Chip bowl trouble

Lindsay MacArthur wrote in
:

I am trying to make a 14"-16" diameter shallow stoneware serving bowl
but I have not had any success. Each of my bowls had cracked while
drying. What am I doing wrong? Since the bowls don't curve up much
could the weight of the sides be pulling downward while it's drying?
Thanks for the help
LMac




When are they cracking?. Drying, bisque or glaze?

Where are they cracking? Base, sides or straight across?

What sort of cracks are they? S shaped, spiral, vertical?

If you have a local library or can buy it, a great book is

The Potters Dictionary of Materials and Techniques by Frank Hamer

Published by Watson-Guptill Publications

US ISBN 0-8230-4210-3

This contains in depth information on cracking

Regards

John

"Uncle John" wrote in message
...
Lindsay MacArthur wrote in
:

I am trying to make a 14"-16" diameter shallow stoneware serving bowl
but I have not had any success. Each of my bowls had cracked while
drying. What am I doing wrong? Since the bowls don't curve up much
could the weight of the sides be pulling downward while it's drying?
Thanks for the help
LMac




When are they cracking?. Drying, bisque or glaze?

Where are they cracking? Base, sides or straight across?

What sort of cracks are they? S shaped, spiral, vertical?

If you have a local library or can buy it, a great book is

The Potters Dictionary of Materials and Techniques by Frank Hamer

Published by Watson-Guptill Publications

US ISBN 0-8230-4210-3

This contains in depth information on cracking

Regards

John

John had all my questions )

Also how long are you taking to dry the piece? What are you drying it on?

DKat

"Lindsay MacArthur" wrote in message
...
I am trying to make a 14"-16" diameter shallow stoneware serving bowl
but I have not had any success. Each of my bowls had cracked while
drying. What am I doing wrong? Since the bowls don't curve up much
could the weight of the sides be pulling downward while it's drying?
Thanks for the help
LMac

If you are letting them dry uncovered, most common cause is uneven drying-
sides will dry and try to shrink much faster than the bottom. Bowls and
tall objects have much smaller flat area in contact with the shelve, so
dying is more even.
Try raising the platter on small supports of the shelve.
Also, when throwing, make sure you compress the base really well as that can
cause s cracks
Andrea

"annemarie" wrote in message
...

"Uncle John" wrote in message
...
Lindsay MacArthur wrote in
:

I am trying to make a 14"-16" diameter shallow stoneware serving bowl
but I have not had any success. Each of my bowls had cracked while
drying. What am I doing wrong? Since the bowls don't curve up much
could the weight of the sides be pulling downward while it's drying?
Thanks for the help
LMac




When are they cracking?. Drying, bisque or glaze?

Where are they cracking? Base, sides or straight across?

What sort of cracks are they? S shaped, spiral, vertical?

If you have a local library or can buy it, a great book is

The Potters Dictionary of Materials and Techniques by Frank Hamer

Published by Watson-Guptill Publications

US ISBN 0-8230-4210-3

This contains in depth information on cracking

Regards

John

John had all my questions )

They are cracking when I'm drying to bone dry. The cracks are on the
rim and run vertically down the sides of the bowl, they usually don't
exceed 1 inch. There is no definitive shape to the cracks, just
vertical. I'm drying them on an elevated wood platform covered with
newspaper. The bowls are uncovered when I dry them but there tends to
be a lot of moisture in the air in my studio

I'll look up the book in my library, thanks for the recommendation.

LMac

On Wed, 10 Mar 2004 20:49:48 +0000 (UTC), Uncle John
wrote:

Lindsay MacArthur wrote in
:

I am trying to make a 14"-16" diameter shallow stoneware serving bowl
but I have not had any success. Each of my bowls had cracked while
drying. What am I doing wrong? Since the bowls don't curve up much
could the weight of the sides be pulling downward while it's drying?
Thanks for the help
LMac




When are they cracking?. Drying, bisque or glaze?

Where are they cracking? Base, sides or straight across?

What sort of cracks are they? S shaped, spiral, vertical?

If you have a local library or can buy it, a great book is

The Potters Dictionary of Materials and Techniques by Frank Hamer

Published by Watson-Guptill Publications

US ISBN 0-8230-4210-3

This contains in depth information on cracking

Regards

John

My guess is that you are drying them too quickly. Are you compressing the
rim when you throw (squeezing and at the same time pressing down on the
rim)? I do this with a chamoise at the end of throwing and by hand after
the first pull (after opening the floor and the pull that evens up wall
thickness). The bottom underside of the plate is not open to air while the
rim is so it is going to be drying/swinking much faster if the plate is not
covered. I have never had this type of cracking but I always cover my pots
or dry them in a damp closet until they are at least leather hard..... DKat

"Lindsay MacArthur" wrote in message
...
They are cracking when I'm drying to bone dry. The cracks are on the
rim and run vertically down the sides of the bowl, they usually don't
exceed 1 inch. There is no definitive shape to the cracks, just
vertical. I'm drying them on an elevated wood platform covered with
newspaper. The bowls are uncovered when I dry them but there tends to
be a lot of moisture in the air in my studio

I'll look up the book in my library, thanks for the recommendation.

