A couple students in my metal clay class have, at different times,
had the CZs they embedded in their pieces turn cloudy. Other CZs from
the same batch in the same firing are fine.
First, the only difference I can pinpoint is that, in the recent
occurrence (I don’t remember about the previous case), the piece with
the problem was fired on a pellet made out of investment to control
shrinkage. So I’m thinking that the investment may have given off
fumes in the 1650F firing that affected the CZs. Does this seem
possible? These were both fairly long firings, as the kiln is brick
and well-insulated, and stays hot a long, lon= g time if not opened,
which it was not until the next morning.
The other question is, what is the best way to remove the CZs? How
hard will they be to break apart? We can, of course, try to peel back
the fairly thick fine silver around the stones, but I’m concerned
about damage. I’ve never removed a stone from fired metal clay, and
would be happy to have input.
So I'm thinking that the investment may have given off fumes in the
1650F firing that affected the CZs. Does this seem possible?
Oh yes, at 1650 you are well above the decomposition point of the
investment and the calcium sulfate in the investment is releasing
sulfur dioxide gas. As to what sulfur dioxide does to CZ I haven’t a
clue but it will severely tarnish the silver.
Well, no, it doesn't-- but this is fine silver, remember.
I know it is fine silver, remember fine silver will tarnish
otherwise you would not be able to patina it with liver of sulfur. No
dark spots where it is in contact with the investment? The rate of
off gassing must not be great enough to cause visible tarnish. So
probably not enough to affect your either CZ’s either.
I have removed stones from metal clay because of discoloration. I
have removed the silver around the stone with not much damage. I put
another stone in it’s place, and used the metal clay syringe to
reset the stone.
I’m sure it would have been easier if I had the chicago pneumatic
hammer Noman suggested.
I'm sure it would have been easier if I had the chicago pneumatic
hammer Noman suggested.
Even without a hammer handpiece, it’s possible to remove damaged
stones without damaging a bezel setting. If a stone is trashed
anway, I smash it into small pieces using a suitably sized steel tool
and hammer, being careful to avoid the setting. Once all the bits are
out, the setting is easy to bend to a position where you can set a
new stone. I do this with the piece set in thermoplastic.
