Edward Cowell on wed 16 feb 00
Why am I getting so many S-cracks in the bottoms of small bowls that I
throw off the hump? I pay attention to removing the water from the bottom,
compress when throwing and compress with a rib again when I am tooling the
bottom. Happens on all my clays - some a little more than others.
Laurie Cowell,
Waterloo, Ontario, Canada
John K Dellow on thu 17 feb 00
Have you tried squeezing the clay under the pot before the final
compression inside. If you can get the Penny Simpson book ,she
gives a good explanation with pictures .
Edward Cowell wrote:
>
> ----------------------------Original message----------------------------
> Why am I getting so many S-cracks in the bottoms of small bowls that I
> throw off the hump? I pay attention to removing the water from the bottom,
> compress when throwing and compress with a rib again when I am tooling the
> bottom. Happens on all my clays - some a little more than others.
>
> Laurie Cowell,
> Waterloo, Ontario, Canada
--
John Dellow "the flower pot man"
Home Page http://www.welcome.to/jkdellow
http://digitalfire.com/education/people/dellow/
Mark & Pauline Donaldson-Drzazga on thu 17 feb 00
----- Original Message -----
From: Edward Cowell
To:
Sent: 17 February 2000 00:53
Subject: Throwing Off Hump - S-cracks
> ----------------------------Original message----------------------------
> Why am I getting so many S-cracks in the bottoms of small bowls that I
> throw off the hump? I pay attention to removing the water from the
bottom,
> compress when throwing and compress with a rib again when I am tooling the
> bottom. Happens on all my clays - some a little more than others.
>
> Laurie Cowell,
> Waterloo, Ontario, Canada
Dear Laurie,
when you cut them off the hump place them on newspaper and do your usual
routine, after stunning results post up to clayart.
Happy potting Marek http://www.moley.uk.com
Lee Love on thu 17 feb 00
Date: Wed, 16 Feb 2000 19:53:20 EST
From: Edward Cowell
Subject: Throwing Off Hump - S-cracks
----------------------------Original message----------------------------
Why am I getting so many S-cracks in the bottoms of small bowls that I
throw off the hump? I pay attention to removing the water from the bottom,
compress when throwing and compress with a rib again when I am tooling the
bottom. Happens on all my clays - some a little more than others.
----------------------------------------------------------------------------
-------
Laurie,
Are you talking about trimmed and footed work? I I trim a
foot on anything I throw off the hump.
At the workshop here, almost all the small things are thrown off
the hump. I've not seen any S cracks yet. Are you drying the bottom
before drying the rim? That can be another problem.
--
Lee in Mashiko, Japan
Ron Roy on thu 17 feb 00
One of the main causes is the twisting of the ball on top of the hump as it
is being centered. That is the reason the crack is S shaped. A combination
of less agressive centering (twisting and pushing off center), good
compression of the bottom from the outside in and careful (even) drying
should cure the problem in any reasonable clay body.
The clay at the bottom of a hump thrown vessel is usually thicker than the
sides. If the sides are allowed to dry faster than the bottom - when the
bottom tries to catch up it will not be allowed to shrink (by the already
drier sides) and this can lead to cracking - in any pot. I recommend
getting them upside down as soon as possible to help the bottom catch up
with the sides and dry more evenly.
RR
>----------------------------Original message----------------------------
>Why am I getting so many S-cracks in the bottoms of small bowls that I
>throw off the hump? I pay attention to removing the water from the bottom,
>compress when throwing and compress with a rib again when I am tooling the
>bottom. Happens on all my clays - some a little more than others.
>
>Laurie Cowell,
>Waterloo, Ontario, Canada
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Don & Isao Morrill on sat 19 feb 00
At 16:22 2/17/00 EST, you wrote:
>----------------------------Original message----------------------------
>One of the main causes is the twisting of the ball on top of the hump as it
>is being centered. That is the reason the crack is S shaped. A combination
>of less agressive centering (twisting and pushing off center), good
>compression of the bottom from the outside in and careful (even) drying
>should cure the problem in any reasonable clay body.
>
>The clay at the bottom of a hump thrown vessel is usually thicker than the
>sides. If the sides are allowed to dry faster than the bottom - when the
>bottom tries to catch up it will not be allowed to shrink (by the already
>drier sides) and this can lead to cracking - in any pot. I recommend
>getting them upside down as soon as possible to help the bottom catch up
>with the sides and dry more evenly.
>
>RR
>
>
>>----------------------------Original message----------------------------
>>Why am I getting so many S-cracks in the bottoms of small bowls that I
>>throw off the hump? I pay attention to removing the water from the bottom,
>>compress when throwing and compress with a rib again when I am tooling the
>>bottom. Happens on all my clays - some a little more than others.
>>
>>Laurie Cowell,
>>Waterloo, Ontario, Canada
>
>Ron Roy
>93 Pegasus Trail
>Scarborough
>Ontario, Canada
>M1G 3N8
>Evenings 416-439-2621
>Fax 416-438-7849
>
Laurie Cowell, When first I began throwing pots,(40yrs back) I
blamed S-cracks on all of the above and definatly included the weather.
Uniform cross section throughout the pot certainly helped. Despite all of
my precautions I continued to have S-cracks betimes. 2yrs ago our fridge
went belly-up and was retired to the backyard where it has been used for
drying ever since and has now been joined by a second fridge. No matter how
badly we turned pieces,they no longer crack.Probably because of the uniform
X-section and the even distribution of water through turning pieces 180
degrees for three days.
In addition to these incredibly valuable secrets
which we share with you at absolutly no cost......there IS a DJINN at work
demanding a long apprentice-ship...BEWARE!
Don & Isao
Don & Isao Sanami Morrill
e-Mail:
Steve McNutt on sat 19 feb 00
One hint I learned for throwing off the hump was to make a lot of marble
sized balls and throw one into the bottom of each cup/bowl at the end. I've
also heard of putting these on the bottom after trimming. Never tried that.
I rarely throw off the hump but when I do I use the ball trick at the end and
never have a crack.
Good luck.
Mary Beth Bishop
SAM YANCY on mon 21 feb 00
S-cracks? Since I like pie, I have saved bunch of pie plates. Into
these, after I cleaned and oiled them, I poured in a plaster of
paris/mixuure. Once set, up, I have used these (bats) for all my
throwings. After making a pot or whatever and cutting it of from the
wheel, once I can move it without warping, I place it bottom down on my
plaster bats. Since I have used this method I have had no cracks or
uneven drying for any reason. Of course for s-cracks you should try to
compress the bottom, but the plaster bats seems to suck up the moisture
and help even out the drying process. I know of at least two potters who
have had trouble with s-cracks who significantly reuced the problem with
plaster drying fixtures (Pie plate plaster batts).Also in my area clay
is generally slow drying due to moisture in the air (san francisco area
near the ocean) so it help sspeed the drying process. gSve it a try.
Alllyou need is to eat a couple of pies (yum-yum) a little oil, and and
mix up a small bit of plaster of paris. P.S. I have about 50 pie bats
now. Regards, Sam
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