigment to the wood's surface, stains will often show lap marks if an area is stained and allowed to dry too long before staining the adjacent area. Normally, careful planning and efficient execution of the staining process can avoid lap marks, but on extremely large and complex surfaces, it may be necessary to choose a product that will not show lap marks. The varnish or oil binder used in stains also means that the job cannot be "un-done" once the color is applied: the binder glues the color to the wood and protects it from chemical bleaching, so the only way to get the color off is to chemically strip off the binder and scrub the color off the wood as best you can, or simply remove the surface by sanding or scraping to reveal the unstained wood beneath.

Dye Stain: See Water-Based Dye under Dyes, below.
Earth Pigment / Furniture Powders: Very fine powder, can be mixed into any liquid base; easy to use, non-penetrating. Can be mixed with protective finishes (such as varnish).
Gel Stain: Gel, pigment in a varnish and jellied petroleum base (somewhat similar to napalm); easy to use, covers more evenly because it does not penetrate, bleed, or even flow readily. Will show lap marks.
Glazing Stain: Gel-like liquid, pigment suspended in varnish; excellent for figuring, shading, correcting sap streaks, and other glazing techniques. Glazing stain is like a more liquid and transparent version of a gel stain. By definition, glazing is applied over already sealed wood, so this type of product is not meant to be used as a stain in the usual sense.
Japan Color: Liquid, earth pigment concentrated in an oil varnish; excellent for tinting varnishes or mixing custom oil-base stains. Tends to dry slowly unless catalyzed with Japan drier. Popular with old-time sign painters, because the high-pigment formula holds sharp edge details without "feathering out." The slower drying time of Japan color makes it ideal for projects where lap marks might otherwise be difficult to avoid, however it also means that the stain must be allowed to dry for a very long time before topcoating, to avoid picking the color back up into the topcoat.
NGR Stain: See NGR Dye under Dyes, below.
Spirit Stain: See Alcohol Dye under Dyes, below.
Water Based Stain: Liquid, pigment or pigment & dye suspended in an acrylic and water base; brilliant, easy to mix colors; non-penetrating (or partially non-penetrating if a dye is used), non-toxic, non-flammable. Will raise grain and will show lap marks.
Water-Based Dye Stain: See Water-Based Dye under Dyes, below.
Wiping Stain: Liquid, pigment or pigment & dye suspended in varnish or oil; non-penetrating (or partially non-penetrating if a dye is used). The most commonly available type of stain, and tends cover unevenly more often than a gel stain, but the thinner consistency spreads on and wipes off of complex surfaces such as carvings more easily. Most wiping stains use a varnish binder, which will show lap marks, but a few use linseed or tung oil as a base, which dries slowly enough that lap marks do not normally occurr.

Dyes:

General Characteristics: dyes color the wood by the action of colored chemicals bonding to the wood's fibers at the molecular level. Unlike stains, dyes do not usually contain a varnish or oil binder, so the color can be bleached out if needed, at least until it's covered by the varnish topcoat or sealer. Because it's individual molecules, not pigment particles, that supply the color, dyes produce totally transparent color, but they're also more prone to fading when exposed to ultraviolet light from the sun or from fluorescent lighting fixtures. Just like water gets the wood's surface equally wet all over, dye tends to color the wood pretty evenly everywhere, regardless of end grain, tearout, or sanding scratches, so blotching is not much of a problem with dyes. (Was that a cheer I just heard?) On the other hand, dyes tend to color the wood pretty evenly all over, pores or no pores, so they don't usually do anything to hoghlight the texture of porous woods like oak or mahogany. For that, I'll generally dye the wood, apply a sealer, and finish the job with a glazing stain to bring out the pore texture without the possibility of blotching (because the wood's been sealed, only the pores are open to hold the glazing stain). After a few coats of clear varnish or lacquer, I'll have a finish with a depth of color you won't see on something that's been merely stained and varnished.

Alcohol Dye / Aniline Dye (alcohol base) / Spirit Stain: Alcohol soluble powder; penetrating, dries quickly, but tends more to show lap marks. Does not raise wood grain the way water based dyes do.
Aniline Dye: See Water-Based Dye below.
NGR Dye / Stain (Non-Grain Raising): Liquid, dissolved in methanol & petroleum distillate solution; does not raise grain, lightfast.
Oil Dye / Stain: Oil soluble powder; penetrating, transparent, slow-drying, needs sealer coat of shellac.
Penetrating Oil Stain: Liquid dissolved in mineral spirits; penetrates open-grained wood, moderately lightfast, transparent, easy to apply & mix colors, bleeds, needs wash coat.
Varnish Stain: Liquid, dissolved in varnish; highly transparent, lightfast, non-penetrating, adds filler, color, and gloss in one operation.
Water-Based Dye / Dye Stain / Aniline Dye (water base): Powdered, water soluble; penetrating, transparent colors, brilliant, compatible with any finish, may be non-toxic, and will raise grain. Water-based dyes are often called aniline dyes, although they no longer contain this highly toxic class of chemicals. These dyes can be used to tint water based finishes, and when applied directly to the wood, they tend to bleed into water based top coats if they are not sealed in first. This can produce problems by highlighting drips, sags, and lap marks; but if carefully used, it can also have the effect of evening out the color absorption in highly figured woods. Bleeding can be prevented by applying a shellac sealer over the dye. Powdered dyes also come in alcohol soluble form (see spirit stain), though the alcohol tends to 'wash out' the color a little.

