John Baymore on mon 25 jun 01
Debbie writes that using plate setters can increase warpage because they
create tension. Does anyone else have something to say on this? I have be=
en
using plate setters and would like to keep using them.
Anne,
Hi. I've been using plate setters for about 23 years and have NO problem=
s
with excessive warping. I woodfire stoneware to cone 10-ish and utilize
numerous claybodies. Without plate setters I'd be firing too many
refractories and not enough plates in a load. Plate setters allow nice
loading densities with flat forms.
Nothing inherent in good plate setters that will cause warping......
otherwise industry wouldn't have developed them . If the setter is
warped...... that is another story.....just like a warped kiln shelf. =
Every now and then I chuck a worn out setter. BTW.... a "plate setter" c=
an
simply be a smaller kiln shelf with three short posts set ont top of a
larger kiln shelf in a stack. I use a bunch of 12 inch x 12 inch x 3/8
inch shelves and 2 inch posts to set my rectangular sushi plates on in ta=
ll
bungs.
Plate warping, in my experience, seems to stem from throwing or
handbuilding techniques, HANDLING of the pieces in process, drying
unevenness, or warped kiln shelves. Pyroplasticity (getting soft in the
kiln) CAN cause problems ........ but plate setters should support the fo=
ot
area enough so that this is not an issue.
Design of a piece CAN affect warping, and design concepts should always
extend to designing for the firing of the pieces. A very pyroplastic bod=
y
used to make a plate that is suspended on isolated projecting feet can
easily sag between the feet. This will warp on either a shelf OR a plate=
setter.
This is also why things like "bone china" (exceptionally pyroplastic) are=
high fired to develop the fluxed body in setters that are more like slump=
molds without glaze, and then glaze fired at a lower temp.
Lee Love's and Ron Roy's comments on this were excellent.
Best,
..............john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
John.Baymore@GSD-CO.com
"Earth, Water, and Fire Noborigama Woodfiring Workshop August 17-26,
2001"
Anne Wellings on tue 26 jun 01
Thanks, John, for your encouraging reply about plate setters.
Some of the plate setters I have bought lately, instead of being flat, have
a corrugated appearance, with rounded-off grooves going in one direction
across the surface. Does anyone see a problem with these or know the
reasoning behind them? I got them from Axner.
Anne
Leslie St. Clair on tue 26 jun 01
I also have a set of that type of plate setter from
Axner. I don't know the theory behind the corrugated
surface, but they work pretty well.
The only thing you need to be aware of is that plates
will warp if the foot ring is not evenly situated on
the plate setter. I've had plates slump on the side
where the plate is not supported by the setter. This
is hard to spot from above, and I usually run my
finger around under the plate to make sure the foot
ring is supported. So this type of plate setter won't
work for plates with a larger size foot ring.
Leslie St. Clair from Kentucky
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Christena Schafale on tue 26 jun 01
I would guess that the corrugated surface is intended to allow air to
circulate underneath the plate, promoting more even heating and reducing
the possibility of cracks.
Chris
At 10:28 AM 6/26/01 -0700, you wrote:
> I also have a set of that type of plate setter from
>Axner. I don't know the theory behind the corrugated
>surface, but they work pretty well.
> The only thing you need to be aware of is that plates
>will warp if the foot ring is not evenly situated on
>the plate setter. I've had plates slump on the side
>where the plate is not supported by the setter. This
>is hard to spot from above, and I usually run my
>finger around under the plate to make sure the foot
>ring is supported. So this type of plate setter won't
>work for plates with a larger size foot ring.
> Leslie St. Clair from Kentucky
>
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WHC228@AOL.COM on tue 26 jun 01
Try disks under your platters.
I use a disk under every piece that will warp. A company in England makes
them [Acme Marls.]
I think that Highwater may have them. These disks come in many sizes, from
several inches across to ten or more. When I still used corderite {sp?] my
shelves were nearly always warped, so I started using them under every pot. I
have not had a warped pot since. I use wash on those disks and it has also
protected my shelves from glaze runs. They are cheap to toss out if they get
a big run.
If anyone is looking for these disks and can't find them email me and I'll
find out who has them.
Bill Campbell
John Baymore on wed 27 jun 01
Hi All.
Got a private email offlist that indicated that I was a little less than
clear with my last post on plate setters. So here is a copy of what I HO=
PE
is a clarification I have sent to that person....... bet I confused other=
s
here too. Sorry about that .
