David McBeth on tue 30 sep 08
Back in the day, grad school we always called rutile - Ceramics Light- =
tone Rutile. Has the material changed, or just the way we talk about =
it?
Dave
David McBeth
330 B Gooch Hall
Department of Visual and Theatre Arts
University of Tennessee at Martin
Martin, Tennessee 38238
731-881-7416
http://davidmcbeth.blogspot.com
-----Original Message-----
From: Clayart on behalf of Ivor and Olive Lewis
Sent: Sun 9/28/2008 2:35 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Rutile blue; a question!!!
=20
Dear Lili,
I had a look in Chappell, page 186 which gives the Floating Glaze
recipe. It contains Red Iron oxide, Cobalt oxide and Milled Rutile. It
also contains Colemanite, a rich source of Boron.
I would suggest the science of this glaze is complex. It contains two
glass forming oxides, Silicon Dioxide and Boric Oxide. Other oxides
are Soda, Potash and Lime. According to Kingery et al these modifying
oxides, especially those of the Alkali Earth Group like Calcium oxide,
influence what happens, promoting two glasses which do not mix. When
the inclusions of one glass in the other are of a favourable size
there is an optical effect. The glaze becomes opalescent and blue. In
effect, it has properties similar to those of a Chun or Jun style
glaze.
What should be expected of The Rutile content ? Under normal
circumstances this is an opacifier, so it either does not enter into
any reactions with other ingredients or it precipitates on cooling.
Why Cobalt in this recipe ? Possibly to guarantee getting a blue if
conditions are not just quite right in the kiln to deliver the desired
effect !
A good source of information relating to opalescence in glazes is
Nigel Wood,"Chinese Glazes". ISBN 90-5703-23-25.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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