Cleaning melting dishes and melting crucibles

Does anyone know of an easy way to clean the residual dirty flux from melting crucibles and dishes?
The flux hardens into a glass like substance… heating it and pour it out doesn’t work because what’s left is very sticky… since it’s borax based, will soaking it in warm water for a long time help slowly dissolve it?

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Other’s may have better ideas, but I’ve soaked & vibrated old crucibles in a heated ultrasonic. They come out totally clean and after drying need to be recoated with borax flux.



sounds good. I don’t have an ultrasonic cleaner so will soaking in hot water work?.. thinking of just simmering it over a stove top in a pot all day.

I have boiled them in concentrated pickle and that seems to help, but I haven’t tried the ultrasonic. I will give that a try later today…Rob

thanks to all for the suggestions…I might start with boiling them on simmer all day… the least dangerous option…then go on to simmering them in pickle if it doesn’t come off well enough…

If it were me, I’d boil them in water and maybe add baking soda, not pickle. You’re the scientist, but I wouldn’t want to boil a porous ceramic material that I’m going to heat up with a torch in any form of acid. That’s just my non-scientific artist’s opinion. With chemicals I strive to play it safe. On the other side of that, I’m pretty sure that just boiling the crucibles in water will be sufficient.

Let us know how it works out.



I think that the safest way to start is just boiling in water with water changes. I do have a problem too with acid pickle… not very safe to boil on the stove…also I don’t think that the pH counts much since borax is neutral… only question left is whether prolonged immersion in water will damage the ceramic… don’t think so but haven’t tried it yet.


My logic is that boiling silver that has a lot of flux on it in pickle removes the flux which is basically what I have in my crucible. I will make sure that it is soaked in plain water after the ultrasonic and then dry it well in a low temperature kiln. I have several, crucibles, so if this one is wrecked, I am still in business. I am not a chemist, so stay tuned…Rob


boiling in pickle doesn’t damage the ceramic? I would think not, but I haven’t done it before… just a question… I have a couple of them are gunked up and need to be cleaned…

Well they came out real clean, but did not take to being recoated very well. Glad that I have more. This was an old one that got messed up melting gold of dubious origin…Rob

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what kind of pickle are you using? All I have left is some old sparex… I have three that are gunked up and don’t want to buy another…
I’m not making jewelry anymore, but I have a lot of silver scrap from old medical electrodes that I have to melt down into lumps before I send it to refiners… actually about 5 lbs or more… the electrodes should be fine silver…they are gold plated. I’ve tried to separate the gold from the silver in a chemical experiment but it’s far far from being cost effective… what I get is very thin gold leaf and finely divided silver chloride that would require a micropore filter to trap… the cost of chemicals and filters would exceed by far any gold recovered, and for that matter, the silver chloride. I can have an ingot of fine silver alloyed with a trace of gold tested for fineness of the silver before I bother to melt down the rest.
if it tests as fine, I will have a lot of melting to do. I think that my crucibles will get gunked up repeatedly much less cleaning them before use once more…

Since the gunk is just contaminated borax, it should eventually dissolve in water… I might try that first… if it takes too long or is ineffective, the I’ll try pickle… I can either use sodium acid sulfate or citric acid which is Lime Off bathroom tile cleaner. The question is what kind of pickle? RSVP thanks

I did soak crucibles in a pickle pot, and it did damage them. The surface became very rough, could not use them again. But I also might have left them in too long, don’t remember at this point how long, it was years ago. Hot water seems to be the sensible first try.

slow cooker or crock pot… plain water seems the first way to try this… thanks for all the input from everyone… i can afford to be patient… if that doesn’t work, even given enough time, then i will try pickle but not a strong acid like sodium bisulfate… citric acid should be gentler.