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Cleaning an old crucible


#1

Good Afternoon Ganoksin,

I have a question about an old crucible I inherited from school some
years ago. According to one of the instructors at the time it was
"overheated". It was going to be tossed, so I grabbed it thinking it
would at least be usable holding steel shot & water for submersed
items during repairs. Now I am looking at it & wondering if it is
saveable.

It was only used for sterling, so I am wondering if there is a way
to clean & recoat the ceramic or if I should even bother with it.
Also, I see a ton of silver “balls” all over stuck to the inside in
layers & layers of blackened flux. (They were doing freeform
castings, and believe me when I say there is a TON of burned &
blackened flux in this thing.

I hate to waste the silver and a decent crucible if it’s cleanable.
Is there a way possible to clean this thing out without just digging
in it?

I’ve charged new crucibles, it’s pretty easy to get a nice glaze on
the inside. I have seen crucibles that are taken care of properly
last years. I am pretty careful to never over flux.

This poor crucible was pretty abused in the studio with several
beginner classes all using it to do freeforms without much guidance
during their studio free time. Is it a lost cause, or maybe there is
a way to clean it out and save the silver?

Thanks for any ideas!
Teresa


#2

Hi Teresa,

I have cleaned overly-fluxed ceramic crucibles by just heating them
with a big torch and pouring/raking out the molten gobs of glassy
flux + debris. The silver balls will come out with it. If you then
crush the glass, you will get to save the balls. which is SO worth
it with gold, but worthwhile with silver, too. HTH.

M’lou Brubaker, Jeweler
www.craftswomen.com


#3

I do this all the time, submerge the crucible in sparex untill the
borax dissolves then soak in clean water for a few days then allow to
dry for a week and sandblast then re glaze with borax

goo


#4

It been a while but if I remember right, I just boil them for a while
in water on the stove and let them dry out for a week or so…seems
some light scraping while in the water helps speed things
along…after the drying period, a very slow heat in the kiln (a
few hours climb to about 700F) to get rid of all moisture. Heat to
red heat without metal, very slowly, the first time using… Can’t be
too careful heating anything that might have locked in
moisture…Almost good as new.

Johnny


#5

At $6.50 a pop (for a 3 inch round, $18 for a centrifugal crucible,
both cheaper by the dozen), I don’t try to clean them, I just break
out a new one. How much is your time worth? If you’re worth more
than about $5 an hour it makes no sense to clean them for reuse. In
addition, if it’s contaminated badly enough to warrant cleaning, the
risk of ruining one casting or ingot to save six and a half bucks
just makes it too risky to even try, imho I chip the larger beads
out and toss them in my sweeps bag and chuck the crucible in the
circular filing cabinet. But then again, I don’t resharpen drill bits
either.

One thing you can do for fun Teresa, is to heat it up and pour (or
should I say drip) the molten flux out of it. You have to really put
the coals to it and you probably won’t get all of the silver out,
but if it’s as heavily fluxed as it sounds like, most of it will drip
out. My wife threatens to slap the molten flux out of me from time
to time, but I think she’s talking about something different.

Dave Phelps


#6

An add on to throw away crucibles is as a last resort put salt in
and fire it up make sure you have good safety glasses on and plenty of
ventilation as the sodium gives a bright orange colour it will make
the borax and crud liquid like water when molten allowing the beads
of metal to coagulate into one blob you can see it rain down the
sides.

If you put to much salt in and you have a full pot just pour out to
expose the metal add a bit of flux and keep going till you’re done.
There are flux thinners out there in jewellery land of metal melt
and on t internet.

For those of you who have one that is brown black and thick with
flux try a 50 /50 mix borax and salt

Remember that salt is corrosive so don’t store it when you pour it
out just solidify and put in the scrap for recycling as there will be
small amounts of precious metal.

Alan