Marcia Selsor on tue 8 nov 05
Dear Paul,
I have fired with diesel so maybe this may help, may not. Back
pressure only means you are pumping a lot of air into a dampered down
chamber.
To reduce you have to cut your oxygen. You can check that by holding
a stick in the peep holes and see if it burns or not.
If it burns, you are not reducing. If it doesn't burn, you are
reducing because there isn't enough oxygen to allow it to burn. Simple.
The smell from the oil may not really indicate reduction but may just
be the burning oil. Smell like french fries, (liberty fries to be PC)?
I can't tell you anything about oxy probes. never used one. Never
seen one. Oil smokes a lot. It is embarrassing to reduce in daylight
even!
But you can get some beautiful reds with oil.
Hope this is a little bit of help.
Marcia Selsor in Montana
white stuff left by 3 and warmed up.
I don't know what type of burner
On Nov 8, 2005, at 2:22 PM, Paul B wrote:
> Early in my apprenticeship i read/heard, not sure which, that a gas
> kiln
> could potentially have back pressure with flames coming out the
> spyholes
> but still have an oxidation atmosphere inside.
> I am not exactly sure where this info came from and i never found
> it to be
> the case in my experiences, but i have only used two different kilns.
> At the moment i have a pair of waste oil burners firing in my kiln
> from the
> back with the damper open only about 1" and fairly long flames
> coming out
> the spyholes, kind of an organge/red color with some blue as well.
> But i
> borrowed an oxyprobe from a friend and mounted it in the door and
> it is not
> giving much of a reading at all. It flicks constantly from one
> number to
> another but stays below 1.0. I know the probe works because my
> friend just
> fired his kiln with it with a reading of about 6.5 throughout.
> The kiln even has a bit of that "monoxide" smell to it that it has
> when i
> reduce with my gas burners.
> Anyone out there have a similar experience or anything to add to
> this? I
> find it hard to believe the kiln is oxidizing right now, but
> according to
> the probe it is. I only have few reds in there, maybe in a couple
> days when
> i open it i will find the answer but i would like to hear some
> opinions on
> this.
> thanks,
> Paul
>
> ______________________________________________________________________
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Frank Colson on tue 8 nov 05
Paul- Excessive backfiring resulting in oxidation is usually the result of
combustion taking place "outside" the kiln. The kiln itself has become
a "stack" from which the flame is passing through. This is almost always
identified by the odor of carbon dioxide which is not so much an order but a
"smarting" of the nose when near this kind of action. You need to pull the
flames back into the kiln chamber!
Frank Colson
www.R2D2u.com
----- Original Message -----
From: "Paul B"
To:
Sent: Tuesday, November 08, 2005 4:22 PM
Subject: DOES BACK PRESSURE IN KILN MEAN REDUCTION?
> Early in my apprenticeship i read/heard, not sure which, that a gas kiln
> could potentially have back pressure with flames coming out the spyholes
> but still have an oxidation atmosphere inside.
> I am not exactly sure where this info came from and i never found it to be
> the case in my experiences, but i have only used two different kilns.
> At the moment i have a pair of waste oil burners firing in my kiln from
the
> back with the damper open only about 1" and fairly long flames coming out
> the spyholes, kind of an organge/red color with some blue as well. But i
> borrowed an oxyprobe from a friend and mounted it in the door and it is
not
> giving much of a reading at all. It flicks constantly from one number to
> another but stays below 1.0. I know the probe works because my friend just
> fired his kiln with it with a reading of about 6.5 throughout.
> The kiln even has a bit of that "monoxide" smell to it that it has when i
> reduce with my gas burners.
> Anyone out there have a similar experience or anything to add to this? I
> find it hard to believe the kiln is oxidizing right now, but according to
> the probe it is. I only have few reds in there, maybe in a couple days
when
> i open it i will find the answer but i would like to hear some opinions on
> this.
> thanks,
> Paul
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Paul B on tue 8 nov 05
Early in my apprenticeship i read/heard, not sure which, that a gas kiln
could potentially have back pressure with flames coming out the spyholes
but still have an oxidation atmosphere inside.
