The SLA master must be fully sanded and polished since the surface finish is critical when making the RTV mold. The mold will reproduce all surface defects left on the master. In turn, it will transfer any imperfections onto the finished part. Even fingerprints will be picked up on an RTV mold and will ultimately appear on each of the parts produced from the mold. The pattern is placed in a wooden box to provide a support structure for the silicone rubber.
Silicone rubber is poured into the box, completely covering the master pattern.
The silicone rubber is allowed to cure and then is cut to form the cavity and core. A two-part urethane is cast into the rubber mold to create the urethane parts. The urethane parts are then pulled from the mold and the process begins again. This alloy fills in the voids in the otherwise porous material, producing a surface with the finish and hardness necessary for an injection mold. An SLA master pattern is created.