Anyway, once you have your empty eggshell, you can mark your proportion lines on it with pencil, making sure you place your eyes half-way down the head. Then you can stand the "egg head" up by putting it in an empty bottle lid; direct your single light source from whichever way you are interested in studying the shadows from, and sketch at least 20 eggheads.
Here are mine: :)
I got a little carried away with #4
I would tell you the name of the book that had this exercise in it, but I've forgotten it, sorry
And here is a weird-sort-of-looking guy from one of my old sketchbooks.... I wonder why he is looking at those planets with such a baleful glare? And why are those planets so small (or him so big, whichever the case may be) I have a feeling he's nothing but a doodle :)