Wood stain

Wood stain is a type of paint used to colour wood comprising colourants dissolved and/or suspended in a vehicle or solvent. Pigments and/or dyes are largely used as colourants in most stains.

The initial application of any paint or lacquer is absorbed into the substrate similarly to stains, but the binder from a stain resides mainly below the surface while the pigment remains near the bottom or at the surface.

Wood stain is a type of paint used to colour wood. It consists of colourants dissolved and/or suspended in a vehicle or solvent. Vehicle is the preferred term, as the contents of a stain may not be truly dissolved in the vehicle, but rather suspended, and thus the vehicle may not be a true solvent. The vehicle often may be water, alcohol, a petroleum distillate, or a finishing agent such as shellac, lacquer, varnish and polyurethane. Coloured or stained finishes do not typically deeply penetrate the pores of the wood and may largely disappear when the finish deteriorates or is removed.

Stain is composed of the same three primary ingredients as paint (pigment, solvent (or vehicle), and binder) but is predominantly vehicle, then pigment and/or dye, and lastly a small amount of binder. Much like the dyeing or staining of fabric, wood stain is designed to add colour to the substrate (wood and other materials) while leaving some of the substrate still visible. Transparent varnishes or surface films are applied afterwards. In principle, stains do not provide a durable surface coating or film. However, because the binders are from the same class of film-forming binders that are used in paints and varnishes, some build-up of film occurs.

Pigments and/or dyes are largely used as colourants in most stains. The difference between the two is in the solubility and in the size of the particles. While dyes are molecules that dissolve into the vehicle, pigments are larger than molecules and are temporarily suspended in the vehicle, usually settling out over time. Stains with primarily dye content are said to be 'transparent', while stains with more pigment in them are said to be 'solid' (opaque); some stains may be called 'semi-solid' or 'semi-transparent', and these may be interchangeable terms, and the relative transparency or opaqueness may fall somewhere between the two extremes.

Typically, dyes will colour very fine-grained woods (such as cherry or maple) while pigments will not colour woods such as these as well. Fine-grained woods generally have pores that are too small for the pigments to settle into. As a result, usually pigment-containing stains will also include a small amount of a 'binder' which helps to adhere the pigments to the wood. A common binder would be a drying oil such as linseed oil.

Most commercial stains contain both dyes and pigments, though often in varying colours and ratios (to each other) depending on the desired colouring effect. Additionally, to some extent, the degree to which a stain will colour a particular wood may be dependent on the length of time it is left on the wood, with longer exposure times accomplishing deeper colouration. Typically a 'transparent' stain will accentuate the wood grain (as it is transparent), while a more 'solid' stain will tend to obscure the wood grain (as it is more opaque, akin to what we would usually call 'paint'). Pigments, regardless of the suspension agent, will not give much colour to very dense woods but will deeply colour woods with large pores (e.g. pine).

A combination of coffee and vinegar or water is a natural alternative to synthetic wood stain.