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Controller


An electronic device attached to a kiln (usually an electric kiln). These 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 industrial kilns, electric or gas, have controllers to assure repeatable firing conditions. All modern electric hobby kilns are equipped with controllers. Hobby and pottery gas kilns are also increasingly employing devices to control the schedule as well as the atmosphere.

Controllers for electric kilns work on a duty-cycle, switching the power to the elements on for a few seconds, then off for a few seconds. The controller adjusts the on/off durations based on how the temperature is following the program. Technically, the controller switches relays (either mechanical or solid state) on and off, and they turn the power on and off to the elements. During a firing relays trigger thousands of times, and you guessed it, they are the most failure-prone part of the system.

Controllers have built-in programs and can also be programmed manually by entering the rate, temperature and hold time for each step. Hobbyists are more prone to rely on the built-in pre-programmed schedules, using these to fire off-the-shelf glazes to low and medium temperatures. However, via manual programming, these controllers have revolutionised the ability of potters and more adventurous hobbyists to create special purpose glazes (e.g. crystalline, silky mattes). By creating drop-and-soak schedules (e.g. PLC6DS), they can to reduce glaze defects and improve surface quality and brilliance. Slow cool schedules (e.g. C6DHSC) are important to enhancing visual effects that depend on crystal growth (e.g. in rutile glazes) and for mattes.

The key motivation for this it to be able to fine-tune the final firing temperature (cone-fire mode on many kilns can fire well below or above the temperature a cone would confirm correct).

Older kilns can often be retrofitted with controllers and these can potentially work well if the relays can withstand the thousands of on/off cycles they will be subjected to. Caution is needed since some of these replacements may employ older programmable devices
(the Bartlett LED/Keypad V6-CF or 3K).

Program your firings manually, calibrate the final temperature

Program your firings manually, calibrate the final temperature

Here is an example of our lab firing schedule for cone 10 oxidation (which the cone-fire mode does not do correctly). We need it to actually go to cone 10, the only way to do that is verify with a cone (self supporting cones are the only accurate way). Then make a note in the record for that schedule in your account at insight-live.com.

Why is the clay blistering on this figurine?

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?

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

Manually programming a typical electric hobby kiln electronic controller

I document programs in my account at insight-live.com, then print them out and enter them into the controller. This controller can hold six, it calls them Users. The one I last 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" (for my cone 6 lab tests). It asks how many segments: I press Enter to accept the 3 (remember, 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.

Programming a Bartlett Genesis kiln controller

Programming a Bartlett Genesis kiln controller

Why program? None of the built-in schedules have hold times on any segments (these are a must for defect free glazes). None of them have controlled cools (a must for enhancing the effects of reactive glazes that develop crystallization or variegation). Tap the blue edit button to edit a program, then tap a column of any segment to edit its value. Tap a segment number to delete or duplicate it. Google "bartlett genesis controller" for short videos on creating and editing a schedule.

A test kiln with firing controller: A necessity.

A test kiln with firing controller: A necessity.

Every potter should have one of these. This one has a separate electronic controller, newer ones have it built-in. Start with one of these and then graduate to having a large, second kiln. Ongoing testing is the key to constant development of product and quality.

Kiln Firing Curve Recorder - Coming Soon

Kiln Firing Curve Recorder - Coming Soon

So many glazes appear as they do because of the firing schedule (especially the cooling curve). Imagine getting an awesome result out of a kiln and not knowing (or being able to replicate) the exact firing schedule that produced it. This device reads and records the temperature once per minute. It is a Raspberry Pi computer with camera, Wifi and custom software we made. It costs about $100 (with the Lego case and GoPro compatible gooseneck mount). Because the device is a full-power Linux web server I can login, see the list of schedules, and download any into my Insight-live.com account. And then I can link that firing it to photos of glaze test results!

Out Bound Links

  • (Project) Ceramic Firing Schedules

    Fast firing is almost universal in most sectors of the ceramic industry now. Companies hire experts to design kilns and firing procedures to successfully handle the type of ware they manufacture. Smal...

In Bound Links

  • (Glossary) Cones

    A pyramid-shaped ceramic device used to quantify the amount of heat delivered by a kiln. These devices are formulated from different mineral mixtures and numbered accordingly. They are placed in a kiln so they can be viewed during firing and when a cone begins to bend it is closely monitored and the...


By Tony Hansen




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