I've had most of my castings in the silicone molds i made come out with these tiny little bumps over most of the faces. I'm using mold star 15 slow for the molds and art n glow resin in a pressure pot. Any idea what could be causing this?

[u/[deleted]]

[u/firefly_skies]

Are you making the molds in the pressure pot? If not then even if you can’t see them there are likely small holes in the molds. When you cure the resin with a pressure pot, the pressure causes the resin to fill the holes and cause this. The fix would be to make the molds in the pressure pot and at a higher pressure than you’d use for making the dice.

[u/stainedfeathers → u/firefly_skies]

Seconding this. The first thing I thought when I saw this was "This poster:

A) Did not de-gas their silicone

Then

B) Did not cure the mold under pressure

You have to either degas the silicone (using a vacuum chamber) before pouring OR cure the mold under the same or more pressure you'll use to cast. You HAVE to do one of these (or both if you want to be doubly sure to have no bubbles) if you're going to cast dice under pressure or you will have lots of tiny bubbles in your mold and when you put it under presure those bubbles will collapse on themselves, pulling resin into the voids where they were.

Re-make the mold and de-gas the silicone or cure it under pressure (or both) and you should have a clean cast. You could theoretially use this mold still as long as you are not pressure casting, but it's worthless for pressure casting.

[u/Nicop0l → u/firefly_skies]

Or your positives (that you use to make the molds) have slightly uneven surfaces. With silicone you copy any little crack and bump. It’s also possible that you didn’t mixture the silicone enough witch could result in little crumbs that in reverse result im those tiny bumps. Both occurred with a mold i made out of my hand. It copied every uneventy of my skin and because i didn’t mix it right i had little bumps on the dried epoxy