tyler on wed 28 may 03
I am having problems with my clay splitting while throwing. I am throwing
tall pots (12") which are wider at the bottom and skinnier at the top.
When i am getting the clay close to thin enough and start to shape the
pot, the walls on the lower part of the pot get many splits in them. if i
am lucky i can squish them closed with a rib, but i don't think this is a
good alternative. Does anyone know what this is from???? cold clay? bad
water? bad clay?
thanks
tyler
Bruce Girrell on wed 28 may 03
> I am having problems with my clay splitting while throwing. I am throwing
> tall pots (12") which are wider at the bottom and skinnier at the top.
> When i am getting the clay close to thin enough and start to shape the
> pot, the walls on the lower part of the pot get many splits in them. if i
> am lucky i can squish them closed with a rib, but i don't think this is a
> good alternative. Does anyone know what this is from???? cold clay? bad
> water? bad clay?
Given a choice of those three, the closest is "bad clay". It sounds as
though your clay has poor plasticity. Are you making up your own clay body
or have you recycled the clay a number of times without adding fresh clay?
Is this a porcelain body?
If you can tolerate some grayness, you might want to try adding some ball
clay or a little (1/2% or 1%) bentonite.
If you are making up your own clay body post the recipe to the list and some
of the clay gurus may be able to make some suggestions. I'm not a clay guru,
but I have spent enough time making bad clay bodies to at least recognize
the splitting that you are talking about.
Bruce "still trying to make a good clay body" Girrell
Elizabeth Priddy on wed 28 may 03
tyler wrote:I am having problems with my clay splitting while throwing
After you have thrown them, you can move to thinner, but unless you are working porcelain, that will be thin enough. And half inch to quarter over a twelve inch span is fine. Also gives you a little room for trimming.
Sounds like tortion. If it is twisting or you are necking in to keep the diameter small, you might have twists developing long before you see them. If they look like cracks, you might be throwing too dry. Keep it wet on the walls and dry in the bottom, sopping it out on each pull to keep a pool from developing, but working with very wet sponge in your palm and squeezing just a little as you come up to keep any drag from developing.
After each pass where you make the diameter smaller, you need to make another pass that recompresses the walls without thinning them. Just make a firm pull from bottom to top without dragging any clay up. It will stabalize the wall and make it ready for the next pass, eliminating any tortion. Use a rib. Try to keep the diameter of the form at least one third smaller than you want it in the end as you pull up. Then you can flare it out in one shaping pull at the end. This works for all size pots in general and kepps it fresh. It's called "springing the form" on my planet.
Also, pull up firmly and without hesitation, but keep the wheel speed slow so that you have more control. Speed will make it seem easier, but will frequently cause more problems than it solves. The taller you get, the slower the wheel speed should be.
More water, less speed, smaller diameter, thicker walls. Could fix it.
Hope this helps. Could be the clay body but not likely. You didn't say what you are using, but most clay can be coaxed into a 12 inch cylinder. If you are using very soft clay, it could be collapsing from the weight, in which case, use stiffer clay. Too hard and you wouldn't be able to center it well enough to throw it on center. You need medium/hard clay for this type of form.
Elizabeth Priddy
www.angelfire.com/nc/clayworkshop
Beaufort, NC
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Jennifer F Boyer on wed 28 may 03
Another way of doing this compression is to throw DOWN every
third pull or so. Start at the top of the area where cracks are
likely and throw moving your hands down the pot to the bottom.
Jennifer
Elizabeth Priddy wrote:
> tyler wrote:I am having problems with my clay splitting while throwing
> After you have thrown them, you can move to thinner, but unless you are working porcelain, that will be thin enough. And half inch to quarter over a twelve inch span is fine. Also gives you a little room for trimming.
>
> Sounds like tortion. If it is twisting or you are necking in to keep the diameter small, you might have twists developing long before you see them. If they look like cracks, you might be throwing too dry. Keep it wet on the walls and dry in the bottom, sopping it out on each pull to keep a pool from developing, but working with very wet sponge in your palm and squeezing just a little as you come up to keep any drag from developing.
