Grisaille (French: 'grey') is a method of painting entirely in shades of grey, or occasionally brown or green monochrome, often to imitate the appearance of stone sculpture. It was used in medieval manuscripts to simulate carved relief, and in Renaissance altarpieces to create dramatic simulated sculpture on the external wings — the famous closed panels of Jan van Eyck's Ghent Altarpiece show grisaille figures that seem to be carved stone statues. Rubens used it to create oil sketches ('bozzetti') for large compositions, working out the tonal structure before adding colour. Picasso's Guernica (1937) was painted entirely in grisaille — grey, black and white — partly as a deliberate homage to newsprint, and partly because colour felt insufficient to the subject.