Don Jung on fri 22 nov 96
Hi all,
I was hoping to get some help in resolving our problems with warping
bowls (and platters). The more delicate and thinner bowls all end up
with a little or a lot of warping which is discouraging. I'm looking
for confirmation that there are certain techniques in the throwing and
drying steps that can minimize the possibility of warping. Then there's
the placement in the kiln, rate of firing and circulation of air.
We try to place large pieces that may be prone to warping in the middle
and fire at a 150 F/hr to cone 6. Loading a kiln often doesn't leave
much of a choice to keep everything in the center...so does loading a
bowl near the corner by the elements (we have a square electric kiln)
increase the chance of warping? We try to keep a 2" clearance from the
elements and a 1/4" space between pieces.
We're also investing in a Bailey double kiln vent (thanks to the
feedback from Clayart on that too) to vent the fumes and get a more even
firing... will that solve some or all of our ills?
Anyways, any ideas and advise would be appreciated.
thx Don
dojun@axionet.com
Kensington Pottery
Vancouver BC Canada
Eleanora Eden on sun 24 nov 96
Hi Don and All,
I throw thin bowls and I turn them upside down on a perfectly flat
surface after I trim the feet and I dry them that way. Makes perfectly
round bowls almost all the time.
Eleanora
Eleanora Eden 802 869-2003
Paradise Hill
Bellows Falls, VT 05101 eden@maple.sover.net
[the address fga@world.std.com is temporary. My mailbox at
eden@maple.sover.net still works -- do not change address books]
Jean Campbell on sun 24 nov 96
Don Jung wrote:
>
> ----------------------------Original message----------------------------
> Hi all,
> I was hoping to get some help in resolving our problems with warping
> bowls (and platters). .
>
> thx Don
> dojun@axionet.com
> Kensington Pottery
> Vancouver BC CanadaYou don't give too many clues but, assuming your work is gl
it sounds as though there is a problem with your clay. Once-fired or bisqued?
With platters and bowls problems with the form can come from the footring. It
has to be carefully sited to provide maximum support - too near the edge will
cause slumping of the centre - too near the centre will cause the edges to
distort. No footrings can cause trapping of the base as the pot
shrinks/expands leading to distortion.
If it is any consolation bowls and platters, platters especially are
responsible for most wasters even from highly experienced production potters.
Unless your kiln is really out of control it should not be to blame!
Marcia Kindlmann on mon 25 nov 96
Subject: warping bowls
Don in Vancouver asked the other day,
> I was hoping to get some help in resolving our problems with warping
> bowls (and platters). The more delicate and thinner bowls all end up
> with a little or a lot of warping which is discouraging. I'm looking
> for confirmation that there are certain techniques in the throwing and
> drying steps that can minimize the possibility of warping. ....
Just a few thoughts from my own experience -- others can add more...
Drying -- be sure it's even, which for bowls is really difficult if
there's a minor air current in the studio overnight that'll dry them
on one side more than on the other. For this (lacking a special
enclosed space) I sometimes cover the pots overnight and uncover
them during the day when I can rotate them around. The most
perfectly centered, lurch-free bowl when thrown can turn into a
bear to trim if one side is moister than the other. The trim
tool cuts more into the softer side, making it thinner, and of
course uneven thickness can push a pot toward warping.
Be sure when trimming that the foot is on a plane -- geometrically
speaking -- or is flatfooted? how to say.... I mean test the
bowl by placing it on a flat hard surface. If it rocks, the foot
will settle down in the firing and the bowl will likely
warp oval.
Be sure the kiln shelf is really flat and level. A domed-up
(or sagging) kiln shelf can tilt a bowl enough to warp when
it's nearly pyroplastic at high temperatures.
Porcelain bowls are particularly eager to warp. I've found that
changing the curve at the rim, i.e. flaring the lip out a bit ,
is the most surefire way of preventing this warp--it even works
when such a bowl is near the elements and not in center of kiln.
Then there's clay body-- particularly if porcelain-- some do
warp more than others.
