vince pitelka on sat 28 oct 00
> wondered if anyone had a specific premixed clay they recommend for coiling
&
> throwing large pots that gives little trouble. My trouble may be in
drying
> improperly, but from time to time I will get a crack around the pot where
the
> coil is joined. I have been scoring and adding a little paper clay slip
> which I am going to stop doing to see if that helps at all. Any
suggestions
> or help will be appreciated.
We have a claybody which I use for bonfire, raku, high-fire sculpture, and
for making large coil-built jars, which are either laminated with patchwork
colored clay patterns and electric-fired, or are left un-ornamented and
wood-fired. The formula is equal parts Cedar Heights Goldart stoneware
clay, Christy Minerals Hawthorne Bond fire clay, ball clay, and very fine
grog.
I do not advocate scoring and slurrying between coils. You are much better
off if you smear the coils together aggressively, giving a vessel as strong
as anything thrown on the wheel. You will never have horizontal cracks if
you do this properly. If you go off and leave the vessel for any period of
time, feather the edge of the previous coil to a sharp edge. When you
return to the pot, score the inside, outside, and top of the edge, and apply
slurry liberally. Place the new coil on top of this edge, and paddle it
down from the top slightly with a wooden paddle. Pinch the coil all the way
around, so that it overlaps the previous edge both inside and outside, and
smear it down with a rib both inside and outside. After that, just proceed
normally, smearing the coils in place aggressively by grasping the coil on
the opposite side of the pot, smearing downwards with your thumb on the
inside surface as you lower the coil in place. To do this effectively, it
is best to either walk around the pot as you lower the coil in place, or
else have the pot on a banding wheel so that it will rotate easily. After
every five or six courses of coils, stop and smear them together with a rib
inside and outside, and let the pot stiffen up a bit before proceeding (and
then score and slurry the next coil as described above). This technique
works great, and is always far more effective than scoring and slurrying
every coils in place.
There is something magical about making very large coil vessels. It is a
great experience for everyone, whether you normally handbuild or work on the
wheel. Anyone can make large coil pots using the proper technique. But I
digress.
Best wishes -
- Vince
Vince Pitelka
Home - vpitelka@dekalb.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
http://www.craftcenter.tntech.edu/
CptGoodwood@AOL.COM on sat 28 oct 00
wondered if anyone had a specific premixed clay they recommend for coiling &
throwing large pots that gives little trouble. My trouble may be in drying
improperly, but from time to time I will get a crack around the pot where the
coil is joined. I have been scoring and adding a little paper clay slip
which I am going to stop doing to see if that helps at all. Any suggestions
or help will be appreciated.
Cindy Strnad on sat 28 oct 00
Hi there, Cpt.
My fix-all suggestion for large pots. Add grog and dry slowly. If you like
the clay you're using, there's probably no need to change it. You can add
one or two cups of grog to 25 or 30 lbs of clay during kneading, and it will
make a big difference.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
earthenv@gwtc.net
http://www.earthenvesselssd.com
Mike Gordon on sat 28 oct 00
Hi,
Try usin amaco sculpture mix #412 it has elastic qualities to be good
for throwing as well as sculpting. You may not be moving enough clay
from the top coil down to the one below if it cracking along the seam,
especially if you are expanding the shape. Mike
Khaimraj Seepersad on sat 28 oct 00
Good afternoon to All ,
Cpt. Goodwood ,
for trouble free coiling , I use 60 % very plastic [ sticky ]
earthenware clay and 40 % fine grog [ -200 mesh ] ,
but a small [ 10 % ] of -80 to + 100 mesh can also be
used .
It is used very wet and is self adhesive , no need for
slip .
This dries well , and fires easily .
I can also go as low as 25 to 30 % above clay and
75 to 70 % [ -200 ] fine grog .
Hope this helps .
Khaimraj
-----Original Message-----
From: CptGoodwood@AOL.COM
To: CLAYART@LSV.CERAMICS.ORG
Date: 28 October 2000 12:12
Subject: coiling & throwing large pots
>wondered if anyone had a specific premixed clay they recommend for coiling
&
>throwing large pots that gives little trouble. My trouble may be in drying
>improperly, but from time to time I will get a crack around the pot where
the
>coil is joined. I have been scoring and adding a little paper clay slip
>which I am going to stop doing to see if that helps at all. Any
suggestions
>or help will be appreciated.
