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Saturday, January 28, 2012

Fire is Life - The Firing Part II

[continued from Part I]

I wondered how my fourteen hour 'soak' had progressed. It's been cold this winter, though I had left the studio heat off. An overnight soak with pilots on would put the kiln comfortably above boiling temperature . . . safe to take bisqued glazed work up rapidly into a firing zone.

Sure enough the soak had progressed. The top thermocouple read 300 degrees, the bottom was cooler by a factor.

There was little to do but check positions of the switches on the main controller and press "Run". The board cycled through the program I had entered, asking the main burners to bring the kiln to the impossible temperature of 2375 in less than a minute. It would hold gas on until that shutoff point was reached, thus allowing me to manually control the firing.

The counter flickered through the numbers, and as soon as the 'call for gas' temp crossed the temperature of the upper thermocouple, the main burners came on with a bang of both solenoids.

I carefully trimmed the gas down to 1/2" of water column, set the burner blowers at 40 cfm, and let her rip. The time was 6:00 PM.

It's a joyous part of the firing. No need to be slow. All the ware within was bisqued, and fully dry. The task was to get hot rapidly, but not crazily so. The kiln wants a reasonable rate of rise, around 250 degrees per hour.

I turned my attention to some cleanup detail. Made a cup of tea, drank it.   . .

And realized . .  once again . . . I had a good five or six hour wait on my hands!

At about 9PM I heard a loud bang. What was that?

Impossible to tell. I looked through my burner ports. The cones all seemed to be in place. I could see them all, though the ones on the top seemed a bit higher than usual.

Probably nothing at all. It possibly was my neighbor in the building, walking out, and slamming his metal door behind him.

If it was something in the kiln there was no sign whatsoever of a problem.

I read. Wrote. Made more tea. The fire hissed and purred, a happy Felix.

I napped, checking first that my CO meter was plugged in reading properly.

At 11:00 PM I had a quick look at my cones. Damm Cone 010 was nearly down, time to go into reduction. I whittled the blower air down by 25%, and increased main gas pressure significantly.

The kiln became quieter. The flame from the top turned a lovely transparent orange.

For the next five hours I managed the temperature upwards, cutting back on the reduction ever so slightly every half hour or so, tweaking this, tweaking that. The kiln was behaving much much better. Yes more improvements could be made. I noticed a few problems with the air blowers, and the burner air intake vents wouldn't hold solidly in position. I rigged them with some tape.

I kept awake by taking temperature readings every 15 minutes. It's crazy, manic, and obsessed. But I needed to stay awake.

At five in the morning I was starting to feel really exhausted. This was the point when Charles Lindberg's little monoplane crosses over Ireland. He has hours of flying left to do. He can hardly keep his hands on the controls.

This firing was almost done.

I checked my cones. The top spyhole spewed a smokey flame powerful enough the singe hair from the top of my head. Where's that hairdryer? Damm I forgot it. I read the cones by blowing into the kiln. It works, . . very briefly. Cone 9 was solidly down on top. Cone 10 hadn't moved. On the bottom Cone 10 was nearly down.

I've learned that with my glazes a firing anywhere from Cone 9 to 10 was fine.

I busied myself with preparations for shutdown. Bits of ceramic to plug up the burner ports. I kept checking the cones . . . but suddenly an inner voice said, "Shut her down."

One has to listen to the voice within. In yoga it's called the 'Teacher Within'. You bow to it at the end of practice. In pottery, work, love, flying airplanes, wherever, it can guide you. Preparations, more than anything else, clear the way for hearing that voice. It will tell you things you need to know.

I shut the kiln off. The room became quiet. The kiln pulsed heat. Cracks from the burner ports showed the temperature, a light yellow heat. My studio heater hadn't been on for two days. I was in my shirtsleeves, sweating.

I plugged the air intakes with ceramic bits, and all the spy holes and side plugs with their pieces of carved kiln brick.

I slid shut the two upper vents, two small kiln shelves that closed off the exit flue at the top.

I murmured another small prayer . . and went home to sleep.


A high-fire kiln dehydrates effect the whole system. The only similarity I can think of is a long day's work in front of old style movie lights. I did plenty of that in my younger days as a gaffer's assistant. Those tungsten bulbs were hot. They suck moisture out of you the way a scale insect drinks sap from a flowering plant.

A bath. Plenty of oil on the skin. Around six that evening I mustered the energy to go back and see how things were cooling.

Not quickly!! Another good sign. The kiln was holding heat well. Still could be better. After thirteen hours the temperature on top was still over 900 degrees.

Home again.

I'll just let a good long time go by, and then go over to open it tomorrow. The hardest thing to do is wait while a kiln is cooling. One day I'll learn to turn my attention to other things, throwing or handbuilding. But I simply cannot. The kiln commands the attention. So if I'm better off leaving it to cool on it's own.


Another daybreak. I decided not to rush going over. I did errands, vacuumed the house. At around noon I took the car over and entered the studio.

260 degrees!

Slowly and carefully I loosened the clamps holding the kiln door shut and gently cracked the door. No noises, no sounds. All good. A collapse could have fallen against the door, and welded itself there. But then  . .  I'd never experienced a collapse or failure of any kiln shelves or furniture.

There's always a first time:

I looked at the arrangement of shelves and ware, in disbelief not disappointment. There had indeed been a collapse. Of sorts.

Yet, little seemed to be damaged. I removed pieces one at a time. The easy ones to get at first, those likely to be crushed if all the shelves went at once.

It was impossible to see what had happened. Somewhere on the left, a set of posts which I was sure I had seated well had given way. But why? Not a trace of evidence.

But what had taken up the load? What had saved me?

Well for one thing the set of posts which I slipped in front as a last minute precaution were doing their job! Glad I did that!

And then, on the left, that little sculpture of the man with his arms over his head, was actually jammed in! He was taking some of the weight, Incredible!

Gently I slipped another set of posts in his place. He popped out into my hands undamaged.

I remembered my poem . . "Some experiments, some accidents . . "

A few of the pieces were beautiful. Temokus broke to a deep red. Shinos turned out well too. Some bowls made by a friend were slightly oxidized, but softly so, and very lovely.

A very few pieces had slid into each other and welded together, but came apart easily without breaking into the clay body.

Not 100% success. . . but a start. The new kiln had performed. Glazes all on track. I anticipated the next firing.

I emptied the entire kiln emptied except for a few wares at the bottom rear. As I reached for the top shelf the whole structure gave way.

I never did find out which bit of ceramic post had failed, cracked or slipped.

One bowl at the very rear bottom was broken by the final collapse. The kiln gods had been paid.

I felt lucky, blessed. Things go wrong, it's a rite of passage. Auspicious it was too.

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