I'm slowly getting back into the swing of things this week. I'll start by continuing where I left off molding the angry clobber monkey. Last post the clay divider was finished for the mold, and the walls of the form were built. Now it's time to pour silicone. Most silicones have the same mixture: 10: 1. I like to use a Vacuum Chamber to de-gas the silicone. This is very important when doing a big mold. I rent time at a local shop. If you don’t have access to a vacuum chamber there are very good brush on methods. Brush up can be done several ways, brushing on several coats of regular RTV Silicone getting rid of all air bubbles. Then finishing with a thicker mixture tobuild up strength in the mold. Check out any supply shop that deals in these materials and they will have info on the different grades of silicone. Carefully mix the silicone according to directions. De-gas if you can.
When I pour it into the mold never pour it directly on the sculpt. Tilt the mold and fill from the side at an angle. Let it fill up gradually at an angle to chase out any air pockets. With all of the holes in the clay that will eventually become the keys of one half of the mold, we want the air to be pushed out.
This is a big piece! Silicone is expensive, so I like to be as economical as possible when making molds. When I have a piece that has a lot of volume I add scraps from old molds. I always save old burnt out molds, cut them up into small chunks and add them as I’m filling the new mold. The old silicone will bond with the new, and it won’t register if it touches the sculpt. IMPORTANT! Only add the filler scraps after you pour new silicone, if you ad it before it will lead to air bubbles and all sorts of trouble.
These are two sided molds I’m working on. The head is a good example:
The Head ready to go
First the layout for the divider.
After the first layer of silicone sets up, carefully remove the clay, and ad a new piece of foam-core for the new form. Next carefully brush a thin coat of Vaseline on the silicone to prevent the new half from bonding. Don’t forget this step, it will make you sad if you do.