Two more trials with revised schedules using a much more conservative drop through the annealing range and two more ruined projects later. This last trial we used some Hotline Hi-Fire that we found on the shelf instead of the Primo Primer. Now my kiln shelf is totally toast! That didn't work as well as the Primo Primer.
So what now? We know that the breakage is occuring at the cooling end of the cycle, because the edges of the pieces are all sharp as razors. We also know that my kiln will not do a 600 F drop per hour....because I get an error message that says so. We also know that the only trial that has come close to working was done with Hotline Primo Primer and your firing schedule....up to the point where the kiln wouldn't do the 600 degree drop. However.... the very first trial piece came out intact and it didn't stick to the kiln; it just had little pin holes all over the top where tiny bubbles popped and the surface didn't heal over.
We also know that.... doing that drop at 9999 doesn't work either. And neither does just shutting the kiln off at 700 and letting it cool naturally.
With the 600 degree drop, what are we trying to accomplish? Cooling the kiln as quickly as possible (in which case, the 9999 should work)? Or cooling it at a rate that is slightly higher than what is possible? If that is the case, then what would be your best guess as to an alternate rate? 500 degrees F? 400?
In the meantime, I will order some BE primer to remove that variable from the trials. And I will also need to order a new shelf (or two)! But I still need some advice re: the schedule. I really want to be able to make this work!