>Then there's the placement in the kiln ....
>does loading a bowl near the corner by the elements
>(we have a square electric kiln)
>increase the chance of warping? We try to keep a 2" clearance
>from the elements and a 1/4" space between pieces.
I've found that shapes which warp easily (eg. bowls with a
continuous curve from body through lip rather than that flared
lip changing direction of curve) will warp even 4 inches from
elements. It seems to help in such cases to put some kiln posts
between the elements and the bowl, if there's not room to put
another pot between.
Good luck.
Marcia in Guilford CT
Anne Bracker on mon 25 nov 96
Something to consider with larger bowls or platters, especially ones
with a wide base, is that there can be a temperature difference between
the rim and the base. Kiln shelves can take a long time to absorb heat
because they are so dense, so the temperature of the air near the rim of
the pot and the temperature of the base of the pot are different, which
can lead to warping during the firing because the piece is not heating
evenly. To try to solve this problem, you need to either increase the
heat at a slower rate so that the shelves have more time to absorb the
heat or you need to find a way to raise your pieces off the shelf just a
little so that the heat can "flow" around the base as well. Kiln shelf
fragments, wads, or stilts can be used. Sometimes a little silica sand
sprinkled on the shelf can also solve the problem - the sand acts like
little ball bearings which raise the piece just enough, as well as
allowing the pot to move easily as it shrinks during firing. Just be
careful with the sand because you don't want it to get in the element
grooves if you are using an electric kiln. Vacuuming is a must if you
try the sand. I am interested in hearing what everyone says about these
suggestions - I haven't tried them all, but I have heard these solutions
from other customers of mine at one time or another. Let me know how it
works,
Anne M. Bracker
Bracker Ceramics
Don Jung on wed 27 nov 96
Re: Warping bowls (Don Jung , Mon 23:37)
To:
Ceramic Arts Discussion List
Thanks once again for the generous and informative posts, both on and
off the list. There were quite a few, all with little treasures of
knowledge imbedded. I'll try to sum it up here and do some testing to
confirm which solution(s) solve it for us (we're a group of potter
wannabes).
1.Use really flat kiln shelves or a flat clay pad (of higher firing
clay) underneath to ensure that the bowl's are fired 'flat'.
2.Throw bowls with even thickness throughout with strong rims, not
tapering off or too thin.
3.Fire slowly to ensure even heating. (I believe 150 F/hr to ^6 is slow,
but no one really specified a rate...just the word slowly)
4.Throw bowls with definite changes in curve or shape to provide
strength...similar to a what a stronger(thicker) rim would do.
5.Dry evenly and upside down. (This is not a problem with us as we do
get perfectly round and flat bottomed pieces out of the bisque).
6.Don't stack a 1/2 kiln shelf edge next to the bowl's lip.(related to
even heating)
7.Ensure the bowl is thrown with a properly proportioned foot...not to
small or too wide and trimmed flat of course.
8.Probably a few more but that covers most of em.
There was also an interesting note from quite a few...that they prefer
the added 'warp' the firing adds to the bowl. I must agree that it does
make a unique and often special piece out of an ordinary one. My only
quibble is that the bottom stay flat and not rock while the rim can sway
just a little. (Potential for an interesting thread here...)
I suspect our shelves as the culprit...so it's off to do some tests.
thanks again
Don Jung
Kensington Pottery
Vancouver BC Canada
(more to do...what have I gotten myself into...)
Jon on tue 17 nov 98
What is it that makes a thrown, circular bowl with a nice defined rim
dry into a somewhat unattractive oval bowl? And how can one prevent
this? I think I used to know the answers once, but can't remember! I
notice that this happens mostly with white stoneware, and only on tall,
narrow-er bowls, as opposed to shorter, broader bowls. I haven't has
this problem in a while then BOOM - suddenly I have them.
Jonathan in DC
"Words don't cook rice." Chogyam Trungpa Rimpoche
June Perry on wed 18 nov 98
Dear Jonathan:
This is the time of year many of us are turning up the heat in our studios.
