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Glazing crucibles

#1

Hello All, Back when I was a crown & bridge lab tech we used to
glaze our crucibles this way: Using a rosebud tip on your torch
apply enough flame and heat to the interior surface of the ceramic
crucible and you can glaze very nicely this wayno need for
borax. You can tell when it is starting to glaze by watching the
surface become shiny as the surface starts to melt. To all a nice day, Gail

#2

Gail, I also was a crown and bridge tech about twenty years ago–
jeweler first, then c & b and then jeweler again. I would also fuse
the surface of my crucibles into glass which worked well save for the
fact that they were Wesco type silica crucibles, as opposed to
standard clay crucibles, which I believe would not fuse.

I use boric acid powder from the drug store to cure and coat my clay
crucibles. (Silica crucibles appear to have a rougher surface and
seem to feel more bisquelike, or hard fired. They are also much more
costly than clay.) I use a rose bud tip, heat the crucible and
shower the boric acid onto the glowing crucible. Sometimes you have
to tilt the crucible to keep the fusing boric acid in place the first
time out.

Good luck, Andy Cooperman

#3

I was taught to glaze a new crucible not by putting the borax in and
melting it, but by bringing the crucible up to heat and then
sprinkling the flux onto the interior surfaces. Moving the crucible
with tongs allows you to cover the entire inside surface.

Tony Konrath

#4

Just got finished glazing my crucibles and found that when they
cooled they had a layer of a glass -like substance (the borax?) on
them. Nice and shiney, and a good coat over the entire crucible.
BUT, the glassy substance is beginning to craze. Did I use too much
borax? And should I have used boric acid instead of borax. The
instructions I had said either was o.k.----but since I am getting
the fractures I wonder. Is this fracturing going to affect my
melt? If so, what should I do?

The crazing of the borax glaze that my crucibles are not clay,
but silica. I heated the borax with a Prestolite Acetylyne torch.
Heated the cruiclbles prior to adding the flux and swished it around
as it was being melted. So far I think I did everything
right—then when they were cooling I could hear little pings–as
the borax glaze began to fracture.

Thanks for your help- Alma

#5

Dear Alma, The borax will fracture. The crucible and the borax cool
at different rates. It will not interfere. IF you have enough to
"pour" off, you should do that. That is the reason that cloisonne
requires counter-enamel on the other side of the metal, or the metal
would bow and pop the enamel off. The only problem would be excess.

Jay

#6

Don’t worry, it’s just the instability-- and perhaps thickness-- of
the fused borax. It will refuse and become liquid again anyway at
molten metal temps.

Andy Cooperman

#7

The crazing is natural. When reheated it heals itself. Since you are
using fused silica crucibles, as do I, you can quench the crucible in
a 5 gal. bucket. Just plunge it in right after you pour, assuming you
are vacuum casting. What you are left with is a nice clean crucible
and a collection of metal at the bottom of the bucket that didn’t
make it into the flask. I also have a separate crucible for every
color gold and every karat to prevent contamination. Using this
technique with fused silica crucibles doesn’t allow glazing to hang
very long. Not a worry. You don’t need it. Doug Perry-casting platinum
and gold in the `Rocker’ Mountains

#8 
BUT, the glassy substance is beginning to craze. Did I  use too
much borax? And  should I have  used boric  acid instead of borax. 
The instructions I had said either was o.k.----but since I am
getting the fractures I wonder.   Is this    fracturing going to
affect my melt? If so, what should I do?

Hi Alma, The cracking is normal and will not affect your melts. Daniel
Grandi

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