Firing art clay

I have fired a jewerly piece with art clay and fire agate.
My fire agate basically blew up and the art clay did not
adhere to my fire agate.
What did I do wrong?
Thank you,
Paul Stemen

[Metalman]

Paul,
Once I have decided that I am willing to risk a stone - I test fire it to the firing temperature with out any Art Clay.  If it comes through well, then I build it into an Art Clay piece and cross my fingers.  I have been told by lapidary people that any time you heat a stone, it is at risk, even if it survived previously.   If you check this thread, there is a larger description of working with stones:
http://www.rings-things.com/cgi-bin....=stones
There are also some helpful hints in the thread called Work Tips

If memory serves, fire agates are based on a water inclusion in the stone, this might be the source of the stone 'blowing up'.
Another aspect might be the shrinkage [8 to 10%] of the Art Clay Silver.  Come back with any further corrections, questions and/ or '>
Hope this helps