Thursday, November 22, 2012

Test firing!

            The first firing of the kiln was successful! I had a lot of fun playing with the controller to practice programming it. The controller is very easy to operate, and I feel that even if I were to lose the manual I would be able to program the kiln to do what I want just fine. The controller has two "modes," one where you can choose a pre-programmed firing schedule, and one where you can program your own firing schedule. For the test firing, I went with a pre-programmed cone 6 firing. This is what cone a normal glaze firing would be for the clay I'm using.
            I was fairly satisfied with the test firing. One thing I was a little worried about for the first firing was that the kiln draws a lot of power, and the house has an old electrical setup, and thus not a whole lot of power available. I was not sure prior to the first firing how using power in the house would be affected by the firing of the kiln. The lights do dim whenever the elements switch on, so there's a sort of flickering effect throughout the firing, but it's not severe enough to be worrisome. At some point in the future I might get the electrical service to the house upgraded, especially if I want a bigger kiln, but for now it's fine. 
            I used pyrometric cones to check on how the kiln fires. I used cones 5, 6, and 7, since I was aiming for cone 6. The thing about cones is that they don't just melt at a certain temperature, but rather once they've absorbed a certain amount of heat. (Yes, these two things are different, for the uninitiated.) So the kiln can fire to a certain temperature according to the pyrometer, yet not bend the cone for that temperature. The opposite happened in my test firing: it seems to have been pretty solidly a cone 7 firing, despite that the final temperature reached was within "cone 6" range. (This is not terribly unusual. The kilns I used at Simon's Rock often over fire by a cone, or at least they did when I was there.) 
            So I don't think I want to use that firing program when I actually have glazed work in the kiln. It probably wouldn't have horrible effects, but the clay and glazes I'm using are formulated for cone 5/6, so over firing them is less than ideal. The clay should be fine, but the glazes will likely be a bit runny at cone 7. There are a few things I could change to fix the problem, but I think the easiest one is to make my own program, and ask it to fire to cone 5 instead of cone 6. If it really does fire to cone 5, that's fine, and if it fires to cone 6 we'll still be good to go. 

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