Alberti's Window and Veil

“First of all, on the surface on which I am going to paint, I draw a rectangle of whatever size I want, which I regard as an open window through which the subject to be painted is seen.”

"I believe nothing more convenient can be found than the veil, which among my friends I call the intersection, and whose usage I was the first to discover. It is like this: a veil loosely woven of fine thread, dyed whatever color you please, divided up by thicker threads into as many parallel square sections as you like, and stretched on a frame. I set this up between the eye and object to be represented, so that the visual pyramid passes through the loose weave of the veil. This intersection of the veil has many advantages, first of all because it always presents the same surface unchanged, for once you have fixed the position of the outlines, you can immediately find the apex of the pyramid you started with, which is extremely difficult to do without the intersection. You know how impossible it is to paint something which does not continually present the same aspect. This is why people can copy paintings more easily than sculptures, as they always look the same. You also know that, if the distance and the position of the centric ray are changed, the thing seen appears to be altered. So the veil will give you the not inconsiderable advantage I have indicated. A further advantage is that the position of the outlines and the boundaries of the surface can easily be established accurately on the painting panel . . . you can situate precisely all the features on the panel or wall which you have similarly divided into appropriate parallels. . . .

Leon Battista Alberti, On Painting and On Sculpture: The Latin Texts of “De Pittura” and “De Statua,” trans. Cecil Grayson (London: Phaidon, 1972) 55; 67-69.