Ivor and Olive Lewis on wed 18 feb 04
Dear Ababi,
The temperature I gave, in the two common scales (700=BAC ~1300=BAF) ,
would be predicted from statements which inform us that mixtures of
oxides provide glazes which fuse due to eutectic melting.
However, my humble experience is that glazes compounded from Soda
Felspar, Potash Felspar or Nepheline Syenite struggle to mature at any
temperature below 1200 =BAC ~2192=BAF even though they may show signs of
melting. Things change when you add one of the Boron Compounds to the
recipe.
In theories given to us by "Glaze Masters", we should be able to mix
Potash Felspar, Quartz and Kaolin and get a total melt at 985=BAC
~1805=BAF from a recipe containing 9.5%K2O, -10.5% Al2O3 - 80% SiO2. I
could not predict this mixture would give a satisfactory glaze.
Similarly, and contrary to what we might expect, using Soda Felspar
with Quartz and Kaolin and the following oxide values; 8% Na2O, 14%
Al2O3, 78% SiO2 melting, in theory, should happen at 1050=BAC ~1922=BAF.
but I would not lay bets on the event.
Layering glazes is not the same as mixing glazes. Used with thought
and knowledge derived from trials of layering by dipping, spraying,
brushing or combining such methods this technique can give
outstandingly attractive and exciting results. The latter part of Greg
Daly's book, "Glazes and Glazing Techniques" , ISBN 0-86417-502-7, is
devoted to this very process.
Best regards,
Ivor Lewis. Redhill, South Australia
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