It's been a day of trying to recharge my battery after an 18 hour day firing the soda kiln. It was a struggle to get it to fire evenly with the the new T shaped bag wall and smaller flues. I know this works well with normal downdrafts; but it definitely did not work well with the hard brick cross draft. The early part of the firing went fine, pretty even for a cross draft; but once I had to up the power I could not get the top hot enough no matter what I did - burner adjustment, active and passive damper adjustments, etc.etc. Even turning off the front burner and upping the others only made the bottom hotter. It did give me one top hot spot on one side at the back of the kiln. Then one of the thermocouples on my double fluke digital pyrometer stopped working - for hours, so I had to dig through cabinets to find a possible replacement and get it hooked up . Needless to stay it was a bit of a frustrating day, ending with me stepping on and breaking the wand on my best sprayers (the one with the power pack that you don't have to manually pump).
Because of the bag wall and flue changes, I put a lot more cones throughout the kiln. It's going to be an interesting unloading!
At one point I seriously considered aborting the firing but the thought of un-bricking and emptying the kiln, re-doing the bag wall, opening the flues,reloading and re-firing was a more dismal prospect than trying to baby this it with the hope of getting it hot enough in some areas without getting too hot in others to save the firing. I know I reached cone 12 in a couple of spots, cone 10 in others and cone 9 only starting in at least one spot - crazy.
I turned the kiln off at 11 o'clock after only doing a couple of rounds of spraying and throwing in about a pound and a half of salt burritos. Between the glitches, a bad headache, strained back, and rushing the time between spraying to end my misery, I'm hoping for the best. My liner glazes have a pretty wide firing range, so I'm hoping for the best. The draw rings showed some gloss which should be fine since I don't aim for heavy salting; and adding 1/2 lb more salt than my usual one pound addition was my frantic attempt to just get the firing over with without straining my back any further.
It's time to start seriously looking at cone 6 soda in these twilight years as well as scaling down this kiln a bit which should make for more even firing.
Sounds like a lovely day. I think I would have been making sledge hammer "adjustments" by the time it was over.
ReplyDeleteGood thing I didn't have one handy or I might have used it! LOL
ReplyDeletejune,
ReplyDeletei didnt want to be a pooper when i saw your previous blog post, but suspected that crazy bagwall setting was going to mess up your firing.
I try not to interfere with folks ideas. Sorry i couldnt be present to help with the thermocouple but assume it worked out? I would reset the bagwall and maybe leave the flues blocked and try that too, kyle has really small flues and his kiln fires fairly even. call if you want help.
shane
Shane, last firing I had the old bagwall and reduced flues(but they were reduced a bit more than this time); and I had the same screwy temperature variations, so I think with this kiln it may be the flues and the T bag wall that Mel Jacobsen recommends and uses on his kilns (which work fine on those kilns). Is Kyles kiln a crossdraft? On another note, I'd like to scale this kiln down and Jim would like a few inches off the front to fit a new car and I'd like to redo the whole catenary arch shape to make it less tall, thereby making the kiln closer to square and a bit smaller. Give me a call or come over and join us for a glass of wine and we can talk about it.
ReplyDeleteBoy, June, I can see by your last comment, that you're up early! You deserved to sleep in after a firing like that!
ReplyDeleteI'm trying to make the shift from ^10 to ^6 reduction (no soda since my kiln is indoors). The firings use so much less gas and are around 2-3 hours shorter. Plus I can open the kiln sooner! Check out Ronan Kyle Peterson's blog post http://ninetoespottery.blogspot.com/2010/07/cone-6-soda-pics.html I'd love to see and read about how you make the transition.
Thanks for the link Karl. John Britt did a cone 6 soda test firing with soda but now borax.I had a lot of tests in that firing and even without the added borax to help at that lower temperature, I got an idea of which flashing slips may work best. I'll refire them with soda/salt and some borax to get a truer idea of how they'll perform in the cone 6-7 range.I have a small Olympic gas kiln and I think once the TRAC tour and holidays are over, I'll use that to do some more cone 6 tests. I already tested a lot of cone 6 in straight oxidation firings, so I have somewhere to start. From doing a bit of earlier research, one person who does lower salt/soda firings said that cone 7 actually works better than 6, so I'll probably aim for that and adjust glazes accordingly. I like the idea of shortening the fire a few hours, saving gas and saving my own energy.
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