Bob Johnson on sun 15 jun 08
Does anyone have guidelines for when (or when not) to reoxidize a kiln at
the end of a reduction firing cycle? I assume that the answer depends on
which colorants one is using: My old standbys involve iron reds, yellows,
and greens. Thanks!
Bob
Southern Oregon
Bob Johnson on mon 16 jun 08
Thanks, Hank, for your thorough and thoughtful reply regarding oxidation at
the end of the firing cycle. I don't have an oxyprobe, but I will try to
imitate your method as best I can by eyeballing the draw at the peep holes.
Is .07 a lot of oxygen or a little?
A couple of other related questions:
1. I fire to ^6 in reduction. Do you think that reoxidizing at 1900 degrees
would be the appropriate temperature, or should I try decreasing that
proportionately, say by ~200 degrees?
2. I have heard potters say that when the kiln gets to its highest
temperature (^6 or whatever the target may be), they oxidize briefly--just
for a few minutes--to "clear" the kiln. Is this a sensible practice--and
does it depend on which colorants are being used?
Thanks,
Bob
So. Oregon
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Hank Murrow
Sent: Monday, June 16, 2008 10:20 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: reoxidation at end of firing cycle?
On Jun 15, 2008, at 11:20 PM, Bob Johnson wrote:
> Does anyone have guidelines for when (or when not) to reoxidize a kiln
> at the end of a reduction firing cycle? I assume that the answer
> depends on which colorants one is using: My old standbys involve iron
> reds, yellows, and greens. Thanks!
Dear Bob;
I fire one of my Doorless Fiberkilns and have been doing a soak in oxidation
during cooling around 1900F for three to six hours. For shiny or semishiny
glazes, this will not make much difference, save that it may matt the glazes
a bit. But for flux matts and semimatts due to slight (or more) excess of
flux; Great color can be achieved this way.
I use an OxyProbe, and after the kiln has been turned off, I damper tightly
for two hours. Then I light the kiln again and set it to 1/3 of the pressure
that it was at the end. I then adjust the damper to yield a strictly
oxidizing fire, around .07 on the OxyProbe. I hold this setting for three to
even eight hours before turning off the gas and allowing the kiln to cool
dampered. I begin to crack the damper around 1400F, and it is full open by
500F.
The result is exceptional color from shinos, khakis, iron reds, iron
yellows, and any other colors from excess flux precipitating on the surface
of the glaze with the oxides. I can send you pics if desired.
Can't wait until Clayart allows pics!
BTW, This regime works a treat with cone 10 oxidation glazes as well.
Cheers, Hank
Hank Murrow on mon 16 jun 08
On Jun 15, 2008, at 11:20 PM, Bob Johnson wrote:
> Does anyone have guidelines for when (or when not) to reoxidize a
> kiln at
> the end of a reduction firing cycle? I assume that the answer
> depends on
> which colorants one is using: My old standbys involve iron reds,
> yellows,
> and greens. Thanks!
Dear Bob;
I fire one of my Doorless Fiberkilns and have been doing a soak in
oxidation during cooling around 1900F for three to six hours. For
shiny or semishiny glazes, this will not make much difference, save
that it may matt the glazes a bit. But for flux matts and semimatts
due to slight (or more) excess of flux; Great color can be achieved
this way.
I use an OxyProbe, and after the kiln has been turned off, I damper
tightly for two hours. Then I light the kiln again and set it to 1/3
of the pressure that it was at the end. I then adjust the damper to
yield a strictly oxidizing fire, around .07 on the OxyProbe. I hold
this setting for three to even eight hours before turning off the gas
and allowing the kiln to cool dampered. I begin to crack the damper
around 1400F, and it is full open by 500F.
The result is exceptional color from shinos, khakis, iron reds, iron
yellows, and any other colors from excess flux precipitating on the
surface of the glaze with the oxides. I can send you pics if desired.
Can't wait until Clayart allows pics!
BTW, This regime works a treat with cone 10 oxidation glazes as well.
Cheers, Hank
Bob Johnson on tue 17 jun 08
Hank: This is very helpful. A good place for me to start. I have a fairly
new Roman arch downdraft kiln--about 30 cu ft.--custom built of soft & hard
bricks, with a fiber door and 2 propane burners. Fires very evenly, if I'm
careful.
Thanks again. (I love the shino mug I bought at your gallery show in
Eugene!)
Best,
Bob
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Hank Murrow
Sent: Tuesday, June 17, 2008 10:11 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: reoxidation at end of firing cycle?
