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killer cracks

updated sun 3 aug 03

 

Bill Buckner on thu 31 jul 03


Hello, all:

I have a Peter Pugger and had been using it to mix and reclaim commercial
bodies. Recently, I started mixing a couple bodies I developed for soda
firing. I worked out a practical way to mix large amounts of clay in
relatively small batches. There are two barrels - one with the clay mixed
to a slip, the other barrel holds a dry blend. Reclaim slop goes into the
slip barrel. When I mix, I blend the slip with enough dry mix to bring it
to proper consistency. I generally mix it for about 20 minutes, and I
always keep the hopper loaded for when I am ready to pug.

Okay, here's the glitch. The body cracks! Actually, I have tried two
blends and both cracked. Sometimes the cracks show up at bone
dry. Sometimes they don't show until bisque. But, I am losing about 80%
of my work. It's killing me!!

The cracks have no particular pattern. They vary between concentric,
spider and completely random. Even odder, they can appear concentric
inside a pot and spider on the exterior (or vice versa). Sometimes they
are just random, like perpendicular across to the foot. Sometimes they are
at the foot. Sometimes they run through the body. Frequently, the cracks
open all the way through the pot. Since the same symptoms have appeared in
both bodies, I suspect it is the mixing that is the source of the
problem. However, I am at a loss as to how to remedy this. I used to mix
a body when I was in school using a similar process. But, I never had a
cracking problem. Additionally, when I remix/reclaim commercial bodies, I
have no cracking problems.

Anyone out there mixing their clay from dry? I would appreciate any
feedback to be had. TIA.

Cheers,
-Bill
Atlanta


billBUCKNER
www.sodaglaze.com

Life is too important to be taken seriously.
-Oscar Wilde

Michael Wendt on thu 31 jul 03


Bill,
Age the pugged extrusions and re run them after they age. I suspect you have
dry zones and wet zones that create a laminar moisture problem. To see if
this is the problem, wedge a piece as follows:
Set up a wire 24" long set 45 degrees from the front of your wedging table
upward to the wall. Select a piece of clay from the pugger and cut it in
half. Stack the piece so that it is doubled and slam first the bottom and
then the top of the stack onto the table to join them. Repeat this process
taking care to laminate the piece with all the laminations in the same plane
and don't make any dents in the surfaces you are joining as they will become
air bubbles. If you double the number of layers 30 times, you will have
created over a billion layers and the clay will change character completely
(I do all my clay this way and it really works).
Regards,
Michael Wendt
wendtpot@lewiston.com
Bill wrote:
The cracks have no particular pattern. They vary between concentric,
spider and completely random. Even odder, they can appear concentric
inside a pot and spider on the exterior (or vice versa). Sometimes they
are just random, like perpendicular across to the foot. Sometimes they are
at the foot. Sometimes they run through the body. Frequently, the cracks
open all the way through the pot. Since the same symptoms have appeared in
both bodies, I suspect it is the mixing that is the source of the
problem. However, I am at a loss as to how to remedy this. I used to mix
a body when I was in school using a similar process. But, I never had a
cracking problem. Additionally, when I remix/reclaim commercial bodies, I
have no cracking problems.

Anyone out there mixing their clay from dry? I would appreciate any
feedback to be had. TIA.

Cheers,
-Bill

Dapogny.Gail on thu 31 jul 03


Bill, We use a Peter Pugger extensively here in our guild, and it sounds
like our methods are similar to yours. We have a dry mixer as well, and
mix our dry bodies in that. For each pugger load we use about a 5-gallon
pail of dry mix, about 10-12 two-handed handfuls of wet scrap, and about
two-thirds of a gallon jug of warm water. These all vary depending on the
wetness of the scrap.

Mix for a while, correct consistency, mix again, check again, and mix a
final time; then pug. Total mixing about 25-30 minutes, not all at once.
If we don't have much scrap, I throw in some vinegar, maybe a cup.

I'll be interested to see if knowledgeable heads on this list think that
your cracks are dunting....

So many variables: clay body, handling of the clay, wedging, consistency
of the clay, etc. Hard to imagine that your mixing is to blame unless you
don't give it enough time after the consistency is finally correct.

Hamer has a lot of valuable info on cracks including illustrations. Very
helpful. Check it out.