Uneven drying will cause the warping you speak of. Make sure your freshly
thrown ware is out of the way of drafts and a direct heat source unless you
are willing to turn the pots a lot to allow even drying. Uneven drying won't
show up as the pot dries, but will show up in the firing.
Also, try firing those bowls further away from any incoming heat source. I try
to place my larger bowls more toward the center of the kiln.
I invert bowls and plates as soon as I am able so that they finish drying
with rim the down, and I fire my bowls upside down in the bisque firing.
Hope this helps.
Warm regards,
June
John Hesselberth on wed 18 nov 98
Jon wrote:
>----------------------------Original message----------------------------
>What is it that makes a thrown, circular bowl with a nice defined rim
>dry into a somewhat unattractive oval bowl? And how can one prevent
>this? I think I used to know the answers once, but can't remember! I
>notice that this happens mostly with white stoneware, and only on tall,
>narrow-er bowls, as opposed to shorter, broader bowls. I haven't has
>this problem in a while then BOOM - suddenly I have them.
>
>Jonathan in DC
>"Words don't cook rice." Chogyam Trungpa Rimpoche
Jon,
Just a guess, but winter has arrived and your heater is probably on.
Could be the air flow from your heater combined with the faster drying
that lower winter-time humidity gives is causing non uniform drying and,
therefore, oval bowls. Try slowing down the drying by covering your bowls
loosely with plastic. If they are drying in a draft from your heater,
move one or the other.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"The whole aim of practical politics is to keep the populace alarmed, and
hence clamorous to be led to safety, by menacing it with an endless
series of hobgoblins, all of them imaginary." H.L. Mencken, 1925
James Shepherd on wed 18 nov 98
Is the warping occuring during drying or during firing? Placement in the
kiln can affect warping, but I have never had a problem during drying. I
suppose that the same could occur, one side drying faster than another.
JP
-----Original Message-----
From: Jon
To: CLAYART@LSV.UKY.EDU
Date: Tuesday, November 17, 1998 7:49 AM
Subject: Warping bowls
>----------------------------Original message----------------------------
>What is it that makes a thrown, circular bowl with a nice defined rim
>dry into a somewhat unattractive oval bowl? And how can one prevent
>this? I think I used to know the answers once, but can't remember! I
>notice that this happens mostly with white stoneware, and only on tall,
>narrow-er bowls, as opposed to shorter, broader bowls. I haven't has
>this problem in a while then BOOM - suddenly I have them.
>
>Jonathan in DC
>"Words don't cook rice." Chogyam Trungpa Rimpoche
>
Donn Buchfinck on wed 18 nov 98
you said: potterdc@erols.com
What is it that makes a thrown, circular bowl with a nice defined rim
dry into a somewhat unattractive oval bowl? And how can one prevent
this? I think I used to know the answers once, but can't remember! I
notice that this happens mostly with white stoneware, and only on tall,
narrow-er bowls, as opposed to shorter, broader bowls. I haven't has
this problem in a while then BOOM - suddenly I have them.
Jonathan in DC
"Words don't cook rice." Chogyam Trungpa Rimpoche
well I am certainly glad I do not live with this individual, kind of like the
hand that rocks the cradle kind of person/ controling.
I think if you look at some of the best potters around they make pots that
warp.
I even warp my bowls to help them along
Michael Simon makes great oval bowls
I like to make mine into squares and triangles
the best thing about making pots it that they CAN be like people
that is to say that there is no NORMAL person out there, you will probably
find it hard to make a non warping bowl.
when I started making pots I used to throw the pot away if it didn't go around
the wheel perfect when I was trimming it, the grad student who was teaching
me said I should just make it on a lathe. that hit home for me.
it's said that Hamada used to bump his pots with his elbow when he thought no
one was looking so they would have a flaw in them.
