Program your firings manually, calibrate the final temperature using cones

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!

Related Pictures

Cones bending theoretically, cones bending actually

Orton cones have become much less relevant in recent years. That being said they are still commonly used to calibrate kiln controllers. Most people just use one cone now (rather than the guard, firing and guide cones of the past). The problem illustrated in this diagram is our reason for doing that. At our typical firing rates, we found that bending the middle cone to 5 o'clock pretty well always started the guard cone. Orton said when that happens "you have exceeded the best time-temperature relationship". Thus, over time, we got into the habit of bending the firing cone to 3 o'clock (as shown in #1). Notice the situation in #2, that is not supposed to happen but often does. The first guide cone should be slumping, not just touching. And the guard cone should not be starting. Now we just use one cone bent to 5 o'clock to callibrate our electronic controllers.

At what point is a self-supporting cone bent to the correct degree?

A self supporting cone in an Orton guide

Orton says “90 angular degrees is considered the endpoint of cone bending”. First, let's assume the normal: Examination of cones on kiln-opening to verify controller operation. Consider the cone on the left: The tip is touching. But it is also beginning to buckle, which means it was touching for a while before the firing ended. Who knows how long! The second one is not touching but has still fallen a little too far. Why do we say that? The third one, positioned on the Orton guide, has reached the recommended 90 degrees. This demonstrates a good reason why self-supporting cones are much better than standard ones: They are not touching when considered done. And standard cones, when sent in a 3/4" plaque, have a less consistent bending behaviour.

Are you using your expensive kiln like a pop-up toaster?

A small controller-equipment kiln and views of programming it

Put the pots in, select a cone, press start. It is time to rethink that approach! The Bartlett Genesis kiln controller is standard equipment on hobby and production electric kilns now. It is not meant to be run like a toaster! Good glazes are about much more than recipes, they are about firing schedules. None of the built-in "toaster schedules" have hold times on any segments, drop-and-hold sequences or controlled cools. Or even fire-to-cone accuracy. Yet such are a must for defect-free glazes, enhancing the effects of reactive glazes that must develop crystallization or variegation or firing accurately. It is easy to program: Tap the blue edit button to edit a program, tap a column of any segment to edit its value. Tap a segment number to delete or duplicate it. Search "bartlett genesis controller" on YouTube for videos on creating and editing a schedule.

Links

Firing Schedules	Plainsman Low Temperature Drop-and-hold Five-step to 1940F, short hold, drop-and-hold, free-fall
Firing Schedules	Plainsman Electric Bisque Firing Schedule Three-step to 1832F
Firing Schedules	Low Temperature Drop-and-Hold
Firing Schedules	Cone 03 Fast Fire
Firing Schedules	Plainsman Cone 6 Electric Standard Used in the Plainsman lab to fire clay test bars in our small kilns
Firing Schedules	Cone 6 Drop-and-Soak Firing Schedule 350F/hr to 2100F, 108/hr to 2200, hold 10 minutes, freefall to 2100, hold 30 minutes, free fall
Firing Schedules	Plainsman Cone 6 Slow Cool 350F/hr to 2100F, 108/hr to 2200, hold 10 minutes, fastdrop to 2100, hold 30 minutes, 150/hr to 1400
Glossary	Firing Schedule Designing a good kiln firing schedule for your ware is a very important, and often overlooked factor for obtained successful firings.
Glossary	Kiln Controller In ceramic kilns the firing schedule is typically managed automatically by an electronic controller. But that may not mean that ware gets automatically fired to the correct temperature and atmosphere.
Glossary	Pyrometric Cone Cones are ceramic and bend through a narrow temperature range. They used to be actively used to determine when firings were completed but now are used to calibrate electronic devices.

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