Gail Dapogny


>I have a Peter Pugger and had been using it to mix and reclaim commercial
>bodies. Recently, I started mixing a couple bodies I developed for soda
>firing. I worked out a practical way to mix large amounts of clay in
>relatively small batches. There are two barrels - one with the clay mixed
>to a slip, the other barrel holds a dry blend. Reclaim slop goes into the
>slip barrel. When I mix, I blend the slip with enough dry mix to bring it
>to proper consistency. I generally mix it for about 20 minutes, and I
>always keep the hopper loaded for when I am ready to pug.
>
>Okay, here's the glitch. The body cracks! Actually, I have tried two
>blends and both cracked. Sometimes the cracks show up at bone
>dry. Sometimes they don't show until bisque. But, I am losing about 80%
>of my work. It's killing me!!
>
>The cracks have no particular pattern. They vary between concentric,
>spider and completely random. Even odder, they can appear concentric
>inside a pot and spider on the exterior (or vice versa). Sometimes they
>are just random, like perpendicular across to the foot. Sometimes they are
>at the foot. Sometimes they run through the body. Frequently, the cracks
>open all the way through the pot. Since the same symptoms have appeared in
>both bodies, I suspect it is the mixing that is the source of the
>problem.
>-Bill
>Atlanta
>
>billBUCKNER

Bill Buckner on thu 31 jul 03


Thanks for the feedback and mixing details, Gail. Our approach to mixing
clay does sound similar, indeed. That's encouraging.

The problem cannot be dunting, however, as it usually occurs before the
pots hit the kiln. Hamer is great with cracking details and
remedies. However, I get so many different cracking patterns, I cannot
identify the problem.

Soda kiln being loaded as I type to be fired off Saturday. We will see how
the current batch fares.

Cheers,
-Bill

At 12:15 PM 7/31/2003 -0400, you wrote:
>Bill, We use a Peter Pugger extensively here in our guild, and it sounds
>like our methods are similar to yours. We have a dry mixer as well, and
>mix our dry bodies in that. For each pugger load we use about a 5-gallon
>pail of dry mix, about 10-12 two-handed handfuls of wet scrap, and about
>two-thirds of a gallon jug of warm water. These all vary depending on the
>wetness of the scrap.
>
>Mix for a while, correct consistency, mix again, check again, and mix a
>final time; then pug. Total mixing about 25-30 minutes, not all at once.
>If we don't have much scrap, I throw in some vinegar, maybe a cup.
>
>I'll be interested to see if knowledgeable heads on this list think that
>your cracks are dunting....
>
>So many variables: clay body, handling of the clay, wedging, consistency
>of the clay, etc. Hard to imagine that your mixing is to blame unless you
>don't give it enough time after the consistency is finally correct.
>
>Hamer has a lot of valuable info on cracks including illustrations. Very
>helpful. Check it out.
>
>Gail Dapogny

billBUCKNER
www.sodaglaze.com

Life is too important to be taken seriously.
-Oscar Wilde

Bill Buckner on thu 31 jul 03


Thanks, Nichole. However, I have considered the drying process as well. I
have dried pots completely under plastic only to have them crack just as
badly as the air-dried ones. -Bill

At 02:45 PM 7/31/2003 -0400, you wrote:
>hello,
>Saw your post on clayart...ever consider the atmosphere your drying your
>ware in? Are you drying too fast? Sometimes when you change the
>composition slightly, you need to change your following processes in order
>to compensate for any characteristics. (i.e. may need to change technique
>of drying, firing cycle, water content, etc.)Do you think the problem lies
>from the composition or the drying technique?
>Nichole

billBUCKNER
www.sodaglaze.com

Life is too important to be taken seriously.
-Oscar Wilde

Paul Herman on thu 31 jul 03


Hi Bill,

I'm wondering what the formulas are for your two blends. Is there a lot
of very plastic stuff, like Ball Clay? The fact that your other clays
don't crack may be pointing to the mix, and not the mixer.

best wishes,

Paul Herman
Great Basin Pottery
423-725 Scott Road
Doyle, California 96109 US
potter@psln.com

----------
>From: Bill Buckner
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Killer cracks
>Date: Thu, Jul 31, 2003, 6:09 AM
>

>
> Okay, here's the glitch. The body cracks! Actually, I have tried two
> blends and both cracked. Sometimes the cracks show up at bone
> dry. Sometimes they don't show until bisque. But, I am losing about 80%
> of my work. It's killing me!!

