I think one of my top zone elements just failed. My elements were approaching their life span, and there was one spot on my second-to-top element that looked more worn than everything else.
This morning I found my kiln was still firing after 12 hours, when it usually takes 9. The top zone was way behind, and the ramp was climbing at roughly 30°/hour. Normal program is 120°/hour for the final segment.
I looked at a cone chart, and the closest the data I could find for my situation was:
cone 5 at 27°/hour is 2118
cone 5 at 108°/hour is 2167
This is pretty close to the ramp I was getting vs the one I'm used to. The difference between then is 49°.
My final temp was supposed to be 2180°. So I subtracted 50 and shut the kiln off at 2130°.
Does anyone have any sense that I did the right thing? If not, it's ok, I'll find out tomorrow morning when I open the kiln. If the top shelf or two is underfired, while the rest of it is ok, I'll consider that a victory.