The Advanced Art of Stop-Motion Animation: Building Puppets: Part 3
The next step is to suspend the skinned sculpt upside-down in a bucket (or in a plastic cup for a smaller-sized head). The post to which the head is attached can be attached to a wooden plank that rests over the top of the bucket or suspended in some other way to hold it there. Another solution, to alleviate the possibility of the head falling off the post and into the bucket, is to fill the bottom of the bucket with a layer of silicone and let it cure. This would act as a cushion to rest the head on while it’s suspended. Once that is all in place, the rest of the space inside the bucket is filled to the brim with more silicone and left to cure overnight. Bubbles are not as much of an issue in this filler space for the mold itself because they will rise to the surface anyway. The post to which the head or object is attached, suspending it into the surrounding mold, will also serve as an entrance channel for pouring the plastic in during the casting process. As another part of this process, it is important to note on the bucket itself (and later on the resulting mold) the positions of the front, backs and sides of the head inside (Figure 3.72).
Once the silicone is cured, it will be more firm on the surface and much less tacky. The mold can then be pulled out of the bucket or cup, and it will have taken on the same shape of the inside, much like a Popsicle (Figure 3.73). The next step is to get the head out! To accomplish this, an X-Acto blade is used to cut through the silicone as strata-cut layers in a zigzag pattern down a side of the mold (Figure 3.74). The cut is essentially acting as the seam for the mold itself. Therefore, it’s important to place this opening near the back of the object being cast, or somewhere the camera won’t necessarily notice it, in the event of cutting into the sculpt. The zigzag pattern also serves the purpose of registration keys so that the mold will always go back together in the same place. Cutting a straight seam line will cause it to slide around and could create inconsistencies in the resulting cast. Once the incision is complete, the flexible mold can be pried open to remove the sculpt, leaving a negative impression of the sculpt inside and a spout for pouring in the casting material (Figure 3.75). All remnants of clay that stray inside must be washed away completely with rubbing alcohol and water to avoid any bits of it getting stuck in anything else. Now, it should be ready to fill with plastic for casting!