Liz Gowen 1 on mon 14 nov 11
I have been making bowls about 2 to 3 inches high and about 8" in diameter
for years. Have been using ^6 standard 365 porcelain for years as well. In
the last couple months I am getting a tremendous amount of rim cracks. I
have tried making the rim thicker but it hasn't helped. It takes next to
nothing to put a hairline crack in these including being too impatient to
get off a plaster bat snap. I am also finding I am now getting circular
cracks about midway down almost 360 round. I have been using a rib to expan=
d
them because I like the shape it gives but between the 2 types of cracks I
am getting about a 50% loss rate lately. Am It hrowing too fast? I lose som=
e
before I trim some before I bisque fire and some during the bisque fire. An=
y
suggestions would be appreciated. This is with new clay as well as 1 year
old clay repugged. I use about 1& 1/2 lbs. of clay for these, have made the=
m
for years but this is the first with any loss from cracks.
Suggestions....Liz Gowen
Steve Mills on wed 16 nov 11
Dear Liz,
That has all the hallmarks of a recipe change.=3D20
Have you asked Standard if that's the case? And if you did, did they admit =
t=3D
o it?
Steve M
Steve Mills
Bath
UK
www.mudslinger.me.uk
Sent from my Ipod touch
On 14 Nov 2011, at 22:00, Liz Gowen 1 wrote:
> I have been making bowls about 2 to 3 inches high and about 8" in diamet=
e=3D
r
> for years. Have been using ^6 standard 365 porcelain for years as well. I=
n=3D
> the last couple months I am getting a tremendous amount of rim cracks. I
> have tried making the rim thicker but it hasn't helped. It takes next to
> nothing to put a hairline crack in these including being too impatient to
> get off a plaster bat snap. I am also finding I am now getting circular
> cracks about midway down almost 360 round. I have been using a rib to exp=
a=3D
nd
> them because I like the shape it gives but between the 2 types of cracks =
I=3D
> am getting about a 50% loss rate lately. Am It hrowing too fast? I lose s=
o=3D
me
> before I trim some before I bisque fire and some during the bisque fire. =
A=3D
ny
> suggestions would be appreciated. This is with new clay as well as 1 year
> old clay repugged. I use about 1& 1/2 lbs. of clay for these, have made t=
h=3D
em
> for years but this is the first with any loss from cracks.
> Suggestions....Liz Gowen
David Finkelnburg on wed 16 nov 11
Liz,
That is a very high loss rate! :-(
The rim cracks are due to different rates of shrinkage. The vertical
rim cracks occur when the rim is shrinking but the foot is not. The rim
can't shrink as much as it wants to and splits. Usually inverting the bowl
as soon as possible is enough to slow the drying rate of the rim and let
the foot catch up.
The circumferential cracks are a different matter. I usually get them
from incorporating a layer of fine slip while throwing.
Shrinkage usually shows up as a problem this time of year. Cold air is
dryer, so in a heated studio drying rate increases dramatically and becomes
an issue.
If you inspect your bone dry greenware with a magnifying glass, I
suspect you would find all of the failures then. Some of the cracks are
just so fine they aren't easy to see until after the first firing.
Given the widely different ages of your clay but the same issues, it
does not--at least on the surface--appear to be a problem with the clay
having changed.
Hope you are able to sort this out quickly,
Dave Finkelnburg
http://www.mattanddavesclays.com
-----------------------------
Date: Mon, 14 Nov 2011 17:00:05 -0500, Liz Gowen 1
wrote:
I have been making bowls about 2 to 3 inches high and about 8" in diameter
for years. Have been using ^6 standard 365 porcelain for years as well. In
the last couple months I am getting a tremendous amount of rim cracks. I
have tried making the rim thicker but it hasn't helped. It takes next to
nothing to put a hairline crack in these including being too impatient to
get off a plaster bat snap. I am also finding I am now getting circular
cracks about midway down almost 360 round. I have been using a rib to expan=
d
them because I like the shape it gives but between the 2 types of cracks I
am getting about a 50% loss rate lately. Am It hrowing too fast? I lose som=
e
before I trim some before I bisque fire and some during the bisque fire. An=
y
suggestions would be appreciated. This is with new clay as well as 1 year
old clay repugged. I use about 1& 1/2 lbs. of clay for these, have made the=
m
for years but this is the first with any loss from cracks.
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