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kiln shutters/dampers and firing

updated thu 22 mar 07


mel jacobson on mon 19 mar 07

i am a bit late into this discussion, but i have some

each kiln in the world is different from all others.

you must take into account:

elevation and then ten other factors.

no one on this list can give a standard setting
for any kiln.

suggest perhaps, but not a final answer.
and the final answer changes each firing.

take for example.

kerry brooks from dock six has a hundred cubic foot car kiln.
it is perfect in every way. donovan palmquist design/ with all
the safety devices...and blowers...big stack.

if the wind blows from the east, let us say at 12 miles an hour
constant...she cannot fire. the kiln blows out.
i know, it does not make sense. but, it does blow out.
she has asked everyone that fires kilns ....`WHY`..????
no one knows, but all say...`man, that is impossible.`
then she went to a fireplace store...and the guy said.
`oh, that happens all the time with gas fireplaces`.

the kiln is in a commercial building, it's chimney is about 30 feet from
a brick wall about 50 feet in the air...if the wind is right...the
air is forced down the stack....the reversal of air pressure blows out
the pilots with a big woooosh. kiln shuts down...relite/air comes back.
\out they it forty times, and the kiln shuts down.
now she knows...don't fire when the wind is from the east.
don't fight it. all the theory in the world does not help her.
it just does not work. she fires a great kiln and knows her stuff.
one of the best kiln firing people i know...but, she hates east winds.
that is the nature of her kiln.

the damper is one way to get reduction, gas pressure is another,
turning back primary air is another...and it is always a dance, knowing
what glazes you are firing, what atmosphere you want, what temp
rise you expect. there is no simple answer.
it always changes for me.

for example:
iron saga firings...take out the damper, put kaowool in the slot.
open the primary air shutters as far as they will go without
back firing. almost no gas pressure. slow firing.

my last firing with experimental glazes:
slow firing, damper half closed, primary air shutters almost
closed. medium heat rise with a smoky atmosphere in the
peeps...all four of them. it was hard to see the cones. back
pressure at the ports...about four inches.
kept it that way for the entire firing.
down fired for two hours.

high gas, power all the way. lots of reduction, both wood
sticks and air shutters half way closed. damper in
often...lots of back pressure. black carbon on the
down fire for three hours.

now, think of my house/studio.
one day:
85 degrees F., clear skies, no wind..barometric pressure
at medium. 41 feel above sea level.

six months later:
-45F, strong wind, heavy snow, barometer is as high as it will
go. still at 41 feet above sea level.

note anything different?
i still have to fire my kiln.
all settings change. i do the dance.
gas pressure, damper and primary air. i have to set the kiln
to fire the pots i want fired. and it all depends.

you learn your kiln, like you learn your clay and glaze.
it all depends on what you are doing.

if you have to follow a schedule or recipe for firing from a manual, and you
want it always the same.....well, you have trouble ahead.

you learn your kiln by doing many things to it while firing.
turn the gas really high, move the damper, mess with the
primary and secondary air.
chart what happens. turn one burner on full, one burner on half.
see the heat move across the kiln. low gas pressure will often
move heat to the top, lots of gas will push the heat down.

you want to find the perfect settings to fire with even heat.
you have to learn it. many firings changing things around will teach
you. when you hit a snag and kiln stalls...what do you do? keep
firing because the instruction manual says...this is the setting?
no, you change things. most often, for a stuck kiln, you turn
down the fuel.
but, like most folks, as with a car....hit the foot feet...turn up the
gas and start warming the world, not your kiln.

from: mel/

Clayart page link:

Ivor and Olive Lewis on wed 21 mar 07

Dear mel jacobson,

You say << no one on this list can give a standard setting for any kiln. =

True, and I agree with what you have written. But there are protocols =
that define best working practices that apply which should be followed =
in the interests of personal safety and the protection of property. (Hey =
John, the pilot's out. No worries Jack, there's a good flame on the =
burner and I've wired up the shutoff valve ! ! )

In the case of a commercially produced kilns there should be precise, =
unambiguous instructions for "Start Up" and "Close Down" relating to the =
ignition and extinguishing of burners. Those of us who build our own =
kilns but use manufactured burners should ask our supplier for =
instructions relating to their products. If instructions are not =
available, national governing councils of our industry can be asked.

Best regards,