Sunday, May 22, 2011
Demolding the plasticine model was a breeze since I had decided to use a universal mold release spray. The plasticine would not have stuck to the plaster too badly had I forgotten this step, but because I remembered the model came out cleanly. I would be able to touch-up the model and remake the mold if necessary and also didn't have to take much time cleaning up the mold before casting.
With the plaster mold cleaned with soap and water and sprayed with universal mold release I was ready to start casting. I did a few quick samples first to figure out the proportion of metallic powders to silicone pigment.
Once I'd determined what proportions I needed to get the correct base color I cast the entire piece in one batch. It took four tries to get a successful casting. The first time I did not mix enough to make the whole piece in one batch. The second and third time the silicone was not mixed thoroughly and parts of the casting did not cure properly. With such a small application of silicone in such thin sections it was crucial that the silicone be really thoroughly mixed. I realized I'd forgotten to double pour - this is when the two part of the casting material are poured together and mixed, then poured into a second container and mixed again. This solved the curing issues and the fourth cast was completely successful. The silicone was easily demolded from the plaster mold. The edges were then all trimmed.