A Treatise on Painting (Trattato della pittura) is a collection of Leonardo da Vinci's writings entered in his notebooks under the general heading "On Painting". The manuscripts were begun in Milan while Leonardo was under the service of Ludovico Sforza and gathered together by his heir Francesco Melzi. The treatise was first published in France in 1632; after Melzi's version was rediscovered in the Vatican Library, the treatise was published in its modern form in 1817.
The main aim of the treatise was to argue that painting was a science. Leonardo's keen observation of expression and character is evidenced in his comparison of laughing and weeping, about which he notes that the only difference between the two emotions in terms of the "motion of the [facial] features" is "the ruffling of the brows, which is added in weeping, but more elevated and extended in laughing."
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.