Earl Brunner on tue 26 aug 03
Chris,
Porcelain is a big field. You didn't say WHAT porcelain, or WHAT
temperature. Every clay has its limitations. Know the limitations, and
then work with them. If you know that the porcelain that you use warps
or deforms with certain shapes, you can't make those shapes with that
clay, find a porcelain that will do what you want.
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of
ccpottery@BELLSOUTH.NET
Sent: Tuesday, August 26, 2003 7:08 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Porcelain firing question
What happens to porcelain during firing that is different from a grogged
clay? Mostly in
reference to its tendency to warp or slump when not supported.
The items I produce fire well when they are 100% self supporting but
wide rims tend to
slump when I leave them just hanging out there.
I have tried firing them unglazed upside down to get the rims flat, but
then the body
slumps. I am still not even pushing this clay beyond it's lowest firing
level.
I have had porcelain artists say that I just have to work with forms
where the slump
enhances the end result or play it safe with stable shapes ... but is
this true?
I am hoping that if I understand the process better I can work with it.
Any books I should
be reading??
Thanks so much
Chris Campbell - in North Carolina - whenever I ask myself why I work
with this crazy
and demanding porcelain, I take a look at the stuff that worked !!
Their beauty is worth
every failed one.
ccpottery@BELLSOUTH.NET on tue 26 aug 03
What happens to porcelain during firing that is different from a grogged clay? Mostly in
reference to its tendency to warp or slump when not supported.
The items I produce fire well when they are 100% self supporting but wide rims tend to
slump when I leave them just hanging out there.
I have tried firing them unglazed upside down to get the rims flat, but then the body
slumps. I am still not even pushing this clay beyond it's lowest firing level.
I have had porcelain artists say that I just have to work with forms where the slump
enhances the end result or play it safe with stable shapes ... but is this true?
I am hoping that if I understand the process better I can work with it. Any books I should
be reading??
Thanks so much
Chris Campbell - in North Carolina - whenever I ask myself why I work with this crazy
and demanding porcelain, I take a look at the stuff that worked !! Their beauty is worth
every failed one.
Chris
Chris Campbell Pottery, LLC
9417 Koupela Drive
Raleigh, North Carolina 27615-2233
Phone : 1-800-652-1008
fax : 919-676-2062
e-mail : ccpottery@bellsouth.net
web : www.wholesalecrafts.com
Ellie Blair on tue 26 aug 03
Porcelain clay has a high shrinkage rate of around 13-14%. When you use =
a grogged clay the grog makes the clay stiffer and as a result it holds i=
t shape. Porcelain is a fine particle clay and needs to be worked fairly=
dry. If you are doing forms that tend to slump you may try throwing wit=
h as little of water as you can without hanging up. You can stretch the =
clay into the form you want. You can also throw until the clay feels lik=
e it is going to slump then quit and let the clay dry for a little while.=
This will vary depending on your climate. You just want to it to stiff=
en up enough to support the rim. I don't know if this will work for you =
and your situation but it is a thought.
Happy Potting
Ellie Blair =20
Blair Pottery
Lawrence, Kansas 66047
----- Original Message -----
From: ccpottery@BELLSOUTH.NET
Sent: Tuesday, August 26, 2003 5:39 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Porcelain firing question
What happens to porcelain during firing that is different from a grogged =
clay? Mostly in
reference to its tendency to warp or slump when not supported.
The items I produce fire well when they are 100% self supporting but wide=
rims tend to
slump when I leave them just hanging out there.
I have tried firing them unglazed upside down to get the rims flat, but t=
hen the body
slumps. I am still not even pushing this clay beyond it's lowest firing l=
evel.
I have had porcelain artists say that I just have to work with forms wher=
e the slump
enhances the end result or play it safe with stable shapes ... but is thi=
s true?
I am hoping that if I understand the process better I can work with it. A=
ny books I should
be reading??
