Nancy Udell on sat 28 aug 04
Hello clay list,=20
We are having some effects from soda/salt firing that we don't like, and =
were wondering if anyone has any thoughts as to the cause. We've tried =
a number of different things from time to time (and probably because =
we've often changed multiple variables, cannot consistently get rid of =
the grey effect described below). =20
=20
Bare clay or clay with slips that are near the soda ports are often =
getting matte gray areas on the sides facing the soda. The rest of the =
pieces are beautiful, toasty tan, and nicely glazed. Also, glazed =
pieces are sometimes overfluxed if near the soda ports. =20
=20
The links below go to two two pieces of unglazed Campbell's white =
stoneware from different spots in the kiln.
=20
1. =
http://home.comcast.net/~greentree1/wsb/html/view.cgi-photo.html--SiteID-=
1768362.html
=20
=20
2. =
http://home.comcast.net/~greentree1/wsb/html/view.cgi-photo.html--SiteID-=
1768363.html
=20
Here's some info on our kiln and firing process. We are firing a =
propane fueled, cross draft kiln - 36.7 cubic feet total inside space. =
The bagwall is 9" from inside the burner ports, is 4 bricks high and is =
fairly open. At cone 010 we are doing heavy body reduction for 1 hour, =
then light reduction for the rest of the firing. At cone 8 we begin =
injecting sodium - 3 lbs of soda (comprised of baking soda, soda ash and =
borax), dissolved in hot water and sprayed, alternating with 5 1lb =
dumps of salt over 2 plus hours. We have been waffling the damper =
during spraying and closing the damper to within 1 inch for 5 minutes =
after salting, then opening the damper to clear the atmosphere, then =
waiting 20 minutes before another round. After the kiln reaches =
temperature, cone 10 tipping half over, we are firing down to 1050=B0 C, =
with one burner on low and damper and air flaps open. This firing down =
has helped to even the color of bare clay from top to=20
bottom.
Thanks very much for any thoughts.
Nancy and Marianne
sdr on sun 29 aug 04
Subject: Grey clay from soda/salt firing
Nancy, many clays turn grey to dark grey in soda firings,
and where they do and the soda is light, the surface will look grey..
Where the soda itself seems to be turning grey, it IS turning
grey- it is a great carbon trapper. Sometimes soda will
turn RED in a firing, because of copper in the kiln plus
the soda's carbon trapping propensities.
Likely the soda is trapping some carbon as it is sprayed
into the kiln, and onto the pots near the spray ports.
regards
Dannon Rhudy
Ivor and Olive Lewis on mon 30 aug 04
Dear Nancy Udell,
Could it be that at some point in your firing you are getting strong
reduction?
Tony makes a valid point that excess soda remaining in the kiln by the
fire ports will start melting early in a firing, though I do not know
how volatile it would be at its melting point (851=BA C). This is well
below the vitrification range of most clay bodies and so any Soda that
impinges on the clay will not enter into a chemical reaction which
would lead to the forming of a layer of glaze.
Although in the past many people have tried to get low temperature
effects with Salt these are know to have an degree of impermanency and
it is suggested that salting is not started before the temperature of
the kiln goes over 1100=BA C. It is my belief that the Chemistries of
Salt and Soda Glaze are dissimilar.
By the way, I thought your images to be out of focus since the detail
is blurred.
best regards,
Ivor Lewis.
Redhill,
S. Australia.
----- Original Message -----
From: "Nancy Udell"
To:
Sent: Sunday, 29 August 2004 5:05
Subject: Grey clay from soda/salt firing
Hello clay list,
We are having some effects from soda/salt firing that we don't like,
and were wondering if anyone has any thoughts as to the cause. We've
tried a number of different things from time to time (and probably
because we've often changed multiple variables, cannot consistently
get rid of the grey effect described below).
Bare clay or clay with slips that are near the soda ports are often
getting matte gray areas on the sides facing the soda. The rest of
the pieces are beautiful, toasty tan, and nicely glazed. Also,
glazed pieces are sometimes overfluxed if near the soda ports.
The links below go to two two pieces of unglazed Campbell's white
stoneware from different spots in the kiln.
1.
http://home.comcast.net/~greentree1/wsb/html/view.cgi-photo.html--Site
ID-1768362.html
2.
http://home.comcast.net/~greentree1/wsb/html/view.cgi-photo.html--Site
ID-1768363.html
Here's some info on our kiln and firing process. We are firing a
propane fueled, cross draft kiln - 36.7 cubic feet total inside space.
