...because the sculptor only removes, and the painter always adds; the sculptor always removes from one same material, and the painter always adds of various materials. The sculptor seeks only the lineaments that surround the sculpted material, and the painter seeks the same lineaments, and beyond those he seeks shade and light, colour and foreshortening, in which things nature continually aids the sculptor, that is with shade and light and perspective, which parts the painter must acquire by force of intellect and turn himself into nature herself, while the sculptor finds them continually made. And if you say: there is some sculptor who understands what the painter understands, I answer that where the sculptor understands the parts of the painter, he is a painter, and where he does not, he is a simple sculptor. But the painter always needs to understand sculpture, that is the natural model, which has the relief that of itself generates light and dark and foreshortening. And for this many return to nature, being unlearned in such discourse of shadows, light and perspective, and so they draw from the natural model, because only such drawing has put them in practice, without other science or discourse of nature in this respect. And of these there are some who, through glasses or other papers or transparent veils, regard the things made by nature, and there upon the surfaces of the transparencies they outline them, and with the rules of proportionality surround them with profiles, sometimes enlarging within such profiles, filling them with light and dark, noting the site, the quantity and figure of shadows and lights. But this is to be praised in those who know how