Randall Moody on wed 7 oct 98
I recently was assigned the task of making 30 tea bowls for my ceramics
class. Even though I dislike making tea bowls I used the opportunity to
attempt throwing off the hump. The majority of the bowls I made have
s-cracks. I know that this is caused by not compressing the bottom enough
but I am not sure how to go about this on the hump. I do not like the idea
of having to wedge 30+ 1/2 lbs. of clay and throw each individually but I
hate the high failure rate.
Andrew Buck on thu 8 oct 98
Randall Moody wrote:
>
> ----------------------------Original message----------------------------
The majority of the bowls I made have
> s-cracks. I know that this is caused by not compressing the bottom enough but
- At a meeting of the New Jersey Potters Guild recently, someone
recommended after spiral wedging to throw the clay down sideways onto
the wheel head. (Cross grain?) Definitely counterintuitive in the sense
that it defeats the purpose of spiral wedging, but it appeared to solve
a serious s crack problem.
- Andy Buck - Hand craft pottery and then some
Cindy Morley on thu 8 oct 98
Get a balloon and put a handful or two of sand in it (whatever would fit
comfortably in the bottom of your tea bowl. Before you trim the bowl, turn
it upside down over your hand which is holding the sand filled balloon and
paddle it with a paddle or wooden spoon. You don't have to do it very
much, just a couple of pats should do.... Good luck.
Cindy Morley
Fayetteville AR
At 08:01 AM 10/7/98 , you wrote:
>----------------------------Original message----------------------------
>I recently was assigned the task of making 30 tea bowls for my ceramics
>class. Even though I dislike making tea bowls I used the opportunity to
>attempt throwing off the hump. The majority of the bowls I made have
>s-cracks. I know that this is caused by not compressing the bottom enough
>but I am not sure how to go about this on the hump. I do not like the idea
>of having to wedge 30+ 1/2 lbs. of clay and throw each individually but I
>hate the high failure rate.
>
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~
Cindy Morley Shire-March of the Grimfells
HL Christean Jansen Kingdom of Calontir
Use the talents you possess; for the woods would be very silent if no
birds sang except the best.
http://comp.uark.edu/~cmorley cmorley@comp.uark.edu
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~
Clyde Tullis on thu 8 oct 98
When ever you push in from the outside,say to define the foot, you
"decompress" the bottom. The clay sort of tornados down the center of the
hump. Therefore the "S" shaped crack. Follow each push in with a compression
and comress the botton the last thing you do before cutting the piece off.
Think of the hump as a 3 D sketch pad. You'll learn to love it.
Clyde, who saw his first bald eagle of the season yesterday.
Randall Moody wrote:
> ----------------------------Original message----------------------------
> I recently was assigned the task of making 30 tea bowls for my ceramics
> class. Even though I dislike making tea bowls I used the opportunity to
> attempt throwing off the hump. The majority of the bowls I made have
> s-cracks. I know that this is caused by not compressing the bottom enough
> but I am not sure how to go about this on the hump. I do not like the idea
> of having to wedge 30+ 1/2 lbs. of clay and throw each individually but I
> hate the high failure rate.
Paul Lewing on thu 8 oct 98
The best way to prevent cracks in ware thrown off the hump is to have
the bottoms be REAL thin. If you're not trimming, you should be able
to see the wire go through as you're looking down into the pot. If
you are trimming, you just need to trim real thin.. Dave Shaner has a
neat trick for this, also. He adds a tiny ball of clay in the center
of the foot after trimming and attaches it with a spin of the wheel so
it has a kind of spiral ridge shape to it. They never crack.
Paul Lewing, Seattle
Donn Buchfinck on thu 8 oct 98
wedge a 15 lb of clay and cut it into 30 balls
i could never throw off the hump
I always got s-cracks
1/2 lb is so small that all you need is a chunk
why not try to make the teabowl out of 2-3 lbs
teabowls were not traditionaly small
Donn Buchfinck
where is your school
Vince Pitelka on thu 8 oct 98
>I recently was assigned the task of making 30 tea bowls for my ceramics
>class. Even though I dislike making tea bowls I used the opportunity to
>attempt throwing off the hump. The majority of the bowls I made have
>s-cracks. I know that this is caused by not compressing the bottom enough
>but I am not sure how to go about this on the hump. I do not like the idea
>of having to wedge 30+ 1/2 lbs. of clay and throw each individually but I
>hate the high failure rate.
Randall -
This is a perpetual problem when throwing off the hump, especially with any
fine-grain claybody. A good sand or grog body will give you far less
problems. You already understand the problem of compressing the bottom when
throwing off the hump. For anyone else out there, the difficulty is that
you do not have the solidity of the wheel backing up the clay while you are
compressing. And of course the problem with s-cracks is diminished when you
throw fast, with minimal water. For me, the most important trick has been
to compress agressively as a final stage, as follows. These directions
apply to a wide teabowl with vertical walls. After working the top of the
hump up into a column of clay, perhaps 2 1/2" diameter and 5" or 6" tall, I
penetrate the top portion (depending on the size of tea bowl I wish to make)
and form the desired shape of bowl, but a little smaller at the base and a
little shallower than I really want. After the upper portion of the bowl is
finished, and the rim resolved, as a final step I remove all water from the
bottom inside, and then press down in the bottom center with several
fingers, forcing a little more clay outwards and bringing the bottom of the
teabowl to the finished shape. I use considerable force doing this, so that
the pressure penetrates into the clay that will form the foot. This also
effectively "wrings" a little more water out of the clay at the bottom.
