Dubuffet's art primarily features the resourceful exploitation of unorthodox materials. Many of Dubuffet's works are painted in oil paint using an impasto thickened by materials such as sand, tar and straw, giving the work an unusually textured surface.[9] Dubuffet was the first artist to use this type of thickened paste, called bitumen.[10] Additionally, in his earlier paintings, Dubuffet dismissed the concept of perspective in favor of a more direct, two-dimensional presentation of space. Instead, Dubuffet created the illusion of perspective by crudely overlapping objects within the picture plane. This method most directly contributed to the cramped effect of his works.