LMac

On Wed, 10 Mar 2004 20:49:48 +0000 (UTC), Uncle John
wrote:

Lindsay MacArthur wrote in
:

I am trying to make a 14"-16" diameter shallow stoneware serving bowl
but I have not had any success. Each of my bowls had cracked while
drying. What am I doing wrong? Since the bowls don't curve up much
could the weight of the sides be pulling downward while it's drying?
Thanks for the help
LMac




When are they cracking?. Drying, bisque or glaze?

Where are they cracking? Base, sides or straight across?

What sort of cracks are they? S shaped, spiral, vertical?

If you have a local library or can buy it, a great book is

The Potters Dictionary of Materials and Techniques by Frank Hamer

Published by Watson-Guptill Publications

US ISBN 0-8230-4210-3

This contains in depth information on cracking

Regards

John

Lindsay MacArthur wrote in
:

They are cracking when I'm drying to bone dry. The cracks are on the
rim and run vertically down the sides of the bowl, they usually don't
exceed 1 inch. There is no definitive shape to the cracks, just
vertical. I'm drying them on an elevated wood platform covered with
newspaper. The bowls are uncovered when I dry them but there tends to


The bok says Page 78.

Crack A

The crack is at right angles to the rim and is wider at the rim and
peters out below.

1 The design is poor giving a structually weak pot. Probably the rim is
too thin to contain the stresses in the remainder of the pot.

2 Method of working was incorrect for the clay used. Probably the drying
was too rapid and unequal

3 If the crack is in newly thrown clay or shows whilst still on the
wheel or soon after removing, it is likely to be insufficient prepared
clay or possibly tired clay or over-short clay. If the clay has had extra
sand or grog added this may have made the clay too short for the type of
throwing used. This crack has the appearance of a fibrous tear.

4 If the crack iis in the rim of a plate or dish, esecially a press
moulded dish, the clay was probably over-wet unequally in some ways. Also
the drying which follows was too rapid for the clay to equalise the
moisture content

5 If a slip coating has been poured or brushed inside the dish it was
done when the dish was too dry

6 If the crack is hair line, it could be that the pot has been waiting
for firing over a period of time which involved dry weather follow3ed by
wet weather. The resulting crack is a result of reasorbtion.


John

just a thought! i make very wide bowls but mine are slipped poured and
i dry them upside down, maybe doing this will help.

Just a thought;
Are you making these pieces out of a smooth clay or does it contain some
grog and if so how much.
If I was going to make a shallow dish of that size (and I used to) I
would want to use a clay that contained at least 10 percent of 30 mesh
grog or sand.

Steve
Bath
UK


"Lindsay MacArthur" wrote in message
.. .
I am trying to make a 14"-16" diameter shallow stoneware serving bowl
but I have not had any success. Each of my bowls had cracked while
drying. What am I doing wrong? Since the bowls don't curve up much
could the weight of the sides be pulling downward while it's drying?
Thanks for the help
LMac



--
Steve Mills
Bath
UK

Lindsay MacArthur wrote in message . ..
I am trying to make a 14"-16" diameter shallow stoneware serving bowl
but I have not had any success. Each of my bowls had cracked while
drying. What am I doing wrong? Since the bowls don't curve up much
could the weight of the sides be pulling downward while it's drying?
Thanks for the help
LMac

Hi there.
I recently made a large platter 62cm (24 inch) dia and had no
problems. The batt I used was 60cm and it took 24lb of clay.
after throwing I placed the platter in the sun for about 3 hours,
rotating it 90deg ever 15-20 minutes. After 3hrs it was loose on
the batt so I placed a 2nd batt on top and turned it upside down.
The throwing batt came off easily!!, and I continued to further
dry (the underside) in the sun for about 1-2 hours. Later that
evening I was able to turn the base and place the platter back on
it's base to dry. I rotate the platter 1/3 of a turn 2-3 times a
throughout drying.

The three main things I have found with all large base ware a
*Throw the pot quickly and work mainly on the base
*Dry the pot as quick as you like, but evenly!
*Get the pot off the bat as soon as you can and turn it upside
down.
Kind Regards
Mike D