bisque cool down schedule

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

Reply to
seasa42
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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

Reply to
Brad Sondahl

Reply to
Sam Kelly

I have an old potter friend who goes by the rule "If it is too hot to hold, it is too hot to take out."

That means wait until around 20-30 Deg Celcius - especially with glazed stuff, I suppose.

Anyway, being patient with kilns has resulted in me having very few problems with cracking and such.

Marianne

Reply to
Bubbles_

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