Geez, uploading this to Scraps because I've already uploaded one too many facial shading things, I know.
But this includes the basic planes of the face, which might
help some people figure out why the face is shaded in a certain way depending on the light source. So Scraps watchers of mine get to see this bonus material first.
This was a copy of an exercise sheet I passed around to students in my latest character illustration class. The face drawings are mine - the students copied the basic planes onto the large face then shaded the six smaller identical ones in different ways.
I referenced the basic planes of the face off of one of Andrew Loomis's books, Drawing the Head and Hands