Edy Nathan on mon 7 mar 05
HI All,
I have been trying to throw large platters for the
last month and have found minute cracks in the base of
the platter. The platters are about 17' in diameter. I
really compress the bottom while I throw, at least it
seems so to me, so I am wondering if it has to do with
how the piece is dried. Should the rate of drying be
very slow? Des the piece need to be flipped a few
times in that drying process.
Any help and shared knowledge would be greatly
appreciated.
Thanks, Edy
Cat Jarosz on mon 7 mar 05
In a message dated 3/7/2005 11:30:03 AM Eastern Standard Time,
ensence@YAHOO.COM writes:
HI All,
I have been trying to throw large platters for the
last month and have found minute cracks in the base of
the platter. The platters are about 17' in diameter. I
really compress the bottom while I throw, at least it
seems so to me, so I am wondering if it has to do with
how the piece is dried. Should the rate of drying be
very slow? Des the piece need to be flipped a few
times in that drying process.
Any help and shared knowledge would be greatly
appreciated.
Thanks, Edy
Hi Edy... you could try having the bottom arc up a bit" along with "all
the compression you do with your pots and dry on wall board or something that
will dry the bottom at similar rate and keep the pot covered most of the
time... I keep my platters covered for weeks..
I think the idea of the arc is the clay has room to move while drying and
wont pull apart...what ever it is it works ...
Just a little tid bit hope it works for you.. cat jarosz in balmy
spring type weather in the blue ridge mnts of nc... that is gonna go caput on
us in next few days... winter aint GONE YET...
http://www.southernhighlandguild.com/directory/memberpages/catjarosz.html
V)''(V woof & >^..^< mew; Chicks with beards rule !!!
(_o_)
\||/
Michael Wendt on mon 7 mar 05
Edy,
You don't say if the cracks are on the inside, outside or go all the way
through so I give you general answers.
If the cracks are on the bottom, it is usually because the cutoff wire
creates small tears in the surface that grow into cracks as they dry.
Burnishing the bottom as soon as possible can help with this problem. Invert
the platter as soon as possible and rib it smooth all over the bottom with a
stainless steel rib.
If the cracks are on the inside, check to see if you are leaving water
standing in the piece. Circular cracks often happen when small rings of
water are left to sit on the platter and soak in causing increased local
shrinkage.
Cracks that go all the way through can originate from either the front or
the back and will show wider from the point of origin on the front or back
to help with the diagnosis.
Radial cracks often appear some time after trimming because of a condition
called case hardening in which the dry outer skin is trimmed away on one
face, leaving the softer core exposed. It continues to shrink and since the
other face has already shrink, it cracks. Waiting until the platter is a
little drier before trimming usually helps with this problem.
If the cracks appear only after firing, they may be the result of firing too
fast through quartz inversion.
In any case, drying rate trials should always be done on any clay body. Make
several pieces alike at the same time and dry them under different
conditions. One or two such trials will help you find the proper drying rate
for the clay.
Slow drying may not be needed. My clay cracks less when dried very quickly.
If dried too slowly, it shows increased cracking.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Edy wrote:
HI All,
I have been trying to throw large platters for the
last month and have found minute cracks in the base of
the platter. The platters are about 17' in diameter. I
really compress the bottom while I throw, at least it
seems so to me, so I am wondering if it has to do with
how the piece is dried. Should the rate of drying be
very slow? Des the piece need to be flipped a few
times in that drying process.
Any help and shared knowledge would be greatly
appreciated.
Thanks, Edy
Jean Cochran on mon 7 mar 05
Dear Edy,
Just my 2 cents worth: I pass the wire between my platters and the batts
every day till the platter slides free. In the meantime, I totally cover
the platter with about three layers of newspaper. Every day I change the
newspaper to dry paper. Even after I turn the foot, I keep doing the
newspaper trick till it is totally dry. Hope this helps.
Jean Wadsworth Cochran
www.foxhollowpottery.com
www.kycraft.ky.gov/craftcgi-bin/index.cgi?busid=186
I have been trying to throw large platters for the
last month and have found minute cracks in the base of
the platter. The platters are about 17' in diameter. I
really compress the bottom while I throw, at least it
seems so to me, so I am wondering if it has to do with
how the piece is dried. Should the rate of drying be
very slow?
Victoria E. Hamilton on mon 7 mar 05
Hi Edy -
Yes, dry slow. Your rims are going to dry faster than the bottoms, so they
should dry under plastic - maybe even paint some wax resist on the rims to
retard drying. The pull of the wet bottom on the dryer rims may cause
warping and raised bottoms. Not sure about your minute cracks in the base.
Vicki Hamilton
Millennia Antica Pottery
Seattle, WA
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Edy Nathan
Sent: Monday, March 07, 2005 06:30
To: CLAYART@LSV.CERAMICS.ORG
Subject: throwing large platters
HI All,
I have been trying to throw large platters for the
last month and have found minute cracks in the base of
the platter. The platters are about 17' in diameter. I
really compress the bottom while I throw, at least it
seems so to me, so I am wondering if it has to do with
how the piece is dried. Should the rate of drying be
very slow? Des the piece need to be flipped a few
times in that drying process.
Any help and shared knowledge would be greatly
appreciated.
Thanks, Edy
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Carole Fox on tue 8 mar 05
Hi, Edy. I assume you mean your platters are 17", not 17' :-). Gotta
watch those fingers on the keyboard! Here are some suggestions:
1. Dry slowly, keeping the platter loosely covered with plastic.
2. When you turn the platter over, do so on a piece of foam packing
material to cushion the rim.
3. When you trim the foot, put some support (such as a piece of foam
cushioning or wadded-up dry cleaning bags) under the center of the platter
for support and use light pressure on the trimming tool.
4. Make sure the center of the platter is completely dry before you bisque.
There is a great section on cracks in Hamer & Hamer, with pictures to help
you compare your conditions to their diagnosis. I have found this
reference of great value.
Carole Fox
Dayton, OH
Edy Nathan on wed 9 mar 05
Hi Carole,
Thanks so much for the help and the reference...yes I
do need to watch those fingers, misplacement can
surely give misinformation...but can you imagine a 17'
platter...really something, huh?
Take care from cold, snowy and icy NYC
Edy
--- Carole Fox wrote:
> Hi, Edy. I assume you mean your platters are 17",
> not 17' :-). Gotta
> watch those fingers on the keyboard! Here are some
> suggestions:
>
> 1. Dry slowly, keeping the platter loosely covered
> with plastic.
>
> 2. When you turn the platter over, do so on a piece
> of foam packing
> material to cushion the rim.
>
> 3. When you trim the foot, put some support (such
> as a piece of foam
> cushioning or wadded-up dry cleaning bags) under the
> center of the platter
> for support and use light pressure on the trimming
> tool.
>
> 4. Make sure the center of the platter is
> completely dry before you bisque.
>
> There is a great section on cracks in Hamer & Hamer,
> with pictures to help
> you compare your conditions to their diagnosis. I
> have found this
> reference of great value.
>
> Carole Fox
> Dayton, OH
>
>
______________________________________________________________________________
> 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.
>
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