The bagwall is 9" from inside the burner ports, is 4 bricks high and
is fairly open. At cone 010 we are doing heavy body reduction for 1
hour, then light reduction for the rest of the firing. At cone 8 we
begin injecting sodium - 3 lbs of soda (comprised of baking soda, soda
ash and borax), dissolved in hot water and sprayed, alternating with 5
1lb dumps of salt over 2 plus hours. We have been waffling the damper
during spraying and closing the damper to within 1 inch for 5 minutes
after salting, then opening the damper to clear the atmosphere, then
waiting 20 minutes before another round. After the kiln reaches
temperature, cone 10 tipping half over, we are firing down to 1050=B0 C,
with one burner on low and damper and air flaps open. This firing
down has helped to even the color of bare clay from top to
bottom.
Thanks very much for any thoughts.
Nancy and Marianne
______________________________________________________________________
________
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.
Lee Love on mon 30 aug 04
Nancy Udell wrote:
>Hello clay list,
>
>
>
>We are having some effects from soda/salt firing that we don't like, and were wondering if anyone has any thoughts as to the cause. We've tried a number of different things from time to time (and probably because we've often changed multiple variables, cannot consistently get rid of the grey effect described below).
>
>
Nancy and Marianne,
If you soda heavy you will get this glaze coating, sometimes even "orange peeling." When the soda is light enough not to cause a gloss glaze surface, you get the blushing. I too prefer color, orange/yellow/red.
There are a number things you can do: don't use as much soda or, introduce smaller amounts at more ports in the kiln (some folks use glazed cups set round in the kiln filled with soda. They should be glazes so the crucibles don't melt through), or you can use shields to protect the work right in front of the soda entry, or use glazes that react well with the soda in that part of the kiln.
>Bare clay or clay with slips that are near the soda ports are often getting matte gray areas on the sides facing the soda. The rest of the pieces are beautiful, toasty tan, and nicely glazed. Also, glazed pieces are sometimes overfluxed if near the soda ports.
>
>
Another thing you have to worry about: I have noticed that
these build ups on the lips of work tend to flake off easily. The soda
glaze doesn't seem to be as durable as what comes from salt. It might
be possible to use a slip including materials that would combine with
the soda to be more durable.
--
Lee in Mashiko, Japan http://mashiko.org
http://www.livejournal.com/users/togeika/ WEB LOG
http://public.fotki.com/togeika/ Photos!
Paul Herman on mon 30 aug 04
Hello Nancy and Marianne,
Well, you've gotten a lot of different theories on this one, so here's
mine.
We get that blue-grey color in the woodkiln. It seems to be related to
the intensity of flame/reduction. More flame/reduction, more grey. I
agree with Tony Clennell, it's carbon trapping in the clay body. Seems
it makes the clay brittle, and easily broken.
It is also more pronounced in more vitreous clays, like porcelain, or
stoneware that has a bit of flux in it.
It got to be too much, and when we backed off the stoking, there was
less blue. It's really nice to have a few touches of the blue on the
corners of pots, but like anything, it can get overpowering.
If it's only right in front of the burner port that you get the stuff,
try using a more refractory clay right there. When we fire Laguna's
"WSO" clay right in the front, it shows little or no bluing. Or perhaps
back off on the fuel a little bit.....
Good salty firings,
Paul Herman
Great Basin Pottery
Doyle, California US
http://www.greatbasinpottery.com/
----------
>From: Nancy Udell
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Grey clay from soda/salt firing
>Date: Sat, Aug 28, 2004, 12:35 PM
>
> Hello clay list,
>
>
>
> We are having some effects from soda/salt firing that we don't like, and
> were wondering if anyone has any thoughts as to the cause. We've tried a
> number of different things from time to time (and probably because we've
> often changed multiple variables, cannot consistently get rid of the grey
> effect described below).
>
>
>
> Bare clay or clay with slips that are near the soda ports are often getti=
ng
> matte gray areas on the sides facing the soda. The rest of the pieces ar=
e
> beautiful, toasty tan, and nicely glazed. Also, glazed pieces are
> sometimes overfluxed if near the soda ports.
>
>
>
> The links below go to two two pieces of unglazed Campbell's white stonewa=
re
> from different spots in the kiln.
>
>
>
> 1.
>
http://home.comcast.net/~greentree1/wsb/html/view.cgi-photo.html--SiteID
-1768362.
> html
>
>
>
>
>
> 2.
