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Another method form making multiple piece molds is to tape up your parting lines, suspend your part, pour the mold using translucent silicone rubber, and simply cut the part out of the mold.
The tape will act as the parting line or divider between the two halves of the mold. Once completely poured, you will cut to the part or the tape and the mold will split open creating the two halves of your mold.
This eliminates multiple pours of silicone rubber as well as not having to clay up and then clean the clay off of your original. Some parts lend themselves better than others for this process. Typically more organic shapes that do not have flat surfaces tend to be more difficult because it is difficult to achieve a smooth and clean parting line on rounded edges rather than square or flat surfaces. Taping to rounded edges is difficult. Here is one example of the process where both a flat and rounded surface is used.
**The original part is an SLA (stereolithography) master that was 3 dimensionally printed from a computer file.**