[Clayart] kilns as ovens

L TURNER magnolia.mud.list at gmail.com
Mon Jan 9 13:21:09 EST 2017


Bruce,

You were supposed to have 'chuckled' ; I certainly did not meet my target,
and I apologize.
We are in agreement on oxidation is a loss of electrons, reduction is a
gain of electrons.  That is a standard definition from physical chemistry
101.

What is 'fuel' and what is 'not fuel' is arbitrary.  In coal and other
gasification processes, the term 'fuel' is often considered to be the
component completely consumed in the reaction -- the limiting reagent --
and that is where I was coming from in my 'semi-serious' post. Increasing
oxygen decreases the product.  You control the process by limiting oxygen
(from all sources, including water).  Too hot, decrease oxygen, too cold,
increase oxygen.  That was the most effective 'analogy' to the operators of
the units -- make your pickup go faster, push down on the gas, slow down,
let off on the gas.  Oxygen was 'the gas' to the plant (and literally in
the coal fed plant).

You said: "I do feel however, that the chemistry of pottery processes is
muddled and mysterious to many potters."

I fully agree with that statement.  And the overly simplistic explanations
of the atmosphere in a combustion kiln used by potters is one of the most
muddled explanations I have seen in my half+ century of engineering.  Using
analogies such as 'carbon stealing oxygen' from metallic oxides is one of
these overly simplistic explanations.  I tolerate it, but it is not good
chemistry and at best a weak analogy.  Unfortunately when I attempt to
explain it, I find myself in the same situation as Fermat had with his last
theorem: I don't have enough room in the margin to present it.  The analogy
works only at an overall 'black box' level; it doesn't work at the level of
the metallic oxide itself which often never comes in contact with carbon.

LT
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