Gouache is an opaque watercolor that has been used traditionally by designers and graphic artists to create posters and other advertising materials. However, because of their strong, opaque colors and versatility, they have become extremely popular with artists. Gouache requires no solvents, is diluted with water, and brushes and other painting materials can be cleaned easily with soap and water. It is the perfect medium for use in colleges, at home or in the studio. 18 color set.