Describes the action of one colour running into another. Most applicable to water-colour, where a second or third colour can be dropped on to an already applied wash while it is wet. To a certain extent the result is uncontrollable, but a wise hand will be able to judge approximately. Bleeding in oil-colours is associated with pigments such as asphaltum that can mix with other colours after application and drastically affect the optical and physical qualities of a painting.