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reduction discussion

updated wed 8 aug 07


mel jacobson on tue 7 aug 07

my take on reducing a kiln is based on
an `assumption`/that supports ron's theory.

i like a constant, consistent amount of reduction.
starting at about 1750F and holding the kiln
so that the back pressure is the same for the
entire firing.

(because of outside forces...wind, outside temperature
and the changes in the barometer as one fires, or
from firing to firing...the damper and back pressure of the
kiln changes. the potter must be aware of these changes and
adjust accordingly. no recipe for firing...only change and
observation. the potter increases or decreases gas pressure
or damper position to create inside the kiln a constant state
of reduction and temperature rise. this cannot always be
predicted. experience and the ability to know your kiln is important.
also, saving gas pressure for hard times is critical.)

i have worked hard over the years to get consistent
reduction. we do the same thing at the farm with group
firings. bob anderson and i have fired together often.
we measure the amount of back pressure, and discuss
the length. we have a like mind...same for cone bend.
we even, at times draw a picture of the position of the cones on
the kiln with chalk. this is how the cones must look for the
kiln to be finished. cone 11 at 3 o'clock. or, depending on
the glazes, the cone may vary...we may look at cone 12
touching. it all depends.

it is hard not to clear a kiln at the end. when you shut off
the gas, you have some minutes to close up the kiln.
we often leave out the peeps and ports, leave the damper
all the way out for a few minutes. then button it up tight.
but, that depends on the glaze load. i often load the
kiln with wood when it is closed up tight. i want those
last iron spots to explode on the surface of the glaze.
(i obviously do this without any great chemical or physics
evidence that it works...can't see in the kiln...and, even
if this is in the theory of `kiln gods` i do it anyway.
all i can ever do for proof is show folks the pots. they
seem to be pretty good, most of the time. and, i don't
want to screw that up.

it is the same for down firing. it sure cannot hurt to re/light
the kiln for an hour at 1900. it just slows things down.
i do it every time...esp for shino and copper red. it works.
and, the kiln seems to even out.

there is a great deal of hocus/pocus and urban legend about
firing. same for reduction. i think i am past a great deal of that.
good science, good record keeping and listening to folks that i
really respect has changed my mind on many `old theories`.

keeping your kiln tight and buttoned up, making sure your stack
is tight as a drum and your fire box clean and tight is damn
critical. never letting that flue opening get big, like 80 sq inches
and understanding how to load the kiln. i also find
that a tuning brick in the flame/way is damn important.
kicking the flame around makes the heat go up or down.

no kiln should stall. if it does...there is something really wrong.
never continue to fire a kiln that stalls. you just heat the atmosphere.
(and get crappy pots.)
many kilns stall because the potter is firing like they drive a car...
`want more speed, push down on the foot feed..` often it is just
the opposite.

from: mel/

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