So I Had two sculpted hands, ready and prepped for mold. Now I need to make the mold. The last mold I made was 10 years ago so I went back to my friend Marty for some pointers. As expected Marty took me to school.
Because Im making silicone hands, I needed to make a stone mold. First I needed to build up a wall of clay (www.kleanklay.com) to block off the plaster for the first half of the mold. I start with a wooden board as a base and rolled out a thin layer of clay. This way if the hands get presses down during the process, there's a water clay buffer between the hands and the board. I put the hands on top of the clay and press them in lightly. The I roll out some more clay. My hands are between ¼ and ½ inch ( they are thin in fingers and thicker in the palm) so the sheet of clay I rolled out was about 1/8 inch thick so that it come halfway up the fingers leaving one half of the hand exposed. I loosely cut out the shapes of the hands in the clay and then lay it down around the hands. Then I smoothed it up against the edge of the hands. You have to get it pushed tight against the sculpt your molding so the plaster doesn't leak in between the Klean Klay and the sculpt. Then I used a rubber sculpting tool and my good old fashioned fingers to smooth it out.
Then I built up a wall about three inches high all around the mold. I smoothed the wall into the base again with tools and fingers. When I was done, it didn't look professional, but it looked good enough to do the job.
I then put some “keys” onto the surface of the clay. The keys are shape that will help register the parts of the mold. Like teeth in two gears, they will fit the halves neatly into each other. I used some silicon keys that we have at bent, but in the past I've uses plastic spheres pushed halfway into the clay. I put some pro-mold release that we have at bent on the hands (you can use Vaseline too) and if I had used the plastic spheres I'd have put Vaseline on those.
Here's where I followed Marty's process very closely. I mixed up the hydra-stone. Starting with a small batch and keeping it pretty thin. Not watery, but not as thick as pudding. This fist layer is about getting into all the crevasses of the hands and getting rid of any air pockets. With a chip brush, I drizzle the plaster over the hands and then shoot a little canned air at it to push the plates into every crack. Once the hands are covered I let this layer set up for 15 minutes or so. Then I did the same thing again this time with a bigger batch of plaster. After that sets up, I grab a little hemp (I've used burlap in the past too) and ball it into little nests under the watchful eye of Marty. I dip those nests in some hydrastone and lay them on top and the drizzle the rest of the mixture over them. After this set up, I did one more thick batch of plaster and put it on. I left the whole thing for about 2 hours to dry.
Next I turned the whole thing over, and pulled out the Klean Klay. You can clean off the rest with a little bestine, but don't rub it too hard on the hands because it will eat through the pint and clay. ILastly I put in a few little squares of clay against the edges of the walls to be pry-points so that I could use a screwdriver to pry open the mold. Once it looked pretty good, I coated it all with Vaseline and did the plaster prosses the same way I did on the other side. 2 hours later voila! I have a mold. It ain't the prettiest thing, but now when my hands break in the middle of a shot, I can make a new one. I casted the hands in silicone, which is a whole other process Ill get into at some point. Its hard to do unless you have access to a place where they use it a lot, so not ideal for your basement. In the past, I have painted liquid latex into the mold, closed it around the armature and squirted in expanding foam, which might be a simpler solution if you have only your basement to work in.
Damn thats a long post.