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crystalline glazes-fluidity and surface tension

updated thu 23 aug 01


Jon Pacini on wed 22 aug 01

Hi Scott--greetings all--
on 8/21/01 9:44 AM, Scott B. Ackerman at Scott@SYNGRAPHICS.COM wrote:

> According to my limited knowledge of glaze formulas this base glaze

> would probably melt at cone 2-4, so why take it to cone 8-9? Does it

> have to reach a certain state of fluidity before cooling, or am I just

> missing something here.

Fluidity may not be as important as surface tension. Though the two are
closely related, one does not lead directly to the other. Alumina in the
glaze will certainly hinder crystal development, so reducing that is
important, but look to add minerals to your base that will reduce surface
tension. There's a good chart in the Hamer's book, The Potter's Dictionary
of Materials and Techniques, that can give you direction.
A mineral that I have been experimenting with that is not on the chart,
that will reduce surface tension and aid in crystal formation, is Molybdic
Oxide. Very interesting results in zinc crystal glazes. It will also produce
translucent-iridescent snowflake/frost like crystals when used in
lead-silicate glazes fired around ^3. Though I wouldn't recommend these
glazes for dinner ware, they are very unique and IMO very beautiful. Look in
Dr. Herbert Sanders' book, Glazes for Special Effects, for formulas.
Molybdic oxide is a very strange material. It seems to go from a solid,
directly into a gas, then back to a solid on cooling. So all your tests need
to be done in an enclosed sagger or it just vaporizes away. Make sure your
kiln area is well vented!

Jon Pacini
Clay Manager
Laguna Clay Co