I had bought a tub of mold making silicone a while ago, I was going to see if I could handle making a decent mold before I spent more money on buying the resin.
what I bought was Alumilite High Strength 3 1lb kit it was all they had at the local hobby shop, it was around 30 bucks.
It turns out that this stuff is best for one piece molds and not very good for a two part mold.
I should have read the box, instead I went online and read a bunch of tutorials, read about vacuum air removal and went and bought building blocks, clay and a bunch of stuff I didn't really need yet.
my first mold was to be a 2 part mold I set it up using clay and poured half of it into a Lego box etc.
this stuff was supposed to be set up in 14hrs, it wasn't, it was a bit more stable that jello, perhaps it was too cold or something I was trying to separate the clay from the rubber and the parts. but it was too gooey.
after another day the rubber had set up and was much more solid, I bet it would have been better to wait 2 days to demold.
I used olive oil between the two halves of the mold and it didn't work at all, this stuff just glued itself to the other half, I had to cut them apart.
anyway the 2 part mold was done and although I had made some mistakes it still worked pretty good, I was happy to find that the air bubble thing was not an issue at all, the mold was very clean and crisp, but the seams were kind of a pain and there were some under cuts in the mold that would leave pockets with out resin getting into them.
after realizing how flexible the rubber mold was I decided to just try a one part mold as a test.
I went super simple on this one I used an old clear blister pack as the frame and just glued the front torso down flat also the shoulder pads standing up on the bottoms and the head I glued upright at the neck.
I poured the rubber and let it set up for two days, I snipped the blister away and pulled out the mold carefully removing the originals from the mold.
This mold has the front torso half, two shoulderpads and six heads.
it worked WAY better, the torso and shoulder pads were perfect and the heads worked great too.
the mold is flexible enough to stretch to allow the castings to pop out without any trouble and you do not need to use a mold release spray.
I bought some Alumilite 2 part casting resin, it was about 30 bucks (they only had black in stock) and some small paper cups and mixing sticks.
the mold is so small that I just mix up a tiny amount and toss any extra out in the used cup as it sets up really fast.
Here are the measuring cups they are about the size of shot glasses, as you can see you don't need much for a small mold, this was actually too much resin, and some got tossed out.
it is ready to demold in just a few minutes, so you can make a bunch in a few hours, you just have to keep mixing more resin up.
Here are some parts from the mold they are still a bit soft, which makes trimming the flash off very easy. You can see the belly torso in the front left and the shoulder pads in front center and right, in the background are threes desert raider heads.
gloves and paper towels is a must, as it gets pretty messy. I clean out the little plastic measuring cups between batches and mark each cup to use the same part in it every time to make sure not to cross contaminate the resin.
I plan on buying some different mold making rubber to try a two part mold again, I think it will be best for larger more complex items.