Rikki Gill on wed 1 aug 07
Hi James and Sherron,
I usually turn the kiln off, open the damper, take out the peep covers, and
let the air clear for about five minutes. Then I seal it 36 hours.
My kiln is an Olsen, and it works okay with this method. I don't know if it
would work for every kiln. It definitely brightens my glazes. It works for
all my glazes including Shino.
Hope this helps
Rikki
rikigil@sbcglobal.net
www.rikkigillceramics.com
www.berkeleypotters.com
----- Original Message -----
From: "James and Sherron Bowen"
To:
Sent: Wednesday, August 01, 2007 6:17 PM
Subject: oxidation vs. reduction at the end of the firing cycle
We just finished a cone 10 reduction firing. Temoku, Kaki and a few
Celadons. During the last phase we discussed what we ahd heard and red
about finishing the firing off by one hour of oxidation
James and Sherron Bowen on wed 1 aug 07
We just finished a cone 10 reduction firing. Temoku, Kaki and a few
Celadons. During the last phase we discussed what we ahd heard and red
about finishing the firing off by one hour of oxidation (clearing the kiln)
or just continue reduction until the end. I know there are those on this
list who have opinions on this based on experience and can explain what they
do and why. Dopes clearing the kiln benefit certain glazes and not others? I
kep thinking we should fire th iron saturated glazes with more oxidation and
leave the heavy reduction for just shinos and celadons. What do you ladies
and gents think about this?
JB
=======================================================
"We literally have come to the decision that not all humans are human- that,
in fact, some humans are more human than others."
Lt. Gen. (Ret.) Roméo Dallaire
Dale Neese on thu 2 aug 07
When I finish up a reduction firing to cone 10 down in my Olsen, I cut back
all the burners equally to 1 inch pressure, slide the damper in avoiding a
reduction reading on the Oxyprobe. I let it "soak" for 5 minutes. This gives
enough time to "clear the atmosphere-glazes in oxidation", equalize
temperature top to bottom. Turn the burners off and close the damper. This
method works for me.
Couple weeks ago here on the list I had posted stuff about China. Sorry that
I had not replied to several comments to some of your posts. I had to
unexpectedly rush off to Tennessee to be with my ailing Mom in the hospital.
Things are still touch and go with Mom's condition but thankfully I have
other family members helping so I could return home for a while.
Dale Tex
"across the alley from the Alamo"
San Antonio, Texas USA
Jennifer Boyer on thu 2 aug 07
OK, Here's a stupid question from me:
I try to imagine what is happening in a gas kiln when the burners are
turned off at the end of the firing:
I don't see how a reduction atmosphere would last very long with the
burners off, since the reduction is created by the fuel: lack of fuel
= lack of reduction.
I don't reduce my gas kiln, so haven't seen what happens on my
Oxyprobe when the burners are turned off.
For those of you that do reduce and use an Oxyprobe, how long does
the reduction last after you shut the burners off and close the kiln up?
Jennifer
On Aug 2, 2007, at 10:37 AM, Dale Neese wrote:
> When I finish up a reduction firing to cone 10 down in my Olsen, I
> cut back
> all the burners equally to 1 inch pressure, slide the damper in
> avoiding a
> reduction reading on the Oxyprobe. I let it "soak" for 5 minutes.
> This gives
> enough time to "clear the atmosphere-glazes in oxidation", equalize
> temperature top to bottom. Turn the burners off and close the
> damper. This
> method works for me.
>
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
*****************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
*****************************
Bill Merrill on thu 2 aug 07
James and Sharon,
=20
Many of the old school potters start their reduction around 1650 degrees
Fahrenheit and reduce until cone 10 is achieved. If the kiln is uneven
in Temp the adjustment can be made in a neutral to oxidizing fire. You
can start the "clearing process from cone 8 to cone 10. I usually clear
and soak my kiln as cone 9 starts to tip, when the cone (10) reaches
1:00 o'clock on a clock face, I turn of the kiln. The cone continues to
fall and ends up at 3:00. The soak, clearing the atmosphere in the kiln
makes for a smooth
glaze surface, the body is richer if you use a body with iron in it. I
get matt, satin matt and glossy glazes in my kiln. There are so many
variables it is hard to tell another what to do. Rules aren't any good
unless the rule serves you. My "rules are what works best for me. I
usually fire from body reduction to cone 10 in no less than 9-10 hours.
