Celeste,
I have been looking for a good demo on fabric. I've found Virgil Elliot's piece at John Hagan's site very helpfull.
www.geocities.com/~jlhagan/advanced/cloth3.htm
What I'm also seeing is the way silk plays with light. At the slightest turn of the cloth the contrast from light/mid/dark range is extreme and very defined. I'm going to apply this to a piece I'm working on now.
I hope this helps us both.