Brad Carter on thu 10 aug 06
Are there any special issues to think about when stacking greenware for a
bisque firing? I beleieve shelves are not necessary, correct? Just pile it
all in the kiln and make sure none touches the elements? Thsnks for answering
a very basic question.
Brad Carter
Grass Valley, Calif.
Ron Roy on fri 11 aug 06
Hi Brad,
It depends a lot on the kind of clay body you are using - if there is a lot
of organic material in it you need to give it time to burn out. If you are
stacking rim to rim you are enclosing the space and it's harder to get the
organics out - if that happens you may have problems with a body that has
iron in it - the more iron the more likely the problems.
Stacking bowls inside each other can lead to the same problem - reducing
the clay inside the foot ring.
If you are using a white body with little iron in it you can get away with
it more but that kind of ware is sometimes not able to take the pressure of
being stacked very high.
If you know what to look for there is are some good arguments to trying it
but - be aware of the problems so you can make adjustments.
RR
>Are there any special issues to think about when stacking greenware for a
>bisque firing? I beleieve shelves are not necessary, correct? Just pile it
>all in the kiln and make sure none touches the elements? Thsnks for answering
>a very basic question.
>
>Brad Carter
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
William & Susan Schran User on fri 11 aug 06
On 8/10/06 7:38 PM, "Brad Carter" wrote:
> Are there any special issues to think about when stacking greenware for a
> bisque firing? I beleieve shelves are not necessary, correct? Just pile it
> all in the kiln and make sure none touches the elements?
Yes, there are issues to consider when loading a bisque kiln.
How the pots are stacked together can determine whether they might crack, or
be stressed and have a crack show up after glaze firing.
Generally, heavier at the bottom, lighter as pots are stacked up.
When I instruct my students how to load a bisque, the guideline is: "lip to
lip and foot to foot." Think of this as if you are building a house. Before
you add the 2nd story, the first story has to have the structure and
strength to support that additional load.
With cylinders, cups, vases and the like, the first pot sits on the shelf,
the next pot with a lip area that has the same diameter lip as the first is
placed upside down on the first. The 3rd pot, that has the same diameter
foot as the 2nd, is placed right side up on the 2nd. This can be started in
reverse - the 1st pot sits on the shelf upside down, 2nd pot sits on the
1st, right side up and so on. This way you can load tall pots and next to
them a stack of cups.
The same goes for bowls & plates, though for plates we usually only stack
two together. If you plan to nest the bowls - smaller bowls inside larger
ones - then it's very important that the bowls sitting/nesting inside are
resting on the area of the foot ring of the one below. If the nesting bowl
rests on the wall of the bowl below, it can push out/down and cause the bowl
underneath to crack or the nesting bowl could get stuck in the one below.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Crista Nelson on fri 11 aug 06
Dear Brad, The issues of stacking green ware that I would be concerned with
first of all depend on how big is the load, how heavy are the pieces, and also
consider any warping of flatter pieces... stacking too many pieces on top of
each other could turn out to be a disaster if the weight is too much for the
bottom pieces to handle it,You may end up with a bunch of cracked or warped
pieces if you do not distribute the weight evenly... Therefore shelves are
almost always a good idea to save this from happening..... hope this helps or
makes sense even...... Happy stacking... Crista
In a message dated 8/10/2006 11:15:45 P.M. Central Daylight Time,
BRADCARTER@AOL.COM writes:
Are there any special issues to think about when stacking greenware for a
bisque firing? I beleieve shelves are not necessary, correct? Just pile
it
all in the kiln and make sure none touches the elements? Thsnks for
answering
a very basic question.
Brad Carter
Grass Valley, Calif.
catjarosz on fri 11 aug 06
Dear Brad.... oh my goodness YES there are many rules for bisquing and
just piling it all in the kiln is NOT a good way to do it.
Problebly a bazillion reasons but I will try to touch on a few
1) Rim to rim is good on plates and bowls but not to high unless your rims
are super strong. THink about stacking plates rim to rim 27" inches worth
and how that bottom plate will carry the brunt of the weight. Remember
that bone dry pottery is the most fragile time of its life and things
break.
2) nesting is not good as you get uneven bisque temps in the same pot.
