Vince Pitelka on fri 17 may 96
Thanks to Marc Ward and Tom Buck for clarifying the issue of neutral vs.
oxidation in electric kilns. In my many years of involvement in ceramics I
have never thought of it that much. An electric kiln is an oxidizing firing -
that has always been my assumption. It is very easy to see, however, that due
to the very small air exchange with the external environment, the air can get
"stagnant", as Tom Buck puts it, meaning that what little oxygen is present has
done it's work, and not much at that, and then the slight pressure caused by
dissociation of materials in the clay and/or glaze reduces the chances of more
oxygen entering the kiln.
I would expect that any kiln with a direct-connected kiln vent, like the Bailey
system, would produce wares that are more oxidized than those in a tightly
sealed kiln, but I have never noticed a difference. Also, as far as I have
seen, wares fired in a tightly-sealed electric kiln come out at least as
oxidized as those fired in the most purely oxidizing gas firing. If the
electric kiln has only the double oxygen molecule available from what little is
in the kiln or gets in from the external atmosphere, and if the gas oxidation
firing is saturated with the single oxygen atoms that are more "hungry" than
the double oxygen molecules, why aren't electric-fired wares less oxidized than
gas-oxidation-fired wares? Or are we talking about degrees to small to notice?
- Vince
Vince Pitelka - wkp0067@tntech.edu
Appalachian Center for Crafts - Tennessee Technological University
Smithville, TN
WardBurner@aol.com on fri 17 may 96
Vince,
No, it's not the small degree of change it's the nature of the change. Sorta
like getting old, huh? Anyway, oxygen is the reactive stuff here. In the
electric it's paired with another oxygen so the bond keeps it from reacting.
If you have free oxygen (unpaired atoms) zinging around in the gas kiln it
will usually pair with another oxygen from clay and glaze. But, if it does
manage to pull this off (the oxygen already paired with something else is
reluctant to let go) that space in the molecular bond is instantly replaced
with another free oxygen atom. Presto!, you have the same molecule you
started with. This is why you can't tell much difference between a neutral
electric firing and an oxidizing gas firing.
Marc Ward
Ward Burner Systems
PO Box 333
Dandridge, TN 37725
423.397.2914 voice
423.397.1253 fax
wardburner@aol.com
Vince asks:
<<<electric kiln has only the double oxygen molecule available from what little
is
in the kiln or gets in from the external atmosphere, and if the gas oxidation
firing is saturated with the single oxygen atoms that are more "hungry" than
the double oxygen molecules, why aren't electric-fired wares less oxidized
than
gas-oxidation-fired wares? Or are we talking about degrees to small to
notice?>>>>
Tom Buck on fri 17 may 96
Vince: May I suggest another component in this system, namely, the
claybody/glaze ingredients. Certainly many glazes and probably most
bodies contain ballclay(s) with their leftover organic detritus. These
are released into the kiln environment during the firing and will affect
the glaze surface in some small way, perhaps in a similar manner to a
gas-firing with excess air. There are also ingredients that outgas
significantly (largely carbon doxide from carbonates) and these gases
will play some small role on the final glaze colour and surface.
The total system is fairly complex and worthy of a research
project by a master's candidate at Alfred or elsewhere.
Perhaps those potters who have experience with the so-called
oxidation environment, both electric and gas, will comment on whether
they have noticed any change in a particular body/glaze combination when
it has been fired both ways. My guess is there would be none or almost so
little that the change would pass notice... that bright glossy glazes look
the same from both enviroments. Good potting. TomB Hamilton Canada
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