Potters & Sculptors - Making Rock from Mud
Our kiln with a Bartlett V6-CF electronic controller uniformly fires exactly one witness cone too hot, whether firing to Cone 016, 04 or 6. Inexplicable, but this is very easy to adapt to by simply choosing one cone cooler than we need.
Even with this odd quirk, I highly recommend the $430 Bartlett V6-CF electronic controller to replace any kiln-sitter. It works like a microwave oven . . .
Cone-Fire 5, Medium speed, 3 hour pre-heat, Add slow-cooling program, Start.
It takes less than 30 seconds to program a firing.
Our Cress E-32 is amazingly even - a handful of witness cones spread through-out the kiln end up looking nearly identical. Larger kilns can vary in heat work from one shelf to another and from the center of a shelf to the edges, unless the firing is done slower.
I would never use a kiln sitter again. With a kiln-sitter, if the little matchstick cone melts partially onto the metal support arms you get an over-fire, with lots of ways to under-fire as well. And the kiln-sitter we used was warped from years of heating and cooling, making even less reliable.
The only change we have made to the controller system over the past five years was replacing the Type-K Ni-Cad thermocouple when it wore out after a couple of years with a Type-S platinum thermocouple, which lasts longer and is more accurate.
Type-K thermocouples cost $46 and are accurate to +/- 10 F. As this type of thermocouple ages their accuracy can "drift" in one direction or another as the metal crystallizes. Even with this known inaccuracy, in our experience, kiln firings were far more correct than they used to be using a kiln-sitter.
The Type-S platinum thermocouple, apart from costing $180 instead of $46, doesn't drift in accuracy as it ages, and is allegedly accurate to +/- 2 degrees. We've had no complaints. You have to push a few buttons to change the controller for the different thermocouple type.
How accurate is +/-10 degrees F?
The difference between Cone 1 and Cone 2 is only 9 degrees F, whereas the difference between Cone 5 and 6 is 65 degrees F. Of course the kiln controller is accumulating the heat readings every 30 seconds or so to determine the total heat work done using an "area under the curve" integral. But the accuracy of each individual temperature reading is what determines the length of each firing.
After initial testing following our installation of the Type-S thermocouple we rarely use witness cones. We no longer need them.
The 3-Key kiln controller on the left costs $100 less ($330). People I know who've purchased one have always regretted saving $100 to end up using this much less capable controller. You want the V6-CF.