A few people have been asking me about the types of clay I use. Whilst at Pixar we were using Chavant CM50. This is a hard styling clay that needs to be softened with heat. The clay does contain sulfur which can be annoying if you're bothered by the smell of rotten eggs. It does tend to stink up the room and the smell will permeate your clothes and skin, but the results are worth the discomfort. Your hands will smell even after washing thoroughly, so be forewarned. The surface of the clay once cooled can be really nicely finished and you can polish the surface to a dull shine using rubbing alcohol and paint brushes or cloth.
At Blue Sky we used Super Sculpey for our maquettes. This material has more of an agreeable odour as there is no sulfur. It can be smoothed done in much the same way as the Chavant clay, with isopropyl alcohol and paint brushes. Unlike Chavant, the sculpey can be put into an oven to cure, so it becomes rock hard. This makes the sculpt easier to make molds from with minimal clean up afterwards.
Some other clays I've used and recommend are:
Super Sculpey Firm... This is a better consistency for me to work with being firmer and gray in colour. Super Sculpey has a translucency to it that makes it a little more difficult to see surface imperfections. The gray super sculpey being opaque makes it easier to do a fine finish on the sculpture.
J-Mac... similar to Chavant, I like the dark brown colour to work with. It is a little stickier than the CM50.
NSP... also available from Chavant, it is non sulfurated for those who hate the smell of sulfur, but it tends to stick to your tools. It's available in several grades of firmness.
For a complete listing of chavant clays here's a link to their product line up: http://chavant.com/new_site/files/pdf/products-2006.pdf
Super Sculpey: http://www.sculpey.com/products/clays