|Monthly Tech-Tip |
In the Plainsman lab we use this for firing glazed ware at low temperatures. We never use the built-in programs on kiln controllers because this schedule gives better results. We never fire cone 06, glazes simply do not melt as well as they do at 05 and cone 04. If you are firing to cone 05, then your top temp will be 1860 and the drop-and-hold temp will be 1760. Fire 04 if you can, the results are best there.
The slower approach at the end is important to even out the kiln chamber, that is why a longer hold is not needed at top temperature. The drop-and-hold is important, this helps heal pinholes and blisters. The cool is freefall. Your rate-of-fall may be quite different than ours, depending on how well your kiln is insulated and how heavily it is loaded.
|1||55°C/hr to 121C||100°F/hr to 250F||60min||2:45||Water smoking step|
|2||194°C/hr to 1004C||350°F/hr to 1840F||0||7:17||As fast as your ware can tolerate|
|3||55°C/hr to 1060C||100°F/hr to 1940F||5min||8:22||Slow approach to top|
|4||500°C/hr to 1004C||900°F/hr to 1840F||30min||8:59||Drop and hold|
|5||0°C/hr to 23C||0°F/hr to 75F||8:59|
Here is an example of our lab firing schedule for cone 10 oxidation (which the cone-fire mode does not do correctly). To actually go to cone 10 we need to manually create a program that fires higher than the built in cone-fire one. Determining how high to go is a matter repeated firings verified using a self supporting cone (regular cones are not accurate). In our lab we keep notes in the schedule record in our account at insight-live.com. And we have a chart on the wall showing the latest temperature for each of the cones we fire to. What about cone 6? Controllers fire it to 2235, we put down a cone at 2200!
I was consistently getting the cone on the left when using a custom-programmed firing schedule to 2204F (for cone 6 with ten minute hold). However Orton recommends that the tip of the self supporting cone should be even with the top of the base (they consider the indicating part of the cone to be the part above the base). So I adjusted the program to finish at 2200F and got the cone on the right. But note: This applies to that kiln at that point in time (with that pyrometer and that firing schedule). Our other test kiln bends the cone to 5 o'clock at 2195F. Since kiln controllers fire cone 6 at 2230 (for the built-in one-button firings) your kiln is almost certainly over firing!
G2853B - Cone 04 Clear Ravenscrag School Glaze
A Ravenscrag Slip base made by simply mixing it 50:50 with a frit
Plainsman Electric Bisque Firing Schedule
Three-step to 1832F