Jonathan Kirkendall on mon 18 nov 96
I have been using the following cone 9 oxidation glaze from Ceramics Monthly
Kentucky Ball Clay 40%
Neph sy 4%
On porcelin, it does fine, runs nicely but not too much. However, on my buff
(almost white) stoneware, each end point of a run ends in a blister, or a
collection of tiny bubbles like soap suds. It seems to blister in this
pattern no matter where I place it in my kiln. I have fired with both a 9
and a 10 in my kiln sitter, and its the same. If I dip it again and refire
to cone 9, it melts just right and looks good. I do use a kiln vent under the
kiln which I keep running after the kiln has shut off as the manufacturer
suggests, but I wonder if this is the problem. Any suggestions?
Baffled in Yonkers,
Craig Martell on tue 19 nov 96
Jonathan: I've had this problem before in both Ox. and Red. at cone 10.
Even though your glaze runs like an ash glaze, it is probably very viscous
at high temperature and the white stoneware could be gassing a little and
contributing to the problem. The tips of the "runs" being thicker, are the
most likely place to see the worst case scenario develop. Seeing as how a
refire corrects the problem, I would try soaking the ware at high temp. to
get rid of the bubbles. If this doesn't work, you may need to make some
adjustments the ball clay or whiting to drop the viscosity at melt and allow
the gas to excape more easily. But, if the glaze works OK on porcelain, you
might want to use it only on that body. I have a cone 10 ash glaze that is
really reliable and would be glad to give it to you if you want to try it.
The glaze uses wood ash so you might not want to use it. Anyway, let me
know if you want the glaze.
Kind Regards, Craig Martell-Oregon