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reduction firing

updated wed 29 sep 10

 

Emily Muench on tue 23 jun 98

I'm having a problem firing the reduction kiln at a studio situation........we
are trying for some consistantancy and are not able to reach success.....one
firing we'll have copper reds in many areas of the kiln....the very next
firing, the copper reds are clear and runny, crackled also????? I would be so
very pleased if a reduction potter would post a firing schedule on this list,
we were told our kiln is in reduction the entire firing. We have some black
smoke at the peeps from the time cone 7 is down in the front of the
kiln......we have one peep on each of the sides towards the back of the
kiln.....we then watch the cones in that area....when 9 is bending, we close
the damper and primary air on each of two burners, reduce for 15 minutes,
black smoke is pouring out of every crevise and peeps.......then we open the
damper and primary airs for a few moments to clean the kiln atmosphere and
turn off the gas. We close the ports, close the damper and of course the
peeps have been plugged, allow the kiln to cool for a week.........opened it
this morning to find some runny glazes..most successful.........but no
reds!!!!! Everyone is so very disappointed when this happens....I need some
professional advice.........please......and thank you. I do enjoy this list
very much!

Nils Lou on wed 24 jun 98

Well, Emily, you describe the classic example of the deterioration of a
functional reduction atmosphere when you fire so gassy as to produce black
smoke and soot. The moment free carbon is produced in the firing
atmosphere reduction effects are essentially nil. This can be demonstrated
with an oxygen probe; you are demonstrating it with clear crackle instead
of reds. Next time you fire adjust the gas air ratio so there is flame,
but no smoke (NONE). If there is flame at the peep holes there is unburned
fuel and a production of carbon monoxide is likely. If you have soot,
black smoke the free carbon will interfere with the reducing effectiveness
of any carbon monoxide. If you try this protocol, please let the list know
what your results are so we can all learn. Nils Lou

On Tue, 23 Jun 1998, Emily Muench wrote:

> ----------------------------Original message----------------------------
> I'm having a problem firing the reduction kiln at a studio situation........we
> are trying for some consistantancy and are not able to reach success.....one
> firing we'll have copper reds in many areas of the kiln....the very next
> firing, the copper reds are clear and runny, crackled also????? I would be so
> very pleased if a reduction potter would post a firing schedule on this list,
> we were told our kiln is in reduction the entire firing. We have some black
> smoke at the peeps from the time cone 7 is down in the front of the
> kiln......we have one peep on each of the sides towards the back of the
> kiln.....we then watch the cones in that area....when 9 is bending, we close
> the damper and primary air on each of two burners, reduce for 15 minutes,
> black smoke is pouring out of every crevise and peeps.......then we open the
> damper and primary airs for a few moments to clean the kiln atmosphere and
> turn off the gas. We close the ports, close the damper and of course the
> peeps have been plugged, allow the kiln to cool for a week.........opened it
> this morning to find some runny glazes..most successful.........but no
> reds!!!!! Everyone is so very disappointed when this happens....I need some
> professional advice.........please......and thank you. I do enjoy this list
> very much!
>

Tina Morris on wed 24 jun 98

There are several resources that I have found invaluable in learning
to fire in a reduction atmosphere. They are:

The Art of Firing By Nils Lou He has included a great section on
fuel saving firing to cone 10 reduction. I have used this schedule many
times with slight changes that were likely due to differences in kiln traits.

I have also found several other sources for firing theory.....both
by Daniel Rhodes.

Kilns: Design, Construction, amd Operation.... this one is out of
print so you may have some trouble finding a copy

and Stoneware and Porcelin: I have not read this section in a
while but I used this resource the first time that I ever fired alone.

tina

J. D. Walker on wed 24 jun 98

Emily,

I use an highly recommend a CO2 analyzer. Then reduce lightly from 1500 to
cone 10, never heavy. I have a 16 cuft up draft and get copper reds from
bottom to top every firing.

Jeff Walker
Burning up in missouri
jdpotter@iland.net

-----Original Message-----
From: Emily Muench
To: Multiple recipients of list CLAYART
Date: Tuesday, June 23, 1998 7:29 AM
Subject: Re: Reduction firing


>----------------------------Original message----------------------------
>I'm having a problem firing the reduction kiln at a studio
situation........we
>are trying for some consistantancy and are not able to reach
success.....one
>firing we'll have copper reds in many areas of the kiln....the very next
>firing, the copper reds are clear and runny, crackled also????? I would be
so
>very pleased if a reduction potter would post a firing schedule on this
list,
>we were told our kiln is in reduction the entire firing. We have some black
>smoke at the peeps from the time cone 7 is down in the front of the
>kiln......we have one peep on each of the sides towards the back of the
>kiln.....we then watch the cones in that area....when 9 is bending, we
close
>the damper and primary air on each of two burners, reduce for 15 minutes,
>black smoke is pouring out of every crevise and peeps.......then we open
the
>damper and primary airs for a few moments to clean the kiln atmosphere and
>turn off the gas. We close the ports, close the damper and of course the
>peeps have been plugged, allow the kiln to cool for a week.........opened
it
>this morning to find some runny glazes..most successful.........but no
>reds!!!!! Everyone is so very disappointed when this happens....I need some
>professional advice.........please......and thank you. I do enjoy this list
>very much!
>

Christopher J. Anton on wed 24 jun 98

Black smoke from a gas kiln does not sound good!

