Jewelers are always molding objects and parts, most often to use for making wax models for casting. There are many vulcanized rubber and silicone mold materials intended for this purpose in the jewelry industry, but what if you need to make a mold outside of your well-stocked studio?
Here are two non-traditional mold-making materials borrowed from the dental field that will work in a pinch.
Jewelers have forgotten how useful plasters can be for certain problems, especially for the duplication of low-relief objects. My favorite serious molding plaster is Vel-Mix, the material used by dentists to make very hard models of your teeth and gums. Vel-Mix works like any plaster, but it’s extremely hard, strong, and durable—and it’s so fine-grained that the surface reproduction it offers is near perfect.
Plaster is excellent for molding medallions. First, you make a plasticine model of the low-relief (no undercuts) image medallion. You then make a wall around it with clay, wax, or paper, and pour in the Vel-Mix. After it sets, you simply remove the model. Before using it to create a wax, soak it in water for 10 minutes to prevent the wax from sticking to it. Melt the wax (injection wax is best), pour it into the impressions, and use a piece of sheet metal to squeegee off the excess wax. (To make a thinner medallion that is 1 to 2 mm thick, simply pour or blow the wax into the plaster mold.) The resulting wax model shrinks slightly and can be re-moved easily from the Vel-Mix mold.
Easy to use and very inexpensive, alginate compounds available from dental, jewelry, and sculpture suppliers make great quick molds. You’re probably most familiar with alginate from your experiences at the dentist’s office. When the dentist puts that tray in your mouth with the goopy material that sets up in a minute, she’s using alginate. It provides excellent detail, sets up really quickly, and is non-toxic. You mix it, pour it, or apply it with a spatula onto the object to be molded, and wait a minute for it to set. You can then remove it from the object and pour molten injection wax into it. As soon as the wax sets, remove it and pour another one. You will get between six and 15 waxes from an alginate mold before it breaks down.
You can store the mold in water to keep it for about a week. Also, if you let the mold dry out it shrinks about 40 percent. If you wet it after it shrinks, you can get a reduced size wax out of it, which can be interesting.