 In 1937, Max Ernst wrote in "Cahiers d'Art" that Leonardo's advice on the studying of stains on walls caused him an "unbearable visual obsession".All editions of the treatise are kept at the Elmer Belt Library of Vinciana at UCLA.The manuscripts were begun in Milan while Leonardo was under the service of Ludovico Sforza (between 1482 and 1499), being worked on substantially for the last 25 years of Leonardo's life.