I haven't used plaster since I attended a sculpture class at the University of Utah nearly 12 years ago, so I wanted to do a project to re-familiarize myself with it. Plaster is a fairly safe and forgiving medium so I wasn't too worried.
Through my research I found that best way to start a chewie mask was to sculpt it directly to my facial contours in order to fit perfectly. So I needed a life-cast of my head. Not something I could do by myself, and my wife rarely has time to help because she is so busy with work. Fortunately we had a vacation coming up. :) With the help of my wife and her cousin, we did a life-cast of my face on the hotel room floor.
This is the basic process:http://www.rebellegion.com/forum/viewtopic.php?t=18217
I wish I could say my process was as seamless as it seems in the tutorial, but alas, it was not.
My mold broke and I couldn't make another life-cast because the vacation was over. So I ended up sculpting my head by looking in a mirror.