I loved doing this in art class. Art With Mr. E: Line Design w/Shading - Grade Very cool, fun art shading project from Art With Mr. E. he's an elementary art specialist. Try this with your kids (but I think grown ups would enjoy this too).
Make It. a Wonderful Life: Owls, Foil, Glue, and Shoe Polish - DIY: Make some fantastic art work by tracing over a coloring book page with glue, covering it with foil and then sponging on and wiping off shoe polish.