Megan Ratchford on thu 3 jun 04
I am a product of the McKinnell's way of firing myself. Jim always
insisted that if you speed cool a kiln, down near to quartz inversion, you
would get richer and cleaner colors. At the Arapahoe Community College it
was standard procedure to pull the damper all the way open, shut off gas and
the blowers then cool till pyrometer reads 1600 deg F when we close the
damper. We've never had a problem and always lovely glazes.
However, at the Arvada Center I always button up my high fire salt kiln
tight as soon as the burners and blowers are off. I think in this instance
I like the atmosphere to hold itself and soak the pots in the residual salt
vapor a little as it's cooling.
Any other styles of cooling a kiln?
Where my pieces were just shoe-horned into the salt kin and I will fire them
Llewellyn Kouba on thu 3 jun 04
I was trained (at least by the person in the studio here) initially when
firing a gas kiln and the cones were down and one determined the load was
finished you would immediately (in a matter of seconds) throw the main
switch cutting the power, slam the chimney flue shut, turn off the gas and
stop up the burner ports. Now I begin to wonder if it needs to be or
should be done that fast or if it makes a difference. Is it possible on
all the variables and intricacy of firing if you come to a sudden stop with
the whole process?
Ivor and Olive Lewis on fri 4 jun 04
Dear Llewellyn Kouba,
That person who taught you the shut down procedure has got it right
from two perspectives
The first is that of safety. If a defined protocol is not applied then
there is potential for accident when the equipment is next used.
The second relates to the convention that at a certain point when a
chosen cone has deformed by a stated amount selected glazes will give
desired effects. This notion relies on the belief in the absolute
value of "Heat Work" which really means that a fixed number of Joules
of energy are absorbed by the Cone in a measure of time at a
particular rate of energy input. The assumptions here are that clay
and glaze which comprise the load absorb heat at the same rate, per
kilogram, as the cone does. At which we introduce the arguments, the
if's, the but's, the maybe's, the perhaps's, the what if's. If it is a
case of "Cone has touched down, firing finished" Your kiln teacher
ignores all of these.
At the moment the "biggie", especially following the publication of
Mastering Cone Six Glazes, is what if you want to encourage some post
maturity crystallisation?. Then, that instantaneous response is always
inappropriate. But the need for a safety protocol remains.
Sounds like there are some choices that have to be made.
Ivor Lewis. Redhill, South Australia
Potters Council Member
Laurie Kneppel on fri 4 jun 04
I've been following this thread with interest because i had felt that=20
my Geil fiber kiln maybe cooled down too fast. I have been firing it=20
using the cone 10 reduction procedure in the owners manual and have=20
gotten good results - even got some nice oxbloods the very first=20
firing. One of the things the manual specifies is when the desired cone=20=
is down to shut off the gas and close off the flue immediately. Then to=20=
put up barriers around the bottom of the kiln to prevent cool air from=20=
swirling around underneath and getting up the burner ports. Though they=20=
say nothing about stopping up the burner ports I wonder what you would=20=
use to do this? Fiber blanket chunks? Or if just putting sheets of=20
metal all around the bottom of the kiln is sufficient. I am still new=20
to gas firing and have only fired the Geil 4 times now, so I am still=20
"getting to know it". It's the small model 802, 8 cu. ft. I'm the=20
second owner and it is in great shape.
The last firing I did I had the kiln stuffed as full as it could=20
possibly get and not have anything stick together and maintaining=20
specified shelf and flue clearances. Every shelf I own for it was used.=20=
I did note that it took a bit longer for the 10 cone to fall with it so=20=
full, but I was satisfied that I had a most economical firing that way.=20=
I think it finally fell at about the 12 1/2 hour mark. And I also noted=20=
that it took a lot longer to cool down, something like 36 hours before=20=
the pyrometer was down to about 200=0F deg F. Usually it is down to =
in about 24 hours. I had gotten the sheet metal really close around the=20=
bottom, which probably helped keep the heat in.
Aside from two ugly brown pots where the blue glaze went yuck on a new=20=
clay body, everything else in the kiln was gorgeous! I think the=20
slightly longer firing (usually it gets to cone 10 in about 10 hours=20
following the manual) and slow cooling made a big difference.=20
Beautiful, non-pinholed orange shinos, some nice Reitz Green to Black,=20=
and a couple good oxblood bowls.
So based on my own kiln I am guessing that closing up everything=20
immediately (as the manual specifies), is the way to go for a basic=20
cone 10 reduction. I am also guessing that different kilns behave=20
differently and you need to do what either your owners manual=20
recommends (if you have one), or what works best to give the desired=20
results and is safe.
Potters Council, member
Sacramento Potters Group, member=