Usually, this is done with drawing pencils or charcoal. Since I am *still* waiting for my Dick Blick order supplies to come in, I decided to let them shade with colored pencils. Doesn't really get the contrast I want, but they really have enjoyed shading with color for once and not a "regular boring pencil" lol!
I got the lesson plan right here:
http://www.incredibleart.org/lessons/high/high17.html
Laterz.
-Mrs. G