vince pitelka on sun 6 may 01
> It would seem that feldspar is not needed for a good soda glaze.
Steve -
It can help give a smoother glaze in some claybodies, but it seems
redundant, since the atmosphere is providing soda. The glaze formed is
composed primarily of sodium, alumina, and silica. That's why we have so
much crazing in salt/soda firing. The action of the soda on the aluminum
silicates and pure silica depends on amount of salt/soda charged into the
kiln, the temperature, and the firing time during and after charging. A
lighter charging of salt/soda on a stoneware body containing some potash
feldspar creates a glaze which crazes less. Also, when the kiln is soaked
for a longer period after the last charging, the soda has more opportunity
to interact with the aluminum silicates and pure silica, and the
concentration of sodium in the glaze surface decreases, which will lessen
the amount of crazing.
I am not a salt/soda firing expert, but the above is based on salt firing
with my students over the years.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
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