I think on some level WE are defined by our flaws, and they are what makes us
unique. same goes for pottery
now I do know an excessive warp can fight the form a potter is working on. I
think you have to look at the clay you are using. if it is comprised of only
fine particles like a porcelain then it will warp in the drying stage if you
make it thin. some type of grog is needed to open up the clay and to cut
down on the shrinkage, this will help in the wet to dry warping. but just
remember that if you are firing the piece on a kiln shelve and if the shelf is
just a little bit off then the bowl will warp durring firing.
So my final opinion is that if it's going to warp, then a potter is best to
figure out how to work with it
the world has enough boring pots out there anyway.
Donn Buchfinck
and words might not cook rice, but to not stimulate the mind with conversation
and thought durring a meal makes the meal only nurishes the body but starves
the mind.
Jon on wed 18 nov 98
Wow Donn! You certainly make a whole lot of (wrong) assumptions about someone
from a few typed sentences! What's particularly humorous and ironic
about your
response is that, in fact, most of my pots ARE warped, manipulated, etc
- I even
have a whole line of bowls that I put my fingers through the rim to
ensure they
don't come out round. But, sometimes I do want round bowls, and, in throwing
them, have noticed with the white stoneware they tend to warp and rock
on their
feet, and wondered why. It seems to me that a good potter can make non-round,
oval bowls - and a good potter understands the materials and processes
enough to
be able to throw a round bowl.
And, I'm actually great fun to live with!
Cheers,
Jonathan in DC, the "hand that rocks the cradle kind of person"
>
>
> well I am certainly glad I do not live with this individual, kind of like the
> hand that rocks the cradle kind of person/ controling.
> I think if you look at some of the best potters around they make pots that
> warp.
> I even warp my bowls to help them along
> Michael Simon makes great oval bowls
> I like to make mine into squares and triangles
> the best thing about making pots it that they CAN be like people
> that is to say that there is no NORMAL person out there, you will probably
> find it hard to make a non warping bowl.
> when I started making pots I used to throw the pot away if it didn't go around
> the wheel perfect when I was trimming it, the grad student who was teaching
> me said I should just make it on a lathe. that hit home for me.
> it's said that Hamada used to bump his pots with his elbow when he thought no
> one was looking so they would have a flaw in them.
> I think on some level WE are defined by our flaws, and they are what makes us
> unique. same goes for pottery
> now I do know an excessive warp can fight the form a potter is working on. I
> think you have to look at the clay you are using. if it is comprised of only
> fine particles like a porcelain then it will warp in the drying stage if you
> make it thin. some type of grog is needed to open up the clay and to cut
> down on the shrinkage, this will help in the wet to dry warping. but just
> remember that if you are firing the piece on a kiln shelve and if the shelf is
> just a little bit off then the bowl will warp durring firing.
> So my final opinion is that if it's going to warp, then a potter is best to
> figure out how to work with it
> the world has enough boring pots out there anyway.
>
> Donn Buchfinck
>
> and words might not cook rice, but to not stimulate the mind with conversation
> and thought durring a meal makes the meal only nurishes the body but starves
> the mind.
Vince Pitelka on wed 18 nov 98
>What is it that makes a thrown, circular bowl with a nice defined rim
>dry into a somewhat unattractive oval bowl? And how can one prevent
>this? I think I used to know the answers once, but can't remember! I
>notice that this happens mostly with white stoneware, and only on tall,
>narrow-er bowls, as opposed to shorter, broader bowls. I haven't has
>this problem in a while then BOOM - suddenly I have them.
Jonathan -
Assuming the clay was well wedged and centered, and the bowls were
symmetrical when you finished throwing them, then I believe that the only
variables could be in how you remove the bowls from the wheel, and in the
way you dry them. If you are not doing so, I suggest you throw your bowls
on bats, so that the entire bat may be removed form the wheel, eliminating
any possibility of warpage at that point. If you lift the bowls off the
wheel by hand in such a way that they are misshapen, and then try to
straighten them out on the ware board, they will very likely warp in drying.
And in drying, make sure there are absolutely no air currents around the
bowls, because this is a sure cause of warping.
