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clay thickness using a slab roller

updated wed 26 oct 11

 

Rlucas on sun 23 oct 11


I have used my slab roller and the "forms" (can't remember the name of them=
)
to make these nice sort of artsy oval platters but have had
problems with them warping. I would guess off the top of my head they are
too thin.

Can anyone advise me the thickness to "roll" out on my slab roller?

Actually any item, bowl, platter, plate etc. If they would all be the same
thickness.

Thank you very much, in advance.

Verna

KATHI LESUEUR on sun 23 oct 11


On Oct 23, 2011, at 6:26 PM, Rlucas wrote:

> I have used my slab roller and the "forms" (can't remember the name of =
=3D
them)
> to make these nice sort of artsy oval platters but have had
> problems with them warping. I would guess off the top of my head they =
=3D
are
> too thin.
>=3D20
> Can anyone advise me the thickness to "roll" out on my slab roller?
>=3D20
> Actually any item, bowl, platter, plate etc. If they would all be the =3D
same
> thickness.>>
>=3D20


I make lots of slab items. My slabs vary in thickness from 3/16" for my =3D
smallest tray, to 1/4" for my medium size trays, to about 5/16 for my =3D
largest platters. Everything but the largest platters are dried face =3D
down on blue styrofoam sheets. The largest platters are dried face up on =
=3D
styrofoam with a thin sheet of plastic over them until leather hard. I =3D
also wax the edges of the largest platters to slow down the drying.

However, I think the clay is more a factor in good slab than anything =3D
else. I use Balcones clay from Armadillo in Austin, TX. I started using =3D
that clay when I lived in south Texas and now ship it up to Michigan =3D
5000# at a time. I think it's worth it. I love this clay and can push it =
=3D
farther than any other clay I've used.

KATHI LESUEUR
http://www.lesueurclaywork.com

Eva Gallagher on sun 23 oct 11


I have found that dropping the slabs on a piece of dry wall first on the
floor several times first really helps to prevent warping. This compresses
the clay. I think this was mentioned on Clayart several years ago, but have
heard it from several other sources since. Once the clay is formed into the
platter I then tamp the bottom over several days with a tamping bag (a clot=
h
bag filled with sand). I also dry the piece on drywall lined with newspaper
which I change several times as the piece dries. This way the bottom gets
dried out as well as the rest. If the platter is especially large I place a
weight on the bottom - piece of clay wrapped in plastic to fit over most o=
f
the bottom which I lift every now and then to reduce the tension as the cla=
y
dries. A lot of trouble but then I find that platters do not warp in my
wood kiln where there is very uneven heat and things tend to warp.
Eva Gallagher
http://newfoundoutpotter.blogspot.com/
http://www.valleyartisans.com/gallagher/Gallagher.htm

----- Original Message -----
From: "KATHI LESUEUR"
To:
Sent: Sunday, October 23, 2011 6:58 PM
Subject: Re: clay thickness using a slab roller


On Oct 23, 2011, at 6:26 PM, Rlucas wrote:

> I have used my slab roller and the "forms" (can't remember the name of
> them)
> to make these nice sort of artsy oval platters but have had
> problems with them warping. I would guess off the top of my head they ar=
e
> too thin.
>
> Can anyone advise me the thickness to "roll" out on my slab roller?
>
> Actually any item, bowl, platter, plate etc. If they would all be the sam=
e
> thickness.>>
>

Eric Koenig on sun 23 oct 11


To me, when I think of warping of a clay wall of any kind, i think of non=
=3D
-
uniform shrinkage; and when I think of non-uniform shrinkage, I think mos=
=3D
tly of=3D20
non-uniform drying.=3D20=3D20

For example:=3D20

Take a slab lying on a countertop. Air can't get under it, so it mostly =
=3D
dries on=3D20
the upper, exposed surface. So only the top surface shrinks and it curls=
=3D
=3D20
upward.

your warpage may have nothing to do with wall thickness, unless that=3D20
thickness is non-uniform throughout your piece; thin parts dry faster tha=
=3D
n=3D20
thicker parts, especially if they dry quickly and there is no time for ca=
=3D
pillary=3D20
suction to draw water out of the thick parts.

