The art of Frottage, or rubbing was popularized by the surrealist Max Ernst in 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. He called this new style of textural impressions “Natural Histories”.
Watch Max Rub: http://youtu.be/5Jm5jHMETfM