Plater of paris AND modelling compound? Girl, you hit pay dirt!
you can make all types of reliefs bypressing things into the comppund and
then pouring the plaster (mixed of course) over the compound. You can
use,tops of shoeboxes, paper cups,pie plates or strips of cardboard taped
you can add vermiculite to the plaster in a 3:2 ratio, pour it into papercups
and have a great easy to carve medium... check the archives. There's tons