Wow I really thought they were dry, I did the moisture test with my finger and they seemed ok, but I guess not
I fire to 1140 °over approx. 12hrs about 100°an hour with a half hour soak. I don't open the door until its under 200°and even then just for a peek. I also never used to cover while drying as It takes so long anyway but will start doing this now. I have to confess these two pieces were left out in the rare sunshine for an hour or two just t speed it up so I suppose that didn't help matters.