N A T U R A L D Y E S
& C H E M I C A L M O R D A N T S

Natural Dyes:

Alizarin: A synthetic dye or the active coloring agent of madder root. Produces "Turkish Red", crimson, orange, yellow, and brown, depending on the mordant.
Alkanet Root: An ancient organic dye from the borage family. Used in french polishing, produces gray tones with alum, a range of reds with linseed oil.
Annato: Seeds from a Central American Tree. Produces oranges and golds with dichromate, tin, or alum, oak brown with lye.
Brazilwood: A popular dye from several species of South American redwood trees. Produces vibrant reds, browns, and purples, depending on the mordant.
Cochineal: Dried tropical insects. Produces many shades of red; mixed with alum.
Cutch: An extract of the heartwood of the Asian acacia tree. Produces various lightfast shades of brown, from beige to chocolate.
Dragon's Blood: A resin from any of various tropical plants, including a Malaysian palm and an agave native to the Canary Islands. Produces bright, lightfast reds. Often used to color violin varnish.
Fustic: An extract from the heartwood of the American Mulberry tree. Orange Yellow on its own, Yellows to greenish-yellows with alum.
Indigo: A dye extracted from Indian indigo plants. Produces deep blue, yellow-white with lye.
Logwood: An extract from Central American campeche hardwoods. produces lightfast grays, browns, blacks, blues, and purples, depending on the mordant.
Madder Root: Extracted from the roots of the Eurasian madder plant. Produces reds, blues browns, and yellows, depending on the mordant.

Mordants:

Note:
Always wear gloves designed to resist the chemical(s) being handled, and wear safety goggles designed for protection from spattered chemicals (these have covered vents). Chemical mordants should always be mixed in clean, non-porous containers. Never mix two chemicals without prior knowledge of any potential reactions between them. When mixing chemicals with water, always add the chemical to the water, never the other way around. It is strongly recommended to do further research into the nature of a particular mordant prior to using or handling it.

Alum (Aluminum Sulphate) A_l2(SO₄)³: White mineral salts, non toxic. Produces purplish and dark crimson tones.
Ammonia NH₄ (aq): Usually in a 28% aqueous solution, highly toxic, used in fuming. Produces dark violet browns with logwood dye, light yellow browns with brazilwood dye, reacts with the tannin present in some species to darken or "age" the wood. Anhydrous ammonia is very dangerous, so avoid it.
Copper Sulfate (Blue Vitriol) CuSO₄: Blue crystals, highly toxic, used for preserving wood. Produces dark gray and olive tones with logwood dye.
Ferrous Sulfate (Copperas) FeSO₄: Crystals, highly toxic, reacts with tannin in wood. Produces steel gray to bluish tones, ebony-like black with logwood dye or alum.
Hydrated Lime (Quicklime, Calcium Oxide) CaO: Crystals, toxic. Produces antique limed finish on hardwoods such as cherry and walnut, must be neutralized with vinegar or other dilute acid.
Potassium Carbonate (Potash) K₂CO₃: Crystals, mildly toxic. Produces a range of greens with alum and fustic.
Potassium Dichromate K₂Cr₂O₇: Crystals, orange in color, extremely toxic, reacts with tannin. Produces deep reds to rich browns, combines well with aniline dyes.
Potassium Permanganate (Violet Potash) KMnO₄: Crystals, mildly toxic, used for ebonizing. Turns wood with high tannin content a purplish brown. Dyes skin brown on contact, won't wash off.
Sodium Hydroxide (Lye) NaOH: White powder, toxic, caustic, and hygroscopic, so keep it in a tightly closed container. Easily obtained as a drain opener, darkens cherry and oak, must be neutralized with vinegar or other dilute acid.
Stannous Chloride SnCl: White crystals, moderately toxic. Produces light red with brazilwood dye, pink with alizarin, combines well with many dyes.
Tannic Acid C₁₄H₁₀O₉: Yellow or brown powder, mildly toxic. Boosts the tannin content in wood. Often used when fuming with ammonia or when ebonizing with an iron acetate solution.

References:

Time Life Books - The Art of Woodworking Series - Wood Finishing, St. Remy Press, 1992

Webster's New World College Dictionary, Third Edition, Simon & Schuster, Inc., 1997