Staining should enhance the appearance of wood by reducing color variation between and within sapwood and heartwood. It also provides a way of giving bland looking woods such as poplar, the appearance of prized furniture woods such as ebony, mahogany or walnut.
Wood can be stained using dyes or pigmented finishes. These finishes are available in a wide variety of colors, many of which are not part of the natural color palette of wood, for example, blues and greens. Pigmented stains tend to highlight the grain (and also sanding scratches), whereas dyes do not have this effect and are more transparent.
Wood can also be colored by exposing it to chemicals that react with the wood to form colored compounds. Chemical staining of wood is rarely carried out because it is easier to color wood using dye or pigmented stain, however, ammonia fuming is a chemical staining method that is still occasionally used to darken woods such as oak that contain a lot of tannins.
Staining of wood is difficult to control because some parts of the wood absorb more stain than others, which leads to problems such as blotchiness and streaking. For this reason, as pointed out by Flexner, many people prefer to omit the staining step when finishing wood.
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