Ornamental Gypsum is the right term for all that plaster molding you find in the classic old homes, and more and more in new modern homes.
There are two basic types of molding. One has all the fancy carving, and it is literally done with a silicone mold taken off of a sculpture or an existing molding. The other ones are smooth and are called extrusions.
The photo shows our master, Rohas, shaping an extrusion after the initial steps of pouring in gypsum, seating a strengthening canvas backer and putting in more gypsum. Several passes with his shaped molding knife as the gypsum sets up gives him a perfected long continuous ornamental molding. Rohas works at Toronto Ornamental Gypsum.