- Good luck -
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Dai Scott on thu 19 nov 98
Hi, Jon! To prevent bowls from warping, I cover the rim with a piece of
drywall (which is what I use for small wareboards) as soon as they pass the
soft and sticky stage; this is usually the day after throwing. After
trimming, I use drywall over and under, and turn them upside down for a day
or so, then rightside up again. By this time, they're usually leatherhard.
Sometimes I'll stack a couple of extra pieces of drywall on the rim, for
added weight. I also use this method for plates and platters, and I have
very few warped pieces. The only downside is if you've thrown a large
number of bowls/plates, it's kind of a hassle to be having to keep turning
things over, and the drywall squares do take up more room on the shelves
than if you just had bare bowls, but.....
We just keep plugging along, don't we?
Good luck!
Dai Scott in Kelowna, B.C.---still no frost, no snow; just noticed I still
have petunias and pansies in bloom in my sidewalk planter---spooky!
"I love deadlines....I especially like the whooshing sound they make as they
go flying by." Anon.
douglas gray on thu 19 nov 98
Could be in the way you remove them from the wheel.
A trick I like to use for removing pots from the wheel, without the aid of a bat
is to place a thin sheet of newspaper over the opening of the form (the paper
has to be big enough to completely cover the opening).
Then you carfully press the paper into the soft rim until it is stuck all the
way around and seals the air in the form. Then you can lift the form with your
hands and transfer to a wareboard.
The seal should keep air in the form which also acts as a support for the form
so that it will not distort. You do have to be careful peeling the paper off,
or you could ditort the form. And don't try to smooth out the imperfections
left on the rim until the leatherhard stage.
And one more thing. Don't try to reuse the sheet of paper. AS it dries, it
crinkles and makes it more difficult to seal the next form.
If that isn't the problem, then you might check your drying method. Maybe the
pots are drying unevenly.
doug
============================================================================ =)
Douglas E. Gray, Assistant Professor of Art
P.O. Box 100547
Department of Fine Arts and Mass Communication
Francis Marion University
Florence, South Carolina 29501-0547
dgray@fmarion.edu
843/661-1535
Donn Buchfinck on thu 19 nov 98
you said: potterdc@erols.com
What is it that makes a thrown, circular bowl with a nice defined rim
dry into a somewhat unattractive oval bowl? And how can one prevent
this? I think I used to know the answers once, but can't remember! I
notice that this happens mostly with white stoneware, and only on tall,
narrow-er bowls, as opposed to shorter, broader bowls. I haven't has
this problem in a while then BOOM - suddenly I have them.
Jonathan in DC
"Words don't cook rice." Chogyam Trungpa Rimpoche
well I am certainly glad I do not live with this individual, kind of like the
hand that rocks the cradle kind of person/ controling.
I think if you look at some of the best potters around they make pots that
warp.
I even warp my bowls to help them along
Michael Simon makes great oval bowls
I like to make mine into squares and triangles
the best thing about making pots it that they CAN be like people
that is to say that there is no NORMAL person out there, you will probably
find it hard to make a non warping bowl.
when I started making pots I used to throw the pot away if it didn't go around
the wheel perfect when I was trimming it, the grad student who was teaching
me said I should just make it on a lathe. that hit home for me.
it's said that Hamada used to bump his pots with his elbow when he thought no
one was looking so they would have a flaw in them.
I think on some level WE are defined by our flaws, and they are what makes us
unique. same goes for pottery
now I do know an excessive warp can fight the form a potter is working on. I
think you have to look at the clay you are using. if it is comprised of only
fine particles like a porcelain then it will warp in the drying stage if you
make it thin. some type of grog is needed to open up the clay and to cut
down on the shrinkage, this will help in the wet to dry warping. but just
remember that if you are firing the piece on a kiln shelve and if the shelf is
just a little bit off then the bowl will warp durring firing.
So my final opinion is that if it's going to warp, then a potter is best to
figure out how to work with it
the world has enough boring pots out there anyway.
Donn Buchfinck
and words might not cook rice, but to not stimulate the mind with conversation
and thought durring a meal makes the meal only nurishes the body but starves
the mind.