The reduction firings I have done have been using a forced draft burner
system. We fire oxidation to appx 1500 F, then cut back the amount of
oxygen enough that we still maintain little or no yellow flame, and maintain
a 50 to 100 degrees per hour climb for one half hour. With the copper reds
we are using we then cut the flames off and let the kiln soak for five
minutes. Next we relight the two burners, adjust for peak oxidation, then
cut the air back again. The kiln remains at that level of reduction until
reaching cone 10 (large).

- Chris

Shelley Potter on thu 11 mar 99

Hi,

Please excuse if this is elementary or a rerun. I have been working with
clay for many years but always had my firing done in a larger kiln by
others. I now have an electric kiln which is great for some things, but I
want to be able to fire in reduction as well so I am looking at a small gas
kiln. I work almost exclusively without glaze. I handbuild all my work using
several clay bodies. SO, here are my questions:

1 What is the difference between the results of using propane for a fuel
and natural gas? I was told by a kiln guy that it would take 3-5 gallons of
propane to fire a 15"square kiln to cone10, and 4-6 gallons of propane to
fire a 18"square. Using a small tank that comes out to a pricey $15 to fire
a small kiln once.

2 If I fire in my electric kiln to cone10, how would I get that wonderful
nutty brown of reduction in my gas kiln after that with the least waste of
time and fuel? I used to bring the pots that didn't look great with their
greyish surface to school after I did my electric c10 firing. I'd put them
in with the reduction firing and then got what I wanted. Since I would have
more controll here with my own kiln, could I fire to a lower temp before
reducing? How long would I have to reduce considering that the pots are
already fully cooked? Remember that I'm not using any glaze here so I don't
have to deal with the emotions and reactions of glazes, nor do I have to
soak. I also don't have to think about maturity if the pots are already cone
10. Right? Well, I guess that's actually a question in itself. Is there a
difference in results if I only bisque as opposed to go to c10 first? I like
to go to cone 10 in the electric because sometimes I really like what the
oxidized surface looks like. But sometimes it's clear to me that they need
reduction. It depends on the pot and what I've done with the surface
designs.

I hope the questions I've asked are clear. Your answers will help me decide
what kind of kiln and fuel to use. I'm thinking of buying the shell of an
old electric kiln and converting it to a gas kiln. I do have gas in our
house, but it's not piped outside so of course propane would be easier.

Shelley Potter
Phoenix ,AZ

Dave Finkelnburg on sun 14 mar 99

Shelly,
There should be a bunch of posts from this year in the archives noting
that the Japanese get virtually all effects using electric kilns. You
should be able to reduce in your electric by several means, one mentioned
recently being a small propane or butane flame into the kiln. With your
electric a very small flame would do the job.
Propane is more expensive than natural gas, if you have gas, but
performs identically.
Dave
-----Original Message-----
From: Shelley Potter
To: CLAYART@LSV.UKY.EDU
Date: Thursday, March 11, 1999 5:59 AM
Subject: reduction firing


>----------------------------Original message----------------------------
>Hi,
>
> Please excuse if this is elementary or a rerun. I have been working with
>clay for many years but always had my firing done in a larger kiln by
>others. I now have an electric kiln which is great for some things, but I
>want to be able to fire in reduction as well so I am looking at a small gas
>kiln. I work almost exclusively without glaze. I handbuild all my work
using
>several clay bodies. SO, here are my questions:
>
> 1 What is the difference between the results of using propane for a fuel
>and natural gas? I was told by a kiln guy that it would take 3-5 gallons of
>propane to fire a 15"square kiln to cone10, and 4-6 gallons of propane to
>fire a 18"square. Using a small tank that comes out to a pricey $15 to fire
>a small kiln once.
>
>2 If I fire in my electric kiln to cone10, how would I get that wonderful
>nutty brown of reduction in my gas kiln after that with the least waste of
>time and fuel? I used to bring the pots that didn't look great with their
>greyish surface to school after I did my electric c10 firing. I'd put them
>in with the reduction firing and then got what I wanted. Since I would have
>more controll here with my own kiln, could I fire to a lower temp before
>reducing? How long would I have to reduce considering that the pots are
>already fully cooked? Remember that I'm not using any glaze here so I don't
>have to deal with the emotions and reactions of glazes, nor do I have to
>soak. I also don't have to think about maturity if the pots are already
cone
>10. Right? Well, I guess that's actually a question in itself. Is there a
>difference in results if I only bisque as opposed to go to c10 first? I
like
>to go to cone 10 in the electric because sometimes I really like what the
>oxidized surface looks like. But sometimes it's clear to me that they need
>reduction. It depends on the pot and what I've done with the surface
>designs.
>
>I hope the questions I've asked are clear. Your answers will help me decide
>what kind of kiln and fuel to use. I'm thinking of buying the shell of an
>old electric kiln and converting it to a gas kiln. I do have gas in our
>house, but it's not piped outside so of course propane would be easier.
>
>Shelley Potter
>Phoenix ,AZ
>