>
http://home.comcast.net/~greentree1/wsb/html/view.cgi-photo.html--SiteID
-1768363.
> html
>
>
>
> Here's some info on our kiln and firing process. We are firing a propane
> fueled, cross draft kiln - 36.7 cubic feet total inside space. The bagwa=
ll
> is 9" from inside the burner ports, is 4 bricks high and is fairly open.
> At cone 010 we are doing heavy body reduction for 1 hour, then light
> reduction for the rest of the firing. At cone 8 we begin injecting sodiu=
m
> - 3 lbs of soda (comprised of baking soda, soda ash and borax), dissolved
> in hot water and sprayed, alternating with 5 1lb dumps of salt over 2 pl=
us
> hours. We have been waffling the damper during spraying and closing the
> damper to within 1 inch for 5 minutes after salting, then opening the
> damper to clear the atmosphere, then waiting 20 minutes before another
> round. After the kiln reaches temperature, cone 10 tipping half over, we
> are firing down to 1050=B0 C, with one burner on low and damper and air fla=
ps
> open. This firing down has helped to even the color of bare clay from to=
p to
> bottom.
>
> Thanks very much for any thoughts.
>
> Nancy and Marianne
Marcia Selsor on mon 30 aug 04
Dear Nancy,
Decades ago when I was a student in Phila. we fired the salt kiln...and
for the purpose of oxidizing the contents of the kiln to get gray
rather than brown, we would tear down the brick door of the kiln after
salting the interior. We would remove about 6 courses of the double
bricked door with raku tongs. Watch the color go from intense blinding
white heat to red. Then we'd brick up the door loosely and black any
draft with a kiln shelf. This leads me to my answer to your problem.
Those pieces near your ports are getting oxidized. Cove the ports when
you are finished using a kiln shelf chink. This should block a draft
and keep the reduction for brown color.
IMHO best I can do.
Marcia Selsor
Ivor and Olive Lewis on tue 31 aug 04
Dear Marcia Selsor,
I am trying to understand what is happening when you suggest....
"Those pieces near your ports are getting oxidized. Cove the ports
when you are finished using a kiln shelf chink. This should block a
draft and keep the reduction for brown color."...
What substance is in the clay or the glaze which has formed from the
soda which turns brown when it is reduced?
Perhaps you would explain.
Thanks in advance.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
.
Paul Herman on tue 31 aug 04
Resending, because it never came through here. PH
Hello Nancy and Marianne,
Well, you've gotten a lot of different theories on this one, so here's
mine.
We get that blue-grey color in the woodkiln. It seems to be related to
the intensity of flame/reduction. More flame/reduction, more grey. I
agree with Tony Clennell, it's carbon trapping in the clay body. Seems
it makes the clay brittle, and easily broken.
It is also more pronounced in more vitreous clays, like porcelain, or
stoneware that has a bit of flux in it.
It got to be too much, and when we backed off the stoking, there was
less blue. It's really nice to have a few touches of the blue on the
corners of pots, but like anything, it can get overpowering.
If it's only right in front of the burner port that you get the stuff,
try using a more refractory clay right there. When we fire Laguna's
"WSO" clay right in the front, it shows little or no bluing. Or perhaps
back off on the fuel a little bit.....
Good salty firings,
Paul Herman
Great Basin Pottery
Doyle, California US
http://www.greatbasinpottery.com/
----------
>From: Nancy Udell
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Grey clay from soda/salt firing
>Date: Sat, Aug 28, 2004, 12:35 PM
>
> Hello clay list,
>
>
>
> We are having some effects from soda/salt firing that we don't like, and
> were wondering if anyone has any thoughts as to the cause. We've tried a
> number of different things from time to time (and probably because we've
> often changed multiple variables, cannot consistently get rid of the grey
> effect described below).
>
Ron Roy on thu 2 sep 04
I might as well add what I think is happening -
If clay is overfired enough - the surface cannot reoxidize - to brown with
iron bearing clays - simply because the clay is melted too much - because
the clay has been in the direct path of the flame - it gets hotter there.
It would be simple enough to do some experiments - place something like a
broken kiln shelf in front of a pot - between the pot and the flame - so
the flame is not impinging on the pot.
Using a more refractory body will help but it also means the clay is going
to be fired higher on the side of the flame - which will not be the best
situation for some functional ware.
RR
>Well, you've gotten a lot of different theories on this one, so here's
>mine.
