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: adjusting clay body expansion

updated fri 8 feb 02


iandol on thu 7 feb 02

Dear Alan D. Scott,

You say <bodies. It seems to me that I should be able to formulate a clay body =
with a calculated expansion using Insight to match a given glaze.>>

This is a very important question, and one for which I feel there is no =
easy answer.

Although Coefficients of Thermal Expansion can be measured for the raw =
materials which contribute to a glaze or clay recipe, how are these =
translated into values which would be appropriate to mature ceramic =
fabrics. I do not think you can go along the abstract pathway and base =
your calculations on the C of TE of contributing oxides. Though these =
are known for various forms of Silica, who has determined them for =
Sodium, Calcium, Barium, Lithium, Strontium and Potassium oxides?=20

There are other considerations. Some materials have dual Coefficients. =
There is one value along one of the crystallographic axes and a =
differing value along another axis, so which would you incorporate into =
your calculations? There is also the question of the influence of phase =
changes, that is, if you have the facilities to identify new components =
in both body and glaze.

No doubt you are correct. It would be possible to calculate values. But =
with these values it would be necessary to add, as a caveat, the =
assumptions you are making in deducing and then applying them as you =
process your work. So, would your guess using Insight be any better than =
mine using Experience?

Wishing you every success,

Ivor Lewis. Redhill, South Australia=20