iandol on fri 16 jun 00
Thanks for summarising that information Des.
Quite a problem you set.
Although the basic recipe gives none of those ingredients which would =
predict the blue colour it is possible that your feldspar has residuals =
in it in sufficient quantity to make a subtle difference. Both Titanium =
and Iron may be there in very small proportions.
However, I suspect talc is the culprit. It has, I suspect a very high =
melting point and also that it may have a low solubility. Your =
observations of what occurs as cone values rise suggests to me that the =
talc, which changes, so I understand to enstatite, reaches a stage where =
the crystals are so small that they contribute to the optical effects =
which produce colour by dispersion. I believe this is called the =
Rayleigh Effect. Nigel Wood describes this and it is independent of kiln =
atmosphere. A lot may depend on the solubility of that small fraction of =
Zinc Oxide as well.
Now this is pure speculation and I would like to see experimental =
evidence if anyone can afford to set up the lab.
Best regards.
Ivor. Redhill Au
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