I have a mechanical cold trap. One of the glass inserts is just absolutely impossibly sealed to itself. I can only put so much pressure trying to twist it before the glass is going to break. I assume the vac grease just became solid over time. So, any trick to separate these two glass pieces before I try a jack hammer
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boiling hot water bath… then try and chill the smaller side only…
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You could try a heat gun to get the glass to expand a bit.
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Heat the outside joint enough to expand it enough to break the interference fit. the trick is to try and keep the inside joint cooler so that only the outside joint expands.
I also swear by taking cheap thin vacuum grease, putting a bead around the top of the joint, heating it intill it starts to “melt” into the joint, im not sure if this does any real help, but i swear by it, i think it works
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A heat gun slowly ramping up temp
All glass. Might get heated but around 250 C they let loose
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Temperature differential. Heat the female joint and try to keep the male joint cool(er). Glass expands roughly .0005" for every 100°F and inch of diameter.
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Use a wooden spoon, whack the joint and rotate, hit it harder than you think is ok, this is the tried and true method for stuck bong slides, downstream, and illidelph coil condensers
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You’ll have to hit it with the torch. The trick is to make the outer part expand more than the inner so it actually requires very brief and fast heating
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I got one loose after boiling it. The other one has been stuck forever and seems cemented lol. I have a heat gun, but I’ll try a torch to really shoot the temp up fast
Fill the inside with ice water (or something colder) up to the joint. Heat the outside of the female joint with a heat gun, and twist hard!
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I second the torch, use two of them, hit the outer glass for 5-10 seconds on opposite sides. With heavy gloves on, twist apart
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I know I’m only a year or so late but…
It stay away from torches. Even if it doesn’t crack the glass now, it will probably put stresses in it. Same goes for hard rapping ( even with a wooden spoon).
Soak it in coca-cola overnight. This is an old glass blower trick that works more times than not…
If you do end up beating the hell out of it to get it loose, take it to your local glass blower and ask them to throw it in their kiln for an annealing cycle. Done properly, all stresses will be relieved and it will be back to original strength.
Credentials: 23 years as a glassblower
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Tricks of the trade tread worthy if you ask me 
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Dammn Coca cola has something in it strong enough to make glass come apart? Does that mean it will make your organs come apart to?
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Itll clean the blue corrosion off your car battery contacts too. 9/10 dentists agree, most of us are using coke wrong haha
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Do you have any suggestions on a good annealing cycle?
I’ve often wondered about using an ultrasonic cleaner every now and then followed by an annealing cycle.
Coke will take paint off of a drive way. Yet people drink it. 
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My most consistent approach is percussive tapping. I just tap it with the hard end of a tool- go slow. Should pop out eventually
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Also works great on rust removal on metal.
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It can be separated by heating with a heat gun or lighter