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cone advice -- asap thank you!

updated tue 7 oct 08


Nan Rothwell on mon 6 oct 08

THANKS! one and all, for your timely response to my question about re-firing
stoneware cones that had gotten to about cone 02 before shutting down the
kiln. The consensus of opinion is that I should be fine to light up again
without replacing the cone pads. Had I had to stop a lot earlier, I might
have had problems with dunting or cracking. (I didn't mention this in my
first note, but this is a raw firing.)

One person suggested that since it is a salt kiln, the cones are "worthless"
since the salt melts them early and they lose their predictive value. I was
told this thirty five years ago, when I first started firing salt. So I
initially ran some tests, with cones out in the full salt atmosphere and
saggered cones right next to them. In those tests, there was about a half
cone differential. With nine was flat, ten over and eleven up but soft in
the exposed cones, nine was flat and ten bending but not over and eleven up
in the sheltered cones. While it was true that the lidded pots I was
sheltering them in allowed a tiny amount of salt in, due to the lids being
wadded, I felt that the interior of the pot and clay on the cone pads were
virtually unaffected by the kiln atmosphere. So ever since then, I have
used cones in salt kilns with the intuitive understanding that they were
reading about a half cone off.

During salt firings, I occasionally fire stoneware glazed pieces in deep
narrow planters with glazes that I know fairly well from my reduction kiln.
The top half of the pot is affected by the salt, but the glaze on bottom
saggered section behaves behave the way I expect it to during a mature but
slightly cool firing. (If you want to try this, Shaner Red will give you a
lovely continuum between mustard gold on top, where it gets the salt, and
regular rust red at the bottom -- great Southwest color range.)

Again, thanks everyone for your advice. Now, if we can just get the kiln
working again today, I will proceed apace. I will report back on results.


Nan Rothwell
221 Pottery Lane
Faber VA 22938

Vince Pitelka on mon 6 oct 08

Nan Rothwell wrote:
"So ever since then, I have used cones in salt kilns with the intuitive
understanding that they were
reading about a half cone off."

Nan -
Whoever told you that cones are worthless in a salt firing doesn't know what
they are talking about, and one of the risks of any discussion lists is
people who dispense information with an air of confidence when they in fact
are clueless. You hit it right-on - in an average salt firing the cones
read about a half cone off. It's easy to compensate for that, and otherwise
cones work fine in salt and soda firings. And of course the degree to which
the cones are off will depend on how heavily you salt or charge soda, and
you can only establish that by doing the kind of testing that you did. I
soda fire pretty lightly, and my cones read accurately.
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University;