Last week I made a line drawing study of one of my favorite classical sculptures, the Laocoön Group from the Vatican Museum.
I had planned to leave it as line drawing, but the temptation was too great and I decided to keep going with a little shading with graphite pencil. Here is a time-lapse video showing some of the refining and shading process:
This drawing, done on a sheet of translucent drafting film, is what I would call "quick and dirty" cast drawing.
A traditional cast drawing of this size and complexity would be drawn on smooth heavy-weight paper called Bristol, and it would take a couple hundred hours, the final refined to a high finish with much more subtlety and detail. But since I'm just doing this drawing for myself, for fun, and not necessarily as a demonstration for my students, I'm doing very basic, fast shading.
However, I still follow a traditional classical drawing method: Establishing shadow shapes with a flat, dark value first, and then rounding the form by shading from the edge of the shadow up towards the light side. Even with a rough drawing it's important to show clearly what side of each form is in shadow, and what side is being touched by light, for a clear, dramatic, and readable drawing.