frottage

Relief image obtained by placing a sheet of paper over a broken, textured, or ornamented surface, and rubbing it with a pencil, crayon, or charcoal. Brass rubbing uses the same technique. The term was invented by the German Dadaist and surrealist Max Ernst, who used the process to eliminate the conscious creative role of the artist. Ernst and other surrealist and abstract artists produced novel and striking effects using sections of frottage in their paintings. Stuck on to a canvas or other surface, frottage is a form of collage.