I am not exactly sure where this info came from and i never found it to be
the case in my experiences, but i have only used two different kilns.
At the moment i have a pair of waste oil burners firing in my kiln from the
back with the damper open only about 1" and fairly long flames coming out
the spyholes, kind of an organge/red color with some blue as well. But i
borrowed an oxyprobe from a friend and mounted it in the door and it is not
giving much of a reading at all. It flicks constantly from one number to
another but stays below 1.0. I know the probe works because my friend just
fired his kiln with it with a reading of about 6.5 throughout.
The kiln even has a bit of that "monoxide" smell to it that it has when i
reduce with my gas burners.
Anyone out there have a similar experience or anything to add to this? I
find it hard to believe the kiln is oxidizing right now, but according to
the probe it is. I only have few reds in there, maybe in a couple days when
i open it i will find the answer but i would like to hear some opinions on
this.
thanks,
Paul
Mark Issenberg on wed 9 nov 05
When im firing my Alpine using the oxyprobe there is a fine line with my
damper. Until the place is met the reading bounce all over scale. In my Alpine
its around 65 to 75. I dont touch the damper again in the firing. As the temp
rises the numbers on the probe go down , a little.
I dont have flame or smoke out of my bottom peep hole but there is flame
from the top peep. Some times there is a really green color in the flames , both
from the peep and also the top at the damper.
Hope that helps
starting to glaze today
Mark on Lookout Mtn
Overall's on wed 9 nov 05
Paul B;
In response to your question if a gas kiln has back pressure with flames coming from peeps/ports, could it be in oxidation? YES!!!!!!!
I learned this numerous times as I was learning to fire. I never could "get it" making adjustments to experiment. After using a friend's oxyprobe one time, I could understand how sensitive the kiln is to proper reduction firings. That convinced me to buy an oxyprobe for repeatable reduction firings.
I have put my oxyprobe through the ringer only having just bought it. I got the 10" as my first kiln is small with 3" walls, but I was still using it in my friend's "properly" 9" bricked kiln. FIRST mistake was not protecting the probe's head from back pressure with kaowool or kiln wadding. The hole was drilled for his 12" probe being 3/4" and mine 10" required a very necessary 1/2" hole. Back pressure flames torched everything inside. Luckily, I have another friend whose husband is an electronic whiz and he fixed it. He didn't charge me anything, but I did get him and my friend some of their favorite goodies from Whole Foods.
SECOND learning experience: the white porcelain ceramic protection sleeve is VERY fragile. Mine snapped in the next firing necessitating me to purchase another one. $25 plus s/h later.
By the next firing I am being super careful and mindful of any body movement around that thing. All during the beginning of the firing is fine. When reduction begins, the probe goes blank, dead no readings of anything and I think, "what the ..." hoping it can't be the back pressure frying the wiring again. As the new protection tube had not arrived, I was firing the probe with the broken sleeve and thought something happened to the wire. Having fired a couple of times with the probe, I thought I could wing it by observing the smell, peeps for back pressure and excess of black carbon, as well as the flame color from the top ports.
When the kiln cooled, I looked closely at the probe's wires and they looked intact. I replaced the 9 volt battery and it lit right up. A huge sigh of relief. Seems if you leave it on all during the firing as I had done, you need spare batteries at hand.
Back to the oxidized back pressure thing. A good indicator, as you will see when you get your oxyprobe, of a great reduction is the color of the flames. I see a more greenish yellow than an orangy blue when reduction is right. When you have orangy blue, that is pure oxydized firing.
Kim Overall
http://www.houstonpotters.com
marvpots@juno.com on wed 9 nov 05
Damper adjustments are important but equally important is to reduce the =
amount of air coming into the kiln; with the proper reduction of air co=
ming in, and the damper closing off enough of the flu opening you'll get=
a reduction atmosphere throughout the kiln and if you are using an oxyp=
robe, it will read numbers associated with reduction, eg., 0.5-0.6. The=
n the damper can be adjusted if necessary.