When the pot is leather hard, I trim the foot, and after trimming I further
compress the bottom by burnishing it with a rounded wood tool. None of
these steps are time-consuming or finnicky. You get use to them and they go
very quickly. And they pretty much eliminate s-cracks on off-the-hump forms.
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
John K. Dellow on thu 8 oct 98
Randall ,if you can find a copy of " The Japanese Pottery Handbook" by Penny
Simpson "Lucy Kitto & Kanji Sodeoka , you will find hump throwing described
very clearly. A tip on making a nice tea pool, before cutting off roll your
thumb & index finger down & in at the base of the tea bowl. The Korean potters
pinched the pot off rather than wasting time to pick up a cutting thread.
John Dellow the flower pot man
ROBERT MCWILLIAMS on fri 9 oct 98
Randall Moody wrote:
>
> ----------------------------Original message----------------------------
> I recently was assigned the task of making 30 tea bowls for my ceramics
> class. Even though I dislike making tea bowls I used the opportunity to
> attempt throwing off the hump. The majority of the bowls I made have
> s-cracks. I know that this is caused by not compressing the bottom enough
> but I am not sure how to go about this on the hump. I do not like the idea
> of having to wedge 30+ 1/2 lbs. of clay and throw each individually but I
> hate the high failure rate.
Aloha Randall - from my experience the problem when throwing off the
hump is not so much compression of the bottoms as it is trimming the
bottoms a little thinner. If theyre thick theyre going to get an S
crack. Let me know how it works. Bob
klauzer jessica a on fri 9 oct 98
I have this obsession with little tea bowls and can't stop making them no
matter how hard I try. I used to have a high failure rate as well with
the S cracks galore, but have found that it is directly related to wall
thickness. If you trim your feet, then the inner wall and the wall of the
foot should all be almost exactly the same thickness as the walls of the
bowl. Even if you are going for the wabe sabe thing. Also, in making the
foot, it helps to compress from the outside and make the whole bowl "stand
up" on top of the hump before cutting it off. Still, about 10% fail --
that's just the nature of the beast. Have fun!!
jessica
On Wed, 7 Oct 1998, Randall Moody wrote:
> ----------------------------Original message----------------------------
> I recently was assigned the task of making 30 tea bowls for my ceramics
> class. Even though I dislike making tea bowls I used the opportunity to
> attempt throwing off the hump. The majority of the bowls I made have
> s-cracks. I know that this is caused by not compressing the bottom enough
> but I am not sure how to go about this on the hump. I do not like the idea
> of having to wedge 30+ 1/2 lbs. of clay and throw each individually but I
> hate the high failure rate.
>
David Hendley on fri 9 oct 98
Compress the bottoms when the bowls are leather-hard.
Try 2 short pieces of 1 1/2" dowel.
Round one end of one dowel so it is the same curve as the inside
of your bowls. Set that dowel, flat end down, on your table,
then put your bowl, upside down, on the dowel.
Put the second dowel on the bottom of the bowl and push
down against the first dowel.
S-cracks have been much discussed on Clayart.
Check the archives, if you can.
David Hendley
Maydelle, Texas
At 09:01 AM 10/7/98 EDT, you wrote:
>----------------------------Original message----------------------------
>I recently was assigned the task of making 30 tea bowls for my ceramics
>class. Even though I dislike making tea bowls I used the opportunity to
>attempt throwing off the hump. The majority of the bowls I made have
>s-cracks. I know that this is caused by not compressing the bottom enough
>but I am not sure how to go about this on the hump. I do not like the idea
>of having to wedge 30+ 1/2 lbs. of clay and throw each individually but I
>hate the high failure rate.
>
Tom Wirt on fri 9 oct 98
-----Original Message-----
>attempt throwing off the hump. The majority of the bowls I made have
>s-cracks. I know that this is caused by not compressing the bottom enough
>but I am not sure how to go about this on the hump. I do not like the id
Hi
When throwing off the hump, jI've found a gentle backward motion, starting at
the outer wall/bottom juncture and lightly running a finger toward the center
until you feel a little back pressure in the clay helps avoid cracks. The other
issue is to get the bottom thin, either by accurate wire cutting (indent with a
thumbnail (mel's technique) or notch with the point of a wood knife) or by
trimming. The indent guides the wire.
If all else fails, a bit of pressure top and bottom can help, but this will
destroy any finger ridges. I do a short goblet that is foot and cup in one. The
base is trimmed out as thin as I can get it, but they still crack if I don't
press them.
Your clay body is probably fairly tight which compounds the problem.
Hope this helps.
Tom
taube wilson on fri 9 oct 98
To prevent s-cracks when throwing off the hump:
after centering the top of the hump I run my sponge across
it two or three times to compress before beginning to
throw. I don't know if this really works or if it's
superstition on my part, but I don't have a lot of s-cracks.
(I throw ^6 stoneware, mostly Campbell's Warm Brown).
-Taube Wilson
Annandale, Va.
tpottery@hotmail.com
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Laurie Friedlander on fri 9 oct 98
I do much of my throwing off the hump from Tbowls to larger pieces. You've got
to start with a well wedged mound and then "iron" across the bottom of your
pots with finger tips(I hate ribs) numbers of times until you actually sense
it firming up. Problem is those spontaneous finger marks from a quick opening
are gone, so I find I have to fake them by moving quickly across the bottom as
Im about to do my first pull. I've often wondered tho' about whether the way
you set down the hump on the wheel head and the direction of the wedging
spiral have anything to do with S cracks - like maybe the clay unwinds - but I
usually never remember to check it out with any kind of control group of pots,
and only 1 or 2 pots might S crack out of a whole day of throwing.
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