Leonardo on painting versus sculpture
These excerpts leave no doubt about Leonardo’s judgment on the question.
37. A Painter and a Sculptor
A sculptor says that his art is more worthy than painting because, fearing humidity, fire, heat, and cold less than painting, it is more eternal. The response to him is that such a thing does not make the sculptor more dignified because the permanence is born from the material and not from the artificer. This dignity can also belong to painting by painting with colored glazes on metal or terracotta…
38. How the Ingegno of Sculpture Is Less than that of Painting and Is Deficient in Many Ways
Practicing sculpture no less than painting and exercising both to the same degree, it seems to me I can give a nearly faultless judgment on which of the two is of greater ingegno, difficulty, and perfection.
41. Sculpture Put upon a Par with Painting
Sculpture is missing the beauty of colors, it is missing the perspective of colors, it is missing the perspective and confusion of boundaries of things distant from the eye, because the boundaries of things nearby will be known just like those which are distant. The air interposed between a distant object and the eye will not fill the space around that object more than it does around a nearby object. [Sculpture] will not produce lucid and transparent bodies like veiled figures which show nude flesh under veils laid against it. It will not produce the minute pebbles of varied colors below the surface of transparent water.
44. On the Indebtedness of Sculpture to Light, But Not of Painting
If sculpture is illuminated from below it will seem to be a monstrous and strange thing. This does not happen to painting, which carries all its parts within itself.
45. The Difference Between Painting and Sculpture
The prime marvel to appear in painting is that it appears detached from the wall, or some other plane, and that it deceives subtle judges about that thing that is not divided from the surface of the wall. In this [specific] case, when the sculptor makes his works, what appears is as much as there is. This is the reason the painter needs to make it his duty to know how the shadows are accompanied by the lights. This science is not needed by the sculptor because nature helps his works just as it makes all other corporeal things. When light is taken away from these things, they are of the same color, and when the light is restored, they are of varied colors, that is chiaroscuro. The second thing that the painter with great discourse needs is to place the true quality and quantity of the shadow and lights with subtle investigation. Here nature alone puts them in the work of the sculptor. Perspective, a most subtle investigation and invention of mathematical studies, by the power of lines, makes what is nearby appear remote, and what is small appear great. Sculpture is helped by nature in this respect and does it without any invention by the sculptor.
Translation in Claire J. Farago, Leonardo da Vinci’s Paragone: A Critical Interpretation with a New Edition of the Text in Codex Urbinas, Brill Studies in Intellectual History (Leiden: E. J. Brill, 1992), pp. 261–5, 275–81 passim.