Watercolour paint consists of fine pigment particles suspended in a water-soluble binder (adhesive substance). It is usually used on paper. As watercolour is semi-transparent, the white of the paper gives 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.
The binder usually used for watercolour consists of gum, glucose, glycerine and wetting agents.