Painted oak . Stained to change its colour or left unstained before application of lacquer, or other types of top-coats. Staining enhance the appearance of wood by reducing colour 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. Oak is stained using dyes or pigmented finishes. These finishes are available in a wide variety of colours, many of which are not part of the natural colour 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. Staining of oak 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 we prefer to omit the staining step when finishing oak.