I often cast a piece several times, so that I can explore how it looks using various materials and pigments. Here are two versions of “Sylvia in Middle Age,” one cast in waxes with a hydrocal backing, the other in hydrocal with embedded and applied pigment (bottom).
Carolyn Wirth 
This life-size piece has two states–one polychromed, the other cast in a variety of waxes and hydrocal, all basically white.
Since I do my own molds and casting, I am able to vary the process and control all materials.
Usually I have two or more models pose for any one piece. I am less interested in individual portraiture than a poetic statement using the figure.