Normally I can clean  most glassware by use of solvent, acid, base, the dishwasher, or some common cleaners. I however have a bunch of glassware with horrible iron oxide stains on them, I also have a beaker that has some bizarre lead compound - the oxides, or carbonates I believe.
I've tried to clean these out with vinegar, hydrochloric and phosphoric acid and of course soap, and all that jazz mentioned above. The beaker with lead compounds stuck in it, I even desperately tried using EDTA with a few different things. I have had no luck how do you think I could clean these pieces of glassware?

Not even scraping seems to work all that well though, I'll work more on it but maybe I will just have to live with it. Sure looks junky.
Yeah I think piranha acid is used mostly for organic compounds, isn't it a mixture of chromates or something like that?

For that try heating them gently around the outside, using a solvent that will dissolve whatever it may be that are holding them together, or a lubricant. I've had S2Cl2 in flasks and it sealed together with the weird ass sulfur that seems to form form the chloride, and I was able to get them separated with using those methods.

I agree with Enkidu here and a powerful oxidizer/acid would be the way to go but if you dont have access to these then try some clean sand. It may take a while but a slurry of sand and some time swirling and shaking can get burnt crude off pretty well. It beats the alternative of jamming rods into your glassware and risking damage. Sand+acid or sand + solvent would work if you can specify what is stuck in there.

~Sedit

Aqua regia is easily prepared from KNO3 (stump remover) and HCl (muratic acid).

It works, Iv done it on a number of occasions. KNO3 + HCl --> NaCl + HNO3.  Excess HCl and your good to go. A better option would be to bubble the HCl into a solution of KNO3 for a more concentrated solution.

Just a layer of H2O over the sand. it dont have to be dry make it so when you swirl the water and make a whirlpool all the sand grinds against the sides. Just try it out how ever you wont be dissapointed. A drop of dish soap dont hurt either but you would have to make damn sure the soap is gone after or youll fuck up reactions down the line.

I just got done cleaning my glass with sand for the first time and it's godly.

Fill the glass 1/4-1/5 full of dry sand and shake the hell outta it.

Works absolutely fantastic. 

...not to mention sand baths in general kick ass over oil baths. No smell, no evaporation, better heat control.

sand<3

That's weird. It should work. I just sit a metal pot on my hotplate/stirrer with the pot filled with sand and put about and inch of sand on the bottom, then surround the rest of the flask with sand up til about the half-full point of the flask.


This might help...

"Good thing I live right by a sand pit!  I got 5 gallon bucket of it for free. I tried to use sand for a heat bath and it didn't work at all. "

LOL yeh where Im at I have 5 sand pits withing 1-2000 ft from my house compleatly surrounded. Thats what you get for having the best sand in the world around you house.

But thats how I learned to clean glass with it. Im glad you liked it poison. I know its always worked great for me but it would suck if yall where cooking up some ungodly concreate that the sand wouldnt handle and makeme look a fool . Iv seen it handle some tough shit before like trying to distill the phosphoric acid from navel jelly(What...... it was there!!!) anyway dont attempt that in your good flask lemme tell ya. It can get really nasty and turn into a black burnt glass, thats how I learned to use sand.

@poision   You get that pic I sent over at SciMad? that shit was brown as a turd before I fixed it.