Mold Making Part 3 - Mold Side 2
After the mold is filled, you will see some small bubbles come to the surface. Some pros use a vibration table to force the bubbles to the surface. I happen to have a table sander mounted to the corner of my work bench. I turn this on for 3-4 minutes and it vibrates the table pretty good. Any stubborn bubbles that rise to the surface and don't pop, I poke with the end of an Exacto knife. Allow the rubber to cure at least 16 hours. I usually allow 20 hours.
Now you need to splay the bottom half of the mold with the Silicone Mold Release. If you don't, you won't be able to separate the two halves. Silicone Mold Release is DIFFERENT from Universal Mold Release. Makes sure you get both if you are making a two piece mold.
Measure out some more silicone rubber and add the catalyst. Stir it up good but try not to whip in too much air when you stir. Here it's a good idea to transfer it to a clean container. You don't want any unmixed material hanging around on the sides of the cup as that could cause a sticky spot in your final mold. I know from experience. I also change Popsicle sticks often to avoid this same problem. Next you will proceed with the degassing.
De-gassing your rubber - I transferred it to a clear container and got some better pictures of the degassing stage this time. You do not want to use the container that you originally mixed it in because there will be some un-mixed rubber stuck to the sides of the container. If you get any streaks of unmixed rubber in your mold you may end up with some uncured, sticky spots.
You can see how it appears to boil. After a few minutes, it will start to collapse as the bubbles pop. Once it has settled, turn off the vacuum pump and open the vacuum chamber. Then give the rubber a minute or so to settle down. You can help settle the rubber by tapping the cup on the table a little.