A mold in silicone generally consists of a membrane in flexible silicone and a screed in plaster which maintains the silicone in position. This mold will allow to pour or to emboss plaster, resin, clay, wax etc. for the realization of an edition. It can also be the first stage towards the realization of a bronze because it is the wax edition which will be used as base to the realization by the bronze-smelter of the mold in refractory plaster which will serve to pour the bronze.
We shall not approach on this text the molding with lost mold which is destroyed during the turning out. It is made by a coat of a centimeter or two maximum of not armed fine plaster and is gradually broken with a hammer for the turning out. Nor shall we approach the lost model molds where it is the model which is destroyed during the process.
Two parts (or more) molds
The mold in two parts is the most wide-spread mold because it can adapt to most of the sculptures and the forms, on the condition of conceiving well his division in two parts. Indeed both parts of the mold must be able to separate without being blocked by parts of the sculpture that are called undercuts.
To note that the mold in two parts can be also realized in plaster, without the use of silicone, generally for economies reasons (the silicone is an expensive product), but be careful because the plaster, contrary to the silicone, is not a flexible material and must not be used only for a sculpture which has absolutely no undercuts.On the contrary, the silicone allows to turn out even when there are small undercuts, often linked to the texture of the sculpture. This flexibility is a significant advantage and allows to simplify molds compared to the solution with only plaster.
When the sculpture includes several undercuts and cannot be thus molded in two parts, you can realize, with the same principles, a mold in 3 (or more) parts. It also happens, to simplify the molding and reduce the number of parts, that you have to cut, when it is possible, the sculpture into several pieces before molding it and then restick it afterward.
This article will explain the realization of a mold in two parts with silicone.
When you wish to mold a sculpture without any undercut and of cylindrical or conical shape, the simplest solution is the realization of a sock mold, which is a mold in silicone directly poured on the sculpture and what you shall remove as a sock.
The realization of a sock mold will be explained in the chapter about the other types of molds.
When you wish to mold a sculpture which is flat on one side (for example a low or a high relief), it is possible to create a boat mold which is very simple to realize. You have to pour the silicone on the sculpture fixed in the bottom of a bowl, which creates the molding on one side of the sculpture, as a cake pan.
The realization of a boat mold will be explained in the chapter about the other types of molds.