In frottage the artist takes a pencil or other drawing tool and makes a "rubbing" over a textured surface. The drawing can be left as is or used as the basis for further refinement. While superficially similar to brass rubbing and other forms of rubbing intended to reproduce an existing subject, and in fact sometimes being used as an alternate term for rubbing, frottage differs in being aleatory or improvisational and random in nature.
It was developed by Ernst in drawings made from 1925. Ernst was inspired by an ancient wooden floor where the grain of the planks had been accentuated by many years of scrubbing. The patterns of the graining suggested strange images to him. He captured these by laying sheets of paper on the floor and then rubbing over them with a soft pencil.
The use of frottage in Surrealism and Surealist art is appropriate, since it also assumed the role of "rubbing" in its sexual context. This is especially relevant to surrealism seeing as much of the content behind the art works were based on that of sexuality, though of course other themes include politics, war, non-conformism, and (one which made up much of the surrealist art works) dreams and automatic thought. In many cases, especially in works of artists such as De Chirico and Dali, some or all of these themes were used in any given work of art. Frottage has also been used in mail art.