iandol on sun 11 nov 01
Dear Suella,
If you are getting bloating it sounds as though you need to slow down =
the firing in the middle stages and ensure that there is always an =
excess of air to keep any iron oxide in its "High Valency" state. It is =
also essential to burn out any organic matter which might tend, at =
higher temperatures, to reduce the iron and release carbon =
monoxide/dioxide gas which I believe are responsible for the bloat =
bubbles.
Early salting, say between 900 Celsius and 1150 Celsius, above which =
the usual chemistry would start to operate, could leave a liquid film of =
molten sodium chloride or sodium carbonate on the surface of your pots. =
This may wet and seal the surface preventing air from burning out =
organic residues in your clay.
I would slow to a temperature rise of about 50 deg per hour in the =
middle of the firing and delay salting until cone 8 is down. Better to =
fire for another six or seven hours and get good work than rush things =
and produce scrap.
Best regards,
Ivor Lewis. Redhill, South Australia
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