[Clayart] Thanks all for bisque info

Snail Scott claywork at flying-snail.com
Tue Feb 11 10:06:38 EST 2020

> On Feb 10, 2020, at 1:13 PM, carol at knighten.org wrote:
> ...Specially thanks to Snail on the lack of need for the slow down during the
> quartz/cristobalite inversions.  That had always seemed like voodoo to me, yet
> I hadn't sufficient data to ignore it…

In the name of strict accuracy, I don’t really have data in any legitimate statistical sense, either; just a lot of anecdotal data points assembled into a working hypothesis in my squishy brain, with no identifiable analytical methodology.  It does seem to dovetail with what I read about fired silicates, though - crystobalite seems to be a non-issue unless you are firing around ^10 with a highly vitrified clay body.  So, firing up = no issue at any temp.  Cooling = possible issues with highly vitrified high-fire work, but not with lower firings such as bisque, earthenware, or even mid-range stoneware and so-called ‘mid-range porcelains’.  

My basic philosophy of oxidation firing: Candling is critical, soaking is frequently useful, and everything in between is actually pretty adaptable.

I agree wth Mel’s view that an extended time frame in the early-to-middle phases of firing is mostly a waste of fuel, but I don’t think that the minimal heat output of a long candling is a big issue - it’s only 190F/90C, after all. 

I will happily yield this mental model of the process to any better-substantiated version.  Carol, your research on ceramic chemistry is a delight, and a pillar of this list!


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