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Mother Mold
*Responsible for all mold-fabrication
Dog Body Mold
A Mother Mold is a rigid outer shell that supports a flexible inner mold (like silicone or latex) during casting, preventing distortion and ensuring accuracy. Here I built a custom rigid housing of the mother mold for the Dog from 3/4" birch wood and then poured the silicone in two parts. The wood frame can be divided and disassembled around the silicone parts with the silicone having registration unique to each half to allow consistent results with a relatively lightweight character mold.
1/3: Mocking Up
Carefully, with consideration for the sculpture, a cardboard mock up was drafted
The mock-up allowed for precise measurements of all faces and the angles that would be necessary to cut out of the birch
Here is the assembly of the mother mold rigid supporting structure
Here are all the parts to the rigid exterior based on the mock up
Side-by-side comparison of the mock-up and the finished birch
Here I am checking the position of the body sculpt before beginning the clay up
2/3: Clay-Up
Krylon Crystal Clear was used to seal the surface of the clay sculpt and the wood of the mother mold before beginning. The clay up had to be built up directly into the rigid form of the mother mold. Here I used oil base, Jolly King to build it up.
As the clay-up took shape, it was important to begin building more of the rigid form as I went to ensure that it would fit together snugly. Delrin Balls from 3/8" - 1" diameter were used as registration keys, since they are round it will be easier to slide the mold halves over each other to snap shut when casting.
3/3: Silicone Pour
Since the character is foam and to be more economical for the volume of this silicone mold, I used silicone chunks to help fill the box. Here I have the box on a jog at an angle to create a high point in the mold to fill last and any bubbles would form furthest away from the model. Once near full I put the lid on which has a series of vents and cups to serve as funnels and hold extra silicone to prevent leaking as it fills.
For the second half, the Jolly King is carefully removed and the rigid structure is rebuilt around the first half. Vaseline is applied as mold release to the mold surface and the inside of birch rigid structure. Once again the mold is placed on an angle to reduce bubbles and encouraged to fill with silicone through the vents and the funnels.
Here the mold is opened and cleaned up. Any flashing that seeped, is trimmed with an x-acto blade to ensure smoother closing of the mother mold during casting.
Final Body Mold
Once the mold is cured and cleaned up, trenches have to be cut from the silicone to allow for the expansion and release of foam. This may include creating more channels through the rigid mold. In this case I did have to open up more vents in the birch, with being able to disassemble the entire box it was easy to use the drill press to make more spots for the foam to escape.
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