Here is another one to do with clay that you can get somewhat contaminated.
Using fist size balls of clay have the students sculpt heads. Cover the heads
with that brown paper toweling that is in just about every school I've ever
The paper is applied using thinned white glue with an old brush. Apply many
layers building up a reasonable thickness. When the Paper covering dries cut
it off in two sections and remove the clay. Join the two halves with more
toweling and glue.
The finished piece has a wonderful almost wood like color and appearance.
Make great puppet heads or light sculpture and the clay can be reused though
not to fire.