Tony Ferguson on fri 19 apr 02
Were the handles pulled, too thin? Were the handles wedged well and
compressed before forming? Amazing they would fall in like that. wow. All
I can say about handles is to make sure the clay is prepared well (wedge,
compress) before forming/pulling.
fergy
----- Original Message -----
From: "Dennis Freeman"
To:
Sent: Friday, April 19, 2002 4:40 PM
Subject: B-mix meltdown
> Clayarters,
> I opened the kiln this morning to a nasty surprise. My colleague had two
> teapots in the fire with fairly tall arched handles. Both were made from
> B-mix, and both of the handles collapsed over the pots. Everything else
in
> the fire made from this clay was fine, including some mugs, pitchers and
> lidded jars of mine.
>
> The kiln was fired to cone 10, reduction. Normal firing time for our new
> Giel, normal results otherwise. We bought 1 ton of dry form B-mix in
> September, and have been using it along with a regular stoneware body all
> year without problems up until now.
>
> Any ideas out there? Thanks in advance.
> Dennis in Wyo.
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
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melpots@pclink.com.
Dennis Freeman on fri 19 apr 02
Clayarters,
I opened the kiln this morning to a nasty surprise. My colleague had two
teapots in the fire with fairly tall arched handles. Both were made from
B-mix, and both of the handles collapsed over the pots. Everything else in
the fire made from this clay was fine, including some mugs, pitchers and
lidded jars of mine.
The kiln was fired to cone 10, reduction. Normal firing time for our new
Giel, normal results otherwise. We bought 1 ton of dry form B-mix in
September, and have been using it along with a regular stoneware body all
year without problems up until now.
Any ideas out there? Thanks in advance.
Dennis in Wyo.
scott lykens on sat 20 apr 02
Could be just a little bit of everything, a little too tall, too thin, and
too hot.
>
>Clayarters,
>I opened the kiln this morning to a nasty surprise. My colleague had two
>teapots in the fire with fairly tall arched handles. Both were made from
>B-mix, and both of the handles collapsed over the pots. Everything else in
>the fire made from this clay was fine, including some mugs, pitchers and
>lidded jars of mine.
>
>The kiln was fired to cone 10, reduction. Normal firing time for our new
>Giel, normal results otherwise. We bought 1 ton of dry form B-mix in
>September, and have been using it along with a regular stoneware body all
>year without problems up until now.
>
>Any ideas out there? Thanks in advance.
>Dennis in Wyo.
>
>___________________________________________________________________________
___
>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.
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John Baymore on sun 21 apr 02
Clay bodies exhibit something called "pyroplasticity" when they are fired=
. =
Basically....they get soft again in the heat of the kiln. If you think
about those teapots... the pot part held it's shape when the clay was
wet...... and soft. That was because of the structural integrity of the
particular form.
The handle however..... probably was put in place when it had stiffened. =
That was because it would not hold it's shape in that big arch when it wa=
s
fully soft.
So when the clay gets soft again in the heat of the kiln...... the handle=
sags and slumps. Sort of the way it would if you tried to attach it when=
it was wet.
The more vitreous the clay body at the maturing point of the firing.....
the more pyroplastic. If the body is being fired past the normal working=
range.... the worse it gets. If the body is mis-mixed and fluxes at a
lower temprature than it is supposed to.... the worse it gets. If the bo=
dy
is not formulated to promote the growth of interlocking crystalline
structures within itself... the more it moves. And so on. The longer th=
e
firing is held at the peak temperature.... the more time the piece is giv=
en
to deform.
Hope this helps understand the possible problem.
Best,
..............................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
"DATES SET: Earth, Water, and Fire Noborigama Woodfiring Workshop Augu=
st
16-25, 2002"
SAM YANCY on mon 22 apr 02
Could it be that you were firing cone b-mix 5 clay and your kiln was not
really at
cone 10 fire? Here in california, b-mix usually can be easily obtained as
cone 5
but much harder to get in cone 10. I have had that slumping problem with
b-mix
which was identified as cone 10, but was really cone five (or more) . Took
quiet a
while and a mess to grind the shelves. Now I only fire b-mix to cone 5. Sam
in
daly city calif.
John Baymore wrote:
> Clay bodies exhibit something called "pyroplasticity" when they are fired.
> Basically....they get soft again in the heat of the kiln. If you think
> about those teapots... the pot part held it's shape when the clay was
> wet...... and soft. That was because of the structural integrity of the
> particular form.
>
> The handle however..... probably was put in place when it had stiffened.
> That was because it would not hold it's shape in that big arch when it was
> fully soft.
>
> So when the clay gets soft again in the heat of the kiln...... the handle
> sags and slumps. Sort of the way it would if you tried to attach it when
> it was wet.
>
> The more vitreous the clay body at the maturing point of the firing.....
> the more pyroplastic. If the body is being fired past the normal working
> range.... the worse it gets. If the body is mis-mixed and fluxes at a
> lower temprature than it is supposed to.... the worse it gets. If the
body
> is not formulated to promote the growth of interlocking crystalline
> structures within itself... the more it moves. And so on. The longer the
> firing is held at the peak temperature.... the more time the piece is
given
> to deform.
>
> Hope this helps understand the possible problem.
>
> Best,
>
> ..............................john
>
> John Baymore
> River Bend Pottery
> 22 Riverbend Way
> Wilton, NH 03086 USA
>
> 603-654-2752 (s)
> 800-900-1110 (s)
>
> JohnBaymore.com
>
> JBaymore@compuserve.com
>
> "DATES SET: Earth, Water, and Fire Noborigama Woodfiring Workshop
August
> 16-25, 2002"
>
>
____________________________________________________________________________
__
> 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.
Dennis Freeman on mon 22 apr 02
on 4/21/02 11:59 AM, John Baymore at JBaymore@COMPUSERVE.COM wrote:
> Clay bodies exhibit something called "pyroplasticity" when they are
fired..
> Basically....they get soft again in the heat of the kiln. If you think
> about those teapots... the pot part held it's shape when the clay was
> wet...... and soft. That was because of the structural integrity of the
> particular form.
>
> The handle however..... probably was put in place when it had stiffened.
> That was because it would not hold it's shape in that big arch when it was
> fully soft.
>
> So when the clay gets soft again in the heat of the kiln...... the handle
> sags and slumps. Sort of the way it would if you tried to attach it when
> it was wet.
>
> The more vitreous the clay body at the maturing point of the firing.....
> the more pyroplastic. If the body is being fired past the normal working
> range.... the worse it gets. If the body is mis-mixed and fluxes at a
> lower temprature than it is supposed to.... the worse it gets. If the
body
> is not formulated to promote the growth of interlocking crystalline
> structures within itself... the more it moves. And so on. The longer the
> firing is held at the peak temperature.... the more time the piece is
given
> to deform.
>
> Hope this helps understand the possible problem.
>
> Best,
>
> ...............................john
To John & all who responded, thanks. Pyroplasticity sounds like the cause,
since my new colleague is fond of forming handles that won't hold up when
wet. I had considered the cone 5 vs. cone 10 bmix possibilty, as well. The
invoice says "cone 10", but who knows? I'll spend the next few weeks
testing handles made from this and our other 10 body, CN1. I also suspect
the cross-setion of the handles (rounded triangles) may have contributed to
the collapse. Mine are flat w/ thickened edges, and I seldom have problems.
To all, thanks! This list is so great!
Dennis in Wyo.
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