František Kupka, Girl with a Ball, c. 1908, Pastel on paper, The Museum of Modern Art, New York. https://dartabase.art/cite/moma/37352

František Kupka, Bather, (1906), Pastel and charcoal on gray paper, The Museum of Modern Art, New York. https://dartabase.art/cite/moma/37271

František Kupka, View from a Carriage Window, c. 1901, Gouache and watercolor on paper with cardboard overlay, The Museum of Modern Art, New York. https://dartabase.art/cite/moma/34108

Karl Wilhelm Diefenbach, Du sollst nicht töten, 1902, Öl auf Leinwand, Städel Museum, Frankfurt am Main. https://dartabase.art/cite/staedel/102642

František Kupka, Prometheus, (1909), Gouache, watercolor, ink, and pencil on paper, The Museum of Modern Art, New York. https://dartabase.art/cite/moma/36018