Monday, March 29, 2010

Firing Log

Note: I will be updating the firing log throughout the day as the kiln fires.

6:30 a.m. It's just getting light and it's raining. Kristin and I (still in my p.j.s) head out to the kiln studio to light the kiln. Kristin has his camera with plans to make a video of the firing process. I place the cone packs in position in the kiln. Using a candle and a book of matches I light the "ring of fire" that lights the eight burners under the kiln. The burners will not stay lit. After several attempts we notice the thermocouple for the safety shutoff is out of place. Even after repositioning the thermocouple, the burners will not stay lit. After consulting with Mr. Dirtywrench we determine to replace the thermocouple but have to wait until the hardware store opens at 8:00 a.m.

8:12 a.m. Kristin returns from the hardware with a new thermocouple. He installs it for me (what a good son!) and I attempt to light the burners again. The wet breeze from the hard steady rain extinguishes every match. Finally, with my very last match, my candle stays lit and I light the ring of fire again. With a whoosh, the burners softly pop with flame. I wait a few seconds and let go of the safety switch....success!! The burners stay lit. I adjust the propane gas pressure as low as I can make it, prop the kiln door open and let the kiln warm slowly for an hour. With this late start it's going to be a long day and a late night.

12:30 p.m. This firing isn't starting out very well. After shutting the door and slowly warming the kiln to take it easy on the cold kiln bricks and furniture, I turned up the gas at 10:30. By 12:30 I was still only at 500 degrees F which was no change in an hour. I should be getting a 200 degree increase per hour. What in the world is going on? I don't know if it is the weather or something with the gas or what. I turned up the fuel gauge again and the temp jumped 60 degrees in five minutes. I had to back it down because we don't want to go too fast.

It's a rainy day and I've been told the barometric pressure on a rainy day is right for a good reduction firing. My experience is that the best firing I've ever done was last summer on a clear, sunny July day. I'm so ignorant and inexperienced that these things really frustrate me. At the rate this firing is going I'll be up with it until 2:00 a.m.

7:30 p.m. Finally, the temperature has reached 1600 degrees F, the first cone in the pack is down and the kiln is ready for body reduction. At this point I slightly close the damper on the flue to restrict the air going into the kiln. This air reduction causes the fuel to be starved for oxygen and to look for it elsewhere. The atmosphere inside the kiln begins to build pressure and to draw oxygen molecules out of the clay bodies and glazes. Drawing oxygen out causes color changes in the clay and glazes. For instance, a reduction atmosphere changes copper from green (oxidized) to red (reduced).

The firing is a good three hours behind the usual schedule. Two hours are due to the delay this morning, the other hour due to a really slow advance of temperature all afternoon. At this rate there is no doubt this firing won't reach final temperature until 3 a.m.

Not happy about that.

1 comment:

  1. For some reason I haven't been getting your posts in my reader. Hmmm. I'm catching up on lunch break.


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