Bert Gibson on tue 29 apr 03
At the community college where I take a Continuing Education class in =
pottery, they fire the gas reduction kiln to cone 10. I glaze my pots =
the same inside and out, usually complete coverage of one glaze over =
another. A significant portion of the time the pots do what I expected =
on the inside, but not what I expected on the outside. I was guessing =
that the inside got to temperature and the outside of the pot didn't, =
but that is just a guess derived from looking at the results on the pots =
and no technical knowledge. I was wondering if someone could explain the =
technical aspects of these results to someone who always wants to know =
"why" ?
Thanks,
Bert Gibson
Snail Scott on tue 29 apr 03
At 08:30 AM 4/29/03 -0500, you wrote:
> I glaze my pots the same inside and out...A significant portion of the
time the pots do what I expected on the inside, but not what I expected on
the outside.
In addition to the temperature aspects, I have noticed
that insides of forms that are semi-closed seem to
hold a slightly reducing atmosphere (even in an
'oxidizing' or neutral firing), due apparently to the
burnout of combustibles in the clay and glaze materials.
This effect is sometimes visible with unglazed reddish
clays, where the ambiguous results of glazing are not
a factor. Can anyone else confirm this observation?
-Snail
Michelle Lowe on tue 29 apr 03
I have seen semi closed forms that have a copper red glaze, with a gorgeous red inside and the green/glassy clear of un-reduced Cu Red on the outside. Seems confirmation of this phenomenon.
Mish
>In addition to the temperature aspects, I have noticed
>that insides of forms that are semi-closed seem to
>hold a slightly reducing atmosphere (even in an
>'oxidizing' or neutral firing), due apparently to the
>burnout of combustibles in the clay and glaze materials.
>This effect is sometimes visible with unglazed reddish
>clays, where the ambiguous results of glazing are not
>a factor. Can anyone else confirm this observation?
-----------
Michelle Lowe potter in the Phoenix desert
http://www.desertdragonpottery.com
Mishy@desertdragonpottery.com
mishlowe@amug.org
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Lily Krakowski on wed 30 apr 03
A vague yes. The inside of pots tends to mature better than the outside.
There are several theories about why, I have never investigated. Inside
tends to get hotter? Inside cools more slowly? The fumes generated tend to
stick around longer inside?
It also sometimes is, especially when one pours, that the inside is coated
more heavily with glaze than the outside. How come? Because the moisture
from the inside glazing , done first, makes the outside less absorbent,
hence the glaze goes on thinner. Try allowing a half hour between inside
and outside glazing...just to check.
Bert Gibson writes:
> At the community college where I take a Continuing Education class in pottery, they fire the gas reduction kiln to cone 10. I glaze my pots the same inside and out, usually complete coverage of one glaze over another. A significant portion of the time the pots do what I expected on the inside, but not what I expected on the outside. I was guessing that the inside got to temperature and the outside of the pot didn't, but that is just a guess derived from looking at the results on the pots and no technical knowledge. I was wondering if someone could explain the technical aspects of these results to someone who always wants to know "why" ?
>
> Thanks,
>
> Bert Gibson
>
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Lili Krakowski
P.O. Box #1
Constableville, N.Y.
(315) 942-5916/ 397-2389
Be of good courage....
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