mel jacobson on thu 8 aug 02
there are some simple steps to follow.
reduction is a combination of events. some work
better than others.
hank is totally correct, a tight kiln reduces better. as kilns
age, and split apart, they are harder to control.
(time for a good itc spray coating.)
i like to look at the three basic elements of reduction.
amount of gas pressure.
size of flue opening.
amount of primary and secondary air.
the one that is the most often ignored is gas pressure.
the more gas pressure you use, the easier it is to reduce.
often potters use so much gas, they cannot fire oxydized.
so:
i use a small cone in front of my big cones to let me know
when to start reduction. put a small thumb impression in the
clay, below the cone to catch the melted cone. you will not like that runny
crap on your shelf. if doing shino, i put in a cone 011, for regular
firing, a cone 08. it is a good reminder when to start.
(also creates consistency, i know, what a concept.)
your kiln will not have very much energy working at cone 011. so,
i add some sticks of wood to the kiln. close it up a bit for shino.
push in the damper, give it full gas, close down the primary air
a bit. to get carbon trapping, you have to fuss.
for a regular firing, i just move in the damper and leave the
primary air alone. full power, or, gas on as much as you have,
damper in until you get two inches of back pressure from the
(half way up) peep holes. don't worry about bottom peeps,
you won't get much back pressure there. top peeps will get
the most back pressure normally...so i gauge from the center ones.
the interior of the kiln will get smokey....if it is clear, you do not
have reduction. check the
interior. the color in the kiln will be red/orange/cloudy.
don't sit around an early reduction kiln...lots of crappy stuff coming
out. check it, and scoot.
leave it that way for at least an hour. the kiln should climb just a
bit. then i back off the gas pressure and open the damper a bit.
try to get the kiln to climb with about and inch of back pressure. it
may be more or less depending on how your kiln fires. moving the
damper in quarter inch increments works. chart it. don't just move
it out three inches or so, tiny increments...and measure the back pressure
flame with a ruler.
you should be able to maintain the back pressure flame even if you
reduce the gas pressure and put the damper in a bit, then reverse
it...open the gas, open the damper and keep the flame coming out
of the kiln.
it is not one thing...it is the combination. turning back your primary
air works, but, you will not get the kiln to climb....you just lost btu's.
dirty flame.
if i want heavy reduction for the glazes i will keep the damper in,
open up the gas pressure, and turn down my primary air. then i will
get a smokey three/four inch flame from middle spy hole. very cloudy
interior.
the critical thing, is to not let your kiln stall when reduction starts.
keep it moving. experiment and chart. weather plays an important
part in how the kiln fires.
minus 55 F. strong winds, snowing. how does the kiln fire?
98F and humid, no wind. how does the kiln fire?
things change. so, you have to change.
gas pressure
damper in and out
primary and secondary air.
all factors. use all of them. chart.
i have wrapped aluminum foil around the back of burners to choke
them off. (hey, dorko, not a full wrap, just a partial to cut
off the primary air on weed burners. they do not have adjustments.)
stuff koawool into the air ports works too. sometimes you just
need to back off the air.
i love wood. i stuff small pieces of wood into my kiln when it is
finished firing. close it all down, and insert the wood in the burner
ports. i can pull back my burners, so it is easy. then close up the kiln
and let it smoke. works. (only if you like medium to heavy reduction.)
i then down fire my kiln. but, that comes about three hours later.
it is all a dance. it is not one size fits all. understand what is going
on. it is never the same. some days you waltz, some days you do
the rhumba.
you may want to burn your old firing schedules...make good fuel.
get the theory of firing in your head. read the kiln as it fires.
the charts and graphs are learning tools, not road maps. you fire
the kiln, not the charts. they are reference points.
if you fire with compressed air/well it all changes. then you can
fire by the chart. you do not need a stack, you just control the air/
gas mix. automatic almost.
wood fire/your life changes again.
mel
From:
Minnetonka, Minnesota, U.S.A.
web site: http://www.pclink.com/melpots
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