Joseph Herbert on thu 19 nov 98
Jonathan: The warping is either from uneven drying or from a "set" induced in
the bowl when you remove it from the wheel. Either problem can be helped by
sticking a sheet of newspaper to the rim before removing from the wheel. The
tight paper holds the rim in shape and also slows drying somewhat. You can
burnish the rim when it is leather hard to remove the marks made by the paper.
Joseph Herbert
JJHerb@aol.com
Vince Pitelka on thu 19 nov 98
>well I am certainly glad I do not live with this individual, kind of like the
>hand that rocks the cradle kind of person/ controling.
>I think if you look at some of the best potters around they make pots that
>warp.
>I even warp my bowls to help them along
Gee, Donn, you've been so civil lately, and now this. Don't try to talk
Jonathan into letting his bowls warp if he wants round bowls. Of course
there are lots of potters out there who are comfortable with out-of-round
bowls. Nothing wrong with that at all. But if a potter wants round bowls,
why don't we all help him or her achieve that objective, instead of making
rude remarks on Clayart. OK?
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
cheryl sanger on fri 20 nov 98
I was taught a neat trick that seems to help. After throwing the bowl,
after it's not so tacky-wet, but the rim is still damp, gently place a
sheet of typing or drawing paper on the rim. GENTLY run you finger
around the top of the rim to adhere the paper to the damp clay. Leave
in place until the bowl is dry enough to invert and cover with plastic
for slow drying. If the bowl is really large, you can leave the paper
on and cover with plastic. I was told the trapped air pressure
prevents the rim from distorting unevenly. Newspaper does not work
well--too thin. Another good paper trick is to place newspaper--not
heavier paper--under large platters or bowls after they're footed and
you're slowing drying them. The newspaper shrinks and moves as the ware
does, preventing a lot of the cracking you can get from the foot
sticking to the bat.
Jon on sun 22 nov 98
Thanks to everyone for their response to my warping problem!
To clarify, my pots were warping in the drying stage. After reading the
responses, I went and threw several bowls to see what was going on, and noticed
couple of things. First, I use Creative Industry bats, and they stick rather
tightly to the wheel head. I noticed that when I remove the bat, if I'm not
paying attention, the bats bend ever so slightly, enough to bend the rims in
towards each other. Also, I've just moved to a new studio space, and I have
just turned my heater on, so not only do I not know how the air currents flow in
the studio, I don't know how the heater is affecting those air currents.
By the way, the bowls that inspired my questions, I bisqued upside down (their
rims on the shelf), and that seemed to have helped. They just came out of the
glaze firing and look ok.
Thanks again!
Jonathan in DC
>
Tom Wirt on mon 23 nov 98
and I have
>just turned my heater on, so not only do I not know how the air currents flow
in
>the studio, I don't know how the heater is affecting those air currents.
Jon.....If you use ware racks to dry pots on, here's another idea. Cut a piece
of plywood just slightly larger than the top of the rack.
Then take 1x2 furring strips and some 2-mil polyethylene sheeting (from Home
Depot or ??). Cut 4 pieces of the sheeting, about 6 inches longer than the top
to bottom measure, and 8 to 10 inches wider for the width and and 2-3" extra
for the depth.
Cut 2 pieces of 1x2 to the width of the cart and 2 pieces to the depth (front
to back). Now center one width piece of 1x2 on the top of one of the width
pieces of polyethylene. Roll down a couple of turns and screw the 1x2 to the
piece on the top of the ware rack (Dry wall screws work great). Do the same
with the other width piece.
Then do the same rolling thing with the side pieces, but when you screw them to
the top, tuck the extra 4 or 5 inches from the front and back under the 1x2 and
set with a screw.
What you get is kind of a portable cabinet, with sides that can be pulled up for
loading and unloading. I find that in winter, with sides down, you can leave a
freshly thrown piece overnight, uncovered, and it will be ready to flip in the
morning. If something needs extra protection, some 1 mil sheeting can hold a
piece for a week or two.
Tom
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