How to Make a Box Mold - Page 3A

• Page 3A: Overview of Materials, cont'd

#1 What are the characteristics of your original?
It is important to know what your original is made from in order to determine which mold material, sealer and release agent* you should use. For Example, if your original material is sulfur-based* or water-based clay* or if it is porous, and you plan to use a polyurethane mold material, you will need to seal your piece using shellac (or similar product) and release the entire original piece. Polyurethanes are inhibited by moisture and sulfur. They are also natural adhesives, hence the need for a release agent. Originals made of porous material must be sealed so the release agent is not absorbed into the original sculpture.

If you plan to use a silicone mold material for the same piece, you will only need to shellac the sulfur –based clay original. Silicone will only chemically adhere to another similar silicone, but can suffer from a variety of chemical inhibitions (like sulfur). Any difficulty you may encounter removing a silicone mold from an original is simply physical, a vacuum made by the rubber going from liquid to solid in direct contact with the original surface. If your original has many deep undercuts or is a high relief you will want to use a softer mold material to make it easier to remove the cast form the mold. If your original is very thick and is not high relief, you may choose a stiffer rubber to avoid having to make a brace or mother mold.