Kyle Carpenter on wed 5 feb 03
i've been reading in a few books on salt firing. I've read that many people
crash cool their kiln until cone 010, then seal it up. i, personally, seal
it up as soon as i shut the gas down.
question: what are the pros and cons to crash cooling, specifically with a
salt kiln. **besides the fact you can open the kiln earlier :) **
kyle
Marcia Selsor on wed 5 feb 03
Kyle,
I haven't done this in a while but we used to crash cool always. The
colors came out oxidized rather than sewer pipe brown. This fall I was
at the Bray and everyone there was using lots of glaze and slips and
fired with an oxidized flame. -lots of air. I never used much glaze when
I use to salt fire. Anyway, we began using soda ash instead of salt.The
basic difference in the crash cooling is brighter color and less browns
more grays if your stoneware tends to go brown. If you are using a light
claybody, I can't see much advantage. We tore the bricks down about 5
levels after the last of the salting was done. then resealed after the
kiln was down to dull red heat by propping kiln shelves over the opening
and shut the damper to avoid drafts. Slowed cooled the rest of the way
down.
Marcia in Montana
Kyle Carpenter wrote:
> i've been reading in a few books on salt firing. I've read that many people
> crash cool their kiln until cone 010, then seal it up. i, personally, seal
> it up as soon as i shut the gas down.
> question: what are the pros and cons to crash cooling, specifically with a
> salt kiln. **besides the fact you can open the kiln earlier :) **
> kyle
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
--
Tuscany in 2003
http://home.attbi.com/~m.selsor/Tuscany2003.html
Craig Martell on wed 5 feb 03
Hi:
Marcia has already talked about the brighter colors that we expect with
quick cooling and from my experience this is exactly what happens. This is
true even with porcelain given that the potter uses iron in slips or uses
flashing slips to produce warm oranges.
If you are using a claybody that is prone to developing cristobalite, a
quick cool will cut the development of this troublesome form of silica
quite a lot. I know some potters in the UK that use clays with little or
no added feldspar and a quick cool is absolutely necessary for them with
regard to avoiding cristobalite development. One person was having trouble
with "Christmas Glitter" forming on his pots with a quick cool so he went
to the slow cool and because of the low spar content of his clay he was
plagued with dunts from cristobalite development.
If you cool fast, devitrification and crystal development are greatly
reduced or completely eliminated. Crystals are an aesthetic choice in most
cases so having or not having them would be based on aesthetics I would think.
I don't think you need to fast cool to cone 010 though. When I've done it,
I drop the kiln quickly to about 1800F or a bit lower and then close the
ports and the damper. If you cool fast to 010 there may be some dunts due
to passing the quartz inversion point too quickly. The quartz inversion
takes place at about 1032F. If you feel the need to cool to 010, then do
so by all means and if there are problems you can clam the kiln at a higher
temp. Some shelves don't respond well to a long, fast, cool. I've seen
silicon carbs crack form this and alumina carbs will definitely crack with
a fast cool.
regards, Craig Martell Hopewell, Oregon
Hank Murrow on wed 5 feb 03
On Wednesday, February 5, 2003, at 05:19 AM, Kyle Carpenter wrote:
> i've been reading in a few books on salt firing. I've read that many
> people
> crash cool their kiln until cone 010, then seal it up. i, personally,
> seal
> it up as soon as i shut the gas down.
> question: what are the pros and cons to crash cooling, specifically
> with a
> salt kiln. **besides the fact you can open the kiln earlier :) **
Dear Kyle;
Your question is a good one, touching on issues which have engaged me
for years, and led to my interest in a period of oxidation during the
cooling of reduction fires. At Anderson Ranch, around '72, we built a
40 cu ft salt kiln and fired it around 80 times. We found that if
cooled very quickly (German practitioners of old dumped water in their
salt kilns) by taking out the top three rows of door brick, we got
consistently 'cold' colors. Letting the kiln cool normally yielded
'warm' colors from the same clays. We theorized that the quick cool
prevented the iron in the salt/glaze from re-oxidizing, giving the
colors typical of iron in solution......bluey and cold. Sometimes we
introduced soluble salts such as barium chloride and silver nitrate to
achieve irridescence on the salt surfaces. I visited Westerwald (center
of salt production in Germany) in '84, and the pots in the museum there
certainly confirmed our experiences. Any micro-crystalline glazes may
be manipulated to achieve a varied color response by changing the
cooling cycle, both in rate of drop AND atmosphere.
Good Hunting, Hank in Eugene
| |
|