>
>We get that blue-grey color in the woodkiln. It seems to be related to
>the intensity of flame/reduction. More flame/reduction, more grey. I
>agree with Tony Clennell, it's carbon trapping in the clay body. Seems
>it makes the clay brittle, and easily broken.
>
>It is also more pronounced in more vitreous clays, like porcelain, or
>stoneware that has a bit of flux in it.
>
>It got to be too much, and when we backed off the stoking, there was
>less blue. It's really nice to have a few touches of the blue on the
>corners of pots, but like anything, it can get overpowering.
>
>If it's only right in front of the burner port that you get the stuff,
>try using a more refractory clay right there. When we fire Laguna's
>"WSO" clay right in the front, it shows little or no bluing. Or perhaps
>back off on the fuel a little bit.....
>
>Good salty firings,
>
>Paul Herman
>
>Great Basin Pottery
>Doyle, California US
>http://www.greatbasinpottery.com/
>
>----------
>>From: Nancy Udell
>>To: CLAYART@LSV.CERAMICS.ORG
>>Subject: Grey clay from soda/salt firing
>>Date: Sat, Aug 28, 2004, 12:35 PM
>>
>
>> Hello clay list,
>>
>>
>>
>> We are having some effects from soda/salt firing that we don't like, and
>> were wondering if anyone has any thoughts as to the cause. We've tried a
>> number of different things from time to time (and probably because we've
>> often changed multiple variables, cannot consistently get rid of the grey
>> effect described below).
>>
>>
>>
>> Bare clay or clay with slips that are near the soda ports are often getti=
ng
>> matte gray areas on the sides facing the soda. The rest of the pieces ar=
e
>> beautiful, toasty tan, and nicely glazed. Also, glazed pieces are
>> sometimes overfluxed if near the soda ports.
>>
>>
>>
>> The links below go to two two pieces of unglazed Campbell's white stonewa=
re
>> from different spots in the kiln.
>>
>>
>>
>> 1.
>>
>http://home.comcast.net/~greentree1/wsb/html/view.cgi-photo.html--SiteID
>-1768362.
>> html
>>
>>
>>
>>
>>
>> 2.
>>
>http://home.comcast.net/~greentree1/wsb/html/view.cgi-photo.html--SiteID
>-1768363.
>> html
>>
>>
>>
>> Here's some info on our kiln and firing process. We are firing a propane
>> fueled, cross draft kiln - 36.7 cubic feet total inside space. The bagwa=
ll
>> is 9" from inside the burner ports, is 4 bricks high and is fairly open.
>> At cone 010 we are doing heavy body reduction for 1 hour, then light
>> reduction for the rest of the firing. At cone 8 we begin injecting sodiu=
m
>> - 3 lbs of soda (comprised of baking soda, soda ash and borax), dissolved
>> in hot water and sprayed, alternating with 5 1lb dumps of salt over 2 pl=
us
>> hours. We have been waffling the damper during spraying and closing the
>> damper to within 1 inch for 5 minutes after salting, then opening the
>> damper to clear the atmosphere, then waiting 20 minutes before another
>> round. After the kiln reaches temperature, cone 10 tipping half over, we
>> are firing down to 1050=B0 C, with one burner on low and damper and air f=
laps
>> open. This firing down has helped to even the color of bare clay from=
top to
>> bottom.
>>
>> Thanks very much for any thoughts.
>>
>> Nancy and Marianne
>
>___________________________________________________________________________=
___
>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
Phone: 613-475-9544
=46ax: 613-475-3513=20
Lee Love on thu 2 sep 04
Ron Roy wrote:
>
>Using a more refractory body will help but it also means the clay is going
>to be fired higher on the side of the flame - which will not be the best
>situation for some functional ware.
>
>
>
http://home.comcast.net/~greentree1/wsb/html/view.cgi-photo.html--SiteID-1768362.html
Please look at the photos. Click on next to see second
example. The first example has a thick enough coating of soda to
cause some pig skinning. When it gets this thick on a white clay
body, the surface is going to be white and can carbon trap. I have two
tumblers from Euan (the 100ths firing of his current kiln) and they show
the same soda effect on white han-jiki (porcelaineous stoneware. half
Mashiko clay, half Aussie porcelain.) I will put up some photos.
The second example has evidence of much less soda. The white
clay is blushed red.
--
in Mashiko, Japan http://mashiko.org
http://www.livejournal.com/users/togeika/ WEB LOG
http://public.fotki.com/togeika/ Photos!
| |
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