Today has been frustrating.
I set up an aperture drop of 550mm diameter to drop 100mm. The glass was St Just red flashed. I don't know the characteristics of this glass in the kiln, so I chose 560C for 120 mins. This was based on the fact that 4mm float glass dropped 90mm in 120 mins at 630C.
I set the kiln up so that it would be reaching its top temperature at 10:00 to be sure I was around long before. After checking every 10 mins, I found it had only begun to slump after 100 mins. So I increased the temperature to 580, but after an hour there was no perceptible difference. Again I increased the temperature to 600C, but after 2 hours there was only about 30mm of a drop. So I tried 610C, but got little if any movement after an hour. Then to 620C and finally after a further two hours, I got my 100mm drop. So I got what I wanted after 7 hours rather than the two I planned on. All the other activities of the day were interrupted or postponed as I was virtually tied to the kiln.
I have now written this up so I should not have to go through another day with the alarm going off every 10 mins. Still, I did get to an exhibition opening before the doors were closed.