One way to get around all that may be to wrap your ware loosely in plasti=
=3D
c=3D20
and maybe also block it up so that air can get under the piece. The plas=
=3D
tic=3D20
prevents errant drafts (say, from heaters or air conditioners or swamp co=
=3D
olers=3D20
or open windows, for example) from hitting your piece. The isolated clim=
=3D
ate=3D20
around your ware makes for uniform high humidity, which means the piece=3D2=
0=3D

dries slower and moisture has a chance to migrate from wetter to drier re=
=3D
gions=3D20
in the clay.

Anyway, that's my two cents.

Eric


Photo of clay curling up on a drying mud flat:

http://farm5.static.flickr.com/4120/4920056082_68a42c0c3f.jpg

Eric Koenig on mon 24 oct 11


Ms Gallagher reminded me of the importance of the alignment of the clay=3D2=
0=3D

particles.=3D20=3D20

Are you turning your slab to face a different direction and flipping it e=
=3D
very time=3D20
you make a pass with the roller?=3D20=3D20

Clay particles are platey, so they preferentially align according to the=3D=
20=3D

compressional force put on them. If one runs the slab through the roller=
=3D
in the=3D20
same orientation every time, the clay will shrink mostly in one direction=
=3D
, not=3D20
uniformally in all directions.

E

Clayart Friends on mon 24 oct 11


Many potters make the mistake to take clay straight from a bag, slice it
into a slab and then roll out withouth wedging to get a uniform moisture
content. The worst results from this mistake is cracking, lesser severe
results will be warping.Another thing that one should consider is to throw
slabs evenly in all directions so that it can shrink back from all
directions. That will cause less stress on a slab and help to keep it more
uniform.
If one take all the mentioned remarks form other potters into account, thro=
w
the thickness of the slab to correspond with the size of the object, the
problems should be eliminated.
Best wishes,
Antoinette Badenhorst
www.porcelainbyAntoinette.com
On Sun, Oct 23, 2011 at 9:13 PM, Eva Gallagher wrote:

> I have found that dropping the slabs on a piece of dry wall first on the
> floor several times first really helps to prevent warping. This compresse=
s
> the clay. I think this was mentioned on Clayart several years ago, but ha=
ve
> heard it from several other sources since. Once the clay is formed into t=
he
> platter I then tamp the bottom over several days with a tamping bag (a
> cloth
> bag filled with sand). I also dry the piece on drywall lined with newspap=
er
> which I change several times as the piece dries. This way the bottom gets
> dried out as well as the rest. If the platter is especially large I place=
a
> weight on the bottom - piece of clay wrapped in plastic to fit over most
> of
> the bottom which I lift every now and then to reduce the tension as the
> clay
> dries. A lot of trouble but then I find that platters do not warp in my
> wood kiln where there is very uneven heat and things tend to warp.
> Eva Gallagher
> http://newfoundoutpotter.**blogspot.com/t.com/>
> http://www.valleyartisans.com/**gallagher/Gallagher.htmartisans.com/gallagher/Gallagher.htm>
>
> ----- Original Message -----
> From: "KATHI LESUEUR"
> To:
> Sent: Sunday, October 23, 2011 6:58 PM
> Subject: Re: clay thickness using a slab roller
>
>
> On Oct 23, 2011, at 6:26 PM, Rlucas wrote:
>
> I have used my slab roller and the "forms" (can't remember the name of
>> them)
>> to make these nice sort of artsy oval platters but have had
>> problems with them warping. I would guess off the top of my head they a=
re
>> too thin.
>>
>> Can anyone advise me the thickness to "roll" out on my slab roller?
>>
>> Actually any item, bowl, platter, plate etc. If they would all be the sa=
me
>> thickness.>>
>>
>>

KATHI LESUEUR on tue 25 oct 11


On Oct 24, 2011, at 10:51 PM, Clayart Friends wrote:

> Many potters make the mistake to take clay straight from a bag, slice =3D
it
> into a slab and then roll out withouth wedging to get a uniform =3D
moisture
> content. The worst results from this mistake is cracking, lesser =3D
severe
> results will be warping.Another thing that one should consider is to =3D
throw
> slabs evenly in all directions so that it can shrink back from all
> directions. That will cause less stress on a slab and help to keep it =
=3D
more
> uniform.>>>>


You have just described how I make slabs. Straight out of the ball. This =
=3D
is one of the reasons why I say that the main key to slab work is the =3D
clay you use. I don't have cracking and warping. Probably half of my =3D
production is slab work and I make my living at this. I go through =3D
almost 5 tons of clay a year. If you are having problems with slab, try =3D
another clay.

KATHI LESUEUR
http://www.lesueurclaywork.com=3D