Tom Buck on mon 23 apr 01
Marj B:
The Shino glaze (American type) is so much outside the usual
Limits for a midfire or highfire glaze that glzcalc is unable to offer a
good prediction as to behaviour.
For example: Mix a Shino with this Seger Formula: 0.1 CaO, 0.9
Li/Na/K Oxides, 0.9 Al2O3, 3.9 SiO2. Will it melt at C10? Most of it will,
but perhaps there will still be some solid in the liquid. With so much
alkali oxides present, claybody silica will be attacked at the boundary
layer between body and glaze, and more silica will be added to the molten
liquid. This in turn will tend to lessen the contraction of the glaze at
the bounday layer, and hence lessen the potential to craze. Moreover,
because there is some crystallization occurring (alkali aluminates), the
values calculated by a glzcalc program will not be maintained.
You suggest your claybody will have high porosity after firing to
C10...very few bodies will sustain C10 and not be tight (under 3%
porosity). Perhaps your claybody is one of those rare types.
You wish to put a "normal" liner glaze on the inside of the pot,
and query whether this will be problem since the Shino COE and Liner COE
are quite different. The Shino undergoes "adjustment" during firing so I
would expect the compression forces in and out to match, and the pot will
not undergo body cracking.
Now, having said all that, I still suggest you do some test
firings and let us know what happens.
til later. Peace. Tom B.
Tom Buck
)
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
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