Tom Buck on sat 21 apr 01
Ms. Beynon:
Insight's expansion numbers for Shinos, while correct, mislead
because of glaze/body interaction. The high KNaO in shinos causes claybody
silica (perhaps some alumina) to enter the glaze and this lowers the COE,
especially at the boundary layer where crazing begins. In the glaze
itself, the high alumina content induces a very high viscosity, so this
glaze hardly is fluid at full cone; the glaze stays put.
A high lithia glaze may release some Li+ ions to acidic foods,
and could be a potential danger. But otherwise shinos would likely be
inert to acids --- teabowls for the tea ceremony are glazed in shino.
To make sure your shino is ok have it tested at Alfred.
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
Craig Martell on mon 23 apr 01
I'm sending this again. I sent this post two days ago and I think it went
into the cyber toilet.
Hi Shino Enthusiasts:
I've come up with the quintessential shino glaze in terms of interest and
endless discussion about certain glazes. I call it Mel's Floating
Shino. OK, this is no time for levity but I couldn't resist.
If you look at limit guidelines for cone 8-10 glazes, the upper limits for
alumina are about .5 moles and silica is anywhere from 5.0 to 7.0 depending
on whose limits you look at. Alumina and silica levels in glazes are
important for durability to little of either, and this is especially true
of silica, will yield softer glass that is more prone to acid and alkali
attack.
Shinos will typically have about .9 moles of alumina and sometimes up to
1.5 moles and the glazes still melt well. Silica, in almost all the shinos
that I've seen and formulated myself, is at least 5.0 moles and some have
been above 7.0. So, with regard to the alumina and silica levels in
shinos, most of the ones I've seen have a good chance of being durable IF
the high alumina levels aren't making the glass unstable. If you use
shinos that have spodumene or another lithium bearing component, it would
be a good idea to have the glaze tested for Li release. If enough of us do
that, a database could be developed that would provide more solid info on
the durability of these glazes.
regards, Craig Martell in Oregon
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