RAJ PAREKH on mon 4 oct 99

-------------------
I AM A NEW SUBSCRIIBER TO CLAYART AND WOULD LIKE SOME INFORMATION ON =
REDUCTION
FIRING. I HAVE A 4 1=5C2 CU. FT KILN WITH 3 BURNERS GAS KILN BUT NEVER USED =
IT FOR
LACK OF KNOWLEDGE OF KILN REDUCTION. I WOULD APPRECIATE ANY INFORMATION ON =
THE
SUBJECT EVEN THE NAME OF A BOOK I CAN REFER TO FOR THE SAME PURPOSE.THANKS.
DHARINI PAREKH. sacrad=40vsnl.com

Steve Dalton on tue 5 oct 99

Hi Dharini,
Go get Nils Lou book 'The Art of Firing'. (Nil you should love the plug)
You didn't mention, but I presume an updraft kiln - guessing on the size.
If you're kiln is an updraft, this is what we did at school. You'll need 6
brick. Take two firebrick and place 1 on each side of the hole on the lid.
Next place two more on top of those...this will look like a bridge. The
remaining two will act as a damper. Either with cones or pyrometer...guage
where you want reduction to start (usually cone 010)...adjust damper bricks
to produce a flame coming out of a spy hole no more than 2-3 inches.
This is just one of the ways of getting reduction out of an updraft. There
are many more.
Steve Dalton
----------
> From: RAJ PAREKH
> To: CLAYART@LSV.UKY.EDU
> Subject: Reduction Firing
> Date: Mon, 4 Oct 1999 18:37:56 EDT
>
>----------------------------Original message----------------------------
>-------------------
>I AM A NEW SUBSCRIIBER TO CLAYART AND WOULD LIKE SOME INFORMATION ON
REDUCTION
>FIRING. I HAVE A 4 1\2 CU. FT KILN WITH 3 BURNERS GAS KILN BUT NEVER USED
IT FOR
>LACK OF KNOWLEDGE OF KILN REDUCTION. I WOULD APPRECIATE ANY INFORMATION ON
THE
>SUBJECT EVEN THE NAME OF A BOOK I CAN REFER TO FOR THE SAME PURPOSE.THANKS.
>DHARINI PAREKH. sacrad@vsnl.com

options in porcelain on tue 11 jul 00


I just finished my first reduction firing in my Bailey
18/12 downdraft natural gas kiln and while nothing
melted to the kiln shelves I obviously missed getting
reduction. I did a 30 minute body reduction at ^010
(yellow flame, 5" backpressure from top spy port) then
another 45 minute one at ^9 bending to ^9 down. I do
not have an oxyprobe so I am trying to wing it based
on damper settings and flame color. Gas pressure is
not a problem.

Does anyone have a schedule they follow for reduction
firing this particular model of kiln? Do I need to do
reduction longer?

I fired a larger model of the Bailey kiln at school
and we had worked out a schedule that gave great
reduction. So I am at a loss as to where I went wrong.


I would also like to know the relationship between the
gas and blower fans. What setting does the fan need to
be on during firing? I started on low with the pilots
and eased up to med-low for the entire firing. Seemed
like if I turned them up on high the temp went down.

Ronda


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Marvpots@AOL.COM on tue 11 jul 00


Hi Ronda:
I would urge you to speak to Bailey on this reduction question. A
combination of damper placement (at about 25% open) during the reduction
periods, more gas, less air should give you good results. But, above all,
speak to Bailey!
Good Luck.

Marvin Flowerman (marvpots@aol.com)

Don Hunt on mon 25 sep 00


I am fairly new to the forum, so forgive me if this is an old topic, I
didn't find it in the archives. Is it possible to lose reduction?
Assuming I had a kiln with good even reduction (reds on every shelf), if
I fired in oxidation for 30 minutes, would I see a reoxidation of my
glazes? I fire in a fiber kiln, so I would like to fire down a little
to give my glazes a little more time to soak. I only seem to have about
30 minutes between cone 9 and 10. The climb rate is about 2 degrees per
minute at this point.
I understand this is typical of fiber updraft kilns. Maybe it doesn't
really matter, but I think some glazes looked better in the brick
kilns. I have no way of knowing if I ever had even reduction or lost it
at the end. Hopefully someone has solved the puzzle.

