'Science is an exercise of the human brain to grasp the principles by which the universe works and to write them down, if possible, in crisp, precise mathematical terms. Science gives us knowledge of our environment. It sets the scene in which we act.'
Magnus Pyke, 1962
Technical information
This is a long page, but I think will be rewarding to anyone setting up a kiln for the first time. During 2000 I acquired a new Evenheat GTS 23-9 glass kiln, and took it through its paces. Being an engineer, I recorded what happened so i could understand its behaviour. This is a record of the results. The kiln is wired for 240V 30A (7200W) single phase 50Hz, and accommodates a 540mm (21") diameter circular kiln shelf. It has a Rampmaster 2 digital controller and a type K thermocouple. Evenheat state that the controller is accurate to ±10°F (for me that means ±5.5°C). The display reads to individual degrees, but I can't remember seeing any statement about the accuracy of the thermocouple system

Pre Firing
Evenheat recommend a Pre Fire before doing any glass work, to drive off moisture and condition the elements. This should be programmed to raise the kiln temperature to 815°C (1500°F) over three hours at 270°C/hr (500°F/hr). OK, being one of those rare people who read manuals, I did this with the kiln completely empty.
        Here is the time-temperature graph showing that the kiln did a good job of meeting the three-hour up-ramp. Each point represents a time when I checked the kiln and read the displayed temperature. The graph also shows the rate at which the kiln cooled with the lid closed after the program was complete, which is as fast as it will ever be. The kiln shelf, glass, and any other hot stuff would add extra mass and result in a slower natural cooling rate. See my page on Cooling Theory and Kiln Design for more information.
Tests on a loaded kiln
Some weeks later I repeated the monitoring during a slump firing of Spectrum glass. This time the kiln was loaded with its shelf and posts, a fiber slump mold, and glass. The performance should be reasonably representative of any firing without a heavy mold. Here is the firing data (black: as planned, pink: what actually happened, and blue: predicted cooling). Nowadays I crash cool to 580 - 600°C, but I was being cautious still then.
        Again, the elements kept the heating ramps almost up to the planned schedule, reaching top temperature only two minutes late. I opened the kiln lid to crash cool the glass down to 626
°C, and then left the kiln alone except for canceling the last segment which was pointless. The cooling from working temperature (ramp 4) put the subsequent annealing ramps 20 minutes behind schedule.
        The cooling rate after leaving the annealing phase corresponds to a time constant of 3.16 hr (3h 10min) to within a degree, so I use this figure generally for prediction. If I am not in a hurry, I leave the kiln to cool this way overnight.
        If I want to get the the glass out quicker (maybe for a second firing, or being impatient) I open the kiln lid by 35mm (1
") and connect it to my chain once the temperature reaches 300°C. Once it reaches 200°C, I open the lid by an extra two links of the chain (another 20mm). When the kiln reaches 55°C, I take the glass out and wrapping it in a towel for a few minutes. This generally speeds the cooling up significantly so that the post-annealing cooling takes 3 hr instead of 6 hr, and for work that is 9mm thick or less it has never caused a cooling crack. I don't do this for thick castings, of course.