>
>___________________________________________________________________________
___
>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.
>
Donald G. Goldsobel on sat 28 oct 00
>wondered if anyone had a specific premixed clay they recommend for coiling
>
My experience has been that if you work without letting the clay get dry,
dont do anything except lay the coil in an even , no air bubles position,
then join on the inside and ouside with downward pushing with the fingers.
Fresh clay to fresh clay joins really well. If the coils have dried score
ans slip with plain vinegar.. Cover loosly with plastic when drying or
cover with a towel and then with plastic. The towl prevents condensed
moisture from going back to the clay from the plastic.
Good luck
Donald in the San Fernando Valley
>
Jeff Campana on sat 28 oct 00
I don't know much about premixed clays, but I would recommend looking for a fairly
un-plastic clay. I mixed a batch that had over 70 percent fireclay.
Coil-throwing does not require a highly plastic throwing body. In fact, the less
plasticity,(less shrinkage) the less chance of cracking, warping, and you get a
bigger pot after drying/firing. Look in you catalog or whatever at the shrinkage
rates. The lower, the better. also, it you add your coils while the pot is still
moist, no need for scoring/slipping, and it won't crack in the way you described.
hope this helps,
Jeff Campana
>
>
> >wondered if anyone had a specific premixed clay they recommend for coiling
> &
> >throwing large pots that gives little trouble. My trouble may be in drying
> >improperly, but from time to time I will get a crack around the pot where
> the
> >coil is joined. I have been scoring and adding a little paper clay slip
> >which I am going to stop doing to see if that helps at all. Any
> suggestions
> >or help will be appreciated.
> >
> >___________________________________________________________________________
> ___
> >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.
DLUmthun@AOL.COM on sat 28 oct 00
Vingear seems to work well for me--brushed on before I add the slip.
You might try it.
Plain old table vingear.
Hope it helps.
iandol on sun 29 oct 00
Can someone explain to me why adding grog to a clay is the answer. What =
qualities are being altered?
As I understand it, none plastic materials add nothing to the strength =
of a plastic clay, they do not enable higher pots. They may even reduce =
compressive strength and reduce the ultimate height to which any pot can =
be built. To increase the ability of a clay to withstand forces which =
cause it to distort, shrink or crack due to excessive shrinkage it is =
necessary to remove water.=20
It seems to me that the only thing the addition of none plastic =
components achieve is the redistribution of water from the plastic part =
to the none plastic part. Coarse bisque grog acts like a sponge and =
achieves this, reducing the water of plasticity of the clay component.=20
Is this correct.
Ivor Lewis. Redhill, South Australia.
Carol Birdsong on sun 29 oct 00
Oops! Didn't intend to give incorrect advice. After reading Vince's post
this a.m. I realize I have always thought of 'smearing the coils together'
as 'scoring'. It is best not to score between the coils. If you follow
Vince's instructions you shouldn't have any problems making large coil
thrown pots.
Good luck,
Carol
Veena Raghavan on sun 29 oct 00
Message text written by Ceramic Arts Discussion List
> coil is joined. I have been scoring and adding a little paper clay slip
> which I am going to stop doing to see if that helps at all. Any
suggestions<
I don't know if you have already tried this, but I like throwing the coil I
am going to add on. I cover the rim of the base pot with plastic to keep it
moist. I then throw the coil I am going to add on (on a bat), having
carefully measured the inside and outside of the rim of the base pot. The
top of the coil should have a rim that is a little thicker than the rim of
the base pot. I then uncover the base pot, invert the thrown coil fitting
it carefully over the rim, so it is centered, evenly over the base pot and
press down lightly. I then wire off the the coil from the bat and finger
the coild onto the base pot inside and outside, until it is joined all
around. I then throw the coil onto the the base pot as you would any coil.
This way, I have an even coil, partly thrown and can do this successively
until I have the height I want. I have never had a problem with cracks at
the joints. I feel that slow drying helps the moisture even out between the
two sections. I use this method with my usual cone 6 throwing clay and work
in both stoneware and cone 6 porcelain.
Hope this helps and good luck.
