So, case in point. I had a recessed Tree of Life. The nature of this kind of carving in plaster on a flat surface, makes it easier to carve into a blank slate than carve the surface down all around every branch, especially when you are trying to make the tree as complex as possible for the size.
But I wanted a positive, which I could not carve directly. The only way to do this is to cast a model, a plaster model, off of the original model. This makes an opposite hand model, but the relief is also opposite of the recessed version.