Suffering clay withdrawal!

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Suffering clay withdrawal!

Post  DWThomas on Thu Feb 05, 2009 6:14 pm

The community college facilities where I was doing my work have been unavailable since last May, and now that this forum is up and I'm seeing all this great work, I really miss it! No

They are doing a major overhaul and expansion of the art facilities, and as of now it's largely complete, alas, except for the gas kilns. They are running mostly beginner classes using low-fired clay in the electric kilns normally used just for bisque firing. Presumably it will be better than ever when all is done, but I suspect I won't be getting my mits muddy until fall.

So anyway, hello to all!

(At least I was inspired to create an avatar!)

DaveT

DWThomas
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Re: Suffering clay withdrawal!

Post  Stone Monkey on Thu Feb 12, 2009 3:31 pm

Dave

Oh dear me clay withdrawl is a terrible illness I would not wish it on anyone who loves the squidgy stuff Sad

Regards

Andy

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Re: Suffering clay withdrawal!

Post  prestontolbert on Thu Feb 26, 2009 8:31 pm

This month's "Ceramics Monthly" had an ad on the back cover with some spectacular electric fired glazes. They seemed a little showy for bonsai, but they were matt and had nice micro crystals, especially for electric.

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Re: Suffering clay withdrawal!

Post  DWThomas on Fri Feb 27, 2009 2:10 am

Yes, in my first foray into the potter's art I took an adult evening school class at the local high school. We worked with low-fired clay and some wild and crazy pre-mixed commercial glazes. The instructor took the work home and fired it in an electric kiln. I have no way to know how good the firings were, but some pots I used on subtropicals, thereby avoiding any outdoor exposure even close to freezing, began to deteriorate in about two years. The effects were cool, for sure.

This remodeling program at the college ran into some unanticipated problems -- like asbestos and some rotted structural beams -- so the project is way behind the original schedule at this point. I have it on good authority that at least one gas kiln is on order, and there is a roofed shelter in place on an outdoor patio for a new salt kiln, so I'm hoping by fall things will get going with full cone 10 reduction firings.

I once had an inspired thought wondering if you could valve propane into an electric kiln to do reduction firing, but I quickly smacked myself and moved to other activities! Shocked

DaveT


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Re: Suffering clay withdrawal!

Post  prestontolbert on Fri Feb 27, 2009 8:11 pm

Quite a few potters DO use propane to reduce electric kilns. Reduction, however quickly breaks down elements, so between electric reduction firings you must do an oxidation firing to put a protective oxide coating back on the elements. Nils Lou, a potter in Oregon, uses a small doll kiln to test ^10 reduction glazes. He simply drilled a hole a little larger than his bunsen burner in the floor of the kiln and an exhaust hole in the lid. The elements deteriorate quickly, but doll kiln elements are only about $20 a set to replace. He uses an oxy probe to get reduction equivalent to his gas kiln. It is such a small amount of propane, that he opens the doors to the room and vents with a fan. You could expect to get 10 or 12 firings per set of elements.
In Japan, due to tight regulations, quite a bit of reduction firing is electric. They actually have electric/gas reduction kilns available for purchase.
Also my boss used to do ^04 salt reduction firings with a black clay that is incredibly vitreous and durable. This clay, only fired to about 1970 deg. F, can withstand freeze/thaw for many seasons. He has massive pieces that have been outside for 20 years with no ill effects. The clay is finicky and will slump at 2000 F, though. It's all about the level of vitrification of the clay. If a clay doesn't absorb water it won't crack in freezing cold. I have personally seen work that was made of very refractory clay, fired to ^12 and cracked during a freeze. It absorbed water.
I got a little long winded. Sorry about that.

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Re: Suffering clay withdrawal!

Post  DWThomas on Fri Feb 27, 2009 8:58 pm

prestontolbert wrote:I got a little long winded. Sorry about that.

Hey, no, that's a bunch of good info to tuck away for possible future use -- by me or other readers here -- thanks!

DaveT

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Re: Suffering clay withdrawal!

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