Richard Mahaffey on fri 26 nov 04
Vince,
I find that if the bottom of a platter is too thin or the foot ring
does not properly support the wall/rim of the plate/platter what you
describe will occur.
I almost never dry my plates or platters upside down or put them back
in a damp box or under plastic when I am done trimming and none of them
in recent memory (10+ years)
come from the fire with a hump in my middle.
I stress to my students that the thickness of a piece and of the areas
in a particular piece, as well as the position of the elements
determines weather the piece you made will withstand
the stresses in the firing process when the clay becomes soft and
"almost an extremely viscous fluid". You can go to any lengths you
want, but if the foot ring is in the wrong place or the
bottom of the plate is too thin it will look as though the foot pushed
up through the bottom or that there is a hump in the bottom of the
plate.
your milage may vary,
Rick
Laurie Cowell on sat 27 nov 04
Rick:
It appears that you are referring to electric firings and my problem only
comes with Cone 10 reduction. My bottoms are not too thin and I place my
foot rings where direction changes for the rim.
Laurie
At 11/27/2004 01:32 AM, you wrote:
>Vince,
>
>I find that if the bottom of a platter is too thin or the foot ring
>does not properly support the wall/rim of the plate/platter what you
>describe will occur.
>I almost never dry my plates or platters upside down or put them back
>in a damp box or under plastic when I am done trimming and none of them
>in recent memory (10+ years)
>come from the fire with a hump in my middle.
>
>I stress to my students that the thickness of a piece and of the areas
>in a particular piece, as well as the position of the elements
>determines weather the piece you made will withstand
>the stresses in the firing process when the clay becomes soft and
>"almost an extremely viscous fluid". You can go to any lengths you
>want, but if the foot ring is in the wrong place or the
>bottom of the plate is too thin it will look as though the foot pushed
>up through the bottom or that there is a hump in the bottom of the
>plate.
>
>your milage may vary,
>
>Rick
>
>______________________________________________________________________________
>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.
Vince Pitelka on sat 27 nov 04
> I find that if the bottom of a platter is too thin or the foot ring
> does not properly support the wall/rim of the plate/platter what you
> describe will occur.
Rick -
That's a very good point. I think that a lot of people try to throw
platters that are as thin and delicate as the finest commercial china. It
is certainly possible, but it seems an odd aesthetic to impose upon
hand-thrown pottery.
As we all know, a platter with the foot ring (or the outer foot ring if
there is more than one) located too far out towards the rim tends to be
pretty clunky. On the other hand, a flat-bottom platter with the foot ring
recessed too far towards the center will certainly sag and warp in the
firing. The foot ring (or outer foot ring if there is more than one) is
best placed where the curve of the rim meets the flat well of the platter.
In other words, a platter with a broad concave shape could have the foot
ring fairly far towards the center, while a platter with a broad flat well
should have the foot ring right where the flat bottom starts to curve
upwards towards the rim.
I don't like the feel of platters that are too thin, and those are the ones
that always give the most problems in drying. A platter that is even
slightly thicker often gives far fewer problems, and has a more comforting
feel to it. A platter with a slightly thicker rim is far less likely to
warp during the drying process.
And as we all know, the secret to firing platters without warpage is to make
sure that the foot is fully supported on a very flat shelf or on
closely-spaced wadding. Normally we only use wadding in salt, soda, and
wood, but I have used wadding to support large platters when the kiln
shelves weren't quite flat, and it helps prevent warpage.
As you say, your mileage may vary. Different platter designs are more or
less prone to shrinkage and warpage problems. I have always had the best
luck drying plates and platters slowly before trimming. With plates and
smaller platters, after trimming I usually just flip them over on a bat and
just let them dry in the open. With platters larger than 14" diameter, I
usually put them back in the damp box or under plastic until they are almost
dry, in order to prevent warpage. That has generally worked well for me an
my students.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Jo Smith on sun 28 nov 04
Vince,
" Normally we only use wadding in salt, soda, and
wood, but I have used wadding to support large platters when the kiln
shelves weren't quite flat, and it helps prevent warpage."
How close are the wads when you do this and what are they made from, I
presume they are wet when placed in the kiln which seems like it could cause
problems, sorry at the moment I only do electric.
Thanks,
Jo
Ken Russell on tue 30 nov 04
Vince wrote:
"They never humped up in the center unless I tried to dry them quickly."
Sorry Vince, but I've been drying 24" platters all the time (several
times per month) over night from leather hard to bone dry on top of a
firing kiln for many years. No humps in the middle. Ever. It ain't
the speed of drying. It's the clay. It used to be the clay, but then I
tried EVERY clay in North America (except Sheffield) until I found one
where the folks who mix it give a damn. It's the clay.
Ken Russell
Vince Pitelka on wed 1 dec 04
> Sorry Vince, but I've been drying 24" platters all the time (several
> times per month) over night from leather hard to bone dry on top of a
> firing kiln for many years. No humps in the middle. Ever. It ain't
> the speed of drying. It's the clay. It used to be the clay, but then I
> tried EVERY clay in North America (except Sheffield) until I found one
> where the folks who mix it give a damn. It's the clay.
Ken -
The clay certainly can have a lot to do with drying problems, but it is very
reckless to definitively say "It's the clay." That makes no sense at all.
How you form the plate, how you trim it, how you dry it, and how you fire
can all cause the plate to warp or to crack or to hump. I don't know you
Ken, and I do not wish to offend you, but after 35 years professional
experience in clay I can say with comfortable certainty that anyone who
makes a 24" platter and then dries it overnight from leather hard to bone
dry on top of a firing kiln doesn't have their head screwed on straight. If
you get away with this, then obviously your entire existence is in extreme
tight allignment with the cosmic forces of the universe. More power to you.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
John Rodgers on wed 1 dec 04
Ken, I use C-5 B-Mix and dry big flat stuff on the top of my kiln when
hot. My B-mix doesn't hump up either. As a matter of fact, when I force
dry any of my B-mix based ware that way, I have fewer cracking problems
of any kind, as well.
