Why model? Well, It's difficult to carve in the round from a 2 dimensional photograph. In this lesson I make a model so I have the all-important side-view.
I'm using 'NewClay' ('NuClay'), which contains fine strands of glass fibre that bind the clay when it dries. The glass fibre gives much greater strength and prevents cracking compared with ordinary clay, which will tend to fracture. Here is a link to Newclay makers, where you can ask about sources.