Jeff Tsai on thu 25 apr 02
Snail said that he heard about firing wet work, stating that he heard it
only
worked if the work was substantially wet and all the pieces were wet, not
half and half. He then said he had heard it had something to do with steam
pressure but doubted kilns were that well sealed.
Snail,
I've heard the same thing. PRessure from steam outside the pots prevents
blowups. I've also heard that because the pots are damp, the high amount of
water conducts the heat through the piece more quickly, thus un-even drying
cracks do not occur as often as one might think.
I've also wondered about how well sealed a kiln can be to make this happen,
but then again, a kiln is under tremendous pressure when you fire up to 1300
degrees C, yet, if you put your hand in front of a spyhole covered by a
plug,
there isn't an unbearable amount of heat or flame shooting out like you
would
expect since the pressure inside the kiln is so high. I'm speaking of
commercially built kilns as each person's individually built kiln is
different. I suppose if the damper is all the way shut, and you fire up
quickly at first, the steam builds up quickly in the kiln and really can't
even escape from the kiln that fast so it is enough pressure...i really
don't
know and wish one of the wiser ceramicists would explain.
on a side note...I recall terry sullivan telling me about building a kiln
god
for a pit fire once at Nottingham It was still wet when they placed it atop
the pile of wood and lit the wood. Supposedly it survived the firing without
a break. Maybe that's proof, not of steam pressure, but of the power of
water
as a heat conduit for even heating and thus crack and breakage reduction.
-jeff
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