Joyce Lee on wed 26 nov 97
I've just reread my folders of Clayarters' comments on cracking,
warping, dunting of plates and platters. If the answer to my concern is
there, I'm missing it. I'm just now finally at the stage where I have
managed to produce a few sorta' decent looking large plates, or
platters. I let them dry until well into the bone dry stage. They
always survive the bisque firing looking fine. I fire on sand, position
them toward the top of the kiln, don't place other pots on top and
pretty much allot one shelf to one large plate. Sometimes I can see
after the bisque firing details that I missed in the greenware. Some of
the rims are a little thin or a little thick, but they basically look
okay to my untutored eyes. However, very few survive the ^10 reduction
glaze firing. They warp or the rims just turn down. No cracks, though.
I intend to continue reading about plates and to go on firing them into
the next world, if needed, in order to get them right. (You reckon hell
is one giant kiln with a little corner for not-too-badly-behaved
potters?) But I hate to just keep repeating the same mistakes. Any
suggestions would be taken to heart, applied and results reported.
Joyce
Not intentionally trying to offend anyone in the Mojave
Dannon Rhudy on thu 27 nov 97
Joyce, if the rims warp or droop without cracking, sounds like
you don't have enough rise in the rim and/or the foot is too
small. Usually the foot of a plate or platter is placed
approximately where the rise of the rim begins, if it is a
flat bottomed plate/platter. If the foot is in the right place,
then look at the "rise" of the rim. A crisp, continuous rise
works best, and is least likely to warp. It also helps to
slightly compress and then round the edge, making it just a bit
thicker at that point. If you pull up the rim and then flatten
or straigten it along the edge, warping and drooping are much
more likely. Take a look at commercial ones, note the angle
of rise - keep in mind that commercial plates often are not
fired to so high a temperature, though.
Dannon Rhudy
potter@koyote.com
----------------------------Original
message----------------------------
I've just reread my folders of Clayarters' comments on cracking,
warping, dunting of plates and platters. If the answer to my
concern is
there, I'm missing it. I'm just now finally at the stage where I
have
managed to produce a few sorta' decent looking large plates, or
platters. I let them dry until well into the bone dry stage. They
always survive the bisque firing looking fine. I fire on sand,
position
them toward the top of the kiln, don't place other pots on top and
pretty much allot one shelf to one large plate. Sometimes I can
see
after the bisque firing details that I missed in the greenware.
Some of
the rims are a little thin or a little thick, but they basically
look
okay to my untutored eyes. However, very few survive the ^10
reduction
glaze firing. They warp or the rims just turn down. No cracks,
though.
I intend to continue reading about plates and to go on firing them
into
the next world, if needed, in order to get them right. (You reckon
hell
is one giant kiln with a little corner for not-too-badly-behaved
potters?) But I hate to just keep repeating the same mistakes.
Any
suggestions would be taken to heart, applied and results reported.
Joyce
Not intentionally trying to offend anyone in the Mojave
John Christie on thu 27 nov 97
Joyce Lee says of her platters -
"However, very few survive the ^10 reduction
glaze firing. They warp or the rims just turn down."
Most pots are thrown so that the outside shape more or less echoes the inside
with a slight thickening towards the base. Not so plates - if you throw them
like that, they'll look OK until the glaze firing when the rims will tend to
drop and the base of the plate will rise at the centre and become convex.
The way to avoid this is to throw the plate so that the outside of the plate
wall is convex almost all the way to the edge of the rim (if it echoed the
inside shape it would be concave). To achieve this:
1. Throw the base - it's a good idea to check the thickness in the
centre with a probe (needle in a cork, perhaps) - if it's too thin, it may
warp, too thick, it'll be heavy.
2. Throw a low wall with a fat bulge at the top.
3. Throw the bulge outwards into a flange keeping a good thickness of
clay at the change of direction to support the flange. This extra thickness
supports the flange on the wheel as well as in the firing.
4. When turning the footring, try to keep the footring in line with the
thrust of the platter wall.
I hope this is helpful - it's a challenge to describe the process without
using a sectional diagram!
John Christie
Elgin, Scotland
JockyC@aol.com
David Hendley on thu 27 nov 97
Joyce,
it sounds like a clay problem to me.
Some claybodies are prone to warping, some are not.
With some claybodies you can have that rim
3 inches wide and at 'near horizontal', and it will stay put.
With others, you will end up with a turned down rim after a high fire.
I have three suggestions for you:
~~Change to a less vitrious claybody. Generally, slightly porous
stoneware bodies with some large particle sizes in the mix are
the most stable. Porcelain is at the other end of the spectrum.
~~Anticipate the movement by throwing the rims higher than
you want them, and with the movement in the firing
they will end up where you want them. Make sure the platter
is thick enough for its size, make it maybe even a little thicker
(bottom and rim) to combat warping.
