From Kirshmans quarry or magnet cove? I would guess you went to high to fast. I have a computerized controller and hold it at 195 for minimum 24 hrs, then slowly ramp ito 725 if its from kirshmans and more if its from Magnet Cove. about 35 degrees an hour then hold it for 8-10 hrs, then slowly ramp it down to 300 and shut it off. The kiln should be full, if you have a temp probe do not let it touch rock. Must only be in the air. If you don't have a controller you should get one.