iandol on mon 24 dec 01
Cornwall Stone is a rock, that is a mixture of minerals. One of these is =
Fluorite, CaF2. Purple stone contains a higher proportion of this =
accessory mineral. Fluorite discharges Fluorine at high temperatures. =
Not an unusual thing since many raw clay minerals also have finely =
comminuted Fluorite in their makeup. But it can be a bit of a problem =
with some early melting glazes and cause pinholing. Calcined stone would =
not suffer from this fault.
Best regards,
Ivor Lewis. Redhill, South Australia
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