Don Hunt
dj_hunt@home.com

Carolyn Nygren Curran on tue 26 sep 00


Dear Don, Other clayarters told me to fire down in my little updraft
(18" X 13" inner cylinder) portable gas kiln, since reds develop in the
cooling. (Directions for the kiln 20 years ago said to fire to maturity in
oxidation, then reduce for 30 minutes and shut down. That was OK for
celadons, but copper reds were always mediocre.) I have had better luck
with the copper reds since I started with the cool down cycle, although
I've been lightly reducing on the way down a couple of times and have had
some sooty glazes. Next time (if we ever have decent weather this year)
I will reduce for 30 minutes or more, then do the cool down in oxidation.
As I recall, some sources mention an oxidation period after the reduction
in any case. I have not been able to really experiment with the outdoor
gas kiln that much recently due to the lousy weather, but I do think I'm
on the right track--thanks to other clayarters who have helped this
essentially self taught potter. So far I've been adding 2 to 3 hours for
the cool down cycle before I turn off the kiln, go to bed and cross my
copper red fingers. Good Luck. cnc

Hank Murrow on tue 26 sep 00


>Don Hunt wrote that he needed help firing a fiberkiln. I tried to answer
>him directly, but the eMail was returned with 'fatal errors'. Don, if you
>are out there contact me directly.
Cheers, Hank in Eugene

David Hendley on wed 27 sep 00


Don, ALL glazes are reoxidized at the end of a firing.
It's called cooling. Unless you keep the gas on low
to keep reducing while the kiln is cooling.

This is a separate variable from the other things you
mention, soaking and cooling. Many glazes will indeed
benefit from a soaking at the top end of the firing.
I would suggest you try to slow down your firing rather
than 'fire down' on cooling.

Some glazes, especially those that can develop micro crystals,
benefit from a slow cooling. This give the crystals time
to develop, and is why slower cooling brick kilns can be
better for this.
Often, people think reduction fired pots look better than
oxidation fired pots, but what they are really seeing
is the slow cooled glaze from a typical gas kiln compared
to the rapid cooled glaze from an electric kiln.

--
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com/




----- Original Message -----
From: Don Hunt
To:
Sent: Monday, September 25, 2000 7:40 PM
Subject: reduction firing


| I am fairly new to the forum, so forgive me if this is an old topic, I
| didn't find it in the archives. Is it possible to lose reduction?
| Assuming I had a kiln with good even reduction (reds on every shelf), if
| I fired in oxidation for 30 minutes, would I see a reoxidation of my
| glazes? I fire in a fiber kiln, so I would like to fire down a little
| to give my glazes a little more time to soak. I only seem to have about
| 30 minutes between cone 9 and 10. The climb rate is about 2 degrees per
| minute at this point.
| I understand this is typical of fiber updraft kilns. Maybe it doesn't
| really matter, but I think some glazes looked better in the brick
| kilns. I have no way of knowing if I ever had even reduction or lost it
| at the end. Hopefully someone has solved the puzzle.
|
| Don Hunt
| dj_hunt@home.com
|
|
____________________________________________________________________________
__
| 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.
|

RJ Shulenburg on thu 17 aug 06


Mel said "`far too much gas is used in many cases to achieve very average
pots.` often the best cure for a stalled kiln is dropping the gas pressure.
most potters just keep turning it up. i have seen stalled kilns with 15
inches of flame pouring out of a kiln that is running on ten pounds of
pressure. i open the damper, turn the kiln to 2 pounds, blue up the flame
and the kiln jumps 500 degrees in ten minutes. and then gets finished in no
time flat. re/adjust the reduction and get a fine firing."
Would you mind clarifying this a little? Open the damper.approximately how
much? Just enough to stop the reduction? Around what temp can this be done
to get the kiln to jump so fast?
I know this is fuzzy, as mileage may vary, but some ballpark figures would
give a starting point.
Thanks, Ronda Shulenburg, Virginia Beach, VA

Ivor and Olive Lewis on fri 18 aug 06


Dear Rhonda Shulenburg,

That rate of climb given by Mel, 3000 deg per hour is a bit of an =
exaggeration, even if they are F degrees. One of Mel's "Whoppers". But I =
agree with him that less gas is best.=20

My suggestion for a gas fired kiln would be to open the damper totally, =
ignite the burners with a minimum of gas to avoid a flashback and adjust =
the air shutter on the burner to get a flame that has a slight white =
tip. Now close the damper in until that white tip starts gets brighter, =
even turn yellow. Now pull the damper out a fraction of an inch to just =
get a slight white tip. If you have a pyrometer record the temperature =
at five min intervals. If possible plot the temperature rise on graph =
paper. After a hour you might notice that the rate of increase in =
temperature slows down. This is a signal to increase gas flow (on my gas =
kiln this is a quarter of a turn on the valves), without altering the =
burner shutter or the damper. Keep on recording temp at 5 min intervals. =
Again when the rate of temp increase seems to slow down increase the =
flow of gas ( same amount, for me quarter turn).

