I fired four of the little hand pressed lions blocks, a cherub plaque and the single section Art Deco in the kiln, and amazingly when I opened the lid, four little shattered lion faces stared up accusingly at me from the bottom shelf of the kiln. I figured at first maybe the vent is cooling the kiln too rapidly but these were not cracks they were blown up under pressure from steam forming inside the clay.
Despite being dry I thought, and sitting them in front of two box fans set on high for three days they apparantly were not really dry.
I looked at what makes up the “Slow bisque” profile on the kiln’s electronic controller, to get to cone 04 with this, it has this ramp schedule, in degrees F:
80 deg /hr to 250
200 deg/hr to 1000
100 deg/hr to 1100
180 deg/hr to 1695
80 deg/hr to 1945
I think the 200 deg/hr from 250 deg to 1000 deg is where the problem is going that fast thru that first critical temperature around 550-600 degrees, I’m going to write a program similar to that but change that segment, add in more preheat time @ 200 deg from 2 hours to 5, and run the other four lion blocks I have and see if that fixes the problem.
On a lighter note, I found the color of the one surviving piece was just perfect, exactly what I wanted, it was right at 2056 deg F or about midway between cone 01 and cone 1, I used a -15 degree offset down from cone 1 which should have made it 2064 degrees but the actual final temperature was 8 degreees cooler than that.
The Art Deco piece was the sole survivor, the single lion block on the left had his face blown off but it was a clean break and I just glued it back on.