Joan Miró was also closely associated with the Surrealists in Paris, who particularly approved of his use of automatism in composition and execution, designed to expose the subconscious mind. Although his later and more popular paintings are refined, whimsical and apparently effortless, his influential period in the 1920s and 1930s produced works that were provocative in their sexual symbolism and imagery, and employing rough, experimental materials, including sandpaper, unsized canvases, and collage. In mature period painting, "La Leçon de Ski", his characteristic language of signs, figures and black linear forms against more textured and painterly background is evident.