~~Make 'firing rings' that the platters will fit into for the glaze firing.
Just throw rings of clay the appropriate height and diameter. The rings
will support the platter rims during firing and keep them from turning down.
This is sometimes the only way that porcelain platters can be successfully
fired.
Sometimes things that seem pretty straightforward
end up being more involved than you think...
Keep trying,
David Hendley
Maydelle, Texas
See David Hendley's Pottery Page at
http://www.sosis.com/hendley/david/
At 08:48 AM 11/26/97 EST, you wrote:
>----------------------------Original message----------------------------
>I've just reread my folders of Clayarters' comments on cracking,
>warping, dunting of plates and platters. If the answer to my concern is
>there, I'm missing it. I'm just now finally at the stage where I have
>managed to produce a few sorta' decent looking large plates, or
>platters. I let them dry until well into the bone dry stage. They
>always survive the bisque firing looking fine. I fire on sand, position
>them toward the top of the kiln, don't place other pots on top and
>pretty much allot one shelf to one large plate. Sometimes I can see
>after the bisque firing details that I missed in the greenware. Some of
>the rims are a little thin or a little thick, but they basically look
>okay to my untutored eyes. However, very few survive the ^10 reduction
>glaze firing. They warp or the rims just turn down. No cracks, though.
>I intend to continue reading about plates and to go on firing them into
>the next world, if needed, in order to get them right. (You reckon hell
>is one giant kiln with a little corner for not-too-badly-behaved
>potters?) But I hate to just keep repeating the same mistakes. Any
>suggestions would be taken to heart, applied and results reported.
>
>Joyce
>Not intentionally trying to offend anyone in the Mojave
>
>
David Hendley
Maydelle, Texas
See David Hendley's Pottery Page at
http://www.sosis.com/hendley/david/
Ray Carlton on thu 27 nov 97
hi joyce.. you need to build your plates a bit heavier between the foot
and rim or get a higher firing clay body
cheers
At 08:48 26/11/97 EST, you wrote:
>----------------------------Original message----------------------------
>I've just reread my folders of Clayarters' comments on cracking,
>warping, dunting of plates and platters. If the answer to my concern is
>there, I'm missing it. I'm just now finally at the stage where I have
>managed to produce a few sorta' decent looking large plates, or
>platters. I let them dry until well into the bone dry stage. They
>always survive the bisque firing looking fine. I fire on sand, position
>them toward the top of the kiln, don't place other pots on top and
>pretty much allot one shelf to one large plate. Sometimes I can see
>after the bisque firing details that I missed in the greenware. Some of
>the rims are a little thin or a little thick, but they basically look
>okay to my untutored eyes. However, very few survive the ^10 reduction
>glaze firing. They warp or the rims just turn down. No cracks, though.
>I intend to continue reading about plates and to go on firing them into
>the next world, if needed, in order to get them right. (You reckon hell
>is one giant kiln with a little corner for not-too-badly-behaved
>potters?) But I hate to just keep repeating the same mistakes. Any
>suggestions would be taken to heart, applied and results reported.
>
>Joyce
>Not intentionally trying to offend anyone in the Mojave
>
>
raycarlt@valylink.net.au
Ray Carlton
McMahons Creek Victoria Australia 3799
Ron Roy on thu 27 nov 97
Hi Joyce,
At least you know your clay is getting vitrified (soft)
To keep plates from warping trim the food rings dead level and fire them on
FLAT shelves - if the foot ring is uneven it will try to touch the shelf
everywhere at the end of the glaze fire. If the shelf is bent then the
plate will again try to touch the shelf everywhere and take on the shape of
that shelf.
If a plate or bowl is thicker on one side than the other the thin side will
move in response to gravity before the thicker side - improve your throwing
and/or trimming.
Extending the rim too far from the foot makes it difficult to solve the
warping - there is always some uneveness and the thiner side will start to
drop first. The softer the clay at top temp the more careful you need to
be. Porcelain is usually softer because it is traditionally more vitrified
than stoneware.
Rims are always a balance between falling the right amount and too much.
Mine always fall a certain amount and I count on it. I cheat a little and
keep the rim thicker where it joins the foot - tapering it towards the
rim.
Break some of those warped plates in half - and have a look at why it happened.
>----------------------------Original message----------------------------
>I've just reread my folders of Clayarters' comments on cracking,
>warping, dunting of plates and platters. If the answer to my concern is
>there, I'm missing it. I'm just now finally at the stage where I have
>managed to produce a few sorta' decent looking large plates, or
>platters. I let them dry until well into the bone dry stage. They
>always survive the bisque firing looking fine. I fire on sand, position
>them toward the top of the kiln, don't place other pots on top and
>pretty much allot one shelf to one large plate. Sometimes I can see
>after the bisque firing details that I missed in the greenware. Some of
>the rims are a little thin or a little thick, but they basically look
>okay to my untutored eyes. However, very few survive the ^10 reduction
>glaze firing. They warp or the rims just turn down. No cracks, though.
