Firing the Wood Kiln at the NCC East 40, Part II

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The burn ban was finally lifted, and on December 18 we finally began the firing. The two anagama firings I did in August and October went on for 5-6 days; but this firing was scheduled to be completed in just over 24 hours. To get the work “fully cooked” meant that we had to actually reach higher temperatures in the kiln than would be the case if we were firing over many days. The cones behind the removable bricks were our only way we could be sure when the work in the kiln was fully “cooked.” The heatwork needed to achieve cone 10, our goal, is considered to be 2,381 degrees. That level of heatwork can be reached by more time at over 2,100 degrees, but for a one day firing we were going to need all 2,381 degrees to get cone 10 to bend over.

Gabby Gentile and Connor McGaughran (my student worker at ESU) had been there since 2 in the afternoon, and stayed with me well past their points of exhaustion until after Dave Graham (Kiln Building Guru) was able to join me. With two fireboxes needing to be stoked every few minutes, this was a skeleton crew. It was after midnight that Gabby and Connor finally went home, and it was just Dave and I for the rest of the night, until the end of the firing the next morning. I took the left firebox, and Dave the right. It’s crazy how kilns have a personality, and how two fireboxes that should be identical, one right next to the other, can behave so differently. The left side of the kiln runs colder, the coals don’t burn down to ash fast enough, so the left firebox can get so choked with coals that it restricts the needed airflow on that side. How much, what size and what kind of wood to put in, and when, are decisions that are constantly being made. You don’t just chuck wood into the kiln and hope it works; this too is an art. Pine combusts faster, but doesn’t have the staying power of hard wood, it’s kind of like a sugar high, you either feed soft wood constantly or it can crash. Hard wood can actually make the temperature drop while it’s trying to combust. Likewise, the thinner the wood is cut, the faster it catches fire-and burns out. Getting the right mix of types and sizes of wood, how much room you leave open in the firebox, how often you stoke-all this has to be right, or the kiln will let you know. There’s a wonderful “roar” when a kiln is really hot, and it’s happily digesting just the right amount of wood.

Sunrise at the East 40-one of the perks of doing all-nighter's at the kiln is getting to see the sunrise

The night was beautiful. It would have been cold being out all night like that, but the kiln generated so much heat that being so close, I didn’t need most of the layers of clothing I had brought. The wind was going in the right direction, I think it actually helped us. Pyrometers that measure the air temperature in the kiln are not terribly accurate at the higher temperatures, but they do let us know if the kiln is getting hotter or cooler, which is critical information for figuring out when to stoke for example. As the kiln heats up, everything wants to expand. I’m glad Dave was there when one of the steel tie rods holding the kiln together popped under the pressure! Wow, that made me jump. He had just replaced the tie rod above the one that broke, and assured me it would be fine. You could see the other tie rods bow with the pressure the kiln was exerting as it expanded, but they held. Even if we hadn’t had the pyrometers, as in olden times, you can really tell when a kiln gets up to those higher temperatures well in excess of two thousand degrees! At 9 something in the morning, Cone 10 had made it’s perfect arc on the top right, and both cone 10 and 11 weirdly were bending together on the bottom left; we got to our goal. ​

Once we reached our cone 10 goal, we stuffed the fireboxes as full as we could get them, then shut off all access of air to the kiln. Kilns go crazy when you do this! Any tiny sliver of space, around a brick, around a door, the flame tries to reach out, gasping for oxygen. That’s when you walk around the kiln-any gaps anywhere become really obvious with flame shooting out of them! The “door” of the kiln is temporary, rebuilt for every firing, so flames shooting out from there are not a problem. But if places that should be tight open up, this is when you find them. The fire just burns itself out, smothers-then you have to wait, and wait, for it to cool down. The bigger the kiln, the better insulated it is, the longer it takes. This post is already way too long, so you have to look at my next post for the unloading!