Periodically look at the flame. If the white tip seems to be growing, =
open your damper a fraction until the whole of the flame is almost blue. =
When you get to the stage where you need to commence reduction you may =
do one of two things. Either, close the damper to make the flame loose =
its blue colour and turn to bright white/yellow or increase gas flow a =
fraction until a flame is emitted from a spy hole when you remove the =
plug. Both may be needed. This means back pressure in the kiln chamber =
and a diminution of the secondary air which contributes to efficient =
combustion at the burner because the damper is preventing burnt gas from =
leaving. In this condition the temperature of the kiln may drop. So =
after a period of reduction pull out the damper to the point where flame =
does not issue from a spy hole and the flames at the burners go blue and =
carry on logging temperature rise. When you catch up to the previous =
high mark reduce again. Continue the cycle for as long as needed then =
just let the temperature climb to a finish with hourly adjustments to =
give more gas.

Efficiency of firing demands a balance between gas flow, primary air =
input, secondary air entrainment and flue volume discharge. Gas does not =
burn if the primary and secondary air cannot get into the kiln. So it =
gets wasted and burns at the top of the stack. Large volumes of gas need =
large volumes of air to be able to burn. A wide open damper pulls hear =
out before it does its work.=20

If you do not understand this please get in touch.

Best regards,

Ivor Lewis.
Redhill,
South Australia.

Hank Murrow on fri 18 aug 06


On Aug 18, 2006, at 5:51 AM, RJ Shulenburg wrote:

> Hank,
>
> Thanks for the information. I was searching the archives for this
> issue and down firing. I understand all of what you said below. I've
> got and use the oxyprobe. I was just trying to figure out how Mel
> could get such a drastic temperature climb and at what temp.

I understand you now. You are further along in the process than I knew
from your note. Why don't you ask Mel directly, as I have no experience
with the Bailey, and perhaps he does. And put out this query to Bailey
operators around the Clayart community.

My Doorless Fiberkiln goes right on up to cone 11 at 5.5" water column,
goes slower at 5", and will take forever at 4.5". I use all three(and
more) settings depending on what I am trying for with the glazes. Since
the kiln is so efficient, I can fire anywhere from 20 to 40 hours if
needed, with the difference in the cost being just one wholesale mug.
Sometimes it is worth a mug to see the difference a few hours makes in
the glazes.

Cheers, Hank
www.murrow.biz/hank

Fred Parker on sat 19 aug 06


Dear Ronda:

I do not have access to a reduction kiln, so what I am about to write
might not be of interest to you or to many others. However, sometimes it
helps to take a clue from another branch of science to better understand
why a gas-fired kiln's temperature is not directly proportionate to fuel
input.

In fact, there is an optimum amount of fuel that can be burned in a kiln
to achieve maximum heat. This is not a MAXIMUM amount of fuel -- an
OPTIMUM amount -- meaning a specific amount of fuel mixed with a specific
amount of oxygen. A kiln is a type of primitive "heat engine" that
produces a certain amount of work (heat) for a given energy (fuel) input.
The key to achieving this is to supply enough oxygen to completely burn
the gas present -- no more, no less. If dampers are adjusted for too
little oxygen (air) intake, the kiln will not be able to burn all the fuel
injected, and the unburned fuel will exit the kiln where it makes contact
with free oxygen in the air and burns there. Mel's "15-inch flame" coming
from the kiln stack is an example of this. When this happens, the fuel
gas actually begins to act as a convective cooling agent instead of a
fuel. It essentially becomes inert while in the kiln, serving no purpose
other than picking up heat from the kiln interior and carrying it to the
exterior via the stack. The result: interior cooling.

Finding the optimum fuel-air mix is often done by observing the flame,
whether you are adjusting a pottery kiln, a gas stove or a welding torch.
There are test instruments available to measure oxygen, temperature etc.
but everyone will not have them. For a welding torch blue means a good
mix, orange means too much fuel and blue-white means too little fuel or
too much oxygen. Pretty much the same is true when adjusting a gas burner
on a stove. I assume the same would apply to fuel gas combustion in a
kiln.

