Karen Nakakihara on sat 6 jan 07
Greetings from Alpine Texas!
Well, I finished my class. I was struggling to make bakers and casseroles and
asked Clayarters for help. I still didn't make my numbers - only 5 out of 40
made it. I tried double-coning, wrapping the rim with plastic, slow drying,
cutting it off the bat, letting it dry on the bat, finishing the bottom with a
rib using alittle water, compressing the clay in one direction, opening with my
fist, etc. - the only suggestions I didn't try were putting a shower cap on my
bakers, and using plaster bats. I figure it must be a problem with the way I'm
compressing the clay. Thought I'd try a new clay even though my classmates
didn't have as many problems as I had. Some of my classmates thought maybe I
was trying too hard. I'll keep trying to find a solution.
Thanks to everyone who so generously shared their knowledge and experience with me.
Cheers,
Karen Nakakihara
Alpine, Texas, the "Palm Springs of the southern Rockies"
Michael Wendt on mon 8 jan 07
Karen,
To add to your list of things to try,
If you are throwing on the bat, try
stack and slam wire wedging.
The idea is to create a laminar
structure that "heads cracks off
at the pass". I think poor clay uniformity
is at the heart of many cracking
and warping problems. Wire wedging
done with 30 doublings creates over
one billion layers and in this way makes
clay so uniform it shrinks in a uniform
manner.
It is also structures so that all layers
are in the same plane as the wheel head
so that there are no nucleation points
for cracks to start.
See PMI March-April 2006 for
detailed instructions.
Side note: I got a DVD recorder so
the plate and platter video is now
also available on DVD and it
contains the wire wedging technique
in full detail along with trimming
and glazing plates and platters
for $13.00 which includes both
purchase price and shipping in the US.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, ID 83501
USA
208-746-3724
http://www.wendtpottery.com
wendtpot@lewiston.com
The Goodsons on mon 8 jan 07
Greeting to you, Karen.
Good for you_ I am glad that you are set on finding a solution. You
know, if making pots were easy, we probably would get bored and go do
something else. I can tell by your determination that you are going to
get this.
There is an excellent article on the subject of s-cracks in "Pottery
Making Illustrated" magazine from the Fall of 2000. It is an article by
Jeff Zamek. The most important thing that I learned from this article
is the importance of coning the clay properly if you do cone it. When I
am throwing small things, I don't cone my clay. If I am making larger
things I do. Here is the important thing from the article. *"If you
create a recessed or a concave area on the top of the cone, the clay
platelets will not align correctly." Jeff Zamek. *In other words be
very careful when centering and coning not to let the center or the top
shrink down inside itself (if you do you will probably get an s-crack).
Keep trying, but try making some small casseroles (individual) and
working your way up to larger ones. I wish you great success!!
Sincerely,
Linda Goodson
208 East Rhodes Street
Lincolnton, NC 28092
goodfun@charter.net
The Goodsons on mon 8 jan 07
Karen Nakakihara wrote:
> Greetings from Alpine Texas!
>
> Well, I finished my class. I was struggling to make bakers and casseroles and
> asked Clayarters for help. I still didn't make my numbers - only 5 out of 40
> made it. I tried double-coning, wrapping the rim with plastic, slow drying,
> cutting it off the bat, letting it dry on the bat, finishing the bottom with a
> rib using alittle water, compressing the clay in one direction, opening with my
> fist, etc. - the only suggestions I didn't try were putting a shower cap on my
> bakers, and using plaster bats. I figure it must be a problem with the way I'm
> compressing the clay. Thought I'd try a new clay even though my classmates
> didn't have as many problems as I had. Some of my classmates thought maybe I
> was trying too hard. I'll keep trying to find a solution.
>
> Thanks to everyone who so generously shared their knowledge and experience with me.
>
> Cheers,
> Karen Nakakihara
> Alpine, Texas, the "Palm Springs of the southern Rockies"
>
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>
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>
Greeting to you, Karen.
Good for you_ I am glad that you are set on finding a solution. You
know, if making pots were easy, we probably would get bored and go do
something else. I can tell by your determination that you are going to
get this.
There is an excellent article on the subject of s-cracks in "Pottery
Making Illustrated" magazine from the Fall of 2000. It is an article by
Jeff Zamek. The most important thing that I learned from this article
is the importance of coning the clay properly if you do cone it. When I
am throwing small things, I don't cone my clay. If I am making larger
things I do. Here is the important thing from the article. *"If you
create a recessed or a concave area on the top of the cone, the clay
platelets will not align correctly." Jeff Zamek. *In other words be
very careful when centering and coning not to let the center or the top
shrink down inside itself (if you do you will probably get an s-crack).
Keep trying, but try making some small casseroles (individual) and
working your way up to larger ones. I wish you great success!!
Sincerely,
Linda Goodson
208 East Rhodes Street
Lincolnton, NC 28092
goodfun@charter.net
Ivor and Olive Lewis on wed 10 jan 07
Dear Michael Wendt,=20
You say <layers >>
Prove it, given that the average size of a particle of clay is one =
micron across and one tenth of a micron thick, that other minerals are =
25 micron or larger blocks and that grog may be 500 micron blocks.
Rather than a perfect lamella structure that, way of treating clay gives =
a completely randomised structure which is highly resistant to crack =
propagation. Laminated structures split easily, think about Shale and =
Slate which start out ass compressed clay.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Jon Pacini on thu 11 jan 07
Greetings All--- The S-crack question seems to be one of those that
repeatedly comes up and seems to have lot's of solutions. That's because it
can be caused by lot's of different things.
Here are two that seem to get over looked many times, though they are fairly
simple to resolve.
#1--- If you are using mechanically pugged clay, it gets compressed at a
different rate around the edge of the pug than in the center. This is
particularly true with commercial clays in which a large diameter pug mill
is used. Many times a section of clay is cut off a prepared block of clay,
rounded out a bit and slapped on the wheel. Well--- if that clay is oriented
with the axis of the original pug vertical, the outside edge of the clay
that your pot is going to be made out of is compressed more that the bottom
is going to be, becaus then the bottom is really the uncompressed center of
the pug. And it's going to take a bunch of coning and compressing to fix
that.
It is not necessary to wedge the clay to over come this or slice it 30
times, but make sure that when you orient the clay on the wheel that you
have the axis of the pug going in another direction other than vertical.
That way the bottom is the compressed outer edge of the pug.
#2--- Lots of potters these days seem to like really soft clay to throw
with. There also seems to be a trend towards non porous bats. Soft clay has
lots of water and tends to shrink allot more that stiff clay. If you are
throwing wide bottoms, with soft clay, you are going to get a lot of
shrinkage across that wide bottom. If it sticks or hangs up, you stand a
chance of problems. But the most common problem is that the sides tend to
dry out before the bottom, this is compounded by non-porous bats. When the
bottom finally starts to dry and shrink, it has no place to shrink to, since
the sides are dry and rigid. So it cracks across the bottom. It may not
always do this in the green state, but the stresses are set up and chances
are the ware will then crack in the bisque or glaze firing.
A damp box is a great solution to drying ware evenly. I like the old broken
refrigeratormethod, they make great damp boxes. And personally, I like to
use stiff clay with a low shrinkage rate on plaster bats. But which ever
method you employ, drying evenly is mandatory with wide bottomed ware.
Best regards,
Jon Pacini
Clay Manager
Laguna Clay Co
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