Silicone (RTV) Molds
Silicone molds are made from the original wax sculpting of the figure in order to produce hard copies. The molds are made by hand and each part of the figure requires a 2-part mold to be made which allows for easy removal of the cast part once it has set. A mold is made for each individual figure piece. It is up to the artist or mold maker to determine where the "parting line" will be. Basically the part to be molded is 1/2 covered in clay so that the opposite side of the part can be molded. This is called the "parting line" of the mold. The parting line separates both halves of the mold and will usually be identical to the parting line set up in the final steel mold. You can look at just about any action figure and see the parting line. Once the first half of the mold is made, the clay is removed and silicone is pored onto the imbedded part against the first half of the mold. This will yield the second, mating, half of the mold. Holes are added so that the material can be poured into the resulting cavity. The urethane material is poured in by hand and no machinery is involved in making the hard copy. Once the urethane is set, the mold is separated and the part is carefully pulled from the mold and the mold is prepared for reuse. Typically a "mold release" agent is sprayed into the mold prior to casting in order to assist the removal process. This would be similar to putting butter in a frying pan to prevent sticking. These silicone molds are relatively crude and will only yield a certain number of copies before they degrade. If all goes well during this process ,and a good hard copy or two is produced, then the mold and the sculpting can be discarded as they have fulfilled their duties. RTV stands for "room temperature vulcanization" which just means that the mold material itself (usually some type of silicone) will cure, at room temperature, without requiring excess heat.

Description: Chris Georgoulias