On Jun 16, 2008, at 10:11 PM, Bob Johnson wrote:
> Thanks, Hank, for your thorough and thoughtful reply regarding
> oxidation at the end of the firing cycle. I don't have an oxyprobe,
> but I will try to imitate your method as best I can by eyeballing the
> draw at the peep holes.
> Is .07 a lot of oxygen or a little?
It is characterized by a complete lack of back pressure at spyholes and at
the flue exit, and a very clear atmosphere inside the kiln.
Just a couple of notches cleaner than neutral.
>
> A couple of other related questions:
>
> 1. I fire to ^6 in reduction. Do you think that reoxidizing at 1900
> degrees would be the appropriate temperature, or should I try
> decreasing that proportionately, say by ~200 degrees?
No, I would keep it the same, unless draw trial testing suggests otherwise.
>
> 2. I have heard potters say that when the kiln gets to its highest
> temperature (^6 or whatever the target may be), they oxidize
> briefly--just for a few minutes--to "clear" the kiln. Is this a
> sensible practice--and does it depend on which colorants are being
> used?
Some who fire electrics with a vent system have reported brighter colors
than when they fired without a vent system. That suggests that clearing the
atmosphere at the end is a good idea, especially with a combustion kiln.
What sort of kiln do you fire in?
Hope this helps.....
Cheers, Hank
Hank Murrow on tue 17 jun 08
On Jun 16, 2008, at 10:11 PM, Bob Johnson wrote:
> Thanks, Hank, for your thorough and thoughtful reply regarding
> oxidation at
> the end of the firing cycle. I don't have an oxyprobe, but I will
> try to
> imitate your method as best I can by eyeballing the draw at the
> peep holes.
> Is .07 a lot of oxygen or a little?
It is characterized by a complete lack of back pressure at spyholes
and at the flue exit, and a very clear atmosphere inside the kiln.
Just a couple of notches cleaner than neutral.
>
> A couple of other related questions:
>
> 1. I fire to ^6 in reduction. Do you think that reoxidizing at 1900
> degrees
> would be the appropriate temperature, or should I try decreasing that
> proportionately, say by ~200 degrees?
No, I would keep it the same, unless draw trial testing suggests
otherwise.
>
> 2. I have heard potters say that when the kiln gets to its highest
> temperature (^6 or whatever the target may be), they oxidize
> briefly--just
> for a few minutes--to "clear" the kiln. Is this a sensible
> practice--and
> does it depend on which colorants are being used?
Some who fire electrics with a vent system have reported brighter
colors than when they fired without a vent system. That suggests that
clearing the atmosphere at the end is a good idea, especially with a
combustion kiln. What sort of kiln do you fire in?
Hope this helps.....
Cheers, Hank
Hank Murrow on wed 18 jun 08
On Jun 17, 2008, at 11:03 PM, Bob Johnson wrote:
> Hank: This is very helpful. A good place for me to start. I have a
> fairly
> new Roman arch downdraft kiln--about 30 cu ft.--custom built of
> soft & hard
> bricks, with a fiber door and 2 propane burners. Fires very evenly,
> if I'm
> careful.
> Thanks again. (I love the shino mug I bought at your gallery show in
> Eugene!)
You may not need a soak @1900F since the kiln is so massive, but
please try it and report back. I am eager to learn.....
Say, when did you get that mug? White Lotus? I open there with
Hiroshi Ogawa July 19.
Cheers, Hank
Bob Johnson on wed 18 jun 08
I did get the mug at White Lotus--a few months ago.
And, by the way, my kiln was built by Howard Kiefer, who was involved in
building Hiroshi's. BTW, weren't you the one who built the fiber kiln at
Umpqua Community College?
bob
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Hank Murrow
Sent: Wednesday, June 18, 2008 7:09 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: reoxidation at end of firing cycle?
On Jun 17, 2008, at 11:03 PM, Bob Johnson wrote:
> Hank: This is very helpful. A good place for me to start. I have a
> fairly new Roman arch downdraft kiln--about 30 cu ft.--custom built of
> soft & hard bricks, with a fiber door and 2 propane burners. Fires
> very evenly, if I'm careful.
> Thanks again. (I love the shino mug I bought at your gallery show in
> Eugene!)
You may not need a soak @1900F since the kiln is so massive, but please try
it and report back. I am eager to learn.....
Say, when did you get that mug? White Lotus? I open there with Hiroshi Ogawa
July 19.
Cheers, Hank
| |
|
