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calcium carbonate in low fired work

updated mon 6 jan 03


iandol on sun 5 jan 03

I seem to have missed the original posting which initiated this topic.
I am concerned that the information being proffered may not paint the =
whole picture.
Either in a low temperature clay body or glaze, Calcium Carbonate or =
Whiting will become Calcium Oxide above 850=B0C or there about. Hamer =
points out that this is highly soluble in water but that it is =
un-reactive as a fluxing agent until the temperature rises above =
1100=B0. So unless there is something in either clay or glaze to mop CaO =
up it is going to cause problems for people who work at earthen ware =
I believe a search of the Chemical Knowledge Base may reveal that there =
is a solid state reaction between Calcium Oxide and free Silica above =
1000=B0Celsius though I am uncertain which of the four Calcium Silicates =
would be produced at this temperature.
If this does turn out to be true then some of the phenomena we observe =
may well be explainable.
Best regards,
Ivor Lewis. Redhill, South Australia