Thanks so much
Chris Campbell - in North Carolina - whenever I ask myself why I work wi=
th this crazy
and demanding porcelain, I take a look at the stuff that worked !! Their=
beauty is worth
every failed one.
Chris
Chris Campbell Pottery, LLC
9417 Koupela Drive
Raleigh, North Carolina 27615-2233
Phone : 1-800-652-1008
fax : 919-676-2062
e-mail : ccpottery@bellsouth.net
web : www.wholesalecrafts.com
_________________________________________________________________________=
_____
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at melpots@pclin=
k.com.
David Hendley on tue 26 aug 03
By definition, porcelain is vitrified clay. That means that it has zero,
or darn near, absorption and the particles have fused together in a
near homogenous mass. It is approaching a glass, or glaze, state,
and you know what a glaze does when heated to firing temperature.
Stoneware is dense, bur still not vitrified, and the different ingredients
are still somewhat separate, so it will mostly stay put.
So, if you want to work with true porcelain, it will slump and there
is nothing you can do to stop it. Your porcelain artist friends are
correct: either plan for the slumping or make stable shapes. You
can also make props to support wide rims during firing, but of course
that means the bottoms of the rims cannot be glazed.
David Hendley
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
> What happens to porcelain during firing that is different from a grogged
clay? Mostly in
> reference to its tendency to warp or slump when not supported.
>
> I have had porcelain artists say that I just have to work with forms where
the slump
> enhances the end result or play it safe with stable shapes ... but is this
true?
>
Waltraud Koestler on sat 30 aug 03
Hello,
I work also with porcelain. Most of the pieces didn't warp during firing.=
=20
Under a few bowls I put three feet. These bowls warped during firing exactl=
y where the feet have been mounted. It warped at the rims above the feet!
I'm thinking about using molochite for the bolws with mounted feet.
I would like to use recycled clay from trimmings etc. and mix it together w=
ith molichite.
My question is: how much can I use? 5% or 20 % of dryed porcelain.
Maybe there is someone who can help.
Thanks very much in advance!
Pieces without feet warped because of uneven coatings on my kilnshelfs.
I corrected this and now I have no problems (up to now - I make only simple=
shapes).=20
Best regards
Waltraud
- Germany -
"iandol" schrieb:
> Dear Chris Campbell,
> Why should you be experiencing slumping and how does Grog influence the b=
ehaviour of clay? Big questions which need more information to get answers =
which might please you.
> First, I would ask if you are maturing your clay? If you are firing at th=
e low end of the recommended range it may not yet be mature. Is it transluc=
ent?
> Second, How much do you know about your clay? What is its composition and=
which additives are used to plasticise it?
> Third point. I'm not sure all grogs would alleviate the problem. I have d=
ifficulty accepting some of the claims made for incorporating Any grog into=
a body mixture. But Molochite might help since it is fired to a temperatur=
e well above usual firing temperatures.=20
> Now it sounds as though you are having difficulty with flanged plates, po=
ssibly handles and spouts as well. If so, you have to allow for pyroplastic=
ity during the forming stage. Leave your flanges with a steeper angle and g=
ive them a tapered profile so clay at the outer rim is thinner than that a=
t the root of the well to reduce cantilevered stress. Same with spouts.
> I don't think there are easy answers on this one.
> Best regards,
> Ivor Lewis, Redhill, South Australia
>=20
> _________________________________________________________________________=
_____
> Send postings to clayart@lsv.ceramics.org
>=20
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>=20
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclin=
k.com.
>=20
Tony Ferguson on sat 30 aug 03
Waltraud,
Treat molichite as you would grog and wedge it into your porcelain claybody.
Also, try using at least 5 wads on the bottoms to reduce or eliminate
warpage.
Thank you.
