Ron Roy on tue 16 jan 07
Hi Ivor,
I am not saying with just ZnO - just saying it is possible to use ZnO and
other alkali and alkali earths - with ZnO to melt glazes at cone 6 - sans
boron - and they can be stable.
I'm interested in seeing just how much ZnO you can get in a glaze and it
still be reasonably stable.
I do think you can make glazes with just the alkaline fluxes by the way -
you would need a combination of Sodium, potassium and lithium to get the
expansion/contraction right for the clay you use. It's because the
expansion of lithium is way lower than KNaO. Have to have a lot of alumina
though to keep the glaze on the pot.
RR
>In your reply to Steve Slatin you say >Oxide - you can melt a cone 6 glaze with just zinc oxide - and it's way
>over in the 11B column.>
>
>Elemental Zinc used to be stored with group 2 element, Copper was classed
>with group 1 . Now Copper is in Group 10 and Zinc in 11 in the modern
>tables, collating them with the Transitional Elements. This is more in
>keeping with the electron structure of the atoms.
>
>Are you saying that a mixture of Zinc oxide, Silica and Kaolin will melt
>at Cone 6 without the intervention of a Boron frit? So that using Zinc
>Oxide, a glaze with the Seger formula of 1.0 ZnO - 0.3 Al2O3 - 3.0 SiO2,
>though impractical, would fuse to a glass if applied to a pot. An
>interesting proposition. Any implications for making crystal glazes ?
>
>I forgot to mention the other problem with limiting the R2O content of a
>glaze to Group 1 Elements. The Coefficients of Linear Expansion would
>create crazy or shivering mayhem.
>
>Best regards
>
>Ivor Lewis.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ivor and Olive Lewis on wed 17 jan 07
Dear Ron,
The reason I suggested making a glaze from a Seger Formula of 1.0 ZnO, =
0.3 Al2O3, 3.0 Al2O3 without any other ingredient containing elements =
for Group 1 or Group 2 is to remove any effects the others might have. =
That formula seems to be basic to Cone 6 glazes and can be compounded =
from Pure Zinc oxide, Kaolin and Quartz. To put it another way, it is a =
"Control". Each additional ingredient, at a guess, can increase =
exponentially the complexity of what happens during a firing.
I have to assume you have not read Chapter Ten in "Introduction to =
Ceramics" . What is written by Kingery, Uhlman and Bowen, all professors =
from Massachusetts Institute of Technology lays down the events that =
take the powders we have mixed in a glaze through the processes of =
sintering and vitrification. Add in Ch 9 and you will understand that =
some materials interact in the solid state. Burned lime, Calcium Oxide =
can react in the dry solid state with silica as low as 600 deg C=20
Always remember, Group 2 metal oxides and Zinc oxide are all refractory =
by nature and do not willingly melt when they are heated. But they can b =
e chemically reactive in the solid state. (Read Cardew).
Best regards
Ivor
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