@Fromphyl I had picture #2 experience the first time I fired bmix with speckles. I fired to cone 6. Which turns out was probably hotter. Closer to 7. But...I called Laguna and they said that clay is definitely a cone 5 clay. I told him it looked like chicken pox or pimples. And he said it was overfired. My bumps/blisters were with 2 different glazes. I now fire to cone 5 with that clay, and so far have only used clear glaze on it and no blisters. I even did a refire and it was fine. Were all the cups in the same place in the kiln? I ask because I now know that my top shelf is a lot cooler than the rest of the kiln.
Roberta
I just had the same problem, but there were unglazed portions that had the same blistering/pimples, Pieces were bisqued to Δ04. I run a manual updraft gas kiln and did a fairly fast fire, ~5 hours to 1000°C which required ~1 hour @ 1200°C for Δ6 to mature. I figure I need to run a much slower ramp and then hold at a lower temperature for this clay.
Blistering clay? Or glaze problem…
in Clay and Glaze Chemistry
Posted
I just had the same problem, but there were unglazed portions that had the same blistering/pimples, Pieces were bisqued to Δ04. I run a manual updraft gas kiln and did a fairly fast fire, ~5 hours to 1000°C which required ~1 hour @ 1200°C for Δ6 to mature. I figure I need to run a much slower ramp and then hold at a lower temperature for this clay.