I am one of those PMC instructors (and here I state it publicly) who
described for her students how to fire diamonds (sapphires, rubies,
too) along with PMC (as I had been instructed). This was years ago,
when only PMC Standard, the original formula, was available.
Therefore, the required temp was 1650 degrees F for the required
duration, 2 hours.
Although I had great success firing small sapphires with PMC, only
one of my students arrived with a diamond she wanted to fire. I
always added the caveat Re: cracks in stones, inclusions, etc. and
she was willing to take the chance that the stone might be damaged
by the process.
The result of that firing was...the stone was GONE! No pieces, no
melted blob, no apparent dust. I have to say that the student was
absolutely certain that the stone was a diamond and, thanks to my
caveats, she was OK with the diamond being gone. Whew! There, I've
cleared my desk of that mess!
Personally, I don't really care what the diamond 'became' in the
process (CO2, fairy dust, etc.). I have never suggested, since that
episode, to any of my classes that diamonds can be fired with
For an excellent list of stones that survive firing in PMC and it's
several formulae, check out Kevin Whitmore's list somewhere on .
Hope this helps (it sure helped me),