Ivor and Olive Lewis on sat 21 jul 07
on COE
Perhaps the way values of Expansively are arrived at for contributing =
oxides gives an artificial value and the only firm information would =
come from testing specimens by dilatometry, as done by Ron Roy.
It is important to ascertain what assumptions were made by those people =
who constructed scales that are employed now in computerised glaze =
calculations.
Other points to consider: If the glazes is in the viscous state then =
Cubical, not Linear coefficients would apply. As viscosity approaches =
infinity, at some point on the cooling curve a point is reached called =
the Glass Transition Temperature and the substance is rigid. Linear =
Expansivity is not necessarily uniform across the temperature range from =
ambient to Glass Transition point
It could be suggested that when layered glazes are being created that =
potters might adopt the Glass Founders process of annealing.
By the way, I do appreciate the idea of using polarised light to examine =
transparent specimens for stress fields.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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