Christine Avery on sat 24 oct 98
I am a "newbie" (I don't really care what I am called - just to let you
know that I know very little) I am a grades 11/12 art teacher who inherited
a full ceramics lab and an updraft reduction kiln. I have had limited
ceramics experience in college and have obtained most of my knowledge from
a couple of GREAT! production potters here in town.(I am a proponent of
both academia and production neither are wrong they are just different -
like our college bound track and our school to work track. thanks for the
great insight Raphael) I digress
The question I have is - a lot of glaze recipes require "soaking time" How
do I do it? I have had it explained verbally once but really don't know how
to do it.
Also we fire our stoneware to fully down ^9 and slightly bent ^10. As a
rule of thumb when is a good time to start the reduction? Good notes in
plain English on reducing in general would be appreciated.
thank you for all the great letters on academia and archaic feminist art.
My mind needs and desires that type of stimulation after spending every day
- all day with 16-18 year olds.
Christine
avery@sendit.nodak.edu
Chess Denman on tue 27 oct 98
Well,
First, you have three ways to initiate reduction. First it by introducing
burning carbon into the kiln eg wood or other vegetable matter. Second by
reducing the air you mix with the gass in the burners (burners will have
little collars near the nozzel to do this. Last by reducing the draft in the
kiln with a damper. Personally I find three ways too many and so I only use
my damper.
Next you have to judge whether reduction or oxidation is occuring. This is
done in three ways. First you can smell reduction and may see smoke at the
stack, second if you are rich there are fancy gass testing meters to measure
the atmosphere in the kiln and the last method is judging the air flow at
the kiln by looking at the peephole. Open the peep and hold a smoking taper
to it. In oxidation smoke is drawn into the kiln because the kiln has
"positive draw" as you close the damper the draw will get less and less
enthusiastic untill the smoke from the taper begins to blow outwards (very
mild negative draw) as you continue to close the damper a little tongue of
flame will appear out of the peep. If you go on closing the damper you will
get flames appearing at the burner ports ( not a good plan). Reasonable
reduction is signaled by a good tongue of flame at the peep.
Next you need to controll the kiln temperature during reduction. I am
affraid I think a good pyrometer would be a wize investment. As you initiate
reduction the temperature in the kiln may begin to fall and you have to turn
the burners up (which increases the depth of reduction by "gassing" the
kiln) to maintain a rise. As you reach your desired soak temperature
controlling the kiln temperature (at least in my case) involves hopping
about and pusing in the damper a tich, cutting back on the burners a tich
and then the other way watching the pyrometer like a hawk. So far I manage a
variation of about 5 C arround my soak temp. I am also balancing the degree
of reduction to be very light just at the end.
Most people start reduction arround 1000 degrees centigrade (if you start
much below 800 you get something called carbon coreing which is a blackening
in the middle of the clay body which weakens it.) often if copper reds are
desired the reduction is fierce at first but then less and less and some
reoxidise at the end (I'm not brave enough to do this and just reduce the
ammount of reduction to a neutral draw at the end.
Chess
-----Original Message-----
From: Christine Avery
To: CLAYART@LSV.UKY.EDU
Date: 24 October 1998 17:52
Subject: Soaking a reduction kiln
----------------------------Original message----------------------------
I am a "newbie" (I don't really care what I am called - just to let you
know that I know very little) I am a grades 11/12 art teacher who inherited
a full ceramics lab and an updraft reduction kiln. I have had limited
ceramics experience in college and have obtained most of my knowledge from
a couple of GREAT! production potters here in town.(I am a proponent of
both academia and production neither are wrong they are just different -
like our college bound track and our school to work track. thanks for the
great insight Raphael) I digress
The question I have is - a lot of glaze recipes require "soaking time" How
do I do it? I have had it explained verbally once but really don't know how
to do it.
Also we fire our stoneware to fully down ^9 and slightly bent ^10. As a
rule of thumb when is a good time to start the reduction? Good notes in
plain English on reducing in general would be appreciated.
thank you for all the great letters on academia and archaic feminist art.
My mind needs and desires that type of stimulation after spending every day
- all day with 16-18 year olds.
Christine
avery@sendit.nodak.edu
Kathi LeSueur on wed 28 oct 98
In a message dated 10/27/98 11:51:01 AM, you wrote:
>I am a "newbie" (I don't really care what I am called - just to let you
>know that I know very little) I am a grades 11/12 art teacher who inherited
>a full ceramics lab and an updraft reduction kiln. I have had limited
>ceramics experience in college and have obtained most of my knowledge from
>a couple of GREAT! production potters here in town.(I am a proponent of
>both academia and production neither are wrong they are just different -
>like our college bound track and our school to work track. thanks for the
>great insight Raphael) I digress
>
>The question I have is - a lot of glaze recipes require "soaking time" How
>do I do it? I have had it explained verbally once but really don't know how
>to do it.
>
>Also we fire our stoneware to fully down ^9 and slightly bent ^10. As a
>rule of thumb when is a good time to start the reduction? Good notes in
>plain English on reducing in general would be appreciated.
I would suggest investment in a good pyrometer and a CO2 analyzer. I use the
CO2 analyzer from Bacarach in Pennsylvania.
My kiln uses forced air burners. I use every tool available to me in firing
my gas kiln. I start a body reduction when cone 010 falls (9% on the CO2
analyzer). By using a cone I know that the kiln is at the proper temperature
to begin the body reduction. I end body reduction at cone 05 and leave it in a
very slight reduction (11% on the CO 2 analyzer) until cone 8 begins to fall.
At that point I slow down the kiln by cutting back on the gas and air.
Reduction is adjusted to 91/2%.
I soak the kiln when cone 10 has fallen by severely reducing both the gas and
air going into the kiln. By using the CO2 analyzer I can assure that the kiln
remains in reduction when I adjust it. I soak for 45 minutes. Because I am
more concerned with the temperature continuing to rise rather than fall, I
include cone 11 in my cone packs.
While many people swear by the color of the flame, the length of it, and the
smell of the gas I tend to not trust these factors. I find that the color and
length of the flame remain the same at 9 1/2 % and 10% reduction. But the
effects on my glazes are significant.
Kathi LeSueur
Ann Arbor, MI
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