OF THE WAY TO MAKE THE SHADOW ON FIGURES CORRESPOND TO THE LIGHT AND
TO [THE COLOUR] OF THE BODY.

When you draw a figure and you wish to see whether the shadow is the
proper complement to the light, and neither redder nor yellower than
is the nature of the colour you wish to represent in shade, proceed
thus. Cast a shadow with your finger on the illuminated portion, and
if the accidental shadow that you have made is like the natural
shadow cast by your finger on your work, well and good; and by
putting your finger nearer or farther off, you can make darker or
lighter shadows, which you must compare with your own.