I totally close up the kiln and don't touch it for 3 days. =20
=20
Reduction of oxides and a highly reducing (no smoke comes from the spy
hole) atmosphere work for my bodies and glazes, I certainly don't speak
for any one but myself.=20
=20
One just has to try, both oxidation or reduction at the end of the
firing to see what best benefits the clay and body you use. How much or
how little reduction is another question. If you have access to a oxygen
you can compare your firings reduction cycle.=20
=20
Regards,
=20
Bill Merrill
=20
billm@pcadmin.ctc.edu
=20
Dave Finkelnburg on thu 2 aug 07
Jennifer,
The precise answer to your question is
uniquivocally, "It depends!" :-)
The tighter the kiln is closed up, the longer the
reducing atmosphere will hold. My downdraft, with two
burner ports, stays in reduction, on average, a few
seconds, say 15, after I turn off the burners. This
is according to the Oxyprobe. I usually can't get the
damper closed up after I shut off the burners before
the kiln is in oxidation.
As always, YMMV.
Good question, BTW.
Dave Finkelnburg
Date: Thu, 2 Aug 2007 12:40:47 -0400
From: Jennifer Boyer
For those of you that do reduce and use an Oxyprobe,
how long does
the reduction last after you shut the burners off and
close the kiln up?
____________________________________________________________________________________
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David Beumee on thu 2 aug 07
James and Sharon,
It's been my experience that clearing the kiln atmosphere near top temperature benefits all glaze types. I fire shinos, temoku's, celadons, copper reds, matt, semi-matt, shiny, clear, white glazes, you name it, all in the same firing to cone ten. Everything comes out great, as long as I begin reoxidation just as cone 9 begins to bend. I turn down the gas pressure to a point where the kiln is held at a soak temperature, not losing or gaining temperature, about 5 WC inches for my particular kiln. I have a brick kiln and reoxidation is complete within one to two minutes of turing down the gas, but being brick, cone 10 is touching within 20 minutes of soak time. I turn off the gas, push the damper in all the way and then back it out about two inches. This allows a slow circulation of air to continue, and I'm able to draw the kiln in about 30 hours.
As to your question of firing iron saturate glazes with more oxidation and leaving the heavy reduction for shinos and celadons, I get great results for all types of glazes by getting into reduction early at cone 012 and firing in medium reduction on the oxy probe all the way to cone 9, beginning to tip.
David Beumee
Porcelian by David Beumee
806 East Baseline Road
Lafayette, CO
www.davidbeumee.com
-------------- Original message ----------------------
From: Bill Merrill
>
> James and Sharon,
>
>
>
> Many of the old school potters start their reduction around 1650 degrees
> Fahrenheit and reduce until cone 10 is achieved. If the kiln is uneven
> in Temp the adjustment can be made in a neutral to oxidizing fire. You
> can start the "clearing process from cone 8 to cone 10. I usually clear
> and soak my kiln as cone 9 starts to tip, when the cone (10) reaches
> 1:00 o'clock on a clock face, I turn of the kiln. The cone continues to
> fall and ends up at 3:00. The soak, clearing the atmosphere in the kiln
> makes for a smooth
>
> glaze surface, the body is richer if you use a body with iron in it. I
> get matt, satin matt and glossy glazes in my kiln. There are so many
> variables it is hard to tell another what to do. Rules aren't any good
> unless the rule serves you. My "rules are what works best for me. I
> usually fire from body reduction to cone 10 in no less than 9-10 hours.
> I totally close up the kiln and don't touch it for 3 days.
>
>
>
> Reduction of oxides and a highly reducing (no smoke comes from the spy
> hole) atmosphere work for my bodies and glazes, I certainly don't speak
> for any one but myself.
>
>
>
> One just has to try, both oxidation or reduction at the end of the
> firing to see what best benefits the clay and body you use. How much or
> how little reduction is another question. If you have access to a oxygen
> you can compare your firings reduction cycle.
>
>
>
> Regards,
>
>
>
> Bill Merrill
>
>
>
> billm@pcadmin.ctc.edu
>
>
>
> ______________________________________________________________________________
> 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.
Eric Suchman on thu 2 aug 07
Don't we need a 1/2 hour minimum to effect a change in the glaze?
-Eric in Oceanside
On Aug 2, 2007, at 1:05 PM, Dave Finkelnburg wrote:
> Jennifer,
> The precise answer to your question is
> uniquivocally, "It depends!" :-)
> The tighter the kiln is closed up, the longer the
> reducing atmosphere will hold. My downdraft, with two
> burner ports, stays in reduction, on average, a few
> seconds, say 15, after I turn off the burners. This
> is according to the Oxyprobe. I usually can't get the
> damper closed up after I shut off the burners before
> the kiln is in oxidation.
> As always, YMMV.
> Good question, BTW.
> Dave Finkelnburg
>
> Date: Thu, 2 Aug 2007 12:40:47 -0400
> From: Jennifer Boyer
> For those of you that do reduce and use an Oxyprobe,
> how long does
> the reduction last after you shut the burners off and
> close the kiln up?
