Janet H Walker on tue 3 sep 96
According to Norton's 1950's book, electric kilns that are tightly
packed can in fact be reducing during bisque as the carbons and
other things try to burn out. (The book was "Ceramics for the
Artist Potter". it seemed to have a lot of interesting information
that I haven't seen in more recent books. Like the fact that light
insulation, small electric kilns cool too fast to give good glaze
results.)
Jan Walker
Cambridge MA USA
ROBERT POGSON on wed 4 sep 96
jwalker@world.std.com wrote:
JW> The book was "Ceramics for the
JW> Artist Potter". it seemed to have a lot of interesting information
JW> that I haven't seen in more recent books. Like the fact that light
JW> insulation, small electric kilns cool too fast to give good glaze
JW> results.)
JW>
JW> Jan Walker
JW> Cambridge MA USA
The rate of cooldown could, in principle, be slowed by reducing the
power instead of cutting it off. Some of the automated controllers are
probably able to do this as they can follow heating rates. A negative value
is just cooling. I have operated my kiln manually after the kiln sitter
tripped to be sure that the cool parts get to the desired temperature but
I don't have a pyrometer (that works) so I haven't tried controlled cooling.
On some large complex pieces (1 to a kiln), I've had to do extra slow heating
and cooling because they would often crack with the routine process for a
kiln full of smaller pieces. I fire to near my limit and just turn down the
power to 80% or so instead of cutting it off. I do this in several steps on
the way down. The rate of cooling depends on temperature differences mainly
so the rate is most sudden at the highest temperatures. I'm not sure where
the greatest stresses are but if it saves a valuable piece, I'm willing to
spend a dollar more on electricity. The glaze effects are probably due to
uneven temperatures just as the thermal stresses are, so controlling power
to hold at the set point and slowing the cooling may be helpful. I've had
no problem producing neat glazes in my kiln but then beauty is in the eye of
the beholder. My problem is applying the glaze uniformly :-(.
.... nfx v2.8 [C0000] Flame: flatulence combusting.
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