František Kupka, [Untitled], 1928, Gouache, watercolor, and pencil on paper, The Museum of Modern Art, New York. https://dartabase.art/cite/moma/38252

František Kupka, [Untitled], c. 1925–30, Colored pencil, pencil, ink, and oil on paper, The Museum of Modern Art, New York. https://dartabase.art/cite/moma/38250