I have calibrated my gas kiln damper so that I can tell (and record) wha=
t percentage of the flu is left open.
Hope this helps.
All the best.
Marvin Flowerman
=
=
Ivor and Olive Lewis on thu 10 nov 05
Dear Paul,
An interesting proposition. But to give a reasonable answer I think you =
need to tell us what sort of burners you are using, about your control =
of both primary and secondary air flow as well as your damper settings =
Are you or are you not using a power blower to atomise your oil feed ?. =
It's a long time since I fired with Distillate with a blower for =
atomisation. But I knew I had to control all of these factors and keep =
them in balance to get a good reduction.
One thing to remember! The flame you describe suggests incomplete =
decomposition of your fuel. So you may not be getting sufficient =
gasification to create a reducing atmosphere. This must happen if your =
are to get a degree of partial combustion that delivers Carbon Monoxide. =
This is the gas which will give you efficient reduction.
I work with LPG. In the reducing phase of a firing I like to see just =
the merest trace of back pressure at the spy and the flame must burn =
with a blue colouration. I do no use any form of gas probe. I feel =
Oxyprobes only tell me about the absence or presence of Oxygen and =
nothing about the chemistry at work inside the kiln. Study of the =
Ellingham Diagram leads me to think that what may be a good atmosphere =
for the reduction of copper glazes might do nothing for Iron or =
Manganese glazes, but that is open to experimental verification.
Hope you come to terms with your kiln.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
William & Susan Schran User on thu 10 nov 05
On 11/8/05 4:22 PM, "Paul B" wrote:
> Early in my apprenticeship i read/heard, not sure which, that a gas kiln
> could potentially have back pressure with flames coming out the spyholes
> but still have an oxidation atmosphere inside.
Used to be back in the ole days, with 2 hardbrick kilns we built, I was
taught to start body reduction by closing the primary air to the burners,
push in the damper and create a long yellow flame from the burner. This als=
o
resulted in a yellow licking flame with black smoke coming from the spy
holes.
Nasty, stinky, dirty with carbon left where ever there was the slightest
opening between bricks.
Where I teach, we now have a Geil kiln. In the instructions, setting the
pressure/damper, so that under 2000=B0F, holding a piece of paper to the
bottom spy hole and it ignites shows you're in reduction. As the temperatur=
e
rises there is a small flame from the bottom spy hole and a stronger/longer
flame from the top spy hole. There is also flame at top of stack. There's
never any smoke.
Glazes come out great - copper reds, shinos, celadons. First firing I had m=
y
doubts based on previous experience, but this kiln is a clean, mean,
reduction machine.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
William & Susan Schran User on thu 10 nov 05
On 11/9/05 7:07 AM, "Mark Issenberg" wrote:
> Some times there is a really green color in the flames , both
> from the peep and also the top at the damper.
In our Geil kiln we get a very pronounced green flame from the top of the
stack.
Is this copper volatizing?
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
steve graber on thu 10 nov 05
i heard once that green is the color of alumina burning. i don't know for sure.
certainly a nice color.... made me stop cooking hot dogs in the exit flame... that was all the rage for a while.
see ya
steve
William & Susan Schran User wrote:
On 11/9/05 7:07 AM, "Mark Issenberg" wrote:
> Some times there is a really green color in the flames , both
> from the peep and also the top at the damper.
In our Geil kiln we get a very pronounced green flame from the top of the
stack.
Is this copper volatizing?
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
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Louis Katz on thu 10 nov 05
>
>> Early in my apprenticeship i read/heard, not sure which, that a gas
>> kiln
>> could potentially have back pressure with flames coming out the
>> spyholes
>> but still have an oxidation atmosphere inside.
>>
Flame occurs where fuel comes in contact with O2 and it is hot enough
to ignite. Heat, Fuel , O2.
You get flame where there is heat fuel and O2.
