Craig Martell on tue 29 dec 98
Shelley asked in a previous post:
>Craig - your comments about bisquing (sp?) the porcelain higher (to >03)
sound interesting. Does this help keep platters from warping as >well? My
porcelain is grolleg based - I don't have cracking but do have >problems
with warping occasionally.
Phase two, when Martell finally gets off his butt and responds!
HI Shelley:
No, the 03 bisque doesn't help minimize warping. It actually promotes some
in the bisque due to the higher temp softening the spar in the body etc.
I've found that careful handling, forming, and drying, will prevent
excessive warping. I think you can't eliminate warping totally but one can
minimize it to the point that the work will still be considered pristine.
Careful setting in both firings helps greatly. I use crystars and advancers
for glaze firing, which are very flat. For large feet, I jump the crack
between the 12 X 24s with 14 X 14s and 16 X 16s to give big platters and
bowls a flat uninterrupted surface to sit on. I also spray my kiln wash on
to avoid bumps, nurds, and other uneven stuff that will interfere with the
ware shrinking at an even rate. I learned this from Tom Turner.
Grolleg won't need an 03 bisque. I've been told that it contains some
sericite mica which aids fusion at lower temp. An 04 bisque will make most
grolleg bodies quite strong enough to survive quartz inversion.
regards, Craig Martell in Oregon
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