Why the second firing cracked
Three bowls out of eleven came apart along the foot ring. The kiln was not at fault, and neither was the glaze.
I had thrown these on a damp week and trimmed them the next morning, which is earlier than I usually dare. The walls were still heavy with water at the foot while the rims had already stiffened. That difference does not show itself at the bisque stage — everything came out of the first firing sound and ringing.
What the break tells you
A cooling crack is clean and often follows the throwing spiral. A drying crack, which is what these were, is duller at the edge and sits where the clay was thickest. Mine were dull. That settles it: the fault was three weeks old before the kiln ever saw them.
The kiln only reveals what the making already decided.
The fix is dull as well: wrap the foot, not the rim, and give the pot an extra day under plastic before trimming. I have written it on the wall above the wheel, which is where I write the things I keep forgetting.
The ones that survived
The eight that held took the ash glaze better than anything I have pulled this year. The iron underneath broke warm at the lip and pooled green in the belly. I will repeat the batch and change nothing except the drying.