I've been firing in my electric kiln for a couple of years now. The last batch of items fired came through the bisque firing without any problem. When I did a 'slow glaze' firing with them two of the pieces cracked. This is the first time I've had this happen. Any ideas why they would crack in the glaze firing but not in the bisque? Both pieces were on the top shelf and near each other and both pieces had the same type of glaze. It's been about 40 years since I've had a ceramics class and am making pieces and running my little kiln from long ago memory. I have no clue what happened.