ClayArt Moderator on mon 27 jul 98
Tony Hansen says about this glaze:
>I'm not sure why this glaze would have
>a powerful flux like lithium when it is already flux-heavy and low in
>SiO2 and Al2O3. That's a lot of titanium also, I've never see it
>that high, I wonder why.
>
>22.9 Zinc Oxide
> 4.6 Whiting
> 5.5 Lithium Carbonate
>20.4 China Clay
> 5.5 Cryolite
>32.0 Flint
> 9.1 Titanium Dioxide
Titanium dioxide can be used as an opacifier, Tony. This is not that much
titanium for that use.
And zinc oxide in large amounts is somewhat refractory (not a flux) and
tends also to opacify the glaze (see "Ceramic Glazes" by Parmelee), so
other fluxes are probably needed. This is a rather large amount of zinc, as
several people have noted - more than even classic Bristol glazes.
Richard
Richard Burkett - School of Art, SDSU, San Diego, CA 92182-4805
E-mail: richard.burkett@sdsu.edu <-> Voice mail: (619) 594-6201
Home Page: http://rohan.sdsu.edu/dept/rburkett/www/burkett.html
CeramicsWeb: http://art.sdsu.edu/ceramicsweb/
HyperGlaze@aol.com & http://members.aol.com/hyperglaze/
Tony Hansen on mon 27 jul 98
Wow, that's a huge amount of zinc. With the added clay this probably
shrinks a lot on drying and it is not surprizing it cracks as it dries.
Cutting shrinkage is the answer. Try a mix of calcined kaolin and
raw kaolin. A drastically reduced amount of zinc may still fire the
same. Cryolite may be reducing the zinc and causing it to volatilize
(fume hazard). I'm not sure why this glaze would have
a powerful flux like lithium when it is already flux-heavy and low in
SiO2 and Al2O3. That's a lot of titanium also, I've never see it
that high, I wonder why.
22.9 Zinc Oxide
4.6 Whiting
5.5 Lithium Carbonate
20.4 China Clay
5.5 Cryolite
32.0 Flint
9.1 Titanium Dioxide
I think it is a good idea to have a clear idea why each ingredient
is present in special purpose glazes like these. That's the only
way you can control them and use them safely and make pots that are
safe to use.
--
T o n y H a n s e n thansen@digitalfire.com
Don't fight the dragon alone http://digitalfire.com
Calculation/Database Software for Ceramic Industry
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