Types of Stain for Wood: Pigment, Dye, Oil, Water, Gel

Wood stains are sorted three ways: by what makes the colour (pigment or dye), by what carries it (oil, water, gel, or a lacquer or varnish base), and, for outdoor work, by how much they hide (clear, tinted, semitransparent or solid colour). Every can on the shelf is one choice from each list. That is why lists of 'the three main types' or 'the four types' disagree - they are counting different axes. The USDA Wood Handbook adds that the naming is confusing partly because manufacturers do not follow a standard set of definitions, so read what the label says the product is made of, not just what it is called.

A stain, as Wikipedia puts it, adds colour while leaving the wood still visible; paint forms an opaque coating. A stain usually contains a colorant, a vehicle or solvent, and a small amount of binder such as a drying oil.

Dyes are dissolved in the vehicle, so they soak into the cell walls and colour evenly; pigments are ground particles that sit in pores, scratches and open earlywood and need a binder to stay put. Wikipedia notes that dyes will colour very fine-grained woods such as cherry or maple, while pigments will not colour those woods as well.

That is why the same brown pigment stain looks dramatic on oak and flat or blotchy on maple. The Wood Handbook explains the grain side: stains absorb differently into earlywood, latewood, knots and vessels, and can even reverse the normal colour gradation by darkening the soft earlywood more than the latewood - the effect you see on pine. A thinned sealer, or 'wash coat', applied first partly fills the voids and evens the colour. If a board still blotches badly, the handbook points to a less obvious cause: blue-stain fungi or bacteria before drying can make wood very porous, and that cannot be fixed once the stain is on.

• Oil-based stains use petroleum solvents, penetrate slowly and give a long working time; the Wood Handbook describes oil-based semitransparent stains as flowing into the wood and not forming a film, so they do not blister or peel even with excess water - unless over-applied.
• Water-based stains dry faster and clean up with water; modern ones may add acrylic or urethane binders for durability (Wikipedia). The handbook cautions that waterborne semitransparent stains often form a thin film and can crack and flake.
• Gel stains are thick (thixotropic) and stay where you put them, which gives better control on vertical surfaces (Wikipedia).
• Lacquer, varnish and shellac-based stains, including one-step stain-and-finish products, colour and build a film in one coat.

For outdoor stains, the blogger Angela Marie Made cites manufacturer claims of 3 to 8 years for water-based products and 1 to 5 for oil-based, noting oil is easier to recoat without sanding; her own outdoor test ran under two years, too short to confirm those figures, so the USDA data compiled from many researchers in the next section is the better guide.

Outdoors, opacity is the axis that matters, because pigment is what blocks the sun. The USDA Wood Handbook's Table 16-3 gives service lives for vertical exposure:

• Water-repellent preservative (clear) - 1 to 3 years; grain visible, wood tan to brown, fades to grey.
• Tinted clear or lightly pigmented deck finish - 2 to 3 years.
• Semitransparent stain - 4 to 8 years on saw-textured or weathered wood, applied as two coats since rough surfaces absorb more. On smooth, unweathered wood only one coat is usually applied, and the life drops to about 2 to 4 years.
• Solid-colour stain - 6 to 15 years; it hides the grain, forms a film like paint, and needs a primer for the best life.
• Paint - 10 to 20 years, for comparison.

On decks the numbers shrink. Table 16-2 gives semitransparent stain 2 to 3 years on new smooth decking and 3 to 6 years on weathered or saw-textured decking, and the handbook recommends penetrating finishes for decks because film-forming ones peel on horizontal surfaces and solid-colour stains lack abrasion resistance. So the stain that lasts longest overall is solid colour on siding; the one that lasts longest on a deck in practice is a penetrating semitransparent stain you renew before it fails.

The quickest way to predict a stain result is to know the species and its pore type, which is our core subject.

• Ring-porous hardwoods - oak, ash, hickory, walnut - have large vessels. The handbook says these may need a paste or liquid filler for a smooth finish; pigment stains lodge in the pores and emphasise the grain.
• Diffuse-porous hardwoods - maple, birch, cherry, aspen - have small vessels, so pigment stains look weak or blotchy; use a dye stain, or a wash coat before the pigment stain.
• Softwoods - pine, fir, spruce - have no vessels but strong earlywood-latewood contrast, so stains can reverse the grain; a sealer first helps.
• Cedar and redwood outdoors contain water-soluble extractives that bleed through film finishes; the handbook advises stain-blocking primers under solid colour and paint, and warns against steel wool, which leaves blue-black iron stains in these tannin-rich woods and in oak.

Not sure what the board is? Take a photo of the grain with WoodLens; it names the likely species. Our wood grain identification page shows the pore check by eye.

Two warnings from the USDA Wood Handbook. First, sponges, cloths and paper towels wet with oil-based stain, any other oil or oil-alkyd, or urethane are particularly prone to spontaneous combustion; immerse them in water and seal them in a water-filled, airtight metal container immediately after use. Second, the fungicides in water-repellent preservatives and semitransparent stains are toxic and may act as herbicides, so avoid skin contact and breathing the vapours, and protect plants and soil. If stain is swallowed or splashed in the eyes, call Poison Control (1-800-222-1222 in the US) or see a doctor.