No vacuum chamber? Four ways to get bubble-free silicone molds

1. Pour from high and thin. Lift the cup 2 feet above the mold box and pour in a pencil-thin stream into one corner. The stream breaks bubbles as it falls.
2. Brush a thin coat on the master first, working it into details with a cheap brush, then pour the rest over it.
3. Tap and tilt. Tap the box on the bench for a minute after pouring; bubbles rise.
4. Use a slower silicone. Longer pot life gives bubbles more time to escape on their own.

For castings (resin) the equivalent is a pressure pot: a $100 paint pressure pot from the hardware store at 40 to 60 psi squeezes bubbles to invisible. That buys more improvement than any other tool in this hobby.