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Conditioning Crucible


#1

Hi! I tried conditioning a ceramic crucible with Borax and ran into
some difficulty. I followed the recent thread, and thought I did
everything I was supposed to. However, I couldn’t get the entire
inside of the crucible covered with the hardened borax. Instead it
pooled in the bottom, making a rather deep, sold pool, and also
turned dark colors. The sides were untouched. I thought the borax
would spread once it was molten and I moved the crucible around, but
it didn’t. I was concerned that the dark color might affect the
silver I would like to melt in it. I would appreciate any
suggestions about what to do now and how to get it to work the way
it should Thanks Sandra


#2

Hi Sandra,

The borax, or powdered casting flux in my case, isn’t very watery
when molten. In order to coat the sides of the crucible, I have to
keep the torch trained on the pool as I tip it to coat the sides, and
it still moves slowly. It has the consistency of molasses on a very
cold day, like today in Charlotte. If spring is here, why is it
still so cold?!? :wink:

Hope this helps,

Dave

Dave Sebaste
Sebaste Studio and
Carolina Artisans’ Gallery
Charlotte, NC (USA)
dave@sebaste.com


#3

Hello Sandra, Dave & All, When coating your crucible it is
unnecessary to melt a bunch of Boraxo and swirl it around to coat the
surface. While it does coat the surface you can also use too much and
have it carry through with the molten metal. This doesn’t happen all
the time but it does happen. If your borax is sluggish when you’re
trying to coat your crucible it may indicate that your torch is not
hot/large enough. Try this procedure with a new or newly cleaned
crucible: Set your crucible up, nipple down, supported by two pieces
of fire brick on a fire proof surface. Have some borax handy in a
saucer or small bowl within reach, not just the box. Use powered
ventilation like an exhaust fan or a fan at your side blowing the
fumes away. Wear your eye protection. Use a hot , slightly hissing
flame, heat the whole crucible until it is glowing yellow hot. In a
simultaneous motion, take a three fingered pinch of borax and throw
it at a specific spot in the crucible as you move the torch away.
Return the torch after each pinch is thrown. Overlap each "throw"
and turn the crucible on its’ side and repeat. Turn the crucible to
each side and finally to its’ operating position for the final
application of borax. You don’t need gobs of the stuff. The crucible
should have a slight shine, not necessarily a glassy enameled look.
If you are using a bowl type crucible on a handle for pouring an
ingot or vacuum casting you need not turn the crucible on it’s side
to glaze it. You merely turn it a little on it’s bottom while you are
applying the borax with the same “throwing pinch” method. When you
glaze your crucibles like this you can add a thrown pinch of borax
when you heat your crucible just before you put your metal. If you
have an old crucible with lots of build up you can clean it by
grinding it with a mizzy wheel in your flex shaft. Grind right
through the old flux being careful not to sink into the ceramic when
you break through the crust. Leave the surface as smooth as possible.
CAUTION: a cracked crucible for a centrifuge will hold together with
the flux when it’s cool and can fly apart when hot and spinning. It
can be quite dangerous, I’ve seen it happen! So discard crucibles
with a crack or that are getting thin, even if they look like they
are holding together. John, J. A. Henkel Co., Inc. Moldmaking
Casting Finishing, Producing Solutions For Jewelry Artists


#4

About borax, this substance should NEVER be used for flux or
crucibles. Borax contains minute amounts of iron which can cause
micro porosity in your castings, especially in white gold. Use
granulated boric acid to coat your crucibles and to use as flux.

Doug Perry / Pierret Designs