Gail Dapogny on sun 8 oct 00
I have a technical question which will take a little explaining.....
In our potters' guild, we fire our bisque in a down draft gas kiln to 06,
and soak at about 1450f.
This past summer, I was chatting with Steven Hill about pitting and
pin-holing, and he felt strongly that we should soak at a higher (maximum)
temp. I realized, after doing some reading, that we had at some point in
the past arrived at 1450 for our soak because it is close to the top temp
for carbons to burn out. However, now I realize that sulfur continues
burning out well past 2000f, so clearly we are missing the boat here.
Currently we use 07 and 06 cones, and turn off when 06 is half over--a
little under 1900f; so we're rising about 175 degrees per hour.
Since we have some problems with pitting, pin-holing, this is really a
relevant issue for us.
Now...keep in mind this is a GUILD, skeptical and slow to change. The
doubts are going to be:
1. How do we soak at the end without over-firing and making the ware brittle?
2. If we are going to soak at the end, should we fire to a lower temp (such
as 07)?
3. At what point should we begin the soak (earlier than top temperature so
as not to overfire?)
4. Should we continue to go slowly in the 1400s? How slow?
5. How long should the entire firing take after the warmup period? (Right
now, after an overnight warmup, we start our main burners at around 800f
and fire for about 6 and a half hours.)
6. How long should the soak take?
My thought is that perhaps we should start the soak when 06 is soft and
soak for a half hour to 3/4 hour, turning back the gas as needed.
Oh..p.s. ..I did check (with a stick) to make sure that we are not reducing
by mistake. Did not appear to be the case.
Any and all advice will be greatly appreciated.
---Gail
Gail Dapogny
1154 Olden Road
Ann Arbor, MI 48103-3005
(734) 665-9816
gdapogny@umich.edu
www.silverhawk.com/ex99/dapogny
scott lykens on mon 9 oct 00
ive had success solving this problem in the past by adding firing length to
the entire firing,
like 100 degrees per hour with a nice long soak(6pm to 6am ) before hand.
i get it up to say 600 by morning and do a slow climb till about 7 pm.
that solved most problems in our clays. the rest were really specialized to
each specific clay body/.
school setting
lots o kinds per firing
>From: Gail Dapogny
>Reply-To: Ceramic Arts Discussion List
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: soaking the bisque, when, how?
>Date: Sun, 8 Oct 2000 22:11:46 -0400
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>I have a technical question which will take a little explaining.....
>
>In our potters' guild, we fire our bisque in a down draft gas kiln to 06,
>and soak at about 1450f.
>This past summer, I was chatting with Steven Hill about pitting and
>pin-holing, and he felt strongly that we should soak at a higher (maximum)
>temp. I realized, after doing some reading, that we had at some point in
>the past arrived at 1450 for our soak because it is close to the top temp
>for carbons to burn out. However, now I realize that sulfur continues
>burning out well past 2000f, so clearly we are missing the boat here.
>Currently we use 07 and 06 cones, and turn off when 06 is half over--a
>little under 1900f; so we're rising about 175 degrees per hour.
>Since we have some problems with pitting, pin-holing, this is really a
>relevant issue for us.
>
>Now...keep in mind this is a GUILD, skeptical and slow to change. The
>doubts are going to be:
>
>1. How do we soak at the end without over-firing and making the ware
>brittle?
>2. If we are going to soak at the end, should we fire to a lower temp (such
>as 07)?
>3. At what point should we begin the soak (earlier than top temperature so
>as not to overfire?)
>4. Should we continue to go slowly in the 1400s? How slow?
>5. How long should the entire firing take after the warmup period? (Right
>now, after an overnight warmup, we start our main burners at around 800f
>and fire for about 6 and a half hours.)
>6. How long should the soak take?
>
>My thought is that perhaps we should start the soak when 06 is soft and
>soak for a half hour to 3/4 hour, turning back the gas as needed.
>Oh..p.s. ..I did check (with a stick) to make sure that we are not reducing
>by mistake. Did not appear to be the case.
>
>Any and all advice will be greatly appreciated.
>---Gail
>
>Gail Dapogny
>1154 Olden Road
>Ann Arbor, MI 48103-3005
>(734) 665-9816
>gdapogny@umich.edu
>www.silverhawk.com/ex99/dapogny
>
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Cindy Strnad on mon 9 oct 00
Hi, Gail.
Your plan sounds good. Try starting at ^07, then soaking for 45 minutes to
an hour--until your ^06 goes down. If the cone goes down before your desired
soak time has elapsed, start with ^08 and soak until the ^06 goes down.
Within reason, a longer soak than planned isn't going to hurt anything, so
long as you keep the kiln in oxidation.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
http://www.earthenvesselssd.com
karen gringhuis on mon 9 oct 00
Gail -
Recommend you contact Orton Fdt. Westerville OH for a
cc of their chart "Ceramic Hetaing Reactions" which
shows cooling reactions as well as firing up
reactions. 614-895-2663 or web site?
Based on a consultation w/ one of their firing experts
for similar problems, I electric fire bisque NO FASTER
than 100 degrees per hour (1.6 degree/minute)
approximately from 1000 degrees F up to top temp and
do not soak at top temp but get large C/06 well over.
I make this determination and I do NOT leave this to a
kiln sitter.
For same problems I also elec. fire glaze w/ a
down-firing cooling rate of NO FASTER than 1 degree
per minute approx. for the second 200 degrees of drop.
Since I soak at top temp, for the first 100 degrees
of cooling I just let the temp. drop, then turn kiln
right back on. This may not be necessary if your gas
(?) kiln cools slowly.
Obviously I use a DIGITAL PYROMETER and wouldn't dream
of firing w/out it. Yes, close monitoring is a lot
more work - but to me it's worth it. (I can recommend
brand, etc. if you want.)
If I can help further, write.
Karen Gringhuis
=====
Karen Gringhuis
KG Pottery
Box 607 Alfred NY 14802
Personal e-mail to:
KGPottery@hotmail.com
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