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wood fire clay body


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#1 Plattypus

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Posted 05 December 2012 - 09:09 AM

I just assumed a teaching position where my predecessor purchased a white clay body for the Feb wood fire. I would prefer a darker one but cannot purchase anything new. I have a small supply of some Standard Clays... Can I use any cone 10 clay for wood fire with decent result?

#2 OffCenter

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Posted 05 December 2012 - 09:37 AM

I just assumed a teaching position where my predecessor purchased a white clay body for the Feb wood fire. I would prefer a darker one but cannot purchase anything new. I have a small supply of some Standard Clays... Can I use any cone 10 clay for wood fire with decent result?


Only testing will tell. Some of the cone 10 clays may look great in a wood firing and some may be disasters (including not being able to take the cone 10+ heat-work of most wood firings). You don't say how big or what kind of kiln it is but filling it with a pots made from a clay you're not happy with even before you fire it seems a questionable decision at best to me.

Jim
E pur si muove.

"But it does move," said Galileo under his breath.

#3 neilestrick

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Posted 05 December 2012 - 12:10 PM

Gonna have to test it. A lot will depend on the actual heat work of the kiln, especially since many wood firings go well beyond cone 10. There's a good chance everything will be fine, though, as long as you don't push cone 14.
Neil Estrick
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#4 OffCenter

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Posted 05 December 2012 - 12:54 PM

Gonna have to test it. A lot will depend on the actual heat work of the kiln, especially since many wood firings go well beyond cone 10. There's a good chance everything will be fine, though, as long as you don't push cone 14.


Couldn't have said it better myself--well, actually, I guess I did. (Insert some sort of smiley face here to show that I meant that in a humorous way.)

Jim
E pur si muove.

"But it does move," said Galileo under his breath.

#5 JBaymore

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Posted 06 December 2012 - 10:42 AM

We tend to think of "wood fire" here in the USA pretty generically to have sort of a "one way" meaning. Most folks seem to visualize it as firing in an anagama using yakishime loading (unglazed) or if with glaze... with American shino.

Woodfire can be in a fastfire kiln fired for 8-10 hours to Orton cone 9, 2 days in a noborigama fired to different temperatures and atmospheres in different chambers, to 5-7 days in an anagama fired from cone 14-15 in the front to cone 8-9 in the back. And everything in between.

One potential issue with very long extended firings on clay bodies is that clay bodies designed for far shorter firing cycles may not have enough fluxes in them to dissolve all of the available silica that is in the body from either added silica bearing materials or from the silica ejection phase of the normal clay crystal changes.

When this happens, the cristobalite form of silica forms from any crystaline silica when it is held at elevated temperatures. The amount of cristabolite developed is directly proportional to the time held at the high temperatures.

Cristabolite has a very high reversible COE... and can cause bodies that are just fine in shorter firing cycle to dunt when fired in a long cycle wood kiln. I've seen this a million times.

As has been said.... only testing will give you the answers you desire. Or find out if anyone has used the bodies you have available to you before in the specific kiln and firing profile that you plan to use.

best,

...............john
John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com




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