Best way to clean ya nasty boiling flask??

Aqua regia is one thing, great for inorganic contaminants and quite good for organics. But if you want ultimate cleanliness from organic contaminants, you want what’s called piranha solution – h2s04 and 30% hydrogen peroxide. It fits the name and has fascinating chemistry such as the production of atomic oxygen as active cleaning agent.


My BF was stuck with some black sugar and it was stubborn to get off.I tried turning on my spd for hours boiling ethanol to try to steam it out. Then I tried putting it in hexane, acetone. Nothing worked. Turns out citric acid and ethanol works like a charm. Just need to rinse it out real well afterwards to make sure nothing is in there or it will mess up the ph of my crude. haha


When I worked in small molecule purification, we would clean our GMP glassware in a base bath. I think standard college SOPs call for dissolving a bunch of KOH in isopropyl alcohol and water and allowing it to sit overnight. If I’m not mistaken this actually begins to eat away at the glass surfaces and it is a super easy way to go full on fight club style caustic burns on your skin without a leather frock and elbow high gloves, oh and a splash mask. It’s not to hard toGoogle, look up base bath for glassware.


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Please be safe. You need to have a DI or RO system on site to rinse your products off.

Note that this method can’t be used on fritted glass as it can fuse all the pores shut.


Fritted disc buchner funnels, there is a trick.
Invert buchner funnel and put in a tray. Spray 99% iso into drain tube. Let gravity drain back out and it will be clean.

I posted this in the tricks of the trade a while ago.

Someone said acetone can also be used

@Chimney100 what was your ratio? I’ve got a couple stubborn charred bf’s that I’m trying to figure out, without using something too caustic.

Chromic acid at 1%

but make sure you rinse the shit out of it in Hot Distilled water to get any residue out and the distilled water wont leave any water stains.

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I use a 5 gallon sonicator and throw all my glass with iso for 20 minutes and everything is brand new everytime. Put a silicone mat on the bottom so it Pampers the glass.


I filled up my BF maybe half full of ethanol and added just a tsp of citric acid and it was enough to do the job


Cafiza espresso machine cleaner has never let me down, even on unfiltered warm ethanol run at 350C on a Across International 2L SPD with a 1/4 HP single stage Zeny pump. Dissolves the gunk, what it doesn’t dissolve just flakes off the flask like it was nothing. (edit): If it doesn’t work within a few minutes, letting it soak work wonders.

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@TerpTeamOfficial I’ve been hearing that you can’t put anything that you use in your short path with deep vacuum in a ultrasonic cleaner? Have you had luck?

no never heard that 1 befor.

I use my ultrasonic cleaner for all my glass…Haven’t had any issues. Saw somewhere on the forum to put a sillicone pad at the bottom just to be safe and I haven’t broke anything yet. The thing is I find some of the sugars used in SPD is very hard to clean off, even with the help of ultrasonic and heat it still doesn’t come off. This is what happened to me


Lol I meant to tag @Digni, sorry :man_facepalming:


So after all my battles trying everything listed getting my flasks cleaned (and failing) I finally came up with a simple solution.
Somewhere above someone mentioned using a kiln to burn off the residue, well i don’t have a kiln but i remembered how well my self cleaning oven cleaned off baked on grease and sugar on the self clean mode.
After 3 hours in self clean I have a brand new looking flask!
I wish I had a before picture, it was horrible though!
Try it!

It looks great! I wonder, though, what effect this is having on the annealing of the glass. The self-clean temps on an oven are the same as used for the annealing of glass (about 900F). There is very specific protocol for how to anneal glass being used in a high-temperature, extreme-vacuum setting. I’m not sure your process for cleaning complies with that protocol.

You may have inadvertently made the glass very brittle and subject to failure with little effort. I’m not saying that you did; I’m merely cautioning you to be EXTRA careful when using the glass cleaned by this process. PPE, which should always be used anyway, is of the utmost importance. Implosions can be life-ending if one is in the wrong spot. You may want to look up the annealing process to learn more and see if what you did comes close. :crossed_fingers:

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Hmmmm this gives me something to think about, I had thought borosilicate was rated up to 500c working temps.
Now I’m scared lol, I may just scrap these for new ones.

Maybe research before scrapping. I just know that glass is usually annealed at 900F, so I wanted to be sure to say something in case there was an issue. Keep the glass you cleaned this way marked as such and separated from the rest of your glass until you research a bit. I have an acquaintance who blows scientific glass. I’ll ask him tomorrow what he thinks.