mel jacobson on fri 9 nov 07
as my years of experience grow, i more and more
think that many potters `over reduce`...many think
that some magic will happen to their pots if they
have lots of smoke/fire and back pressure.
in many ways it is not good for your pots, it knocks
out wonderful color and in general, ruins very fine pots.
many of you that fire fuel kilns have found
very good methods that serve the pots you make. that
is how it should be. every kiln or set of glazes has parameters
that are perfect for your system. the learning curve is very
exact in many cases. if you have learned that...and you are
happy with your pots...great.
there is tons of b.s. and false information on what happens
when the kiln goes into reduction, how much you need, and
how long you should reduce.
here are some things that we/mel and friends have found
out over years of firing.
1. lots of back pressure and carbon filled smoke with dirty
flame does not mean you are getting perfect reduction in
your kiln. in fact...you may be in neutral, with your reduction
all spilling out of the kiln. you want the carbon in the kiln, not
spilling outside. if there is flame from the stack...you are doing
something wrong. back off. some kilns fire with a very clear
atmosphere and are reducing like mad...some are very smoky.
depends.
2. firing with blue flame, as clean as you can fire is the
sensible way to fire. get as many btu's out of your
fuel as you can get. fire for economy...good sense..never
waste fuel.
3. use your damper and your gas pressure to assure your
kiln is in reduction. back pressure is the first key. measure
that flame coming from your middle peep hole. always use
one peep as your standard for reduction.. that peep high
in the kiln will always show some back pressure..the one at the
bottom may never show back pressure. pick a peep and stay
with it. it is your control. 3-5 inches is plenty of back pressure
in most kilns...it may vary...but not that much.
4. some glazes need early reduction..shino is one. but, most
glazes do fine with a start at 08 or so. when in reduction, leave
it be. when you are sure the kiln is chuggin along...perfect gas
pressure, soft reduction...the temp will just make a steady
climb. if the kiln stalls, back off the gas pressure a bit. open
the damper a half inch. it should start right back up...wait for
it. don't stare at the pyrometer...every thirty seconds.
don't wring your hands and say `oh my, oh my`.
wait for it. you can adjust the damper and the gas pressure
and watch the back pressure out the center peep. keep the
length of the flame the same...move the damper and gas
and see what happens.
5. try moving one burner to full pressure, and lower the other
one...see the heat move across the kiln. try full pressure
and see where the heat goes...turn the kiln way down...chart
what happens. often heat high or low will depend on the amount
of gas pressure you are using. splash bricks in the flame-way will
help heat go up. break up the flame...make turbulence. it helps.
if things go wrong...change what you are doing. chart it.
never fire over and over the same way...with poor results.
that is really dumb. `man, i fired this kiln 83 times and never
reached cone 10.` now that is a dumb jerk. rebuild the kiln
if you have to ...but never keep firing and not good get results.
6. oxyprobes are great teaching tools. they are expensive
and very breakable...so, i have found that sharing one, or
borrowing one for a few firings is wise. once you have probed
your kiln a few times...you will better understand what is going
on with reduction. i sure do not need one on my kiln any longer...
i know that kiln. i have used my oxyprobe often to fix other
people's kilns. it is good to show them what they are doing wrong.
sort of black and white evidence.
7. clearing the kiln at max temp is good, for most glazes. some
however do not need it. you will find out if you chart your
firing. crash cooling from cone 10 to cone 6 works...but, it
depends on your glazes. (and, your own courage.)
8. firing wood in a closed up kiln will certainly help to get very
even reduction. i use small sticks and start about 2200f. just
adding sticks every 10 minutes. i mean small sticks...quarter/half inch,
four inches long..maybe 5 at a time.
9. understanding slow cooling is the wave of the future. down
firing at 1900f.
in fact....how you cool is more important than how you fire.
bob anderson and mel have done a dozen firings in oxidation and
down fired and then burned sticks until 1700 and got great/ perfect
reduction...now hear me, no reduction on the way up...none.
reduced on the way down. it was perfect each time.
i know some will not believe that...they were told that clay seals up.
does not happen to me. nice brown/toasty pots...reduce during
cooling.
10. heavy reduction can be a flux and warp or melt your pots...esp
if you use iron bearing clay. heavy reduction can flux your glazes
and cause them to run....it also makes some wonderful glazes very
metallic and ugly.
12. be smart, experiment, chart your firings...note the weather,
wind direction...barometer. they all count. note the position
of your gas pressure valve system. add a gauge if necessary.
i mark my ball valves. full, half, quarter. use paint on your
valves. and, for safety...show a pix of off. show people you
live with how to shut off the main gas tank or gas valve.
have more than one on/off system. we have a rule at the farm.
if someone yells... `TURN OFF THE GAS`....everyone should
run for all the tanks. everyone should know how to do it.
it should take 10 seconds..max to get them all off.
all burners should be on a `regulator` system.
AIR HAVE LOTS OF air
moving around your kilns...if indoors, use fans...four or five of them.
floor, ceiling, around the kiln...vent fans and air moving fans.
get some box fans at a garage sale...place them in the room facing
different directions. put them all on low. moving the air is very
important. do not sit around a firing kiln. back away. never
stay in a kiln room...get in, get out. check things...see that
it is all working...and get out.
NEVER TRUST A KILN/GAS/ELECTRIC/WOOD. NEVER TRUST A KILN SITTER.
NEVER TRUST A HOSE. NEVER TRUST A GAUGE. BE CAREFUL.
PLAN FOR THE WORST, HOPE FOR THE BEST.
IT WORKS AS A MOTTO. keep a chemical fire extinguisher near your
kiln. remember, never spray water on a kiln fire. it could explode
the kiln...and kill everyone...esp fire fighters. carry a timer with
alarm in your pocket. when it goes off...check the kiln now.
use oven timers...alarm clocks, have people/friends/ loved ones remind
you of timing. `dad, did you check the kiln?`
so...LOTS TO THINK ABOUT.
my favorite kiln/dumb guy story.
went to an center...looked at the new kiln donovan palmquist
built for them. saw the c clamp on the baso valve. two weeks
later she blew up. no one hurt...but the kiln had to be rebuilt.
of course...it was an accident.
sure.
dumb shit.
`we don't need mel to tell us how to fire kilns or anything
about safety. and `so`...we use barium and manganese in
our temmoku...who cares? and sure, we mix glazes with our
arms...who cares?` lots of `dumb` out there folks.
we must all make a difference.
mel
from: mel/minnetonka.mn.usa
website: http://www.visi.com/~melpots/
Clayart page link: http://www.visi.com/~melpots/clayart.html
William & Susan Schran User on fri 9 nov 07
On 11/9/07 4:43 PM, "mel jacobson" wrote:
> try moving one burner to full pressure, and lower the other
> one...see the heat move across the kiln. try full pressure
> and see where the heat goes...turn the kiln way down...chart
> what happens.
Mel makes many good points.
To illustrate:
Have Geil kiln, natural gas fuel.
Went through year of firing trying different things to affect
reduction/firing times/eveness.
Set primary air opening on burners, never change that, got blue flame, get
great reduction.
Have been playing with reducing gas pressure.
Now use half the pressure that I started with 2 years ago.
Firing time actually still almost the same, but getting more even temps top
to bottom.
Now addressing stacking of the kiln.
Taller pots on the bottom.
First added shelf now above flue level.
More even temperature.
No smoke, no flame from stack - never.
Great shino, celadon, copper reds.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
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