Regards,
John Rodgers
Chelsea, AL
Ken Russell wrote:
> Vince wrote:
>
> "They never humped up in the center unless I tried to dry them quickly."
>
> Sorry Vince, but I've been drying 24" platters all the time (several
> times per month) over night from leather hard to bone dry on top of a
> firing kiln for many years. No humps in the middle. Ever. It ain't
> the speed of drying. It's the clay. It used to be the clay, but then I
> tried EVERY clay in North America (except Sheffield) until I found one
> where the folks who mix it give a damn. It's the clay.
>
> Ken Russell
>
> ______________________________________________________________________________
>
> 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.
>
>
Gay Judson on wed 1 dec 04
OK, Ken, WHAT IS the clay?
Gay Judson
> -----Original Message-----
It used to be the clay, but then I
> tried EVERY clay in North America (except Sheffield) until I found one
> where the folks who mix it give a damn. It's the clay.
>
> Ken Russell
>
Vince Pitelka on thu 2 dec 04
> I do know Ken. He is a professional production potter who has earned
> his living from making pots for a number of years. He has his head
> screwed on straight--if you knew him I think you would agree. I think
> Ken has discovered something here that we could learn from. How about
> it Ken--will you tell us more? What about the clay is so critical here?
Ken and John -
My apologies if my message seemed to exclude the possibility of a reasonable
explanation. I would love to learn more about this. Ken, your original
message was a little frustrating, offering no details. Now, several other
people have mentioned drying platters quickly, and this is a new one on me,
even after 35 years in clay. So, I am suitably humbled, and anxious to hear
more.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
bonnie staffel on thu 2 dec 04
I am thinking that the fact the heat is coming to the bottom of the platter
on top of a hot kiln is the reason you are having success. I have done a
similar thing but not with a kiln. We made a hot drying box at the Folk
School where the heat was in the bottom of this 4'x2'x8' high cupboard, with
slat shelving and vent at the top. I don't remember if we had a fan down
there as well, but don't think we did. Students would make pots MTW in the
one week class, bisque fire Wednesday night, out and glazed Thursday, in the
electric glaze kiln Thursday night and out Friday afternoon in time for the
student exhibit for all the students to see. Hardly anything cracked except
maybe an odd piece badly constructed but the plates came out fine. I also
taught the coil and slab method back in the late 80's at the school. A
friend taped my first video at that time that I sold to interested students.
I really put the students through a heavy week of work but during the drying
and firing process, I would add other projects to teach relating to clay and
glazes so there was no time wasted in not having anything to do.
At that time I felt like a one-armed paper hanger as I was also fulfilling
my program director duties after class or the early morning exercise classes
before the day got going. Sure wish I had that energy now.
Warm regards,
Bonnie Staffel
John Hesselberth on thu 2 dec 04
On Wednesday, December 1, 2004, at 09:26 PM, Vince Pitelka wrote:
> I don't know you
> Ken, and I do not wish to offend you, but after 35 years professional
> experience in clay I can say with comfortable certainty that anyone who
> makes a 24" platter and then dries it overnight from leather hard to
> bone
> dry on top of a firing kiln doesn't have their head screwed on
> straight.
Hi Vince,
I do know Ken. He is a professional production potter who has earned
his living from making pots for a number of years. He has his head
screwed on straight--if you knew him I think you would agree. I think
Ken has discovered something here that we could learn from. How about
it Ken--will you tell us more? What about the clay is so critical here?
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Kathi LeSueur on thu 2 dec 04
Over the many years of making pots I've found that there is no one
proper way to dry them. Each form has its own problems. With large
platters, I've found that cutting off as soon as possible and flipping
onto the rim is important. The bottom sags at that point. When they are
a little drier, I flip them again, push down the center, and then flip
them back on their rims. I don't trim them with a foot ring.
Some forms like casseroles need to be dried up side down. Other forms
need to be put on a wire rack when leather hard. I have one form that
must stay on the wood shelves until completely dry. If I don't do that
the bottom cracks.
We all want a quick solution to our problems. But, learning your clay
and your forms requirements is the only solution to drying problems.
Kathi
Lee Love on fri 3 dec 04
Ken Russell wrote:
> It ain't
> the speed of drying. It's the clay.
Ken, I think you may have a point. I was shocked when I first
arrived at my teacher's studio here in Mashiko. I saw plates and
platters (all the way up to the largest platters) dried sitting up
right, from the rim in, after trimming. They never cracked. I
can only attribute it to the high sand content and the mixed particle
size of unrefined Mashiko clay.
The larger platters aways had cardboard spacers inside the
foot ring. I am not exactly sure why, but one thing I thought of, is
that this may take some of the weight off of the foot ring.
Forgiving Mashiko Nami Tsuchi spoilt me. Both
co-Shigaraki hosome and Bizen 1230*C will crack if you look funny at
it, especially the Shigiraki clay . So, when I switch from Mashiko to
one of these two, I have to be more careful.
Many of my teacher's plates and platters are coated with slip
on the inside. The Forman often had to push the center of these
plates down with the heal of his hand, right after trimming. The
slip seem to make the platters rise in the midde, maybe because they
were only slipped on the inside and the wettness and shrinkage was
differet on each side.
--
Lee in Mashiko, Japan http://mashiko.org
http://www.livejournal.com/users/togeika/ WEB LOG
http://public.fotki.com/togeika/ Photos!
| |
|
