In the past, this soap was used as a mold release in the ceramics industry when making a plaster mold of a plaster part. It is still used for this purpose, and is also useful when making a plaster mold of just about any surface.
Today, we find that it is also an effective pattern release agent for many of the polyurethane elastomers such as PMC-724 and PMC-744. It may be used straight from the container as a paste or diluted in water, ethanol or a water/ethanol mixture. Normal ratio is about 4 parts water to 1 part soap.
Apply by brush or spray, allow to dry, apply the rubber and you're on your way. The nice part about using this material is that unlike petroleum jelly and some of the other oil based release agents, Potter's Soap may be removed with water once your mold is made.