That will mess up your glaze results usually and could prevent the organics
from all burning out and with some glazes this can cause pits. Not to
mention uneven heat can sometimes cause cracking due to thermal shock.
3) if you use witness cones it can be difficult as you will need to leave
space to arrange posts to hold them in front of the peeps.
Is there a reason you dont want to use shelves ? Do you own shelves ?
It would be helpful to know these reasons and the type of work you are
bisquing and how thin /thick they are. Can your work handle the
tumblestack ?
Keeping the work away from the elements by about 1" is good. This helps
the heat distribution... Staggering shelves is problebly the best way to get
a good flow and even heat distribution but For yrs I have used solid
shelves with good results.
There are rules about things that really are not hard and fast but thru
yrs of bisquing have held true with firing platters neither on the bottom
shelf nor the top shelf without a way to keep the thermal shock from
cracking it. Try using posts under the rim to help and I also have a few
layers kiln blanket on my lid to help slow down the loss of heat. But this
stuff is BAD NEWS for your lungs so dont be messin with it without that in
mind.
Cripes I could sit here all day and have reasons not to just pile pots
into a kiln or think of how to load a kiln properly ... I'll let some
others chip in here and DOING is the best teacher over time...
I really believe there are different answers for every situation and
what is wrong for some is right for others. I have seen potters break all
the rules and have success... of course I have also seen way more disasters
when the rules are broken.
Hope this helps.. Cat Jarosz sitting here thinking about piling
pots in a electric kiln with mugs ontop of platters and casseroles thrown
on top of goblets etc.. heebie geebie shiver
www.catjarosz.com
www.guildcrafts.com/cat/
V)''(V woof & >^..^< mew
(_o_)
\||/ chicks with beards rule!!
Bonnie Staffel on sat 12 aug 06
Dear Clayarters,
While I agree about equalizing the weight issue in stacking greenware, =
much
of the cracking can be avoided by placing shards between say, stacked,
nested bowls. You have to allow the heat to get to the inner parts of a =
pot
easily and if restricted by another pot nesting without a heat flow
allowance, it could lean towards warping and cracking/ stress problems =
that
show up after the glaze firing. Seems that there are more reasons for
stacking in a wood kiln by the use of wads between the stacked pots.
Besides allowing the heat and ash to flow into the inside of the pot, it
also equalizes the heat penetration. =20
When I bisque fire plates, for instance, I put shards in the same =
pattern
under each plate and can stack up to 6 - 8 plates on top of the other. =
This
includes even under the bottom plate. When I bisque fire large =
platters, I
place shards under the piece so that the heat can get under the pot and =
not
retard heat penetration of even the shelf at this point. =20
If you approach your work practices with common sense it is much easier =
to
eliminate many problems that might occur by just going ahead without
thinking of what is happening in the kiln.
Regards,
Bonnie Staffel
http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
DVD Throwing with Coils and Slabs
DVD Beginning Processes
Charter Member Potters Council
Snail Scott on mon 14 aug 06
At 07:38 PM 8/10/2006 EDT, you wrote:
>Are there any special issues to think about when stacking greenware for a
>bisque firing? I beleieve shelves are not necessary, correct? Just
pile it
>all in the kiln and make sure none touches the elements?
The main thing is to make sure that the
greenware on the bottom is strong enough
to support the greenare on top. Save the
most fragile stuff for the top of the stack.
but...
Another thing which isn't often considered
is 'nesting' - a fairly infrequent issue,
but it does happen. It's tempting to put
bowls, for instance, inside one another.
This optimizes kiln space by using all that
interior volume inside the larger pieces
to hold smaller pieces. The problem is
that the outer pieces will heat up first,
while the inner ones stay cool a little
longer. Thus, the outer bowl actually gets
slightly larger before the inner stuff
catches up, which sometimes allows the
inner stuff to shift a bit. The real
problem will arise during cooling, though,
whenthe outer bowl shrinks first and the
stuff inside won't let it. Sometimes they
just get wedged tightly together, but
occasionally it will actually crack the
outer bowl.
Tightly nested bisque is a false economy if
work gets damaged, and you'll get a cleaner
burnout if there is a bit of space around
the work, anyway. Note that what I'm talking
about here is _very_ tight fit; it's still
better to load a bisque full than to do two
firings.
-Snail
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