>I intend to continue reading about plates and to go on firing them into
>the next world, if needed, in order to get them right. (You reckon hell
>is one giant kiln with a little corner for not-too-badly-behaved
>potters?) But I hate to just keep repeating the same mistakes. Any
>suggestions would be taken to heart, applied and results reported.
>
>Joyce
>Not intentionally trying to offend anyone in the Mojave
Ron Roy
93 Pegasus Trail
Scarborough,Canada
M1G 3N8
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
Joseph Herbert on sun 30 nov 97
I would like to point out the possibility that we are misled by the
dinnerware industry into having unreasonable expectations for our plates and
platters. The "Fine China" people often fire their plates to the highest
temperature first, before glazing. This unglazed firing allows the plate to
be totally supported by fine silica sand, or some other material, so it holds
its shape during its most vulnerable time. Such a plate can be very shallow
and very thin.
In a plate that is to be fired in a more normal (for studio types) way, the
rim must act as a tension band to keep the side of the plate stable. If the
shape of the plate is such that the rim only has to expand a little to go
past horizontal and flop down, it can very easily happen. If the side of the
plate is more erect, there is much less chance of the flop happening.
Joseph Herbert
JJHerb@aol.com
Kris Baum on mon 1 dec 97
I was interested to read about the placement of the foot, as that was
new to me. However, I was taught to thicken the side of the plate
slightly just below the point where the rim would start to flare out,
and to make the angle of the rim more upright (i.e., pointing in a
more vertical direction) than you want it to end up, to allow for
some sagging in the kiln. Hope this helps, and I guess I'll try
moving the feet on my platters out more towards the rims!
> ----------------------------Original message----------------------------
>
>
> Joyce, if the rims warp or droop without cracking, sounds like
> you don't have enough rise in the rim and/or the foot is too
> small. Usually the foot of a plate or platter is placed
> approximately where the rise of the rim begins, if it is a
> flat bottomed plate/platter. If the foot is in the right place,
> then look at the "rise" of the rim. A crisp, continuous rise
> works best, and is least likely to warp. It also helps to
> slightly compress and then round the edge, making it just a bit
> thicker at that point. If you pull up the rim and then flatten
> or straigten it along the edge, warping and drooping are much
> more likely. Take a look at commercial ones, note the angle
> of rise - keep in mind that commercial plates often are not
> fired to so high a temperature, though.
>
> Dannon Rhudy
> potter@koyote.com
>
> ----------------------------Original
> message----------------------------
> I've just reread my folders of Clayarters' comments on cracking,
> warping, dunting of plates and platters. If the answer to my
> concern is
> there, I'm missing it. I'm just now finally at the stage where I
> have
> managed to produce a few sorta' decent looking large plates, or
> platters. I let them dry until well into the bone dry stage. They
> always survive the bisque firing looking fine. I fire on sand,
> position
> them toward the top of the kiln, don't place other pots on top and
> pretty much allot one shelf to one large plate. Sometimes I can
> see
> after the bisque firing details that I missed in the greenware.
> Some of
> the rims are a little thin or a little thick, but they basically
> look
> okay to my untutored eyes. However, very few survive the ^10
> reduction
> glaze firing. They warp or the rims just turn down. No cracks,
> though.
> I intend to continue reading about plates and to go on firing them
> into
> the next world, if needed, in order to get them right. (You reckon
> hell
> is one giant kiln with a little corner for not-too-badly-behaved
> potters?) But I hate to just keep repeating the same mistakes.
> Any
> suggestions would be taken to heart, applied and results reported.
>
> Joyce
> Not intentionally trying to offend anyone in the Mojave
>
>
===============================================
Kris Baum, Shubunkin Pottery
mailto:shubunki@erols.com
===============================================
shelford on mon 1 dec 97
I've been out of things for a bit, so if this point was made before, forgive
me. When I do plates, apart from compressing and thickening a bit on the
rim (I think someone - Dannon? - mentioned this), I also introduce a
not-quite-perceptible curve upward in the flat rim area (if it is wide). I
had some notion that this would provide a bit of structural strength against
flopping, and it certainly seems to work. But I do mean virtually invisible
- otherwise you end up with two bowls in one!
This, by the way, is attempting to support and elaborate what Joseph Herbert
was saying:
>If the
>shape of the plate is such that the rim only has to expand a little to go
>past horizontal and flop down, it can very easily happen. If the side of the
>plate is more erect, there is much less chance of the flop happening.
- Veronica
___________________________________________
Veronica Shelford
e-mail: shelford@island.net
s-mail: P.O. Box 6-15
Thetis Island, BC V0R 2Y0
Tel: (250) 246-1509
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