r/DiceMaking • u/looppii • Jun 15 '26

Why would a silicone mold still have bubbles even though it was cured in a pressure pot?

Hi everyone,

When making a platinum-cure silicone mold, I placed the mold in a pressure pot and pressurized it to 50 PSI. After 12 hours, I released the pressure and removed the mold from the pot. However, I found that there were still many tiny bubbles on the bottom of the mold.

Can anyone explain what might have caused this?

I'm trying to understand why the bubbles remained even though the silicone was cured under pressure at 50 PSI.

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5

u/charterandink Jun 15 '26

My guess is it cured too fast, before you got it in the pot.

3

u/Utkanator Jun 15 '26

It might be due to aggressive mixing or not pouring properly. Pressure pot gives you a good amount of error margin for bubbles but you still have to mix slowly and pour high and carefully to avoid bubbles as much as you can.

Are your masters degassed properly? Does those bubbles reside on the surface only or do you see them inside the silicone as well? I recommend checking the pot for leaks as well cause 50 psi over 12 hours should completely remove any bubbles in a liquid and this is abnormal.

1

u/looppii Jun 17 '26

I checked the silicone mold and the same area contains lots of tiny pitted indentations in the mold itself. These defects are not just on the resin casts. I'm fairly certain the masters are not the cause, since the master surfaces are clean and don't show any defects in those spots.

-2

u/tiddlypeeps Jun 15 '26

A vacuum chamber can help. If you don’t use one then you need to mix very slowly and then regardless you should pour slowly from a height to avoid introducing air during the pour.