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Tip Time: Under Pressure

Updated: Sep 21, 2022

This post is mainly for beginners.

I am going to clear up some misconceptions about working with a vacuum chamber and a pressure pot...

It only makes sense that putting resin in a vacuum chamber while it cures will suck all the air bubbles out...


A vacuum chamber is strictly for degassing silicone. You never put your resin in the vacuum chamber. I've seen a lot of people make this expensive mistake.

You would think that pressurizing your resin would push the resin though out your mold getting a perfect pull every time.

Wrong again.

You need to vent your piece adequately (Venting Blog coming soon). Fingers (for example) are usually problem areas. You need to glue toothpicks or bamboo skewers (Called Bleeders) to each finger on your piece before you cast. Otherwise, you will still get air bubbles in them no matter how much pressure you put in the tank.

Resin is a thermosetting plastic which means that it heats up as it cures. The heat creates bubbles (they look like little soda bubbles).

Quick set resin heats up hotter and quicker, creating more bubbles.

When you use a pressure pot it shrinks those bubbles.

Thats it.

It actually doesn't eliminate them either. But it does shrink them to a microscopic level. They even exist in a crystal clear piece.

And don't crank the PSI! I do a lot of clear casts and I only fill the tank up to 30 PSI for resin ( 50 for Silicone). Cranking the PSI load after load puts strain on the bolts and you will strip them.

There is a great chapter on modifying a pressure pot to use for resin casting in this book, "Pop Sculpture"

I highly recommend it.

This doesn't even scratch the surface of pressure pots! I will do more on this subject in the future because I think it is important.

But I have seen at least half a dozen people make the mistake of buying a Vacuum Chamber when they should be buying a pressure pot.

It is an easy mistake, I know. Because I did it too,

In summation:

Vacuum Chamber is really only for silicone.

Pressure pot is for silicone and resin.

Any questions, comments or concerns?

Please leave a comment below and I will reply.

Thanks for reading.

Your Friend,

-Scott Cherry


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