Foreshortening a Figure onto Wall and Vault to Double Its Height
A twelve-braccia wall made to read as twenty-four; a screen bent to wall and vault
Leonardo explains how to make a figure on a twelve-braccia wall appear twenty-four braccia tall by painting its lower half on the vertical wall m r and its upper half on the overhanging vault m n. One diagram traces the visual ray from an eye at f up the virtual wall and onto the vault at n; a second, an overhead view showing a man in profile with arms akimbo, sets a perspective screen bent to match wall and vault so the painter can take the foreshortening marks. He notes that perspective makes the plane seem in relief and relief seem plane.
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A twelve-braccia figure made to appear twenty-four
To make a figure appear twenty-four braccia high, first draw the lower half of the man on the vertical wall m r, then make the upper half on the vault m n. A visual ray from the eye at f to the virtual height f strikes the vault at n, giving the foreshortening the upper body needs.
The profile figure projected for foreshortening
Behind a perspective screen laid on the floor, draw the figure in profile at any size and extend all its lines to point f. Where the lines cut the bent screen m n you take the heights and projections for the wall; the widths keep their true sizes on the upright wall m r, since the figure diminishes of itself in receding.
A perspective screen shaped to wall and vault
The screen is arranged on the floor to resemble how the wall stands to the vault where the figure is to be made: its flat part aligns with the vertical wall (base m, departure point r) and its curved part with the vault (end n). Only by matching the screen to the built surfaces can the painting on the relief wall come out right.