This technique has been favoured primarily as a medium for making quick preliminary sketches, occasionally for roughing in the background of a larger work, and increasingly since the late Renaissance as a medium in its own right for finished drawings. In the 16th and 17th centuries, Peter Paul Rubens (Rubens, Peter Paul) and other artists often combined black and white chalk, a technique known as aux deux crayons. As developed by Rococo (Rococo style) artists such as Antoine Watteau (Watteau, Antoine) and François Boucher (Boucher, François), the expressive range of chalk drawings grew as broad as that of watercolours or pastels. The devices employed in the 18th century to achieve this subtlety of effect included the use of coloured paper; combining red, black, and white chalk (a technique known as aux trois crayons); and manipulating the medium to create an effect of mass rather than of line. In the 20th century, chalk was principally used by artists adhering to traditional art styles but also by such avant-garde painters as Henri Matisse (Matisse, Henri), Pablo Picasso (Picasso, Pablo), and Willem de Kooning (de Kooning, Willem). See also sanguine.