Tony Hermsen on sat 25 may 96
Dear Linda:
Usually the molecular equivalent of silica in a glaze is 8 to 10 times the
alumina. Of course, the higher the maturing temperature the more silica
required. However, too low a silica content may also make the glaze too
refractory. This is the eutectic principle at work. The famous Dr. Seger states:
"The ratio in molecular equivalents between the fluxing bases, including the
intermediates and the acid members, i.e., silica, etc., must lie between the
bisilicate and the trisilicate. If it is too close to the former the glaze may
be too fusible; if it exceeds the latter, the glaze will not mature properly or
will be stringy."
So, to have the proper viscosity, refractoriness and texture [gloss] the most
frequent ratios used are most often between 1:7 and 1:11 and go as high as 1:15
for glossy glazes.
All that said and done, you still have to fire the stuff to see what happens.
Oh, the joy of Alchemy!
All the best
Tony
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