As I mentioned before, in most cases, a hard mold is required to create a soft cast, but it is also possible to create a silicone mold (using molding silicone) for a silicone puppet (using casting silicone). If it is a two-part mold similar to the plaster ones I just described, the steps for creating it, like using the Lego wall around the clay bed and pouring over it, are basically the same. The big difference in using this method is that you mustapply onto your mold and sculpt a universal release agent so that the silicone will not bond to itself and can easily be pulled apart. If you miss a spot, it will bond as one piece because silicone only sticks to itself. If you are casting silicone within silicone, this is very important.
The advantage to a flexible silicone mold is that it is more forgiving than a plaster mold when it comes to undercuts. An undercut is any surface on the sculpt (and resulting cast) where the mold can easily get locked in underneath and cause damage to the cast when pulling it apart. Undercuts on the sculpt
it, but if they do occur, a flexible silicone mold is a bit easier to twist around it when releasing the cast. Creating a two-part mold that fits together and comes apart like the plaster mold can be done easily in silicone, and then it can be filled with any material that will create a hard cast. Within a soft silicone mold, you can cast duplicate hard copies of props, toys, and any hard parts of a puppet (Figure 3.68), such as accessories or entire heads. Silicone molds can be filled with resins, plastics, and even melted clay for clay puppets.
Figure 3.68
Sculpt for one of Charlie’s chest plates in a silicone mold.
For Ava, the heads for both puppets were cast in plastic in a silicone mold. A different approach was taken in creating these molds, which were created as one piece in a bucket instead of a two-part mold created in two halves. The sculpt for the head is first done in sulfur-free plasticine clay and then attached to a post to hold it in place. For a head or any other object like this, it’s a good idea to build the initial sculpt around a ball of foil attached to the post. This will help cut down on the weight and help keep it from slipping off when it’s suspended in the mold later.
The next step is to cover the sculpt in a thin skin of molding silicone to create the detailed impression that will be inside the mold. The silicone is drizzled over the top of the sculpt and pushed around with a brush to get inside every nook and cranny, without bubbles. Rather than brushing the silicone on, which creates more bubbles, it’s more like pushing it around and into the
cracks, without worrying about washing the brush, either. As the silicone drips and collects at the bottom, it can be lifted back onto the top and essentially pushed around to coat it completely. The idea is to skin the entire sculpt in a layer of silicone without bubbles (Figures 3.69 to 3.71).
Figure 3.69
Pushing silicone around the head and into all the sculpted details.
Figure 3.70
Drizzling silicone onto the head slowly to continue covering it.
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 any- way. 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 plas- tic in during the casting process. As another part of this process, it is impor- tant 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).
Completed sculpt covered with a layer of silicone.
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 regis- tration 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!
Figure 3.72
Bucket filled with cured silicone, marked with reference points to the positions of the front and sides of the sculpt.
The completed cured mold, now free of the bucket in which it was created.
Figure 3.74
A zigzag-shaped seam is cut into the mold in order to get the sculpt out.