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Low-Tech Overtemp Protection

The Auto-Cone shuts off the kiln when a pyrometric cone bends.


Low-Tech Overtemp Protection

A Kiln Story: The Quikfire That Almost Ran Away

Memorable Quote

Item Of Interest: Glass Clay



Someone recently asked for a low-tech system that would protect his digital glass kiln from over-firing. He wanted “bicycle technology” rather than digital technology. There is an answer, and it applies to digital pottery kilns, too.

The answer is the venerable Dawson Kiln Sitter. A clone of the Kiln Sitter is manufactured by the Orton Ceramic Foundation as the Orton Auto-Cone.

The Kiln Sitter, or Auto-Cone, uses a pyrometric cone to sense when to shut off the kiln. The cone is inserted into the Auto-Cone. When the cone has been subjected to the proper amount of heat, it bends, releases a trigger, and shuts off power to the kiln.

To use the Auto-Cone as a safety backup, select a pyrometric cone that is rated to a higher temperature than the glass (or pottery) yet lower than the kiln's maximum temperature. If the kiln ever begins to overfire, the cone will bend, and the kiln should shut off.

Suppose you fire glass to 1350 F. You could load an 014 cone rated to 1485 F in the Auto-Cone. It ordinarily bends at 1485 F, so the Auto-Cone would not shut off and interfere with the glass firing unless the kiln became too hot. The only way for cone 014 to deform, in this case, is if the temperature were to approach 1375 F at a heating rate of only 1 degree F per minute.

You can also do a long annealing segment after the glass fuses and still not bend the cone. Slow down the cooling rate in the annealing temperature range, which is typically 900 F - 700 F. The cone will not receive enough heat work in the low temperature range to bend and shut off the kiln. Use a new pyrometric cone with every firing.

Of course, the best overtemp protection is to monitor the kiln during operation.



A glass teacher unplugs her Paragon QuikFire after she has fired glass and the kiln is cooling. She no longer just turns off the switch. This is because someone turned the kiln back on while she left it to cool. She came back to the kiln a few minutes later and wondered why it was at 1700 F. A line of orange light glowed around the bottom edge of the kiln top. The glass inside the kiln overfired, but the kiln was okay.

She also tells students, “If you are going to use my QuikFire, you have to watch it. You cannot leave it while it is firing.” This is because the QuikFire can reach 1000 F in five minutes. “I’ve had my QuikFire 18 years. I love that kiln,” she added. I heard this story last week at the Glass Art Society conference.



“The best way to cheer yourself up is to try to cheer someone else up.” -- Mark Twain



The Summer, 2010 issue of Glass Patterns Quarterly magazine contains a project tutorial about a moldable clay that turns to glass inside the kiln. The tutorial shows how to fire slices of Glasclay into a plate. This is the best article I have seen on the material. Robin of Cherry Heaven reports that glass clay is becoming popular in England.


Last week John Hohenshelt and I attended the Glass Art Society show in Louisville, Kentucky, where I acquired a glass pendant made by Sabina Boehm. Inside the glass were dark metal particles arranged in the shape of a butterfly. The delicate creature looked like it was ready to fly.

At the show I met a doctor who fires glass in his spare time. He told me about a basket-weave glass vase he owns that was made by a retired neurosurgeon. People of every background find joy in the fired arts.

Thank you,

With best wishes,

Arnold Howard Paragon Industries, L.P. – Better Designed Kilns 2011 South Town East Blvd., Mesquite, Texas 75149-1122 Voice: 972-288-7557 & 800-876-4328 / Fax: 972-222-0646 / / /

PRIVACY NOTICE: Under no circumstance do we share or sell your email address.

Copyright 2010, by Paragon Industries, L.P.

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