Bill Buckner on fri 1 aug 03


At 02:29 PM 7/31/2003 -0700, you wrote:
>Hi Bill,
>
>I'm wondering what the formulas are for your two blends. Is there a lot
>of very plastic stuff, like Ball Clay? The fact that your other clays
>don't crack may be pointing to the mix, and not the mixer.
>
>best wishes,
>
>Paul Herman

Sorry. I meant to include the recipe in my original post. But, I don't
the plasticity is the culprit. I have formulated lots of clay bodies and
never seen this problem.

25 Hawthorn Bond FC (35m)
25 Goldart
25 kaolin (EPK, Tile 6)
25 XX sagger clay

+10 potash feldspar (G200)
+ 5 silica (200m)
+ 5 Kyanite
+ 5 silica sand, fine

This simplified recipe allows me to mix the slip and dry blend batches in
whole bag increments, which avoids having to weigh out the units.

Thanks,
-Bill


billBUCKNER
www.sodaglaze.com

Life is too important to be taken seriously.
-Oscar Wilde

Ron Roy on fri 1 aug 03


Hi Bill,

Sounds like the clay is not well mixed enough - leave some overnight and re
pug the next day - aging for a week or two in a warm place will do wonders
as well.

RR


>I have a Peter Pugger and had been using it to mix and reclaim commercial
>bodies. Recently, I started mixing a couple bodies I developed for soda
>firing. I worked out a practical way to mix large amounts of clay in
>relatively small batches. There are two barrels - one with the clay mixed
>to a slip, the other barrel holds a dry blend. Reclaim slop goes into the
>slip barrel. When I mix, I blend the slip with enough dry mix to bring it
>to proper consistency. I generally mix it for about 20 minutes, and I
>always keep the hopper loaded for when I am ready to pug.
>
>Okay, here's the glitch. The body cracks! Actually, I have tried two
>blends and both cracked. Sometimes the cracks show up at bone
>dry. Sometimes they don't show until bisque. But, I am losing about 80%
>of my work. It's killing me!!
>
>The cracks have no particular pattern. They vary between concentric,
>spider and completely random. Even odder, they can appear concentric
>inside a pot and spider on the exterior (or vice versa). Sometimes they
>are just random, like perpendicular across to the foot. Sometimes they are
>at the foot. Sometimes they run through the body. Frequently, the cracks
>open all the way through the pot. Since the same symptoms have appeared in
>both bodies, I suspect it is the mixing that is the source of the
>problem. However, I am at a loss as to how to remedy this. I used to mix
>a body when I was in school using a similar process. But, I never had a
>cracking problem. Additionally, when I remix/reclaim commercial bodies, I
>have no cracking problems.

Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513

Bill Buckner on sat 2 aug 03


Thanks, Ron. I have tried what you suggest (even for several weeks), but
to no avail.
-Bill

At 07:07 PM 8/1/2003 -0500, you wrote:
>Hi Bill,
>
>Sounds like the clay is not well mixed enough - leave some overnight and re
>pug the next day - aging for a week or two in a warm place will do wonders
>as well.
>
>RR

billBUCKNER
www.sodaglaze.com

Life is too important to be taken seriously.
-Oscar Wilde

Ron Roy on sat 2 aug 03


Hello again Bill,

I just compared you body to one I monitor for Tuckers - very similar - a
little on the tight side for cone 10 though.

Anyway - my point is - the crackes are not due to the clay formulation - as
you say.

I'm betting there is significant cristobalite in that body - unless you are
firing and cooling real fast above 1100C.

I still think it's the mixing.

RR


>Sorry. I meant to include the recipe in my original post. But, I don't
>the plasticity is the culprit. I have formulated lots of clay bodies and
>never seen this problem.
>
> 25 Hawthorn Bond FC (35m)
> 25 Goldart
> 25 kaolin (EPK, Tile 6)
> 25 XX sagger clay
>
>+10 potash feldspar (G200)
>+ 5 silica (200m)
>+ 5 Kyanite
>+ 5 silica sand, fine
>
>This simplified recipe allows me to mix the slip and dry blend batches in
>whole bag increments, which avoids having to weigh out the units.
>
>Thanks,
>-Bill
>
>
>billBUCKNER
>www.sodaglaze.com
>
>Life is too important to be taken seriously.
> -Oscar Wilde
>
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Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513