Sherrill Eatherly on mon 8 dec 03
I have begun making some double wall bowls. I am having a problem with =
them cracking on top during the bisque firing. I have been completely =
closing up the bottom and putting a foot on it, being sure to leave an =
air hole. I leave the tops thicker than the walls at first because I am =
carving on them. I have done this same carving on other work and have =
not experienced this problem. I use Highwater raku clay which I have =
never had any trouble with cracking before, even when I raku. I have an =
electric controller kiln and fire slowly, candling at first, and then =
using the program mode on slow to fire to ^06. Does anyone know why I am =
having the problems with cracking and suggestions to prevent it?=20
In advance, thank you for your information,
Sherrill
gferguson@ATT.NET on tue 9 dec 03
Sherrill:
How are you constructing the Double-walled Bowls? Are you throwing them all
in one piece or are you constructing them with a combination of thrown and
slab pieces? I throw and Raku double-walled bowls and have not had any
cracking problems, but I throw them all in one piece (upside down) so I think
the stresses are more equalized than if you throw part, slab part, and then
combine the two.
Gary Ferguson
Raku Artist
Nampa, ID
Gallery: http://www.garyrferguson.com
Raku Newsletter: http://www.justraku.com
Got Raku? right here: http://www.cafepress.com/gotraku
> I have begun making some double wall bowls. I am having a problem with them
> cracking on top during the bisque firing. I have been completely closing up the
> bottom and putting a foot on it, being sure to leave an air hole. I leave the
> tops thicker than the walls at first because I am carving on them. I have done
> this same carving on other work and have not experienced this problem. I use
> Highwater raku clay which I have never had any trouble with cracking before,
> even when I raku. I have an electric controller kiln and fire slowly, candling
> at first, and then using the program mode on slow to fire to ^06. Does anyone
> know why I am having the problems with cracking and suggestions to prevent it?
> In advance, thank you for your information,
> Sherrill
>
> ______________________________________________________________________________
> 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.
Sherrill Eatherly on tue 9 dec 03
Gary:
I am throwing them in one piece upside down,too. I also compress the bottom
(top of the bowl) well.
Any thoughts?
Sherrill
----- Original Message -----
From:
To:
Sent: Monday, December 08, 2003 11:32 PM
Subject: Re: Double Wall Bowls Cracks
> Sherrill:
>
> How are you constructing the Double-walled Bowls? Are you throwing them
all
> in one piece or are you constructing them with a combination of thrown and
> slab pieces? I throw and Raku double-walled bowls and have not had any
> cracking problems, but I throw them all in one piece (upside down) so I
think
> the stresses are more equalized than if you throw part, slab part, and
then
> combine the two.
>
> Gary Ferguson
> Raku Artist
> Nampa, ID
> Gallery: http://www.garyrferguson.com
> Raku Newsletter: http://www.justraku.com
> Got Raku? right here: http://www.cafepress.com/gotraku
> > I have begun making some double wall bowls. I am having a problem with
them
> > cracking on top during the bisque firing. I have been completely
closing up the
> > bottom and putting a foot on it, being sure to leave an air hole. I
leave the
> > tops thicker than the walls at first because I am carving on them. I
have done
> > this same carving on other work and have not experienced this problem. I
use
> > Highwater raku clay which I have never had any trouble with cracking
before,
> > even when I raku. I have an electric controller kiln and fire slowly,
candling
> > at first, and then using the program mode on slow to fire to ^06. Does
anyone
> > know why I am having the problems with cracking and suggestions to
prevent it?
> > In advance, thank you for your information,
> > Sherrill
> >
> >
____________________________________________________________________________
__
> > 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.
>
>
____________________________________________________________________________
__
> 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.
>
gferguson@ATT.NET on wed 10 dec 03
Sherrill:
Another thought would be your drying process. Since you say you are
completely closing the bottom (other than a small hole), I would assume the
inside is staying much wetter, much longer than the outside of the piece,
unless you are drying very slowly. I would think very uneven drying could
cause your cracking problem.
Have you tried creating one with an open bottom and see if you have the same
cracking problem?
Also what size are these pieces. The wider the flat surface the more stress
would be placed on the piece. Or if the inner section walls are extra thick
(heavy) which would cause more stress.
Another thought would be to place an extra ridge underneath the flat
surface. When throwing the piece create an extra band of clay that runs half
way between the inner walls and the outer walls. This could act as an extra
stress brace and prevent some cracking.
Just some ideas to try.
Good Luck,
Gary Ferguson
Raku Artist
Nampa, ID
Gallery: http://www.garyrferguson.com
Raku Newsletter: http://www.justraku.com
Got Raku? right here: http://www.cafepress.com/gotraku
> Gary:
> I am throwing them in one piece upside down,too. I also compress the bottom
> (top of the bowl) well.
> Any thoughts?
> Sherrill
>
>
> ----- Original Message -----
> From:
> To:
> Sent: Monday, December 08, 2003 11:32 PM
> Subject: Re: Double Wall Bowls Cracks
>
>
> > Sherrill:
> >
> > How are you constructing the Double-walled Bowls? Are you throwing them
> all
> > in one piece or are you constructing them with a combination of thrown and
> > slab pieces? I throw and Raku double-walled bowls and have not had any
> > cracking problems, but I throw them all in one piece (upside down) so I
> think
> > the stresses are more equalized than if you throw part, slab part, and
> then
> > combine the two.
> >
> > Gary Ferguson
> > Raku Artist
> > Nampa, ID
> > Gallery: http://www.garyrferguson.com
> > Raku Newsletter: http://www.justraku.com
> > Got Raku? right here: http://www.cafepress.com/gotraku
> > > I have begun making some double wall bowls. I am having a problem with
> them
> > > cracking on top during the bisque firing. I have been completely
> closing up the
> > > bottom and putting a foot on it, being sure to leave an air hole. I
> leave the
> > > tops thicker than the walls at first because I am carving on them. I
> have done
> > > this same carving on other work and have not experienced this problem. I
> use
> > > Highwater raku clay which I have never had any trouble with cracking
> before,
> > > even when I raku. I have an electric controller kiln and fire slowly,
> candling
> > > at first, and then using the program mode on slow to fire to ^06. Does
> anyone
> > > know why I am having the problems with cracking and suggestions to
> prevent it?
> > > In advance, thank you for your information,
> > > Sherrill
> > >
> > >
> ____________________________________________________________________________
> __
> > > 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.
> >
> >
> ____________________________________________________________________________
> __
> > 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.
> >
>
> ______________________________________________________________________________
> 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.
Bonnie Staffel on thu 11 dec 03
Clayarters,
My suggestion here is to throw several of your double walled pots and cut
each one in half. That might tell you where there are discrepancies in the
wall thickness or variations that might be causing the uneven drying
problem. You might also create some sort of suspension device so that the
"doughnut" is exposed to the air more evenly, such as a cone or cloth
hammock so that it can dry easily.
Another thing that is a weird happening is when one sticks a pin tool into
an enclosed pot, a little bit of the clay pushed in sometimes travels back
on the tip of the pin and plugs the hole, especially if the clay is on the
soft side. A double poke or a larger pin may eliminate this problem.
Regards, Bonnie Staffel
http://pws.chartermi.net/~bstaffel/contactlinks.htm
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