Saturday, May 28, 2011

My First Woodfire

If you’ve read more than one entry in this blog, or know me at all, you know that I didn’t just do my first woodfire. But in a way I did. I called the shots for the first time instead of just doing what I was told. Carol and I (finally!) rented MHCC’s Little Woody kiln, and fired it for about 15 hours.

Little Woody is a small, downdraft wood kiln. It held about...40 cubic feet (?) of work, and regularly fires easily in 12 hours. We took a few extra hours because we had the time and the wood, and didn’t really know what we were doing.

So...the firing actually went pretty well, but I didn’t realize it at the time. We got cone 11 down and 12 soft all around. Our cone packs were almost identical front to back, and pretty close top to bottom. We candled with gas overnight (felt a bit like cheating, but that’s how they do it there), and started with wood at 5:30 am. Once we started stoking, we let the kiln take off and gained 300-400 degrees F per hour until we got cone 010 down, did some body reduction, and kept cranking.

Around noon we had our first mishap. Four bricks from the bag wall and into the fire box (the bag wall is a brick screen separating the fire box from the pots, which helps direct the flame up and over instead of letting it short-cut through to the chimney). We were lucky that they fell away from the pots. We didn’t know whether we had inadvertently caused damage to the kiln, and weren’t sure how the large hole in the bag wall would affect our firing, so the fall really put a damper on our moods.

All was well for the next hour or two, and we still felt like we were gaining temperature well. We had pyrometers at the top and bottom of the ware chamber, and for the first several hours the temperature at the top and bottom was within 50 or so degrees. After the bag wall fell, the gap widened, and the variation in the bottom temperature with each stoke became more pronounced. Suspecting that this had to do with the gaping hole, I suggested that we stop looking at the bottom pyrometer, and judge the temperature variation by the comes, which were falling within about a half-hour of each other, indicating that the kiln was fairly even. We continued to increase in temperature, though less steadily and with more effort until we reached about 2200 degrees F.

We had planned to stop firing at about 6:30. We were supposed to be off campus by 7pm, and had left ourselves plenty of time. But around 5pm, the kiln stalled out. We were stuck at 2200 and unable to get any hotter. We opened this and closed that, increased the size of our stokes, decreased the size... tried everything we could to get the temperature to raise. Cone 10 was down and 11 was slightly soft, so we knew we had gotten up to temperature for a while at least. My main concern was whether we could end at a hot enough temperature to avoid crusty unmelted ash on the pots. Cone 11 had been slightly soft for hours, and the fact that it wasn’t moving any farther made me think we’d cooled off too much. I was determined not to stop firing until I got it to move even a hair more.

We hit 2300 (according to the pyro), but I couldn’t hold it for more than a stoke. Around 8pm I decided the next stoke would be the last, no matter what, but I over did it and the temperature plunged. Finally, at 9pm, after holding around 2250-2290 for about two hours, we called it a night and closed up the kiln even though cone 11 on the top never moved beyond slightly soft.

Two days later we opened the kiln. I had nightmares the night before about crusty, ashy pots and unusable bowls. Much to my surprise, the pots were perfectly smooth. That stubborn top cone 11 had melted into a perfect arch and 12 even softened slightly. The ash was amazing--some lovely green drips.

We learned three major lessons from the firing:
1) More body reduction! We both knew we needed to do a body reduction at cone 010, but didn’t know how long it should last. Funny the things you pick up from firings, and the things that slip through the cracks. Our shino glazed pots were white, and the iron-rich clays that should have been dark brown and burgundy were toasty. We got some beautiful colors, but not the richness that we would have had if we’d reduced for longer.

2) Don’t rely on pyrometers. We knew this--everyone says to use them to get an idea of whether your temperature is rising or falling, but not as an absolute number. Everyone says it, but no one does it.

3) Two people can fire a kiln for 15 hours, but it’s a lot of work! We probably could have planned better. One of us could have started the firing at 5:30am, traded off in the late morning, and worked together in the afternoon, once the stoking got more intense. This time we both wanted to be involved all the way through, but next time we could probably arrange shifts for the first half of the day. Or add a third person and take even longer breaks. I think we would have been more successful at the end (had more energy left to experiment) if we hadn’t been so tired.

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