Craig Martell on wed 24 sep 03
Hi amigos:
This is for Wayne and anyone else who might be interested. I hope there's
something here that will help.
Throwing taller pots with porcelain can be difficult depending on the
form. Spheres and eliptical shapes aren't too bad because you can swell
them out as you throw and this helps with thinning. Cylinders can make you
a bit testy and put you off your feed. But learning to throw straight up
tall cylinders will increase your skills with porcelain and make everything
else seem easier.
The hardest cylinders I make are 12 inches high and taller and about 3 to 4
inches in diameter. The wider cylinders are easier. I like to do them in
4 pulls or less. If the clay is at the right consistency and I'm feeling
really froggy I can do them in three pulls.
Malcolm gave you the correct advice about using stiffer clay for taller
forms. The thing you need to figure out is, how stiff does the clay need
to be. It it's too soft you'll know right away. If the clay is too stiff,
it's hard to work and the yield point goes way up and the forms are thicker
than they should be when you're done etc. etc.
I open the clay and set the bottom diameter about one quarter inch less
than what it will be when I'm finished. The first two pulls are faily
aggressive and the clay comes up to about 2/3 the finished height and I
keep the walls as even as I can. On the third pull, I thin the upper third
of the pot to almost the finished state. This works to eliminate lower
wall torque on the last pull. So, here I go, I'm gonna finish this baby
off and head for the 'fridge. The first three pulls have been wet and
after adding water to the walls I use a sponge on a stick to clear any
water from the bottom of the pot. On the last pull, I wet the inside of
the pot and clear the bottom, but on the outside I add water to my fingers
from a sponge in the palm of my hand. I add as much water as I need to
eliminate any drag on the clay. Finger friction and drag will torque the
wall. You also need to apply "almost" equal pressure inside and out, but I
use just a bit more pressure from the inside and expand the form to it's
final diameter during the last pull. I also stand up during the last two
pulls and place my eye directly over the rim and pull the clay straight up
to my eye so I don't get a lumpy, wavy, cylinder. On the last two pulls,
increase the frequency of the throw rings and this will help to eliminate
torque. What I mean here is pull "up" slower.
I try to get these cylinders as thin as I can. I don't trim any clay off
the wall later. Only around the foot and the very bottom to avoid
cracking. For really tall stuff, I throw in sections. I usually throw 6
or eight lower walls then go back and add clay to number one and throw more.
regards, Craig Martell Hopewell, Oregon
Pamela Watkins on fri 26 sep 03
Craig:
I have'nt been following this thread.....but I read your reply and wanted to thank you for a detailed post. I work in porcelain and white stoneware; porcelain being my pet. I was never so intimitaded by a claybody until I got my hands on Grolleg instead of my ususal porcelain. And Whoa.....I was into throwing Philadelphia cream cheezel!!!! The technique demanded immeditae revisions! Do you have any suggestions in thinning out the pieces? Three pulls is ideal, and I can do that with stoneware, but porcelain I spend way too much time on?! Does porcelain demand to be babied or is it me?
Pamela
jaq
Craig Martell wrote:
Hi amigos:
This is for Wayne and anyone else who might be interested. I hope there's
something here that will help.
Throwing taller pots with porcelain can be difficult depending on the
form. Spheres and eliptical shapes aren't too bad because you can swell
them out as you throw and this helps with thinning. Cylinders can make you
a bit testy and put you off your feed. But learning to throw straight up
tall cylinders will increase your skills with porcelain and make everything
else seem easier.
The hardest cylinders I make are 12 inches high and taller and about 3 to 4
inches in diameter. The wider cylinders are easier. I like to do them in
4 pulls or less. If the clay is at the right consistency and I'm feeling
really froggy I can do them in three pulls.
Malcolm gave you the correct advice about using stiffer clay for taller
forms. The thing you need to figure out is, how stiff does the clay need
to be. It it's too soft you'll know right away. If the clay is too stiff,
it's hard to work and the yield point goes way up and the forms are thicker
than they should be when you're done etc. etc.
I open the clay and set the bottom diameter about one quarter inch less
than what it will be when I'm finished. The first two pulls are faily
aggressive and the clay comes up to about 2/3 the finished height and I
keep the walls as even as I can. On the third pull, I thin the upper third
of the pot to almost the finished state. This works to eliminate lower
wall torque on the last pull. So, here I go, I'm gonna finish this baby
off and head for the 'fridge. The first three pulls have been wet and
after adding water to the walls I use a sponge on a stick to clear any
water from the bottom of the pot. On the last pull, I wet the inside of
the pot and clear the bottom, but on the outside I add water to my fingers
from a sponge in the palm of my hand. I add as much water as I need to
eliminate any drag on the clay. Finger friction and drag will torque the
wall. You also need to apply "almost" equal pressure inside and out, but I
use just a bit more pressure from the inside and expand the form to it's
final diameter during the last pull. I also stand up during the last two
pulls and place my eye directly over the rim and pull the clay straight up
to my eye so I don't get a lumpy, wavy, cylinder. On the last two pulls,
increase the frequency of the throw rings and this will help to eliminate
torque. What I mean here is pull "up" slower.
I try to get these cylinders as thin as I can. I don't trim any clay off
the wall later. Only around the foot and the very bottom to avoid
cracking. For really tall stuff, I throw in sections. I usually throw 6
or eight lower walls then go back and add clay to number one and throw more.
regards, Craig Martell Hopewell, Oregon
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Craig Martell on sat 27 sep 03
Pamela commented:
>I was never so intimitaded by a claybody until I got my hands on Grolleg
>instead of my ususal porcelain. And Whoa.....I was into throwing
>Philadelphia cream cheezel!!!! Do you have any suggestions in thinning out
>the pieces? but porcelain I spend way too much time on?! Does porcelain
>demand to be babied or is it me?
Hello Pamela:
A friend who lives in Southern Oregon actuall threw some cream cheese cups
for a dinner pary she was having. When she told me about it she was
laughing so hard she could barely finish the story. She said it was just
like a porcelain body that she'd worked with. :^) Of course, I was ticked
off because I hadn't been on the guest list. I would have taken my camera
for that little number.
The short answer to your question is: "it depends", and "yes", porcelain
has to be worked with a bit more time and care. The part that depends is
in relation to the body that you are using. Some porcelains throw quickly
and a more casual approach by the potter is fine. Other bodies require a
more careful forming technique and some extra work. The usual approach to
a lot of different forms is more turning at the leather hard
state. Especially when you are just getting started with porcelain or
perhaps just a new porcelain body. Sometimes it's necessary to force dry a
piece to thin it out more. I try and avoid that but on larger stuff and
wide bowls and platters I will thin the edges and rims, dry them off, and
then drop the rim or lip to the flatter position. You can also throw
things in sections. You can only go so high and big with a porcelain
body.It helps to rib off the slurry once in awhile too. This keeps the pot
from getting too soft. On some forms I will do all the pulling and then
rib off the slurry and stretch them out dry and thin them that way.
Once you find a body you can live with you learn it's limits and work from
there.
regards, Craig Martell Hopewell, Oregon
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