iandol on wed 3 jul 02
Dear Paul,
You search for the "Grail"
Like a lot of "Facts" relating to ceramic materials I suspect that =
information about things "Volatilising" are spurious and do not =
represent the true nature of our materials.
If it is considered that the red nature of a reduced copper glaze is due =
to Red Copper Monoxide, this material melts at 1235 Deg Celsius then =
decomposes at approximately 1800 deg Celsius. Alternatively, if it is =
due to metallic Copper the MP is 1084 C with a boiling point of 2580 C. =
It seems unlikely that copper vapour would discharged at atmospheric =
pressure during a stoneware firing.
What does Tichane say in his book on the subject? Do your glazes =
incorporate Tin oxide as a stabilisng agent? Since you seem to be using =
a single firing technique, is there a temperature difference between the =
two sessions of reduction?
The idea that an Oxyprobe can indicate a kiln atmosphere is "neutral" =
intrigues me. I thought these instruments indicated the presence or =
absence of Oxygen and from this, an inference is made about the presence =
or absence of reducing gases.
Again, potters seem to make suppositions, disregarding things like =
thermodynamic equilibrium within the nature of a chemical reaction. =
Things happen depending on the conditions relating to thermal energy and =
pressure. The chemistry of the gases involved is ignored. For example, =
Carbon dioxide, which would have been in the combustion gases of your =
friends neutral atmosphere kiln, has the ability at elevated =
temperatures of participating in a reversible reaction to give Carbon =
monoxide and Oxygen. I think you will agree this is contrary to what is =
taught to pottery students.
I am looking forward to reading other replies to your request.
Best regards,
Ivor Lewis
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