Illustrator Mark Crilley's tutorial on adding shading to faces

My kids and I like to draw. We sometimes go to the weekly figure drawings sessions at the Art Directors Guild in LA, or we just sit at the dining room table and draw. As an amateur sketcher, I'm in awe of illustrator Mark Crilley's skill with a pencil, and with his instructional books and videos. His videos are enjoyable and useful -- he explains what he is doing with a calm, soothing voice, and the tips he offers are often just what I need to gain new understanding about drawing. In his latest video, Mark shows how to add shading to faces.

Image: YouTube