How would you create a life-like model of your face? A simple approach is to cover your face with papier-mâché, let it dry, detach it from your face, then fill the inside of the mask with plaster, let that dry as well, and detach the papier-mâché from the plaster. The result of this process is a plaster cast of your face—a representation, not an actual copy of your face.

Now, this only works because you have copied but one simple layer, namely the surface. Real three-dimensional copying (incl...