2- Frottage (rubbing), developed by Ernst and described by him in Beyond Painting, (1948).
3- Grattage (scraping), also a discovery of Ernst, which transferred frottage to to oil painting. In decalcomania (transferring) the image was obtained by laying arbitrary patches of color on a piece of paper. A clean piece was then rubbed gently on top. When separated, strange grottos, exotic vegetation and underwater scenes suggested themselves to the imagination. A picture was made by chance.