iandol on wed 26 mar 03
Dear David Hendley,
The behaviour of Zinc oxide under the circumstances of a Reducing =
Atmosphere is a fact. Although Zinc oxide is a refractory material Zinc =
Metal has a low melting points and a moderate boiling point, 913 deg =
Celsius at atmospheric pressure. This metallic vapour readily oxidises =
again on contact with air and gathers as an incrustation which is yellow =
when hot and white when cold around bung holes, etc.
As you say, Zinc oxide can have an effect on the quality of a glaze =
which is fired to high temperature under reducing conditions. It is =
observations such as yours which have to be objectively documented if we =
are to understand why Zinc Oxide might be included as a minor ingredient =
in high and middle temperature glazes where volatilisation might be a =
problem.
Common acceptance that "Fluxing Oxides" are added to cause a greater =
degree of melting or induce melting via a "Eutectic Effect" in oxides =
which have exceptionally high melting points may be statements which =
need to be examined. Commentaries on glazing that I have read are =
unclear about the exact influence of Zinc Oxide. Its purpose is pretty =
well undefined, except as an opacifier, its use in Bristol Glazes where =
it replaced Lead and as a source for crystalline glazes.
Best regards,
Ivor Lewis
Rod on wed 26 mar 03
It is interesting while I was reading Parmlee last night looking for help
with another problem
I read that ZnO had "flotative" properties, read flocculent. Surely there is
not enough Zinc in
these recipes to get any benefits for the "flotative" properties that Zinc
would provide is there?
Something to ponder.
Everything is possible,
Rod
> -----Original Message-----
> From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of iandol
> Sent: Tuesday, March 25, 2003 10:49 PM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: : Re: Zinc Oxide in Reduction?
>
>
> Dear David Hendley,
>
> The behaviour of Zinc oxide under the circumstances of a Reducing
> Atmosphere is a fact. Although Zinc oxide is a refractory
> material Zinc Metal has a low melting points and a moderate
> boiling point, 913 deg Celsius at atmospheric pressure. This
> metallic vapour readily oxidises again on contact with air and
> gathers as an incrustation which is yellow when hot and white
> when cold around bung holes, etc.
>
> As you say, Zinc oxide can have an effect on the quality of a
> glaze which is fired to high temperature under reducing
> conditions. It is observations such as yours which have to be
> objectively documented if we are to understand why Zinc Oxide
> might be included as a minor ingredient in high and middle
> temperature glazes where volatilisation might be a problem.
>
> Common acceptance that "Fluxing Oxides" are added to cause a
> greater degree of melting or induce melting via a "Eutectic
> Effect" in oxides which have exceptionally high melting points
> may be statements which need to be examined. Commentaries on
> glazing that I have read are unclear about the exact influence of
> Zinc Oxide. Its purpose is pretty well undefined, except as an
> opacifier, its use in Bristol Glazes where it replaced Lead and
> as a source for crystalline glazes.
>
> Best regards,
>
> Ivor Lewis
>
> __________________________________________________________________
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