Sunday, March 29, 2015
Fast and Easy
Um. I guess I thought the fastest and easiest was the one everybody already knows?
None of that has anything to do with this post.
I just wanted to say, this firing - the one that went off an hour and a half ago - was the fastest and most even firing I've done in this kiln. It was a ^10 firing - the ^6 ones are quicker, of course - and it took 11 hours. I candled overnight, but started turning the burners up around 7 AM, and it went off at 6 pm. That has never happened before!
I just changed one tiny little thing.
It's always scary to change something about the way you fire, if you have a way that works reasonably well, because if you try to improve on it, you can make it MUCH worse. And then you've lost a month's worth of work, because you just had to go experimenting!
In this case, this kiln has always fired unevenly - hotter on one side than the other. At first blush, you might say, Well, duh. It's got two burners on one side, and only one on the other. I guess that could be it, but it's a pretty small kiln - maybe 22 cf - and I have fired many kilns with two burners at the back and none at the front, and those can be perfectly even. So I was never completely satisfied with that explanation, but I didn't care that much, because the kiln was giving me good pots.
Not sure what possessed me to try and change it this time. I knew the kiln on the one-burner side always had much heavier back pressure, and I knew that a reducing lame produces less heat than an oxidizing flame, and this effect becomes more pronounced the heavier the reduction. The primary air was already all the way open, and I couldn't easily change the secondary air - the ports are hardbrick. But just today, I thought: the soda port.
My ports are low, so I can dump the soda mix right into the burner channel. Maybe low enough, I thought, to serve as a kind of secondary secondary air. Tertiary air?
Just pulling the brick didn't work; that side of the kiln lost all back pressure. Instead I found a fraction of brick and blocked a little less than half the port.
Oh, I lied. I said I only changed one thing but I just remembered I changed another. I started to wonder if I could manipulate the flow of air into the kiln using the passive damper. Not just control how much, but where. So I blocked just a couple of inches far to the cool side of the damper.
Not sure if one or both of these adjustments was responsible, but the kiln climbed quickly and evenly right up through ^8. Got a little uneven after that, but not out of hand. I drew a line to indicate the position of the damper, and the brick blocking the passive, so I can find the sweet spot again.
Unloading this kiln on Wednesday.