James and Sherron Bowen on thu 9 aug 07
When I started this thread we had just finished a firing where for the first
time we put the kiln into oxidation ( open primaries, open damper steady
temp rise) at cone 9 after reducing from 011(closed primaries, smoke out the
flue, back pressure at the bottom spy hole). We stayed with oxidation all
the way to the end. This was a very uneven firing according to the cones.
From cone eight in the middle front to cone eleven on the sides of the top
shelf. Cone 9 bottom and top center. If we do that again we will have to
learn how to use the damper to even out the firing. We got great oil spots
on the tenmokus and olive drab celadons. The kakis were bright and clean.
White shinos. No fire color.
JB
===============================================================================
"What did you learn in school today? Did you learn how to believe or did you
learn how to think?"
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----- Original Message -----
From: "mel jacobson"
To:
Sent: Thursday, August 09, 2007 7:51 PM
Subject: reduction thread
Lee Love on thu 9 aug 07
On 8/9/07, mel jacobson wrote:
>
>
> we have folks that cannot see cones...need glasses because
> the kiln is so opaque, others can see the texture of the back wall.
> goes to show.
> things are very different, in different firings.
> i do admit that.
>
Isn't telling a potter "I can't see the cones." a little like telling a
Canadian, "I can't see the puck!" ;^)
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://mashikopots.blogspot.com/
"To affect the quality of the day, that is the highest of arts." - Henry
David Thoreau
"Let the beauty we love be what we do." - Rumi
mel jacobson on thu 9 aug 07
bill, and others.
i think we do have a very odd and interesting
thread.
we have folks that cannot see cones...need glasses because
the kiln is so opaque, others can see the texture of the back wall.
goes to show.
things are very different, in different firings.
i do admit that.
as a teacher, i still love to teach that we see a bit of turbulence
and opacity.
does not mean it always works. there sure are no absolutes.
mel
from: mel/minnetonka.mn.usa
website: http://www.visi.com/~melpots/
Clayart page link: http://www.visi.com/~melpots/clayart.html
Chris trabka on fri 10 aug 07
James and Sherron Bowen,
I have only 1 kiln a MFT with 6 venturi burners per side that uses natual
gas. I use the same kiln for both bisque and glaze firings.
The primaries are never changed - they are always completely open.
For the bisque I have a completely oxidation firing.
For the glaze firing I have oxidation to about ^015 and then go into
reduction.
The oxidation/reduction is controlled by the gas preasure, the positive
damper, and the passive dampers in the chimney.
The settings for a reduction firing is not always the same. A bright cool
crisp autumn day has different settings compared to a steamy sultry summer
day.
Chris
Lee Love on fri 10 aug 07
On 8/9/07, James and Sherron Bowen wrote:
>
>
> shelf. Cone 9 bottom and top center. If we do that again we will have to
> learn how to use the damper to even out the firing. We got great oil spots
> on the tenmokus and olive drab celadons. The kakis were bright and clean.
> White shinos. No fire color.
>
I think the iron saturated glazes were traditionally fired in oxidation.
Mashiko glazes were all in oxidation.
In this situation, try a high alumina shino. It is what I had to
do.
--
Lee in Minneapolis, Minnesota USA
discussion on Beauty:
http://journals.fotki.com/togeika/beauty/
http://mashikopots.blogspot.com/
"Let the beauty we love be what we do." - Rumi
William & Susan Schran User on fri 10 aug 07
On 8/9/07 9:51 PM, "mel jacobson" wrote:
> we have folks that cannot see cones...need glasses because
> the kiln is so opaque, others can see the texture of the back wall.
> goes to show.
> things are very different, in different firings.
> i do admit that.
>
> as a teacher, i still love to teach that we see a bit of turbulence
> and opacity.
> does not mean it always works. there sure are no absolutes
You are correct with that last statement.
I was taught back in the early 1970's to fire a hardbrick downdraft kiln in
oxidation to ^08, then shut the primary air & close down the damper,
creating a very opaque, turbulent atmosphere with great yellow flames and
black sooty smoke belching from any opening in the kiln until the end of the
firing.
Certainly the design of the kiln will have an impact on how it should be
fired to produce the desired results.
But I also wonder, is there much difference firing between natural gas &
propane? Is it correct that natural gas contains more "moisture" thus making
it easier to achieve reduction?
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Lee Love on fri 10 aug 07
On 8/10/07, William & Susan Schran User wrote:
>
>
>
> But I also wonder, is there much difference firing between natural gas &
> propane? Is it correct that natural gas contains more "moisture" thus
> making
> it easier to achieve reduction?
>
>
There is a great article I have shared here before from Ceramics
Technical on Water Reduction.
At lower temps, water oxidizes. So it is possible that it would
make body reduction more difficult. At cone 10plus, it reduces.
Let me know privately if you would like to read the
article.
--
Lee in Minneapolis, Minnesota USA
discussion on Beauty:
http://journals.fotki.com/togeika/beauty/
http://mashikopots.blogspot.com/
"Let the beauty we love be what we do." - Rumi
Dave Finkelnburg on fri 10 aug 07
Dear Bill,
Yes, there is some difference between burning
natural gas and liquid propane. The natural gas is
mostly methane, CH4. When it burns in oxidation, for
every molecule of CO2 formed you have two molecules of
water.
