Painting made with a pigment ground in gum, usually gum arabic, and applied with brush and water to a surface, usually paper.
The pigment is ordinarily transparent but can be made opaque by mixing with a whiting to produce gouache . Transparent watercolour allows for freshness and luminosity. Whereas oil paintings achieve their effects by a building up of colour, watercolours rely on what is left out, with empty, unpainted spaces being an integral part of the work.