Veena
Veena Raghavan
75124.2520@compuserve.com
Gail Dapogny on sun 29 oct 00
Veena,
Was interested in your "thrown coil" technique. How thick is the base pot
at this point both at the joining place (top) and lower than that? I.e.
Will more than the top inch or so still need to be pulled up more?
Also, do you let it set up some before joining the two parts?
Thanks.
----Gail Dapogny
Veena said: >I don't know if you have already tried this, but I like
throwing the coil I
>am going to add on. I cover the rim of the base pot with plastic to keep it
>moist. I then throw the coil I am going to add on (on a bat), having
>carefully measured the inside and outside of the rim of the base pot. The
>top of the coil should have a rim that is a little thicker than the rim of
>the base pot. I then uncover the base pot, invert the thrown coil fitting
>it carefully over the rim, so it is centered, evenly over the base pot and
>press down lightly. I then wire off the the coil from the bat and finger
>the coild onto the base pot inside and outside, until it is joined all
>around. I then throw the coil onto the the base pot as you would any coil.
>This way, I have an even coil, partly thrown and can do this successively
>until I have the height I want. I have never had a problem with cracks at
>the joints. I feel that slow drying helps the moisture even out between the
>two sections. I use this method with my usual cone 6 throwing clay and work
>in both stoneware and cone 6 porcelain.
Khaimraj Seepersad on mon 30 oct 00
Good Morning to All ,
Ivor Lewis ,
I use cullet or pitchers [ self grog ] as my grog .
Both open the extremely plastic [ sticky ] clay
I use , providing a passage for water to get
out .
By means as you have stated below , or along the
outside of the ground cullet [ -200 mesh ] , the
water gets out .
[ grog % from 40 to 75 . at -80 to -200 mesh ]
Pitchers do not weaken the body , as they take
part in the equation as the earthenware bodies
reach vitrification [ 1130 to 1150 deg.c ]
The cullet forms a glass matrix linking throughout
the body . I am not sure how much clay
particle to cullet melting maybe taking place as I
fire this body to 980deg.c .
However , sticky plastic, finely , particled earthenware
clay maybe more capable of self fluxing at lower
temperatures.
[ I draw my conclusion from the -600 mesh Silica
self fluxing information ].
There are also %s of 5 to 10 % CaC03 in our clays.
We do have a plastic , finely particled off white clay ,
off white when fired to maturity . That will become
vitreous at 1200 to 1230 deg.c , sometimes as
low as 1180 deg.c .
Self grog works very well here from as low as 900 to
950 deg.c . So there maybe self fluxing taking place
early o'clock .
This clay also has some mica content .
Hope this helps ,
Khaimraj
-----Original Message-----
From: iandol
To: CLAYART@LSV.CERAMICS.ORG
Date: 30 October 2000 4:13
Subject: Coiling & throwing large pots
Can someone explain to me why adding grog to a clay is the answer. What
qualities are being altered?
As I understand it, none plastic materials add nothing to the strength of a
plastic clay, they do not enable higher pots. They may even reduce
compressive strength and reduce the ultimate height to which any pot can be
built. To increase the ability of a clay to withstand forces which cause it
to distort, shrink or crack due to excessive shrinkage it is necessary to
remove water.
It seems to me that the only thing the addition of none plastic components
achieve is the redistribution of water from the plastic part to the none
plastic part. Coarse bisque grog acts like a sponge and achieves this,
reducing the water of plasticity of the clay component.
Is this correct.
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.
Tom Wirt/Betsy Price on mon 30 oct 00
Ivor...
Being far from an expert on this, but having studied it a lot over the
last 3 years, I'm going to take a stab at it. You are right, in my
reading and experience, that adding grog does not necessarily add size
throwing capability to a clay body, unless the clay body was not
properly formulated to begin with.
Most clay bodies offered by most (BUT DEFINITELY NOT ALL) suppliers
were formulated when some potter brought in a recipe, they mixed it,
someone liked it, and they appropriated it, with or without asking or
crediting. The problem is that most of these bodies were formulated
by dumping various clays into a bucket mixing, throwing (or
handbuilding) maybe adjusting and then using. Rarely were they tested
for absorption and shrinkage or strength at various stages.
