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
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!