Isn't a shelf, i.e., a plate setter, a refractory in the sense you're usi=
ng
the word here? That's my confusion . . . by using plate setters
(refractories), doesn't each one add to the "too many refractories"
condition
and limit the number of plates in a load? I'm missing something here,
because
you're obviously getting a nice dense loading with flat forms.
And if a small shelf qualifies as plate setter, I don't understand why th=
e
underlying main shelf on which the small shelf sits isn't good enough all=
by
itself . . . assuming it a good flat shelf to start with, Maybe it's
because a
large shelf is more likely to warp during the firing and then return to
flatness as the kiln cools?
...... ..............................
What is a plate setter if it's not a just another smaller kiln shelf?
Perhaps
a sort of bisqued slump mold for plates without a foot ring?
What's a "tall bung?"
Typically, a handcraft potter just utilizes a "normal" kiln shelf to set
plates on. This might be a 12 x 24 x 3/4 silicon carbide shelf with mayb=
e
three 2" x 2" x 2" posts to support it. This shelf might only hold two 1=
0"
dinner plates plus a couple of small low "fillers". The thermal mass of
this shelf / post combination is about 20 pounds of what will take totall=
y
wasted heat energy to fire up. The same two plates can be placed on
individual plate setters that weigh only about 5 pounds (or less) each. =
That is about a HUGE 50 percent savings in the heat energy utilized to fi=
re
the SHELVES and POSTS ....not the ware. If you can "cram" three plates o=
n
the normal shelf using a lot of overhang.... watch warping ......... =
this STILL represents at least a 25 percent savings in heat energy.
That is the main reason why someone would use plate setters.
This is also why modern (expensive) shelves like the Crystar and Advancer=
are so nice. They are thinner and hence weigh much less than "traditiona=
l"
shelves for the same "span", yet are actually stronger than a "traditiona=
l"
shelf. Yes... they save a little space to stack more stuff in........
maybe 1/2" of height per shelf used......... but that is incidental to th=
e
heat energy savings. =
The big reason to use these if you can is the save your BACK.......... th=
ey
are SO thin and light!!!!! A true JOY!
Plate setters ALSO minimize your handling of so many larger kiln
shelves.... and therefore help your back too.
Next......... all of the thermal mass of large "normal" kiln shelves
stacked close together with layer after layer of plates causes a "lag" in=
the penetration of the heat energy to the interior of all those shelves. =
Cordierite and high alumina shelves are worse in this regard than silicon=
carbide due to differences in thermal conductivity figures..... but all
shelves exhibit this tendency. If this isn't taken into account in the
firing schedule, it is possible to have defects and seconds caused by the=
fact that the center of the stacking is not at what the witness cones SAY=
the reat of the general kiln chamber is at. So not only do you have to
heat all those heavy refractories, you often have to lengthen the
firing...... which utilizes even MORE heat energy.
You can "open up" the height of the stacking on the "normal" shelves to
improve heat transfer by giving the plates a lot more clearance ...... bu=
t
that defeats the efficiency purpose even more.
A plate setter exposes the plate all along it's outer periphery to the
radiant heat energy bouncing around the kiln, so it fosters excellent
transfer to the center of each individual plate..... even though the
vertical clearance from one setter to the next is pretty darn
tight.....which saves space in the kiln. Plus...the setter each plate's
foot is sitting on is very thin and lightweight and doesn't take much hea=
t
energy to "heat up". So there is less "thermal lag" in the stack of plat=
es
on setters.
A plate setter can "get away" with being thin because it spans only a ver=
y
short horizontal distance and carries very little weight on that span. =
They don't sag much because of this and remain flat for a LONG time. The=
vertical "legs" line up directly one over the other and in compression ca=
n
support a lot of weight.... so they can easily be stacked in tall columns=
,
usually called "bungs" (after "bungs" of saggers.....haven't got a clue a=
s
to the exact historical derrivation of THAT term ). Sometimes I will
fire "bungs" of plates on setters that are 3 feet tall. These tall stack=
s
go on the top of the general stacking, along with the other tallest piece=
s.
Hope this clarifies my last post.
BEst,
.......................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
John.Baymore@GSD-CO.com
"Earth, Water, and Fire Noborigama Woodfiring Workshop August 17-26,
2001"
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