Reconditioning used crucibles

Jewelry Discussion
1

I am in the process of acquiring a used casting machines that
include with it two used crucibles that have a heavy coating of
flux glass on them from use. How would one go about removing
said flux glass and reconditioning the crucible for use??

Jones

2

Hi Jones

I recondition my used crucibles about every 3 months or when the
borax has built up and got messy. I find that leaving them in a
solution of old or used pickle for a couple of days does the trick.
They then need a new light coating of fresh borax.

I hope this helps.
John Derek Designs

3

I would buy new crucibles. O:-)

Jerry in Kodiak

4 
    I am in the process of acquiring a used casting machines that
include with it two used crucibles that have a heavy coating of
flux glass on them from use.  How would one go about removing said
flux glass and reconditioning the crucible for use??

I just do a dry run with nothing but molten flux in the crucible. It
cleans out the old flux just fine.

Bruce D. Holmgrain
http://www.goldwerx.com
@Red_Rodder
JA Certified Master Bench Jeweler / CAD/CAM Solutions

5

Hi Jones,

I’m assuming that you have white molded clay crucibles that fit into
a tray on one end of the centrifuge arm.

Put on your respirator and some wrap around goggles. Put a 1 inch
Mizzi heatless wheel in your flexshaft. Grind out all the old flux
glass. Grind right down, barely into the softer crucible material.

Oh, you know what? I’d look the crucible over before I started. Use
some magnification and see if you can see any big cracks that run
all the way through the crucible. If you see a crack, pull on it a
little to see if the crucible will break. I don’t mean for you to
Really Crank Down on it and apply a lot of force. Just apply a few
pounds of pull across the crack. If it stays intact, proceed with
the grinding.

I mix borax and boric acid, 50/50 by weight, making sure that it’s
all evenly powdered. I heat the crucible incandescent with my torch
and sprinkle the flux over the glowing surface. I used a big spoon,
although I’ve seen a salt shaker or a chili pepper shaker used. I
like the spoon cuz I have more control over the placement and amount
of the powder.

Just barely coat the crucible. Too much flux and you’ll end up with
globs of unwanted flux in the melt/casting. Too little flux and
oxygen may come through the crucible wall and contaminate the melt.

Good luck. Remember that there’s only one rule in this process -
Don’t burn yourself.

Chuck in Las Cruces where it’s windy springtime in New Mexico!

6 
    How would one go about removing said flux glass and
reconditioning the crucible for use??

I wouldn’t. They are cheap enough to replace.

James in SoFl

7

You might try soaking them in pickle. Afterward, soak in baking
soda. It works for me.

rp leaf

8

Cleaning up used crucibles.

Ive got a plastic bucket with lid out in the back yard with
Hydrochloric acid where I soak the crucibles for a week, more or less
then change to another bucket with water and bicarbonate of soda. The
crucibles come out as new!..or nearly.

Considerable gold is found in the bottom of the bucket, The
hydrochloric acid must be at least 50% concentration. A lot of
Hydrochloric acid sold for house hold cleaning purposes is only 10
to 25% concentrate which will not work.

I have noticed that apart from and acid smell when the crucible is
used for the first time again there is a purifying effect on the
gold.

Regards

Colin Waylett
Spain

9 
I have noticed that apart from and acid smell when the crucible is
used for the first time again there is a purifying effect on the
gold.

There would be. The residual Hydrochloric acid would contribute
chloride ions to the melt. The result would be about the same as
adding a pinch of ammonium chloride (sal ammoniac) to the melting
metal. It bonds with baser metals forming insoluable chlorides,
which then slag off, leaving the gold and silver slightly purer.
Reduces things like zinc, tin, iron, etc, from the melt. Note that
the fumes you’re smelling are Chlorine gas. Use those newly cleaned
crucibles with enough ventillation so the smell is not all that
strong. It’s not friendly stuff to lungs (neither, of course, are the
direct acid fumes).

Peter

10 
I have noticed that apart from and acid smell when the crucible is
used for the first time again there is a purifying effect on the
gold.

if you use sparex for this process and then soak in clean water for
several days you wont have this problem - gh