From what I glean the point to be, in reduction firing the goal is to
provide sufficient temperature to reach the cone target, and to do so in a
neutral to slightly fuel-rich atmosphere. "Some" flame escaping from a
stack might indicate a fuel rich atmosphere; however, it might be far too
fuel-rich to achieve the temperature goal.

So the bottom line is, "if a little gas is good, more is not always
better." The basic laws of oxidation reactions -- that specify amounts of
fuel and oxygen in an optimum mix -- still hold.

Finally, apologies to you and other reduction potters for which this is
elementary and overly basic. I thought there might be some potters who
are just now getting into reduction firing, who might not quite understand
this aspect of the process.

Regards,

Fred Parker


On Thu, 17 Aug 2006 18:28:51 -0400, RJ Shulenburg wrote:

>Mel said "`far too much gas is used in many cases to achieve very average
>pots.` often the best cure for a stalled kiln is dropping the gas
pressure.
>most potters just keep turning it up. i have seen stalled kilns with 15
>inches of flame pouring out of a kiln that is running on ten pounds of
>pressure. i open the damper, turn the kiln to 2 pounds, blue up the flame
>and the kiln jumps 500 degrees in ten minutes. and then gets finished in
no
>time flat. re/adjust the reduction and get a fine firing."
>Would you mind clarifying this a little? Open the damper.approximately how
>much? Just enough to stop the reduction? Around what temp can this be done
>to get the kiln to jump so fast?
>I know this is fuzzy, as mileage may vary, but some ballpark figures would
>give a starting point.
>Thanks, Ronda Shulenburg, Virginia Beach, VA

Gene Arnold on sat 23 feb 08


Kurt, Vince, Shane and all others that want to comment

I'm new to this reduction firing so I'll be asking a lot of questions of the
list from time to time. I built this MFT 40ft. down draft kiln in October,
not only was it the first I had built it was the first I had fired or even
seen fired. And no one else with in an hour and a half of me with a gas
kiln. So you kind of see where I'm coming from and I've only been doing
pottery 7 years now.

I plan to try what has been suggested so far by raising my first shelf
2 1/2 inches above the floor of the kiln. I will also move my burners
(B-4's on propane) in to a distance of about 3/4 inch. And I will try adding
a short bag wall by the burners as Kurt suggested. I have the small bag wall
and the split brick on an angle at the front of the kiln as Nils recommends
in his book.

The temperature seems to be doing well, only about 1/2 cone difference from
top to bottom and back to front.

Just out of curiosity what does raising the bottom shelf actually do to aid
in the firing and or reduction process ??? Also Shane what are passive
holes??

Gene
mudduck@mudduckpottery.net
www.mudduckpottery.net

Kurt Wild on sun 24 feb 08


Personally, I would be quite happy with only a 1/2 a cone difference
from top to bottom.

Why raise the shelf? I found the bottom to be a bit cool and
I believe it's a bit difficult to get the very bottom as hot as
the rest of the kiln.

Kurt

Kurt Wild
River Falls, WI
web: www.kurtwildpottery.com

Chris trabka on tue 4 mar 08


Gene,

I have a modified MFT with about 32-cubic feet of stacking space that uses
natural gas. The modification is 12 venturi burners in lieu of the 2 power
burners.

I struggled for quite a while getting the reduction firing consistent
and "right" where the outside temperature varied from 20 degrees to 80
degrees and the dew point varied from 20 degrees to 80 degrees. The MOST
IMPORTANT tool I have ever used when firing the kiln is an oxypobe. Yes
they are expensive. However I believe mine paid for itself after 3 firings.
I can now fire any time under any conditions and it looks just like the
last firing, and the one before, and the one before...

Yes you can learn about your kiln without an oxyprobe. However the cost is
some marginal, and perhaps some failed firings.

Chris

Wyndham Dennison on fri 18 apr 08


On Wed, Apr 16, 2008 at 9:11 PM, jonathan byler wrote:

> > I was wondering if having flame present at the spyhole really is an
> > indication that the kiln is reducing, or is it just showing back
> > pressure? Flame at the top of the chimney could indicate reduction
> > also, correct? I have always assumed this to be the case, but I was
> > curious if it is possible to have flame showing, because of back
> > pressure, but to not be an actual reduction flame.
> >
> > thanks,
> >
> > jon
>
Jon, kiln firings for reduction is a mystery to some and a walk in the
park for others. I have my own set of rules and beliefs for my kiln that
work for me. I'm not saying what I do is correct or the most efficient
but the results are what I am seeking. My kiln is a about 40 cu ft
stacking space(80 cu ft overall) with 6 raku burners(3 on a side)5lb
pressure downdraft(I use only about 2-3 lbs divided over the 6 burners).
I start reduction at about 1500 f where I turn the PAP's(primary air
ports) closed then back them off one turn. I push the damper in til I
get a wisp of smoke out the bottom peek hole. This produces a back
pressure in the kiln and makes a reduction atmosphere. My belief is that
for good reduction there needs to be constant positive pressure in the
kiln or the colors will not develop or inconsistent pressure leads to a
loss of reduction colors, sort of like keeping a balloon inflated that
has holes in it. As the kiln heat climbs(heat expands), I open the
damper a bit, trying to keep the same ratio. If there is flame coming
out the chimney then the ignition of the gas is outside the ware
chamber and wasted. Try to keep the heat work inside where the ware is
for better, faster, more consistent results.
Once I reach about 2100-2200 deg f I open the PAP's a half turn to a
full turn and a touch more open the damper OR reduce the main high
pressure regulator by a 1/4 turn The flame that I have seen from the
beginning to now is an orange flame but now it change to a lite orange
and sometimes a blue with orange tip. I thinks this might be lite
reduction. If I see the lower peep flame no longer there I either
increase the gas pressure a touch or push the damper in a touch. At cone
6 I'll open the pap's a nother 1/2 turn and 1hr later cone 9 is touching
the shelf and 10 is bending10 o clock. Shut'er down, closed the damper,
come back in the morning to check the results, 9-10 hr firing 75-80 gal
of propane.
As I said it's just how I do it. I would be interested in changing the
burners to 2 burners in back as I think the bag wall might be sucking up
a lot of BTU's that I don't need to spend but right now this kiln is
consistent top to bottom 1/2 cone difference. I have worked with the
notion that a positive pressure, push system is better that a draft
which may allow slip streams of oxygen to give problems
There are many variables in kilns so what works for me might have to be
taken with a grain of salt for someone else's design.
I wonder about burner placement bottom up (Geil), mine from the side w
bag wall or from back and little or no bagwall is more efficient or
practical and for what size kiln. Wyndham

Anne Chambers on mon 27 sep 10


Hi everyone,

I have been firing with an electric kiln for over 25 years, six months ago =
I
switched to a gas kiln.

I have a question about rutile blue glazes. Is it possible to get a bluer
colour on porcelain? I'm sure I have seen it.
The past two firings of testing rutile blues I am getting mostly mauves and
pinks with a bit of light blue where the glaze pools. I reduced at ^05 unti=
l
^1 then less reduction the rest of the way up to ^10.
Could it be not enough reduction, not reducing early enough or simply on
porcelain I will always get mauve/pink and need stoneware to obtain a more
blue colour. I have tried a Clayart Opal Rutile blue glaze and John's Rutil=
e
Blue 2 in my testing.
My porcelain does not contain grolleg. The kiln is 50 cu ft. so that's a lo=
t
of pots to make and fire to test out glazes. I'm trying to limit my losses
as much as I can.

The information from the archives does not answer my question and all the
potters in my area fire in salt or with wood so I am hoping someone on
Clayart can help me out.
Otherwise no blue glazes for my studio tour coming up in October.

Thanks,
Anne Chambers
www.annechambers.ca

Eva Gallagher on mon 27 sep 10


Hi Anne,
Rutile blues have been a hit and miss with us. Generally I have found that =
a
stoneware does better (the best result we had with Tuckers Sandstone) - in
fact it seems to me that we brushed on our fe underglaze and then wiped it
off when we used porc. It also needs to be on thick - but tends to run so
not good on tall pieces unless one just uses it near the top half. We have
tested I am sure over 10 variations of rutile blue sand so far Rutile I or
II from John Britt's book was the best. Someone (maybe on Clayart) mentione=
d
that one should use the very old rutile as the composition of today's stuff
has changed somewhat. Have not been able to test that one!
Also we used to have better luck with it a few years ago and perhaps it is
due to the fact that we have changed our firing schedule - we deoxidize onc=
e
we hit cone 8 until cone 10 is down and this give us brighter colours - but
it may have a detrimental effect on the rutile blue. Before we continued
redux until cone 10. We do start the reduction much earlier than you - at
012 for around one hour and then light to med redux until cone 8. However s=
o
far not a popular glaze with our group. Robert Tetu in his workshop here a
few years ago said he always added a bit of Co just in case the rutile
failed.
Eva Gallagher
Deep River Potters Guild
http://newfoundoutpotter.blogspot.com/
http://www.valleyartisans.com/gallagher/Gallagher.htm



----- Original Message -----
From: "Anne Chambers"
To:
Sent: Monday, September 27, 2010 10:09 AM
Subject: reduction firing