The best way I've found to develop clay bodies is to get pure clays,
mix them to usable consistency, and then use them as a pure clay to
throw with or handbuild....and then see how the work fares through the
process. You need to also do shrinkage/absorption test bars at the
same time. You will then discover the working attributes of a given
clay.
Then, given your target attributes, you mix the clays together and
each contributes whatever it had as a pure clay. One of the things you
are looking for is to get a variety of particle sizes in the
body...this is where a body really gets it's working characteristics -
strength, plasticity, feel, etc. Grog CAN add the impression of
improved workability if the body isn't properly formulated in the
first place. And it will improve the drying characteristics of some
clays...especially those with small particle sizes.
Then once you get a basic working body, add ingredients like
Pyrophyllite, Kyanite for thermal shock improvement. Feldspar, talc,
pyrophyllite, wollastonite for melt and silica handling properties.
Maybe some clean, virgin grog for improving drying characteristics
although it would be better to add a large particle plastic clay to do
this than a non-plastic grog..
This is greatly simplified, but hopefully you see the process.
But, you are right grog is non-plastic and will decrease the
cohesiveness/plasticity of the body. Take a fine ball clay and mix
some up as a pure clay. Then take the same clay and mix it with 10%
fine grog. Roll pencil size rods and bend. You'll see considerably
more cracking in the grogged sample.
>From: iandol
>Subject: Coiling & throwing large pots
>Can someone explain to me why adding grog to a clay is the answer.
What qualities are being altered?
>As I understand it, none plastic materials add nothing to the
strength of a plastic clay, they do not enable >higher .pots. They may
even reduce compressive strength and reduce the ultimate height to
which any pot can >be built.
>It seems to me that the only thing the addition of none plastic
components achieve is the redistribution of >water from the plastic
part to the none plastic part. Coarse bisque grog acts like a sponge
and achieves this, >reducing the water of plasticity of the clay
component.
Conventional wisdom suggests that the grog doesn't act so much as a
sponge, as it adds channels for the water to escape from the clay as
it dries and is fired. The difficulty here is that those large
particles can also offer the starting points for body cracks in the
finished pot because the other materials don't fit closely with those
large particles..
Hopefully Jonathan Kaplan, Ron Roy, Tom B and others truly versed in
clay body development will weigh in here and correct me if I've erred
in my understanding.
One thing I have learned, is that most who have done significant body
development (clay) have a group of materials they are familiar with
and will tend to use those materials in just about everything. To
break a new material into the mix is difficult and I understand why.
The physical and chemical properties are complex and when you find
something that works, you tend not to disrupt it by much. If someone
tells you to put in a given material, ask why. Especially if it is
non-plastic.
Clays, after formulating, seem to be much the same. They feel similar
after firing, may have similar appearances. The focus is on the way
the end product feels and looks. The only way to actually find out
what a clay body is, is to test it. As Ron R has so often pointed
out, there is no such thing as a 4 or 5 cone range for a body. Yes
the clay will fire over that range, and appear to be solid. But at
one end it will be overabsorptive and structurally weak, and maybe at
the other end over fired, brittle and totally non-absorptive.
Tom Wirt
PS Ivor...Thank you for doing my homework. Your article in Pottery
Making Illustrated re: where the clay goes when throwing was very
helpful...documented what I suspected was happening in throwing.
CINDI ANDERSON on sun 5 nov 00
Hi Vince,
Do you have any of these great pots on a website somewhere?
Thanks!
vince pitelka wrote:
> > wondered if anyone had a specific premixed clay they recommend for coiling
> &
> > throwing large pots that gives little trouble. My trouble may be in
> drying
> > improperly, but from time to time I will get a crack around the pot where
> the
> > coil is joined. I have been scoring and adding a little paper clay slip
> > which I am going to stop doing to see if that helps at all. Any
> suggestions
> > or help will be appreciated.
vince pitelka on mon 6 nov 00
> Hi Vince,
> Do you have any of these great pots on a website somewhere?
> Thanks!
Cindy -
I don't have a website yet, but you can see several of my colored clay
laminated jars at Michael McDowell's website at http://www2.memes.com/mmpots
Click on the workshop link, and then click on "Handbuilding: Tricks of the
Trade."
Thanks for asking -
- Vince
Vince Pitelka
Home - vpitelka@dekalb.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
http://www.craftcenter.tntech.edu/
| |
|
