Max Ernst was a German (naturalised American in 1948 and French in 1958) painter, sculptor, graphic artist, and poet. A prolific artist, Ernst was a primary pioneer of the Dada movement and surrealism. He had no formal artistic training, but his experimental attitude toward the making of art resulted in his invention of frottage—a technique that uses pencil rubbings of objects as a source of images—and grattage, an analogous technique in which paint is scraped across canvas to reveal the imprints of the objects placed beneath. He is also noted for his novels consisting of collages.