When you are reducing the gases coming out of your kiln contain fuel
in this case CO carbon monoxide.
In a reduction kiln all of the O2 in the kiln is consumed. If the fuel
is hot enough when it comes out of the kiln in mixes with the O2 in the
air and burns. Look at these flames from the side and you will see that
they are hollow, only the outsdie of the flame is mixing with the air
and burning.
If you have blowers you can close down the damper far and turn the
blowers up and still be putting enough O2 to all the fuel in a kiln and
still have an excess of air. There will be no flame at the spys, but
there may be back pressure .
http://falcon.tamucc.edu/~lkatz/articles/firing.html
Louis
Hank Murrow on thu 10 nov 05
On Nov 10, 2005, at 5:38 AM, William & Susan Schran User wrote:
>
> Used to be back in the ole days, with 2 hardbrick kilns we built, I =
was
> taught to start body reduction by closing the primary air to the=20
> burners,
> push in the damper and create a long yellow flame from the burner.=20
> This also
> resulted in a yellow licking flame with black smoke coming from the =
spy
> holes. Nasty, stinky, dirty with carbon left where ever there was the=20=
> slightest
> opening between bricks.
>
> Where I teach, we now have a Geil kiln. In the instructions, setting=20=
> the
> pressure/damper, so that under 2000=B0F, holding a piece of paper to =
the
> bottom spy hole and it ignites shows you're in reduction. As the=20
> temperature
> rises there is a small flame from the bottom spy hole and a=20
> stronger/longer
> flame from the top spy hole. There is also flame at top of stack.=20
> There's
> never any smoke.
>
> Glazes come out great - copper reds, shinos, celadons. First firing I=20=
> had my
> doubts based on previous experience, but this kiln is a clean, mean,
> reduction machine.
Dear Reduction potters;
In the 'old days', we built our kilns of brick with no facing metal or=20=
fireproof boards covering the joints, so our kilns were pretty leaky.=20
Thus, to get reduction in the bottom of the chamber, one had to suffer=20=
a nasty atmosphere at the top. Nowadays, our kilns are built much=20
tighter, so less back pressure is needed to get an even reduction. I=20
thought I had been building tight kilns until I began my Doorless=20
Fiberkiln project. Now, a very small damper change will make the=20
OxyProbe jump and the kiln will go into strong reduction.......... the=20=
whole shell is sealed with silicone....... no leaks......... even back=20=
pressure throughout the chamber. Sometimes the damper is so sensitive=20
that I adjust the reduction with the gas valve.
Just an observation from experience over the last 40 odd years. We are=20=
tightening up in this fuel-dear environment.
Cheers, Hank
Michael Wendt on thu 10 nov 05
Every once in a while we get reduced effects even though
we normally fire oxidation. This happens because we fire as close to neutral
as possible.
Kiln settings are done this way after we are on full burner:
1) record current temperature on a white board every 20 minutes.
2) subtract the previous reading from the new one and record that difference
to the right halfway between.
3) adjust the damper setting to get the fastest possible rise rate. The
jumps are fairly large at first and gradually slow near cone 10.
4) when the kiln does stop rising, open the damper 1/8" and watch the
change. If the temperature drops, we tighten the damper gradually until the
rise rate climbs again at the fastest rate. The fastest rise rate happens
for us when the kiln shows no flame out the top but does show a "corona"
effect of very hot incandescent gas flickering out about 1-2".
One thing I noticed: even a slight backpressure from the damper slows the
rise rate in out updrafts and results in reduced effects on the glazes.
One key factor in all kilns is how tight the jacket is. You can have
reduction in the upper half of a loose, leaky kiln and be in oxidation in
the lower part. Tightening up the kiln and sealing leaks not only makes
reduction more uniform, it also saves fuel and allows faster firings and
slow cool down.
As to flame colors from oxides: each metallic oxide has a characteristic
emission patter. In the astronomy class I took as a physics student, we saw
the various interference patterns created by heating different metals to a
high temperature. Copper is blue, sodium is yellow,... etc.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
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