Lisa and Ginny on sat 6 sep 97
Is there such a thing as clay for gas kilns that is different from clay
for electric kilns? I just unloaded both a gas and an electric kiln.
Both kilns had pots made from the same claybodies, with the same glazes,
fired to ^6 Oxidation, but the claybodies in the gas kiln have a lot of
bubbles. I'm using recycled commercial claybodies from Kickwheel and
Highwater. Help!
--
Lisa Skeen
Living Tree Pottery & Soaps
http://www.uncg.edu/~lpskeen
YesIAmRU?
Ron Roy on mon 8 sep 97
Hi Lisa,
Clays with little iron in them will work in both - porcelain for example.
Fe2O3 is not much of a flux in oxidation but when reduced to FeO in a
reduction firing it becomes a big time flux. The more iron in the body the
more the fluxing in reduction.
So, I surmise these clays are brown rather than white or buff.
>----------------------------Original message----------------------------
>Is there such a thing as clay for gas kilns that is different from clay
>for electric kilns? I just unloaded both a gas and an electric kiln.
>Both kilns had pots made from the same claybodies, with the same glazes,
>fired to ^6 Oxidation, but the claybodies in the gas kiln have a lot of
>bubbles. I'm using recycled commercial claybodies from Kickwheel and
>Highwater. Help!
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
Lisa and Ginny on tue 9 sep 97
Ron Roy wrote:
> Clays with little iron in them will work in both - porcelain for example.buff.
Yes. One of them is a body with a Barnard clay base (50%) that I got
from a fellow clayarter. The other is a recycled conglomerate of
Kickwheel's Gray Speck, and Standard's Brooklyn Red, all of which are
very high in iron. It seems that no matter what the temperature (^6 or
^10), if I fire these in the gas kiln (ox, not redux) they bubble. It's
nasty, and I bet I pitched about half a kilnload Friday.
--
Lisa Skeen
Living Tree Pottery & Soaps
http://www.uncg.edu/~lpskeen
YesIAmRU?
Craig Martell on tue 9 sep 97
Hello Lisa:
When firing in reduction, you have to be careful not to start reducing too
early in the firing due to the fluxing action of the iron, which Ron Roy has
already addressed. If reduction is begun before all the carbonates are
burned off, you get bubbles and bloating from trapped gasses. The fluxed
iron tightens the claybody and the gasses cannot escape, or their exit is so
slow that they never quite make it out and you then have bubbles and bloating.
With iron bearing clays, I usually begin reduction at about cone 08. Some
people start as low as cone 012 with no problems. It depends on the
composition of the claybody.
Regards, Craig Martell-Oregon
Lisa and Ginny on wed 10 sep 97
Craig Martell wrote:
> With iron bearing clays, I usually begin reduction at about cone 08. Some peo
> composition of the claybody.
Hmmmm...What if it still does the bubble thing in oxidation?
Thanks for that info too, because I generally start reducing when ^06 or
^1 goes down.
--
Lisa Skeen
Living Tree Pottery & Soaps
http://www.uncg.edu/~lpskeen
YesIAmRU?
Craig Martell on fri 12 sep 97
Lisa wrote:
>----------------------------Original message----------------------------
>Hmmmm...What if it still does the bubble thing in oxidation?
Hi Again Lisa:
As I remember, you said that you were using a mixture of recycled clays?
Perhaps the mix of different bodies matures at a lower temperature than you
are firing to. Overfiring clays can cause bubbles and bloating too. If
this is a possibility, or is positively the problem (a bit hard to prove
conclusively) you may want to avoid these kinds of mixes. It's really
discouraging to have your pieces spoiled by variable compositions of
recycled clays. Conservation is a good thing only if it works. I'm not
preaching at you, just passing on a thought for whatever it may be worth.
Sorry to be so long in responding too but I was rebuilding the stack to my
salt kiln and it took more time than I thought.
Regards, Craig Martell-Oregon
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