Once the silicone is mixed, it must be degassed. The yellow bell jar connected to the blue vacuum tank is what we use for degassing. You put your mixed silicone in the jar and crank up the vacuum. It's pretty fun to watch the air (bubbles) being pulled out of the mixed rubber. Once the rubber is mixed, it's time to pour.
We are located in NY, and it's July- so it is really hot and humid. We're not doing this in a temperature controlled environment as we should be. Water (humidity) getting into the silicone can cause it to not cure, and heat can cause the silicone to kick (cure) faster than is optimal, trapping bubbles.
The pressure tank to the right is what the mold is placed in to further draw bubbles out of the casting.
This project details a mold made to cast a unicorn horn about 2' long. Inside of the horn is an insert which lights LEDs.
Oliver Tanner did most of the work here. Fun fact: we met in 2000 at a prototyping company where I was a mold maker, now I am his assistant!
The mold is made from silicone P44 and the casting is made from the same material. The trouble with using the same material (or two silicones) for the mold and the casting, is that the casting can stick to the mold permanently.
This happened to me once, and it cost $500 in material and 2 days of time. The director of the movie I was working on at the time was furious!
A foolproof way to prevent this from happening is to spray the mold with mold release, or I like to use PAM cooking spray.