terry sullivan on thu 14 nov 02
In the part of this discussion regarding oxidation atmosphere as
contrasted to "neutral" one might contact the Orton Fdn. ( sorry, don't
have their web site handy).
I took a workshop with a rep from them several years ago at the Laguna
Clay facility in CA.
Here's the basics distilled: You are firing low fire in an electric
kiln. There's lots of stuff coming out of the clay body and even more
coming out of the low fire glazes. These are LOS ( loss on ignition )
and other stuff that burns off during the firing. Stuff like carbonates
and such. This stuff in a closed electric kiln contaminates the
atmosphere and often affects the glazes in an adverse way. Makes the
atmosphere in the closed electric kiln unpure.
The folks at Orton developed their Kiln Vent system to slowly draw fresh
air from the top of the kiln and out the bottom ( like a cubic foot of
air per minute). A very slow flow that did not significantly affect the
temperature but got the "bad" burn out stuff out of the kiln and
maintained a true "oxidation" atmosphere.
Some of the results were dramatic ! They showed us identical tiles
fired with the same glazes in the same kiln with and without the venting
system. Without the venting, tiles glazed with a fire engine red glaze
were uneven and splotchy, while the ones with the venting were perfectly
bright red and even.
I'm sure you can get more info from Orton on all this.
As a side note; there is a lot of nasty stuff that burns out of clay
even during the bisque fire. Make sure you have the kiln area well
vented. You don't need to be breathing lots of CO2 and CO along with
sulfer gasses.
Yours,
terry sullivan
Nottingham Arts
www.nottinghamarts.org
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