Tony Ferguson
On Lake Superior, where the sky meets the Lake
Custom & Manufactured Kiln Design
Stoneware, Porcelain, Raku and more
by Coleman, Ferguson, Winchester...
http://www.aquariusartgallery.com
218-727-6339
315 N. Lake Ave
Apt 312
Duluth, MN 55806
----- Original Message -----
From: "Waltraud Koestler"
To:
Sent: Saturday, August 30, 2003 12:58 PM
Subject: Re: Porcelain firing question
> Hello,
>
> I work also with porcelain. Most of the pieces didn't warp during firing.
> Under a few bowls I put three feet. These bowls warped during firing
exactly where the feet have been mounted. It warped at the rims above the
feet!
> I'm thinking about using molochite for the bolws with mounted feet.
> I would like to use recycled clay from trimmings etc. and mix it together
with molichite.
>
> My question is: how much can I use? 5% or 20 % of dryed porcelain.
>
> Maybe there is someone who can help.
> Thanks very much in advance!
>
>
> Pieces without feet warped because of uneven coatings on my kilnshelfs.
> I corrected this and now I have no problems (up to now - I make only
simple shapes).
>
> Best regards
> Waltraud
>
> - Germany -
>
>
> "iandol" schrieb:
> > Dear Chris Campbell,
> > Why should you be experiencing slumping and how does Grog influence the
behaviour of clay? Big questions which need more information to get answers
which might please you.
> > First, I would ask if you are maturing your clay? If you are firing at
the low end of the recommended range it may not yet be mature. Is it
translucent?
> > Second, How much do you know about your clay? What is its composition
and which additives are used to plasticise it?
> > Third point. I'm not sure all grogs would alleviate the problem. I have
difficulty accepting some of the claims made for incorporating Any grog into
a body mixture. But Molochite might help since it is fired to a temperature
well above usual firing temperatures.
> > Now it sounds as though you are having difficulty with flanged plates,
possibly handles and spouts as well. If so, you have to allow for
pyroplasticity during the forming stage. Leave your flanges with a steeper
angle and give them a tapered profile so clay at the outer rim is thinner
than that at the root of the well to reduce cantilevered stress. Same with
spouts.
> > I don't think there are easy answers on this one.
> > Best regards,
> > Ivor Lewis, Redhill, South Australia
> >
> >
____________________________________________________________________________
__
> > Send postings to clayart@lsv.ceramics.org
> >
> > You may look at the archives for the list or change your subscription
> > settings from http://www.ceramics.org/clayart/
> >
> > Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
> >
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
John K Dellow on sun 31 aug 03
May be you could fire on wasters. What I mean is clay dicks placed under
the pot. They could
be made out of a fine stoneware and biscked. Place on a bed of alumna
and sprinkle alumna
on top. Place your porcelain bowl on top.
John Dellow
Waltraud Koestler wrote:
>Hello,
>
>I work also with porcelain. Most of the pieces didn't warp during firing.
>Under a few bowls I put three feet. These bowls warped during firing exactly where the feet have been mounted. It warped at the rims above the feet!
>I'm thinking about using molochite for the bolws with mounted feet.
>I would like to use recycled clay from trimmings etc. and mix it together with molichite.
>
>My question is: how much can I use? 5% or 20 % of dryed porcelain.
>
>Maybe there is someone who can help.
>Thanks very much in advance!
>
>
>Pieces without feet warped because of uneven coatings on my kilnshelfs.
>I corrected this and now I have no problems (up to now - I make only simple shapes).
>
>Best regards
>Waltraud
>
>- Germany -
>
>
>"iandol" schrieb:
>
>
>>Dear Chris Campbell,
>>Why should you be experiencing slumping and how does Grog influence the behaviour of clay? Big questions which need more information to get answers which might please you.
>>First, I would ask if you are maturing your clay? If you are firing at the low end of the recommended range it may not yet be mature. Is it translucent?
>>Second, How much do you know about your clay? What is its composition and which additives are used to plasticise it?
