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firing fast/heat work/cristobalite?

updated thu 17 jul 03


Barry Salaberry on tue 15 jul 03

I guess the heat work is accomplished, since that's what the cone is =
telling us when it bends...

But, when the 'fast up, quick cool, hold to reduce' method is used, does =
the potter with a given

suite of glazes find that they fit as well?

Don't the free silica particles need time to convert to cristobalite, so =
that they will then

shrink enough on cooling to put the rigid glaze under compression?

Is this accomplished in the cool and hold zone, or is this too to be =
thrown out with the bath?

You have blown ideas out of my water by getting copper reds with a late =
reduction, after the glazes

are melted, at a time when I thought it was too late to affect colour.

I had always thought that Hank was using that technique in oxidation....

This is threshold work, to be sure.

But will it, perhaps, require re-tooling the glaze family or clay body =
to account for any=20

aberration in the cristobalite formation rate?

Thanks for being so open about your adventures, and encouraging all of =
us to test=20

the waters of new experience.


where I just witnessed "my" first-ever gladiolus come into bloom, with =
red lace around white centres,=20

just like a string of can-can skirts on a stem. Wow!

Bonnie Staffel on wed 16 jul 03

Hi Clayarters,

Way back in the 50's I experimented with reduction of copper on cooling
starting at 1500 deg. F. to the best of my recollection. There were not
many resources for glazing and firing for me in those days, but think I
gleaned this information from Carlton Ball's experiments. I fired these in
my electric kiln normally up to Cone 04, cooled to 1500 and introduced
combustible materials into the kiln until it reached 1000 deg. Got the most
beautiful copper reds, sometimes a luster with this method. Never thought
that it would work with high fire so never tried it. I didn't like the
crazing at this low fire, so bisque fired the porcelain to Cone 9, heated
the objects and dipped in the Cone 04 glaze plus spraying to get a heavier
coating. Wonderful results with no crazing. I believe I related this
process before.

Regards, Bonnie Staffel of Charlevoix, MI.