On Friday, with a certain amount of trepidation, I opened the kiln after my first glaze firing.
All looked well; but on closer inspection all the porcelain pieces, bar one, have spiral cracks. After a bit of research I now understand this to be dunting, and is a result of the kiln cooling too fast through two critical points at 573°C and 226°C. I thought I had been careful not to open the kiln too soon, so it appears that I may need to look into a way of slowing the cooling process… By overriding the kiln sitter after it has shut off I should be able to hold it at a medium heat for a while. I hope this may help things. The stoneware pieces have fared better.
Luckily all the things in the kiln were just test pieces – I’m still sad though.
At least my test tiles have survived – before firing (l) and after (r).