>
>
>
>
>
>
>
> ______________________________________________________________________
> ______________
> Choose the right car based on your needs. Check out Yahoo! Autos
> new Car Finder tool.
> http://autos.yahoo.com/carfinder/
>
> ______________________________________________________________________
> ________
> 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.
Ron Roy on mon 6 aug 07
What Ben is saying here makes sense to me.
In my first kiln (800 firings) I had gates on my burner boxes so I could
control the secondary air - so closing those gates would bring more primary
air through the burner. All fined tuned with the dampers as well to get the
best rise in reduction.
The result was a better mixed flame and the cure for my initial flashing
when I was learning to fire it.
RR
>I found it a little confusing too but Here is what I think David is trying
>to say and hopefully if I am wrong I will get set straight shortly.
>
>It is better to use the damper to control secondary air to create reduction
> than to use the burners primary air control to create reduction.
>
>As the column of burning fuel is propelled into the kiln under pressure it
>creates a venturi in the burner port. This port venturi draws in the
>"secondary air". It is possible to choke off this effect somewhat by closing
>off the damper at the output of the kiln making it harder for this secondary
>air venturi to get air into the kiln thus making the combustion more
>reducing IN THE KILN. The burners can be set with a compact, strong, neutral
>to oxidising flame with good shape and energy throughout the firing. If we
>try to shut off the burners primary air to create reduction, the flame will
>soften and yellow and not be nearly as forceful.
>
>I THINK the indication is that the softer flame is less likely to mix well
>throughout the kiln giving less than even reduction results.
>
>thats what I took from this passage and it fits with my experience and other
>reading
>
>Ben
>
>______________________________________________________________________________
>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.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
David Beumee on thu 9 aug 07
Ben Shelton wrote,
"I THINK the indication is that the softer flame is less likely to mix well throughout the kiln giving less than even reduction results."
My experience has been exactly as you say. Shutting down primary air at the beginning of reduction, creating a long, slow, oily yellow flame, causes "streaming." Pots come from the kiln reduced on one side and oxidised on the other, from a firing that took far longer than it should have to reach temperature because of massive inefficiency.
Increasing both gas and air at 012 causes much more complete combustion because gas and air are given a greater opportunity to properly mix; increased amounts of carbon monoxide are produced, and heat is given off where it is needed, inside the kiln instead of up the stack.
Ron's right. Use the DAMPER to control secondary air and adjust backpressure for proper reduction, while watching the temperature rise.
David Beumee
Porcelain by David Beumee
Lafayette, CO
www.davidbeumee.com
-------------- Original message ----------------------
From: Ben Shelton
>
> I found it a little confusing too but Here is what I think David is trying
> to say and hopefully if I am wrong I will get set straight shortly.
>
> It is better to use the damper to control secondary air to create reduction
> than to use the burners primary air control to create reduction.
>
> As the column of burning fuel is propelled into the kiln under pressure it
> creates a venturi in the burner port. This port venturi draws in the
> "secondary air". It is possible to choke off this effect somewhat by closing
> off the damper at the output of the kiln making it harder for this secondary
> air venturi to get air into the kiln thus making the combustion more
> reducing IN THE KILN. The burners can be set with a compact, strong, neutral
> to oxidising flame with good shape and energy throughout the firing. If we
> try to shut off the burners primary air to create reduction, the flame will
> soften and yellow and not be nearly as forceful.
>
> I THINK the indication is that the softer flame is less likely to mix well
> throughout the kiln giving less than even reduction results.
>
> thats what I took from this passage and it fits with my experience and other
> reading
>
> Ben
>
> ______________________________________________________________________________
> 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.
Chris trabka on thu 9 aug 07
Jennifer
After about a minute or two my Oxyprobe goes from .625 to .000
Chris
>For those of you that do reduce and use an Oxyprobe, how long does
>the reduction last after you shut the burners off and close the kiln up?
>Jennifer
Jennifer Boyer on fri 10 aug 07
Yeah, so everyone who fires reduction has an oxidation phase at the
end, when they turn the kiln off....
I just don't understand when people talk about whether or not to have
a cleansing oxidation phase at the end. It'll happen anyway. When the
burners are shut off.
Right?
Jennifer
On Aug 9, 2007, at 3:15 PM, Chris trabka wrote:
> Jennifer
>
> After about a minute or two my Oxyprobe goes from .625 to .000
>
> Chris
>
>> For those of you that do reduce and use an Oxyprobe, how long does
>> the reduction last after you shut the burners off and close the
>> kiln up?
>> Jennifer
>
> ______________________________________________________________________
> ________
> 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.
*****************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
*****************************
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