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Posted by Brad Sondahl on May 24, 2007, 8:39 pm
Please log in for more thread options seasa42@yahoo.com wrote:
> I have been having a lot of cracking/pinging in some of my bisque
> ware, and I am wondering if anyone has advice on what rate I should
> ramp down. I am firing in a gas kiln, 4 burners, and it's about 8
> cubic feet. I am doing cone 05 for bisque, to then fire to cone 5,
> and using Laguna B-mix, no sand, and also Hagi porcelain. In the
> trouble shooting notes about the clay, they say one reason for cracks
> can be from cooling down to fast, what isn't there is any advice on
> how to go about the cool down. I usually don't control the cool down,
> I just let the kiln sitter trip, and maybe damper down.
>
> What I plan to do with my next bisque fire is put a higher bar in the
> kiln sitter, a cone 06, keep my eye on the witness cones that will be
> cone 04 & 05, then when cone 05 bends I will turn down the kiln, not
> turn it off. My question is, about how much should I lower the temp,
> and in what sorta time increments?
> Thanks
> Sa
>
Well, first, the cones with a 0 on it get hotter in reverse of how
you're suggesting--Cone 06 is cooler than cone 05. When you rise above
cone 01 it switches to the way that makes sense...
With a gas kiln, dampering down is essential for cooling, as the draft
would shock pots going through the quartz inversion temperature. You
shouldn't have to fire down, but you might have to block both input and
exhaust areas to keep it from cooling too fast. I think that's probably
the reason most folks bisque with electricity...
Brad Sondahl
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