This was a recent class project. We made thick disc-shaped plaster blocks, and created faces, using the "subtractive" method, a.k.a. "carving". Here are some very nice examples from some of the students.
(First, a sample piece I made prior to starting the project-- this piece remains unfinished, but I think it helped in getting them off to a good start.)
Jacobi (unfinished sample piece)