Torture. Pure and utter torture. I hate being dirty and this exercise gives you black buggers for weeks. Not to mention it gets all over anything you touch and makes you look like a chimney sweeper. Still, the point was to get dirty and to let go. After all, you're using a paper towel with charcoal dust to get the gestural shape of the figure. Then going back in with a pencil to get some more detail. Finally, you're using a big fat Steadler eraser to create form. The trick is to hard edges vs. soft edges.
So after class ended, I asked my teacher, Bob Kato, if there was a cleaner way to re-create this exercise. Because in all honesty, they are some of my best drawings from school so far. He said yes: Photoshop. Give it a try!