>
> After each pass where you make the diameter smaller, you need to make another pass that recompresses the walls without thinning them. Just make a firm pull from bottom to top without dragging any clay up. It will stabalize the wall and make it ready for the next pass, eliminating any tortion. Use a rib. Try to keep the diameter of the form at least one third smaller than you want it in the end as you pull up. Then you can flare it out in one shaping pull at the end. This works for all size pots in general and kepps it fresh. It's called "springing the form" on my planet.
>
>
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
Jennifer Boyer mailto:jboyer@adelphia.net
Thistle Hill Pottery Montpelier VT USA
http://www.thistlehillpottery.com/
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for web hoaxes and junk:
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http://snopes.com
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Donald G. Goldsobel on wed 28 may 03
I wonder how wet your clay is? Clay looses its strength when overly wet.
Perhaps you can try a heat source to firm up the base of the vase form.
Donald
----- Original Message -----
From: "Bruce Girrell"
To:
Sent: Wednesday, May 28, 2003 10:32 AM
Subject: Re: splitting/cracking problems while throwing
> > I am having problems with my clay splitting while throwing. I am
throwing
> > tall pots (12") which are wider at the bottom and skinnier at the top.
> > When i am getting the clay close to thin enough and start to shape the
> > pot, the walls on the lower part of the pot get many splits in them. if
i
> > am lucky i can squish them closed with a rib, but i don't think this is
a
> > good alternative. Does anyone know what this is from???? cold clay?
bad
> > water? bad clay?
>
> Given a choice of those three, the closest is "bad clay". It sounds as
> though your clay has poor plasticity. Are you making up your own clay body
> or have you recycled the clay a number of times without adding fresh clay?
> Is this a porcelain body?
>
> If you can tolerate some grayness, you might want to try adding some ball
> clay or a little (1/2% or 1%) bentonite.
>
> If you are making up your own clay body post the recipe to the list and
some
> of the clay gurus may be able to make some suggestions. I'm not a clay
guru,
> but I have spent enough time making bad clay bodies to at least recognize
> the splitting that you are talking about.
>
> Bruce "still trying to make a good clay body" Girrell
>
>
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melpots@pclink.com.
Lily Krakowski on wed 28 may 03
I'll probably hate myself in the morning and you may hate me more, but how
wet is all this? How fast are you going? You can't tell me about cold
clay! Bad water? Are you using different water than before? If I
understand you correctly you are using the same clay you have used for other
shapes? And in this wide base/narrow top pot shape the walls split?
My guess is that you do not take into account how MUCH water a wide base can
hold. As the wheel spins, centrifugal force splashes the water onto the
lower part of the walls....As you narrow your pot at the top, you no longer
look inside,do not realize there is a pond down there. Also even dry
throwers tend to use water when narrowing a neck....
Get a pair of bamboo tongs of the kind used to retrieve toast from the
toaster. Pick up a nice round sponge with them and dry the inside of the
pot bottom everytime you pull up...
ALSO ARE YOU RETURNING EVERY PRECIOUS DROP OF THROWING WATER/SLURRY TO THE
CLAY AS YOU RECYCLE, RECLAIM?
Bruce Girrell writes:
>> I am having problems with my clay splitting while throwing. I am throwing
>> tall pots (12") which are wider at the bottom and skinnier at the top.
>> When i am getting the clay close to thin enough and start to shape the
>> pot, the walls on the lower part of the pot get many splits in them. if i
>> am lucky i can squish them closed with a rib, but i don't think this is a
>> good alternative. Does anyone know what this is from???? cold clay? bad
>> water? bad clay?
>
>
Lili Krakowski
P.O. Box #1
Constableville, N.Y.
(315) 942-5916/ 397-2389
Be of good courage....
iandol on thu 29 may 03
Dear Tyler,
This sounds very much like a "Short" Clay, one with an over abundance of =
non-plastic ingredients.
The answer may be increase the weight of Ball Clay in the recipe. This =
will increase the cohesive strength of your plastic clay. You may find =
the down side of this remedy is a slight increase in shrinkage.
Best regards,
Ivor Lewis.
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