Digitalfire Ceramic Glossary



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Controller


An electronic device attached to a kiln. Controllers are usually capable of firing a kiln to a specific schedule and can shut it off at the right time, soak it for a specified period, and cool it down at a controlled rate. All modern electric kilns are equipped with controllers and most industrial gas kilns. Hobby and pottery gas kilns are increasingly employing controllers to control the schedule as well as the atmosphere. Controllers for electric kilns have built-in programs and can be programmed manually by entering the rate, temperature and hold time for each step. These controllers have revolutionized the ability of potters to create special purpose glazes (e.g. crystalline) for which they are almost always programmed manually. Potters and hobbyists are more prone to rely on the built-in pre-programmed schedules in the device, but it is better to manually program controllers and adjust the temperature according to observations about the state of cones from previous firings. This is because choosing a cone-fire mode does not normally enable overriding the final temperature.

Pictures

Why is the clay blistering on this figurine?

This is an admirable first effort by a budding artist. They used a built-in cone 6 program on an electronic controller equipped electric kiln. But it is over fired. How do we know that? To the right are fired test bars of this clay, they go from cone 4 (top) to cone 8 (bottom). The data sheet of this clay says do not fire over cone 6. Why? Notice the cone 7 bar has turned to a solid grey and started blistering and the cone 8 one is blistering much more. That cone 8 bar is the same color as the figurine (although the colors do not match on the photo). The solution: Put a large cone 6 in the kiln and program the schedule manually so you can compensate the top temperature with what the cone tells you.

Two electric kiln controllers firing test kilns. Why are they so different?

Red controller on the right: A Skutt Kilnmaster. Blue controller to the left of it: An Orton Autofire. These controllers both attach to a thermocouple in the kiln so they know the temperature. Both are external to the kilns (but there is a big difference). The controllers monitor the temperature change as they turn the power on in bursts, changing the length and frequency of the bursts to control temperature rise. The KilnMaster controller is attached to the 220V power line and the kiln power line attaches to it (there are heavy duty electrical relays inside). The blue Autofire controller connects to the switching mechanism in the other kiln (built to receive it), thus no heavy duty relays are needed within it. The KilnMaster is more flexible since it can connect to any kiln, but it is also triple the price.

Manually programming a typical electric hobby kiln electronic controller

I enter (and tune) programs manually and document them in my account at insight-live.com. This controller can hold six, it calls them Users. Whatever program I last entered or edited is the one that runs when I press "Start". When I press the "Enter Program" button it asks which User: I key in "2" (my cone 6 test bar firing program). Then it asks how many segments: I press Enter to accept the 3 (I am editing the program). After that it asks questions about each step (rows 2, 3, 4): the Ramp "rA" (degrees F/hr), the Temperature to go to (°F) to and the Hold time in minutes (HLdx). In this program I am heating at 300F/hr to 240F and holding 60 minutes, then 400/hr to 2095 and holding zero minutes, then at 108/hr to 2195 and holding 10 minutes. The last step is to set a temperature where an alarm should start sounding (I set 9999 so it will never sound). When complete it reads "Idle". Then I press the "Start" button to begin. If I want to change it I press the "Stop" button. Those ten other buttons? Don't use them, automatic firing is not accurate. One more thing: If it is not responding to "Enter Program" press the Stop button first.

Out Bound Links

  • (Project) Ceramic Firing Schedules

    Fast firing is almost universal in most sectors of...

In Bound Links

  • (Glossary) Cones

    A pyramid-shaped ceramic device used to quantify t...


By Tony Hansen




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