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HOW TO MAKE A TWO-PART RUBBER MOLD OF A COMPLICATED MODEL You
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2 3 5 10) Let the rubber set until cured, then remove the foam board walls and the clay. Remove the foam board carefully, because you will want to reuse it for the second half of the mold.
Your funnel and vent wires may pull out of the rubber. They need to be replaced, so the funnel and vents are formed in the second half of the mold as well as the first half.
Clay may stick to the first half of the mold, and your model. Every bit of clay needs to be removed. If there is clay on your model, the second half of the mold will reproduce the clay instead of your model. If there is clay on the first half of the mold, the second half of the mold will not sit directly against the first half, creating a void where casting material may go and create “flashing” that will need to be cleaned off every casting made in the mold. The only exception is for the funnel and vent wires. If you need to use clay to connect the funnel or vents to the model, that is OK. 11) Reassemble the foam board walls around the first half of the mold. Apply release agent to keep the second half of the mold from sticking to the first half. Add braces to the foam board.
Mix and pour rubber for the second half of the mold, just like the first half. Wait until the rubber is cured, then remove the foam board walls and separate the two halves of the mold. Remove the vent wires and the funnel, and clean the mold completely. This is the finished mold.
12) This type of mold can be held together with two flat boards and any sort of clamps or bands. The clamps in the photo look very powerful, but they are actually applying only light pressure - just enough to keep the two halves of the mold together. In the photo, the funnel opening and the ends of the vent holes are visible.
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