Jeff Lawrence on fri 27 aug 99
Hello Clayart,
I fire almost exclusively in oxidation for production, but want to master
reduction firing in my kiln. I use an oxyprobe to monitor the atmosphere,
which works great to keep from my oxidation firings, but indicates that my
reduction technique has problems. My reduction firing results already
tipped me off to the need for improvement!
I've tried reduction firings at several temperature ranges - 04, 6 and
9-10, and had the same problem at each temperature. The Oxyprobe manual
says light reduction is a one range (.2-.4) medium range another (.4-.6)
and heavy reduction is achieved above that range. I've been trying to get a
light reduction environment without success. The probe only ever stabilizes
at .6 and above. Any time I try to get a steady reading in the light or
medium range, I get values all over the chart, from neutral to heavy.
These flickers appear no matter how I try for lighter reduction:
- getting a neutral atmosphere and upping the gas a bit
- getting a neutral atmosphere and cutting the air a bit
- getting a neutral atmosphere and dampering in a bit
I've considered that I might be putting two much gas and/or air into the
kiln, but find that I'm using the minimum to maintain the temperature rise
(the other day, I snuck up to cone 6 at 50 degrees F for five hours, so I
don't think I'm being prodigal with the gas).
My results indicate inadequate reduction (iron-rich glazes didn't melt
completely by the flue, copper reds were mottled green and red). When I
lock the oxyprobe on the first steady reading I can get (about .65 or so) I
get results that indicate overreduction (blackish copper reds) and at .78
or so, tin reduced to metal crystals in the glaze (pretty neat looking,
except the copper was blah reddish black).
How does one avoid this choice between too little and too much?
almost reduced to Metallica myself over this, heartfelt thanks in advance!
Jeff
BTW: The kiln is a downdraft design similar to the MFT, with ceramic fiber
walls and an IFB floor. Situated at 7000 feet in elevation, the stack is
9X9 and the flue is maybe 7X7. I fire with natural gas using two forced air
burners.
Jeff Lawrence Sun Dagger Design
jml@sundagger.com Rt. 3 Box 220
www.sundagger.com Espanola, NM 87532
vox 505-753-5913 fax 505-753-8074
Louis H.. Katz on sun 29 aug 99
Make sure your door is well sealed, especially if the Oxyprobe is inserted
through the door. Try more back pressure (close the damper and turn up the
blowers). This should create better mixing, a more even atmosphere and
compensate for a leaky door(if it is leaky)
Louis
Lkatz@nceca.net
Robert Santerre on tue 31 aug 99
Hi Jeff,
I have an AIC oxy probe and experience the same problems you have with wide
swings in reading at the lower reduction levels and especially at lower firing
temps. I haven't really tried to remedy the situation, I've just learned to
fire the kiln by eye during those times and rely on the probe readings only
after things stabilize (above cone 5). I don't experience your problem of
over-reduction. My reds stay red, mostly. I try to maintain 0.6-0.65 from
cone 7 to cone 10 (if I go below this , e.g., 0.4, I will get under-reduction),
then fully oxidize for about 20 minutes at the end just before shutting down
the kiln.
My probe is located in the exit flue(just as it exits the firing chamber) in my
down draft kiln. Because there's a lot of turbulence there and the possibility
of some fully oxygenated air sweeping directly into the flue from the burner
ports, I've assumed that is what causes the fluctuations in the probe. If I
were going to make changes to eliminated the fluctuations I'd start by moving
the probe to a different location, perhaps more toward the middle or upper
middle of the firing chamber.
Sorry I can't offer a more informed solution. If you solve the problem I'd
sure be interested in hearing about your solution.
Good luck, Bob
rfsanterre@iquest.net
////////////////////////////////////////////////////////////////////////////////
Jeff Lawrence wrote:
> ----------------------------Original message----------------------------
> Hello Clayart,
>
> I fire almost exclusively in oxidation for production, but want to master
> reduction firing in my kiln. I use an oxyprobe to monitor the atmosphere,
> which works great to keep from my oxidation firings, but indicates that my
> reduction technique has problems. My reduction firing results already
> tipped me off to the need for improvement!
>
> I've tried reduction firings at several temperature ranges - 04, 6 and
> 9-10, and had the same problem at each temperature. The Oxyprobe manual
> says light reduction is a one range (.2-.4) medium range another (.4-.6)
> and heavy reduction is achieved above that range. I've been trying to get a
> light reduction environment without success. The probe only ever stabilizes
> at .6 and above. Any time I try to get a steady reading in the light or
> medium range, I get values all over the chart, from neutral to heavy.
>
> These flickers appear no matter how I try for lighter reduction:
> - getting a neutral atmosphere and upping the gas a bit
> - getting a neutral atmosphere and cutting the air a bit
> - getting a neutral atmosphere and dampering in a bit
>
> I've considered that I might be putting two much gas and/or air into the
> kiln, but find that I'm using the minimum to maintain the temperature rise
> (the other day, I snuck up to cone 6 at 50 degrees F for five hours, so I
> don't think I'm being prodigal with the gas).
>
> My results indicate inadequate reduction (iron-rich glazes didn't melt
> completely by the flue, copper reds were mottled green and red). When I
> lock the oxyprobe on the first steady reading I can get (about .65 or so) I
> get results that indicate overreduction (blackish copper reds) and at .78
> or so, tin reduced to metal crystals in the glaze (pretty neat looking,
> except the copper was blah reddish black).
>
> How does one avoid this choice between too little and too much?
>
> almost reduced to Metallica myself over this, heartfelt thanks in advance!
> Jeff
>
> BTW: The kiln is a downdraft design similar to the MFT, with ceramic fiber
> walls and an IFB floor. Situated at 7000 feet in elevation, the stack is
> 9X9 and the flue is maybe 7X7. I fire with natural gas using two forced air
> burners.
>
> Jeff Lawrence Sun Dagger Design
> jml@sundagger.com Rt. 3 Box 220
> www.sundagger.com Espanola, NM 87532
> vox 505-753-5913 fax 505-753-8074
Lee Marshall on wed 8 sep 99
My oxyprobe is in the top of the kiln smack dab in the middle and i still get
fluctuations of +_ .05 in the readings
lee marshall
lmarsh1220@aol.com
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