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Burno Crucibles


I have been using my Burno crucible for melting sterling silver, and
notice that the borax which used to completely coat the inside of the
crucible is all pooled up on the bottom of the crucible.

Is it necessary to recoat the crucible,so that the section that
holds the metal is completely coated with borax?. If so, should I
remove the old glassy borax at the bottom of the crucible? If so, how
should I remove it? The old borax is sort of brownish red, caused I
believe by the cuperous oxides in the sterling.

I read somewhere that one could coat the cruicible by filling it 1/3
full of borax, and putting it in the kiln to heat, rotating it around
so that the molten borax completely covers the sides of the crucible.
If this is the proper proceedure, what temperature should I heat my

Even with heavy leather gloves and tongs, this seems like a
difficult proceedure. Is there a better way than using the kiln?

I will appreciate advice on the proper care of my crucibles so as to
insure longevity.

Thanks Alma



Do not worry about the brown color flux coating the bottom of your

I have crucibles I have been using for 25 to 30 years that have gone
through color changes of light straw to brown to black in color and
I am still using them.

After coating your new crucible the first time with a good coating
of borax the need for adding flux each time you melt metal should not
be necessary unless you are melting dirty metal.

I generally only add a pinch of additional flux to my crucible on a
as needed basis.

I generally heat up my crucible until the flux begins to melt and
then I add my metal. As the metal begins to melt I rock the crucible
side to side to allow the impurities on the metal to move off to the
flux coated crucible.

If you build up to much flux in the crucible simply heat the
crucible with a torch until the flux becomes liquefied and then with
heavy tongs turn the crucible to the rear corner and pour off the
excess. Make sure you do not over heat the flux or it will burn and
not run.

Use the same procedure to coat the crucible the first time or any
time you need to coat areas of the crucible that flux is missing

Good Luck
Greg DeMark
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I saw this before, but I guess nobody replied yet… All you need to
do is coat the crucible, like paint, on the inside. 1/3 full of borax
is a LOT of borax. We use the boric acid/methanol dip that goldsmiths
use, and I just spritz the inside of a new crucible with that. That
would represent more like 1/2 teaspoon, not 1/3 full. Anyway, there
is no way that I know of to remove old borax from a crucible that
won’t do damaqe to it, and, besides, they do not last forever. If it
seems really grungy, just get a new one. If you are getting good
results in melting and casting, don’t worry about the appearance -
they always get colorful, no matter what metal. But they are
consumables, and you’ll only get a certain number of melts out of
them, and then they need to be replaced.


If you’re talking about the white ceramic ones, and not the black
ones used in electric melt pots, the excess flux should be removed.
Just heat it with your torch until it becomes a glassy liquid and
pour it off into some very dry sand. Too much borax causes rough
castings. If you use a graphite or quartz rod and draw through the
molten metal before pouring it into your mold, not only does it mix
the metal consistently, say as in an alloy, but it also removes the
excess borax and the entrapped junk. You will have to reheat your
metal again to the liquidus state, as the rod absorbs heat.
Occasionally you have to get rid of the junk on your rod by gently
tapping it, ever so gently, with a hammer against a steel block.

I read somewhere that one could coat the cruicible by filling it
1/3 full of borax, and putting it in the kiln to heat, rotating it
around so that the molten borax completely covers the sides of the
crucible. If this is the proper proceedure, what temperature should
I heat my kiln.?. 

OK, I’m a low techie kind of person. I mix boric acid, which is
available at a pharmacy, and a little finer grade of borax, with
alcohol. You want the boric acid to just be at the supersaturated
stage in the alcohol, where it won’t pick up any more boric and some
of it is still in the bottom of the mixing vessel. Then paint it onto
the walls of your crucible, as well as top and bottom, and any pour
gates and fire holes. Then fire it with your torch. Do it several
times until you’ve built up a nice glaze.

Just the way I do it, which may, or may not be “correct”.


I have cleaned a fluxed crucible of extra flux by heating it kind of
slowly with a large torch, and pouring the flux out onto a heat
proof surface (steel, firebrick, etc.). I think I kind of raked it a
bit with a steel pick, as well, while it was sliding out. It was very
slow and sticky, but I got a lot of it out of the crucible. I held
it with tongs.

M’lou Brubaker
Minnesota, USA


I have a question about excess borax. My instructor was sprinkling
borax into my silver to cast and the top came off and about a quarter
cup ended up in my very large amount of silver for a very special
casting I didn’t want to ruin. She pulled some of it out, but
couldn’t get it all. We proceded with the heating and tried to pull
more molten borax out with the graphite rod. There seemed to be too
much borax still in the metal when we went ahead and cast.

The casting came out FULL of firescale and with quite a bit of
porosity. Is there an excess of oxygen caused by the excess borax,
thus the firescale? And is the porosity because of overheating the

Essentially, what caused the problems and how can I avoid that




I use 1/4" carbon welding rod to stir the molten metal. It is cheap
and lasts forever. The copper coat is very very thin and seems ot
no difference. Since I like ‘improving things,’ I push a piece of
brass tubing on the end for a handle. That gives me reach and tells
which end is not hot. I got the tube from the K&H (?) metal display
the hardware store for hobbyists and such.

My entire can of borax sits on the floor of my centirfuge, right
alonside my peanut butter jar full of water. I pick up borax on the
end of the heated rod and skim detritus off with the rod. Then I
quench the end of the rod in the water to clear it of slag. The
carbon rod conducts heat poorly so does not seem to affect the
temperature of the melt.

If I use reducing flux, I apply it with a salt shaker made of a film
can with holes drilled in the center of the top. That would work for
borax as well.

I can only assume you overheated the silver while trying to
eliminate the excess borax.

I hope this helps.
Jon Abbott