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fwd: : metallic cao-al2o3-sio2 eutectic

updated sat 14 jun 03


Ron Roy on fri 13 jun 03

Hello Ivor,

I believe they are all fluxes - just a question of time and temperature.

If you are correct then we need an experiment - a glaze fluxed without
KNaO, LiO2 and boron at cone 10 - using common materials available to
potters. Actually - I think Louis Katz has already done it at cone 9.

Every author I have read on this subject calls them fluxes - their melting
points are not germane to the argument - even the mixture of alumina and
silica has a lower melting point than either material separately.

What if we take a common cone 6 glaze - keep everything but the mid range
fluxes - do you think the glaze will melt properly?

I am sure there are many who are confused by this debate and I wish it were
not so - believe me when I say - if it aids melting it is perfectly
reasonable to describe the material as a flux.

Boron is a special case but many glaze technicians see it as a flux - as in
causing mixtures to melt at a lower temperature.


>>I am pleased you have given the quotations from Taylor and Bull they
>>illustrate clearly what other commentators omit when explaining the
>>behaviour of the Alkali Earth Elements.
>>These authors do not say that the group 2 elemental oxides will
>>cause more melting. The say that the effect is to cause a greater
>>degree of fluidity. This is not the same as changing the temperature
>>of fusion.
>>I am prepared to say that raw CaO, BaO, SrO, ZnO, MgO, all well
>>known refractory compounds, do not change the temperature of fusion.
>>They change fluidity (...reducing viscosity...)when accepted into
>>solution in a solvent silicate melt. Increasing the pace or rate of
>>flow is a change in Flux. These oxides also have an effect on
>>Surface Tension, but until problems happen this seems to be ignored
>>as well. Those teaching "Glaze Preparation and Use" should be aware
>>of this and mention it in their presentations.
>>How great it would be if the a segment, similar to the calculation
>>of C of E, could be included in glaze calc programs to estimate the
>>degree of fluidity and measure of surface tension.
>>Enjoy your travels.
>>Best regards,
>>Ivor Lewis
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Ron Roy
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K0K 1H0
Phone: 613-475-9544
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