Jeff Tsai on sun 20 jan 02
Hi Martin,
Actually, I myself usually only bisque work if I'm loading it in a pit with
other people...I don't want my work to accidently blowup and scratch their
work right next to mine...it's a courtesy I've picked up working in a
multi-person environment.
The truth is you can pit fire greenware. The breakage is sometimes greater,
but can be reduced with a few simple precautions:
Dry your work completely before firing it. Let it sit out in the sun for
several days after it has already become bone dry.
Dry your work in an oven right before you put it in the pit. The Mata Ortiz
potters have (to some extent) taken this habit up. Right before the work goes
into the pit (well, for them it's not really a pit) they dry the piece in a
conventional oven to about 400 degrees F for a couple hours. Start out at a
the lowest temperature setting (hopefully below 200 degrees, for an hour or
so and then raise it up towards 400. Really what your trying to do is force
out all the water. Water turns to steam at 212 degree F and that reaction
(water to steam) is what causes a lot of breakage in pit fire work). After it
has dried in the oven, take it out and keep it wrapped in a towel until you
place it in the pit.
make sure the ground of your pit is dry. Residual steam and moisture from the
ground can also cause problems. I live in San Diego...but if it does rain,
I'll light a small fire in the pit a day before I use it to dry the ground.
Lighting the pit evenly (by using paper and lighter fluid) helps also. The
most common breakage I see in pits even with bisqued pots is when one side of
a piece is hotter than another side. Usually at the end of a firing I see a
piece half submerged in hot coal and the other half has blowout holes because
it's in open air.
Use a claybody with a lot of grog. Grog will help the piece heat evenly. If
you burnish and can't stand the idea of using grog, try using a body with a
lot of talc. This might be hearsay especially because I don't recall who told
me, but talc seems to absorb shock pretty well. Hey, I fire my 50/50
talc/ball claybody up to 1700 degrees in less than an hour and I haven't had
one break yet...so there might be something to it...
hope that helps.
-jeff
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