The Advanced Art of Stop-Motion Animation: Building Puppets: Part 3
Making a Silicone Mold
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 must apply 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 can be avoided by always creating shapes that are angled the right way toward 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.
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).