> Hi everyone,
>
> I have been firing with an electric kiln for over 25 years, six months ag=
o
> I
> switched to a gas kiln.
>
> I have a question about rutile blue glazes. Is it possible to get a blue=
r
> colour on porcelain? I'm sure I have seen it.
> The past two firings of testing rutile blues I am getting mostly mauves
> and
> pinks with a bit of light blue where the glaze pools. I reduced at ^05
> until
> ^1 then less reduction the rest of the way up to ^10.
> Could it be not enough reduction, not reducing early enough or simply on
> porcelain I will always get mauve/pink and need stoneware to obtain a mor=
e
> blue colour. I have tried a Clayart Opal Rutile blue glaze and John's
> Rutile
> Blue 2 in my testing.
> My porcelain does not contain grolleg. The kiln is 50 cu ft. so that's a
> lot
> of pots to make and fire to test out glazes. I'm trying to limit my losse=
s
> as much as I can.
>
> The information from the archives does not answer my question and all the
> potters in my area fire in salt or with wood so I am hoping someone on
> Clayart can help me out.
> Otherwise no blue glazes for my studio tour coming up in October.
>
> Thanks,
> Anne Chambers
> www.annechambers.ca
>
>

Elizabeth Willoughby on mon 27 sep 10


Hi Anne,
I have used a rutile blue on Harlan House Porcelain, fired to cone 10R in m=
y
Bailey gas kiln. I fired shinos, so I would go into reduction at 012, heav=
y
for an hour, lighten up, but still keeping it in good reduction to the end,
then shutting it down and closing everything up fairly soon. Maybe you need
to go into reduction a little sooner, say 08?
The glaze that I used was called Woo Blue. A definite warm blue, a light
dip would give me a caramel color, a thicker dip would give me blue. There
would be gold highlights, sometimes a greenish cast, but really mostly a
kind of mottled blue that I liked. And as you probably know, I am not
really fond of blue pots, but this one I did like.

Woo Blue (cone 10 R)

G-200 42
Silica 27
Whiting 18
OM4 13
100

plus
RIO 8
Rutile 8
Bentonite 2

Good luck
Liz

On Mon, Sep 27, 2010 at 10:09 AM, Anne Chambers
wrote:

> Hi everyone,
>
> I have been firing with an electric kiln for over 25 years, six months ag=
o
> I
> switched to a gas kiln.
>
> I have a question about rutile blue glazes. Is it possible to get a blue=
r
> colour on porcelain? I'm sure I have seen it.
> The past two firings of testing rutile blues I am getting mostly mauves a=
nd
> pinks with a bit of light blue where the glaze pools. I reduced at ^05
> until
> ^1 then less reduction the rest of the way up to ^10.
> Could it be not enough reduction, not reducing early enough or simply on
> porcelain I will always get mauve/pink and need stoneware to obtain a mor=
e
> blue colour. I have tried a Clayart Opal Rutile blue glaze and John's
> Rutile
> Blue 2 in my testing.
> My porcelain does not contain grolleg. The kiln is 50 cu ft. so that's a
> lot
> of pots to make and fire to test out glazes. I'm trying to limit my losse=
s
> as much as I can.
>
> The information from the archives does not answer my question and all the
> potters in my area fire in salt or with wood so I am hoping someone on
> Clayart can help me out.
> Otherwise no blue glazes for my studio tour coming up in October.
>
> Thanks,
> Anne Chambers
> www.annechambers.ca
>



--
Liz Willoughby
Brighton/Grafton,
Ontario, Canada

David Hendley on mon 27 sep 10


Yes Anne, rutile blue glazes are very sensitive to reduction. My rutile blu=
e
glaze can vary from ivory, to light blue, to very deep dark blue.
I have used this glaze for 20 years and know it well. When my copper
red glaze comes out clear (lack of reduction), I know before I see a
single pot that the rutile blue glaze will also be washed out with little
blue color. The same firing that produces perfect copper reds also
makes beautiful deep blue rutile blues.

Fire like you are firing copper reds - reduce early and reduce heavy,
gradually backing off as you approach final temperature.

I also strongly recommend you run a line blend for your rutile blue
glaze. It is critical that you have the proper amount of rutile in the
glaze, for your particular situation. Fire tests with 2, 2.5, 3, 3.5, 4,
4.5, 5, 5.5, and 6 % rutile. Do this over several firings and determine
which one is best for you. A half per cent difference in the amount
of rutile can make a big difference.

David Hendley
david@farmpots.com
http://www.farmpots.com
http://www.thewahooligans.com



----- Original Message -----
> I have been firing with an electric kiln for over 25 years, six months ag=
o
> I
> switched to a gas kiln.
> I have a question about rutile blue glazes. Is it possible to get a blue=
r
> colour on porcelain? I'm sure I have seen it.
> The past two firings of testing rutile blues I am getting mostly mauves
> and
> pinks with a bit of light blue where the glaze pools. I reduced at ^05
> until
> ^1 then less reduction the rest of the way up to ^10.
> Could it be not enough reduction, not reducing early enough or simply