>>Third point. I'm not sure all grogs would alleviate the problem. I have difficulty accepting some of the claims made for incorporating Any grog into a body mixture. But Molochite might help since it is fired to a temperature well above usual firing temperatures.
>>Now it sounds as though you are having difficulty with flanged plates, possibly handles and spouts as well. If so, you have to allow for pyroplasticity during the forming stage. Leave your flanges with a steeper angle and give them a tapered profile so clay at the outer rim is thinner than that at the root of the well to reduce cantilevered stress. Same with spouts.
>>I don't think there are easy answers on this one.
>>Best regards,
>>Ivor Lewis, Redhill, South Australia
>>
>>______________________________________________________________________________
>>Send postings to clayart@lsv.ceramics.org
>>
>>You may look at the archives for the list or change your subscription
>>settings from http://www.ceramics.org/clayart/
>>
>>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>>
>>
>>
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
>
>
--
John Dellow "the flower pot man"
Home Page http://www.welcome.to/jkdellow
http://digitalfire.com/education/people/dellow/
Ron Roy on sun 31 aug 03
Hi Chris,
There are any number of porcelain bodies and some are much more prone to
slumping than others.
Where do you buy it and what is the recommended firing temperature. Most
clay companies say there is a range over which a clay is to be fired - with
porcelain it should (but rarely is) have a specific temperature at which it
is properly fired.
Porcelain is made from refractory clay because it is expected to be white -
so lots of melter needs to be used - this makes for a short firing range.
Still - with porcelain - special attention needs to be applied to the ware
so that the slumping is taken into account - as other have noted.
Even throwing and trimming of walls and feet is important - everything
taken into account - including strong rims - if warping is to be avoided.
If kiln shelves are uneven the ware will conform to the uneveness and
warping will result.
On the other hand many of us go to certain lengths to cultivate the warp -
adds to the visual interest - and many times does not interfer with
function.
RR
>What happens to porcelain during firing that is different from a grogged
>clay? Mostly in
>reference to its tendency to warp or slump when not supported.
>
>The items I produce fire well when they are 100% self supporting but wide
>rims tend to
>slump when I leave them just hanging out there.
>
>I have tried firing them unglazed upside down to get the rims flat, but
>then the body
>slumps. I am still not even pushing this clay beyond it's lowest firing level.
>
>I have had porcelain artists say that I just have to work with forms where
>the slump
>enhances the end result or play it safe with stable shapes ... but is this
>true?
>
>I am hoping that if I understand the process better I can work with it.
>Any books I should
>be reading??
>Thanks so much
>Chris
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
ccpottery@BELLSOUTH.NET on sun 31 aug 03
A huge thanks to all who took the time to reply to my questions on porcelain slumping
and firing.
It pretty well confirmed what I was learning from the clay ... but at least now I don't think it
is just my lack of knowledge. I feel re-energized to get back to work and let the porcelain
do what it will ... after I've had my turn.
During a recent trip to Toronto, I was thrilled to visit the studio of Kayo O'Young and his
wife Diane Nasr ... both incredible porcelain artists ... totally different approaches and
breathtaking work.
I believe Kayo is having a show during the month of September at the Gardiner Museum
and I encourage everyone to go see it. You will be blown away !!
Chris Campbell - in North Carolina - I walked through his studio when it was wall to wall
white pots waiting to be bisqued or glazed. The forms were so beautiful ... it was hard to
imagine covering them with any kind of glaze ... until I touched his glazed pots ... I was
lost .....
Chris
Chris Campbell Pottery, LLC
9417 Koupela Drive
Raleigh, North Carolina 27615-2233
Phone : 1-800-652-1008
fax : 919-676-2062
e-mail : ccpottery@bellsouth.net
web : www.wholesalecrafts.com
Janet Kaiser on tue 2 sep 03
Technical question: would they be circumsized or not...?
John, you are JOKING too, right?
Janet :-)
>May be you could fire on wasters. What I mean is clay dicks
placed under
>the pot.
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