Gail Dapogny on sun 13 aug 00
I was mulling over the recent S-cracking/particle orientation
communications on clayart and thought of something that might be of
interest. This summer, I decided to throw some disk wall hangings, so I
threw two flat disks about 15-16 inches in diameter, carved and tooled then
with a foot appropriate for hanging. They cracked, not long after. Dried
too fast, I thought. So, I threw three more and dried them much more
slowly and carefully. Two of the 3 cracked. I was baffled since I don't
often have cracking problems.
A friend suggested that I roll them out instead, citing less handling and
stress, and all that. I did so although, since my first love is throwing,
my pride was hurting mightily. I rolled out four, and three survived with
no problems.
Later I realized that, when I throw, I lightly wedge the pugged clay, smack
the spiraled ends down and place one of those ends onto the bat on the
wheel.
When I slab-rolled, I lightly wedged the pugs but put them through the slab
roller sideways, with the spirals facing outward.
Food for thought, eh? Do you all think it's the spiral direction here that
is the culprit?
To muddy the waters a bit...when I throw platters of the same width, I
seldom have problems. However, my platters are slightly curved on the
bottoms and have raised, curved sides: in other words, they are almost
shallow bowls, so they are not really the same kettle of fish, I suppose.
----Gail in pleasantly sunny, 70s, Michigan (not as exotic as Joyce in the
dessert! but still nice).
Gail Dapogny
1154 Olden Road
Ann Arbor, MI 48103-3005
(734) 665-9816
gdapogny@umich.edu
www.silverhawk.com/ex99/dapogny
Nils Lou on mon 14 aug 00
Gail, try this:
After centering on the wheel wire the lug off and replace upside down;
then proceed with with throwing. This has helped me with certain porcelain
bodies that have a tendency to s-crack. nils
On Sun, 13 Aug 2000, Gail Dapogny wrote:
> I was mulling over the recent S-cracking/particle orientation
> communications on clayart and thought of something that might be of
> interest. This summer, I decided to throw some disk wall hangings, so I
> threw two flat disks about 15-16 inches in diameter, carved and tooled then
> with a foot appropriate for hanging. They cracked, not long after. Dried
> too fast, I thought. So, I threw three more and dried them much more
> slowly and carefully. Two of the 3 cracked. I was baffled since I don't
> often have cracking problems.
>
> A friend suggested that I roll them out instead, citing less handling and
> stress, and all that. I did so although, since my first love is throwing,
> my pride was hurting mightily. I rolled out four, and three survived with
> no problems.
>
> Later I realized that, when I throw, I lightly wedge the pugged clay, smack
> the spiraled ends down and place one of those ends onto the bat on the
> wheel.
> When I slab-rolled, I lightly wedged the pugs but put them through the slab
> roller sideways, with the spirals facing outward.
>
> Food for thought, eh? Do you all think it's the spiral direction here that
> is the culprit?
>
> To muddy the waters a bit...when I throw platters of the same width, I
> seldom have problems. However, my platters are slightly curved on the
> bottoms and have raised, curved sides: in other words, they are almost
> shallow bowls, so they are not really the same kettle of fish, I suppose.
>
> ----Gail in pleasantly sunny, 70s, Michigan (not as exotic as Joyce in the
> dessert! but still nice).
>
> Gail Dapogny
> 1154 Olden Road
> Ann Arbor, MI 48103-3005
> (734) 665-9816
> gdapogny@umich.edu
> www.silverhawk.com/ex99/dapogny
>
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Craig Martell on mon 14 aug 00
Gail sedd:
>Later I realized that, when I throw, I lightly wedge the pugged clay, smack
>the spiraled ends down and place one of those ends onto the bat on the
>wheel.
Hi:
I make a lot of big porcelain bowls and platters. Only once in a great
while will I get a crack during drying. I have a 4" Venco mill. I cut the
pugs to size for the piece I'm going to make and then I wedge the pugs. By
wedging, I mean that I cut the pugs in half and slam them together on the
table in an opposite direction of orientation and I do this about 5 to 10
times. This creates a very random order to the clay and totally erases
auger memory from the pugmill. Then I knead the clay thoroughly in a spiral
and put the spiral up and the point of the cone against the wheel head when
I throw. I was taught this method by Harry Davis and it works very well.
later, Craig Martell in Oregon
Gail Dapogny on tue 15 aug 00
>I make a lot of big porcelain bowls and platters. Only once in a great
>while will I get a crack during drying. I have a 4" Venco mill. I cut the
>pugs to size for the piece I'm going to make and then I wedge the pugs. By
>wedging, I mean that I cut the pugs in half and slam them together on the
>table in an opposite direction of orientation and I do this about 5 to 10
>times.
CRAIG, DO YOU MEAN THAT YOU CUT THEM IN HALF NORMALLY OR LENGTHWISE; ALSO,
WHAT EXACTLY DO YOU MEAN WHEN YOU SAY YOU "SLAM THEM TOGETHER ON THE TABLE
IN AN OPPOSITE DIRECTION OF ORIENTATION"? Sorry to be dense about this,
but I'd like to really understand and try what you suggest. ---Gail
This creates a very random order to the clay and totally erases
>auger memory from the pugmill. Then I knead the clay thoroughly in a spiral
>and put the spiral up and the point of the cone against the wheel head when
>I throw. I was taught this method by Harry Davis and it works very well.
Craig Martell on tue 15 aug 00
Hello Gail:
You weren't being dense, I was being vague which is sort of my hobby. But
you didn't have to yell at me! :>)
The 20 lb pugs are about 30 or so centimeters long. I cut them in half at
15 centimeters. No, I don't actually measure them. I rotate the half that
i pick up 180 degrees and slam it down hard on top of the other pug that is
on the table. I pick this mass up and slam it into a cube and then cut
this cube in half. I place one half on the table with the cut edge to the
left and slam the other half down on top of this with the cut edge to the
right. I repeat this process about 5 to 10 times depending on how
energetic I'm feeling. You are basically turning the center of the clay to
the outside with the cut edges at opposite sides. This is what wedging is,
technically, although the term is used interchangably with kneading.
There is a good explanation of this process in: The Craft of The Potter by
Mick Casson and also in The Art of Throwing by John Colbeck.
hope I've been clearer this time, Craig Martell in Oregon
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