Propane is mostly C2H6, so in oxidation for every
molecule of CO2 formed you get 1.5 molecules of water.
Reduction involves using less air, hence less
oxygen. So, theoretically the methane (natural gas)
may get to reduction quicker. On the other hand,
since you control this with the damper, you may
struggle to tell the difference between the two fuels
unless you fire a very large kiln with very
sophisticated burner controls.
Good potting!
Dave Finkelnburg
Date: Fri, 10 Aug 2007 10:29:58 -0400
From: William & Susan Schran User
But I also wonder, is there much difference firing
between natural gas &
propane? Is it correct that natural gas contains more
"moisture" thus making
it easier to achieve reduction?
____________________________________________________________________________________
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Ron Roy on mon 13 aug 07
Hi JB,
Part of the problem with uneven firings is the clay as well as the glazes.
If a clay is vitrified properly at cone 10 it may very well not be water
tight at cone 8. In other words it's not only the glazes that are affected
by uneven firing.
Did your firing go faster? An oxidizing stage can be hotter for instance.
If that was the case perhaps less air and gas would slow it down and give
it a better chance to even out.
RR
>When I started this thread we had just finished a firing where for the first
>time we put the kiln into oxidation ( open primaries, open damper steady
>temp rise) at cone 9 after reducing from 011(closed primaries, smoke out the
>flue, back pressure at the bottom spy hole). We stayed with oxidation all
>the way to the end. This was a very uneven firing according to the cones.
>From cone eight in the middle front to cone eleven on the sides of the top
>shelf. Cone 9 bottom and top center. If we do that again we will have to
>learn how to use the damper to even out the firing. We got great oil spots
>on the tenmokus and olive drab celadons. The kakis were bright and clean.
>White shinos. No fire color.
>JB
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Lee Love on mon 13 aug 07
On 8/13/07, Ron Roy wrote:
> Hi JB,
>
> Part of the problem with uneven firings is the clay as well as the glazes.
> If a clay is vitrified properly at cone 10 it may very well not be water
> tight at cone 8. In other words it's not only the glazes that are affected
> by uneven firing.
What would firers do, who get a welcomed variety in their
kilns, is use different kinds of clays in different areas.
Where I get over cone 13 at the fireface, I use co-shigaraki
hosome and shino mogusa. THey take the temperature well. At the
top by the door (cone 11`) to the middle, I use nami (common)
shigaraki clay. Shinos like the hot part and my ash glaze at the
cooler end. At the coolest place, in the chamber, I put nami
Mashiko clay which is usually fired to cone 8 seger. In the flue
channel, I can but bizen cone 6 glaze.
A kiln that has a variety of temperatures and
atmospheric effects is very useful, if you listen to it.
--
Lee in Minneapolis, Minnesota USA
"For a democracy of excellence, the goal is not to reduce things to a
common denominator but to raise things to a shared worth."
--Paolo Soleri
James and Sherron Bowen on mon 13 aug 07
Thanks, Ron.
"Did your firing go faster?"
Yes by several hours.
We normally use 75 gallons of gas and according to the tank gauge we were
under 50 this time.
The clay used was mostly Soldate 60 from Laguna via Mile Hi Ceramics.
JB
----- Original Message -----
From: "Ron Roy"
To:
Sent: Monday, August 13, 2007 2:58 PM
Subject: Re: reduction thread
> Hi JB,
>
> Part of the problem with uneven firings is the clay as well as the glazes.
> If a clay is vitrified properly at cone 10 it may very well not be water
> tight at cone 8. In other words it's not only the glazes that are affected
> by uneven firing.
>
> Did your firing go faster? An oxidizing stage can be hotter for instance.
> If that was the case perhaps less air and gas would slow it down and give
> it a better chance to even out.
>
> RR
Ron Roy on thu 16 aug 07
Hi JB,
Well fast firing can result in eneven firings - unless you have a well
designed kiln. Sometimes kilns with not fire evenly no mater what you do.
RR
>Thanks, Ron.
> "Did your firing go faster?"
>Yes by several hours.
>We normally use 75 gallons of gas and according to the tank gauge we were
>under 50 this time.
>The clay used was mostly Soldate 60 from Laguna via Mile Hi Ceramics.
>JB
>
>----- Original Message -----
>From: "Ron Roy"
>To:
>Sent: Monday, August 13, 2007 2:58 PM
>Subject: Re: reduction thread
>
>
>> Hi JB,
>>
>> Part of the problem with uneven firings is the clay as well as the glazes.
>> If a clay is vitrified properly at cone 10 it may very well not be water
>> tight at cone 8. In other words it's not only the glazes that are affected
>> by uneven firing.
>>
>> Did your firing go faster? An oxidizing stage can be hotter for instance.
>> If that was the case perhaps less air and gas would slow it down and give
>> it a better chance to even out.
>>
>> RR
>
>______________________________________________________________________________
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>
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>
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Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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