I have a problem with cracking only on my platters. I throw them on the wheel about 11" diam and@ 1" thick bottom and rim with buffalow wallow clay. I have had one platter make it without cracking but in the glaze firing it warped because of the stilts I used. Am I drying the platters to fast, I used to store in pottery barn uncovered for 1 week-cracked down center. Then I put one in uninsulated building 1/2 covered for a week, this one is still drying. Do I need to leave it covered for 2weeks? I don't know? Also How do I place a fully glazed platter on a kiln shelf without it warping?