ivor & olive lewis on tue 1 jun 10
Dear Joan Slack,
Just one more fact to consider regarding a clay that will or may bloat.
If a clay body contains both Organic Carbon and Pyrites (Iron Sulphide) the
Iron sulphide will not be completely oxidised unless all the carbonaceous
materials have been burned out of the clay. This has to happen before glaze
materials have commenced fusion.so that Oxygen can diffuse into a porous
clay body and the other gases can diffuse from the porous clay. It seems
that a kiln that is firing in reduction prevents the burn off of
carbonaceous compounds. To remove the carbon there must be an ample supply
of air into the kiln.
This technology is explained in W. E. Brownell, "Structural Clay Products".
ISBN 3-211-81382-9. 1976. See Ch 6. Firing Process.
Best regards,
Ivor Lewis,
Redhill,
South Australia
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