I hand made a set of coasters, in a white clay body that I have been using for the last two years. They were about 3.5 inches round, 3/16th thick and bisqued to 04. I glazed the rims with Amaco glazes that I have not had issues with. I used a clear glaze on the center portion (it was at SG 1.2) and I had waxed the bases. I put them in my kiln and put blue glass chunks on the center. I fired to Cone 6. It was pretty fast about 8 hours (I have a kiln sitter, so I am basing my time off the timer and when I was upping the heat). I followed my basic cone 6 firing schedule that has always worked. I let the kiln completely cool before opening. When I did all most all of the rims on the coaster has broken off and left the area. I found a piece stuck in the kiln brick and on all 3 shelves and the bottom (this is fun because now I have to figure out how to get it off without damaging the floor. I can only think that since I had wax on the bottom and glaze everywhere else that there must have been water that was not burned off when the glass melted and this caused the rims to blow off.
If anyone has any advice, I really like the look and would like to me a set again (they were supposed to be a Christmas Gift, and I still want to give it, although not for a little while).
Thank you,
Z
