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zinc crystal fundamentals

updated wed 22 jan 03


iandol on tue 21 jan 03

Dear Friends,
Good mail came yesterday, a copy of Diane Creber's "Crystalline Glazes". =
How wonderful it is that international publishers dump their remainders =
on Good Old Oz.
Nice book. Some stunning illustrations and a fair swatch of recipes. =
Looks like a good place to start and reinforces information from Sauders =
Book "Glazes for Special Effects"
Well, I like to understand the science and technology and it all seems =
pretty straight forward. Pick a reliable commercial frit, load it with =
Zinc oxide and silica, fire up, switch off then interpose a session of =
constant temperature. Cool down and crack the kiln and there should be a =
wonderful sample of crystals.
But,...I would like to know how the ratio of ZnO to SiO2 is determined =
because there seems to be wide spread of this ratio, from 0.5/1 to 4.4/1 =
if you ignore that in the frits or spars. Can anyone explain why there =
should be such a wide spread of values? Or is this rule of thumb based =
on prior case histories and the experience of people who supplied the =
Now I can understand that pushing the content up ZnO up would help to =
offset loss during a reduction firing but it seems to me that the =
logical thing to do if you are wishing to gain the most benefit in terms =
of Willemite crystals is to incorporate a ratio of ZnO/SiO2 which =
matches the molecular composition of Willemite. Otherwise you have =
deficiency of ZnO or an paucity of SiO2, either of which would restrict =
the potential of a sample to produce crystals. My calculation gives me =
near enough to 2.7/1...ZnO/SiO2 (someone may wish to confirm this.)
Or is there a Knowledge about Zinc Crystal Glazes which has not, so far, =
been told?=20
Oh for a cool change!!!! and a day without a Fire Ban.
Best regards,
Ivor Lewis. Redhill, South Australia.