Jonathan Kaplan on sat 23 apr 05
It would appear that there are varying s and symantic issues with much
of this dialog.
I don't know what fully reduced means, nor do I understand partially
reduced, or any of the many variations one could possibly construct for
a "reduction condition." Is it like being "half pregnant" or :almost
drunk?"
What I would posit that even with an oxygen probe or what ever device
one uses to measure or quantify the atmosphere within a fuel burning
kiln, they are at best, only as good as the sophistication of the
combustion system. Most potters using burners made from pipe and pipe
fittings are not getting really true stoichiometric combustion. Its
true the kiln gets hot and fires to temperature but its usually with a
great waste of fuel because of very poor combustion technology. With
added forced air and some other controls and devices, it gets much
better.
The point being is we really don't know what is going on in that kiln
in every square inch. Why do thermoclines exist? Why is one side of a
copper red pot beautiful red and the other liver colored? Why is the
"reduction" spotty? And a host of other "whys".
We know what happens chemically to iron when it is in a reduction
atmosphere, as well as to our glazes. We know how clays "look" in
reduction, or supposed to look? If we believe the color charts of clay
bodies that we see from the manufacturers. But the point is we really
don't know what is going on in the firing chamber because our burners
and instrumentation are at best, mediocre.
Potters concerned about the efficacy of their fired work need to place
a little more money, concern, and effort into combustion systems that
offer a high penetration, low turn-down, efficient, and almost true
stoichiometric combustion. Yes, with all the bells and whistles. With
proper combustion and instrumentation, we might be able to talk with a
better vocabulary about reduction, partial reduction or whatever one
chooses to call it. But we choose to just get by.
You might say, "Hey I don't have the cash for a decent combustion
system and I can put some pipes together" We have all done it. Even
someone posted a week or so ago about whether or not to use a flame
retention tip. Its the least you can do. Not that we need to generate
an argument here but there is no common or accepted amount of
"reduction" that we can quantify. My oxyprobe, one of the original ones
from AIC back in the day provides me with a digital number that seems
to work for me and I can hit it every time, adjust it when i need to,
but it still doesn't provide me with a quantifiable number or data that
really tells me something other than "that's the number to hit."
I might concur with Pacini that there are no criteria and that our
assumptions are indeed only that, "assumptions." I think anything more
than assumptions might border on conjecture and really don't have the
data to back them up. There really is no "common amount" of reduction.
That's way to big a generalization for me. We look at the flames from
the spy holes, maybe get a reading from an oxygen probe, give a nod of
consent and acceptance and say "Hmm...looks good to me!" Even if the
pots come out fabulous, we are still at best, firing by the seat of our
pants. We don't know what conditions the clay will be put through when
it leaves the warehouse.
When I formulate clay bodies either for our in house use or for
clients, I don't know the total conditions under which they will be
used. I do know that I stay away from clays that are high in iron and
try to include clays that have a low LOI, low silica, and are
airfloated. I use a very very small amount of Red Art or Newman for
color, but usually stay away from them. I am more concerned with how
the fired glaze will sit on them. I don't agree with the "clay bodies
need tooth" thing, but then my requirements might be different. No
better just different.
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
(970) 879-9139
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1280 13th Street Suite K
Steamboat Springs CO 80487
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