What is the max a stoneware can be cooked at? I can't find that information anywhere on the Pampered Chef web-site. I had a customer e-mail me saying she was using her Pizza Stone to cook some pizza's at 500 degrees and was on the 4th or 5th pizza and it cracked in half on her. She has had this stone for at least a few years so its had many uses. She said there was no temp change so shock was not the problem.