Gouache, in art, is a form of water-color using opaque pigment rather than the more traditional transparent (aquarelle) technique. The pigments employed are essentially the same as those for transparent watercolor (finely ground powdered pigment, with a small amount of glycerin, honey, and oxgall in an aqueous solution of gum), but they are made opaque by the addition of white. The gouache may be applied to white or tinted paper in the same manner as transparent watercolor.
In contrast with the delicate and luminous effects possible through the glaze system of transparent watercolor, the gouache technique has something of the free, direct, and expressive quality characteristic of oil painting. The stronger brushstroke and heavy impasto that the medium affords has, therefore, made it especially suitable to the more expressionist temperament of many 20th century artists. Among the outstanding painters who have used the gouache technique are Georges Rouault, Boardman Robinson, Jose Clemente Orozco, Graham Sutherland, and Morris Graves.