Watercolour is a medium or work of art made with paint consisting of fine pigment particles suspended in an aqueous binder which usually consists of gum, glucose, glycerine and wetting agents, applied to paper. As watercolour is semi-transparent, the white of the paper give a natural luminosity to the washes of colour. White areas of the image often are merely left unpainted to expose the paper. Watercolours are sold as cakes of dry paint or as liquid in tubes, to which water is added. The paint can be applied in various techniques such as wet-on-wet and wet-on-dry to obtain different effects.