# Silver stuck to crucible



## TomVader (May 9, 2014)

I melted some silver powder in a ceramic crucible. Turns out I didn't "season" the crucible well enough before using it. The silver is stuck quite solidly to the surface. When I pulled on a bit of it that hung over the edge, it peeled some of the crucible surface away with it. There's a crack in the crucible, so I think if I put it back into my furnace it will come apart and damage the furnace. Can I use nitric to dissolve it out or will the acid eat the crucible? Thanks in advance.


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## glondor (May 9, 2014)

Just a thought, if you do use nitric, how much silver nitrate will the crucible soak up? If it is cracked, and slated for non use in the furnace anyway you could break it out, or if it is not much more than a few ounces, melt it with a mapp gas torch with some borax, chase it down the sides and pool it in the bottom of the vessel. Dump it out as a hot solid disc.


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## Lou (May 9, 2014)

Heat the area til red and the silver almost melts, then a small pinch of carbonate should get it unstuck.


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## TomVader (May 9, 2014)

Thanks for your suggestions. I don't use a torch at all, I use a crucible furnace. Yes, the crucible is junk, I was just wondering if the nitric would dissolve the crucible along with my silver. I guess I can just smash it with a hammer and keep pounding on the silver until all (most) of the ceramic is gone. Maybe I should think about getting a torch set-up... Thanks again.


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## MysticColby (May 9, 2014)

I use dilute nitric to remove silver and borax flux from crucibles. I won't say 'all the time', as I've only done it like 4 times total. usually I will just include the silver that's stuck to the crucible in the next batch I make, but when a crucible gets messy enough I'll clean it with dilute nitric (like 1-5%).
I put the crucible in a 1L beaker, cover it with water, add ~10 ml of 70% nitric acid, put it on a hot plate on low. about an hour later, all the silver is in solution, and all the flux is either also in solution or sitting on the bottom as a powder. I'll pour the liquid into another beaker (add copper to cement the silver, then recover it). Then for a rinse: cover the crucible with more water, put on a hot plate on low, wait an hour, decant that water into the 2nd beaker. then a 2nd rinse. It always seems like some water/nitric/silver nitrate soaks into the crucible; rinsing it will dilute that out of it. After this, set the crucible aside to dry at least overnight. Next time you use it to melt silver, heat it up /very/ slowly (until it's above 200ºC).


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## TomVader (May 10, 2014)

OK, thanks. I'll try that.


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## TomVader (May 14, 2014)

Submerged crucible in dilute copper nitrate/silver nitrate solution. Bubbled away for three days. No noticeable effect on the crucible. Silver is just about gone. Lots of black powder in the bottom of the container, not really sure what it is...


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## g_axelsson (May 14, 2014)

TomVader said:


> Submerged crucible in dilute copper nitrate/silver nitrate solution. Bubbled away for three days. No noticeable effect on the crucible. Silver is just about gone. Lots of black powder in the bottom of the container, not really sure what it is...


Why? Where did you read to use copper and silver nitrate? What is it supposed to do?
It doesn't make sense to me.

Göran


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## TomVader (May 15, 2014)

The copper nitrate/silver nitrate is from my nitric wash. I'm refining gold. After you treat with nitric the resultant liquid is copper nitrate/ silver nitrate. The nitric acid dissolves the copper and silver that is in your gold alloy, leaving the gold sponge behind. Rather than use clean nitric, I used this mixture to clean my crucible. Since I already had some silver in solution that I was going to recover later, I put it all together into one batch.


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## g_axelsson (May 15, 2014)

Then you washed the crucible with nitric acid, which dissolves silver, not silver nitrate which does nothing.

Try to keep the chemistry correct so we don't confuses the newbies. They are so easily confused... 8) 

I would recommend to pre soak the crucible in water before the treatment, to keep down the amount of silver nitrate absorbed into the porous crucible.

Göran


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## TomVader (May 15, 2014)

Yes, there was free nitric in my solution. Any idea what the black powder might be? There was a very small graphite stain on the outside of the crucible, but that would not account for even a fraction of one percent of the black powder. Would borax look like a black powder when exposed to nitric acid?


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