Paul Borian on thu 12 apr 07
Hello,
Summer here is usually very humid and I have no a/c in the studio so it
can take a very long time for pots to dry enough even to trim and put
handles on, then they can sit for days before they look even close to
bone dry. I have always wanted to take the leather hard pots as soon as
they are trimmed and put them in my electric bisque kiln for a very slow
firing. My main concern was not blowing them up but rather getting a
higher percentage of cracks from the fast drying.
However I have learned a lot about clay bodies, shrinkage, cracks, etc.
and as far as I know, most cracks that take place during drying are
caused by shrinkage - and the most accelerated phase of shrinkage takes
place early in the drying process when the pots come off the wheel and
start moving toward leather-hard stage.
My clay body has fairly low shrinkage because I add a lot of
non-plastics like kyanite and mullite and as a result I get very few
cracks. Most of the cracks I do get are either because the base was too
thin or else way too thick. Even during the coldest part of this past
winter with the heat on high for several weeks continuously and pots
drying very fast I did not get many cracks.
=20
So, is it reasonable to think that putting leather hard pots right into
the bisque kiln will not result in any increase in cracks, provided that
appropriate care is taken during the early stages of drying? Does anyone
do this?
=20
Thanks,
Paul
Leticia Duenas on thu 12 apr 07
Paul,
I have done it to speed things up with success, however, I was told that I
am reducing the life of the elements of the kiln, all that moisture
corrodes the elements, so if I must I leave the lid up at least 4-5 inches
until all the moisture is fired out.
Hope that answers your question.
Leti
in sunny northern CA
Judy Rohrbaugh on thu 12 apr 07
Paul, I have the same problem in the summer.
I found a switch on my heating thremostat for "fan only" and I run that to dry out the air in the room.
It might be easier to find a way to keep your workspace/storage area dry. I remember
people using fans in school to speed up drying pieces.
I have stuck stuff in the kiln that is not completely dry, but I rarely do it. Too much water
escaping, and I feel that it just can't be good on the kiln.
Judy Rohrbaugh
Fine Art Stoneware
Ohio
Paul Borian wrote:
Hello,
Summer here is usually very humid and I have no a/c in the studio so it
can take a very long time for pots to dry enough even to trim and put
handles on, then they can sit for days before they look even close to
bone dry. I have always wanted to take the leather hard pots as soon as
they are trimmed and put them in my electric bisque kiln for a very slow
firing. My main concern was not blowing them up but rather getting a
higher percentage of cracks from the fast drying.
Thanks,
Paul
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Vince Pitelka on thu 12 apr 07
Paul -
We do it on a regular basis, although we never pile up plates or bowls
one-inside-the-other if they are still damp. Cups or bowls can be piled
rim-to-rim and foot-to-foot even if still leather hard and it doesn't seem
to do any harm. Any flat things that are still slightly damp should be
fired up on wads or shims to let heat and atmosphere circulate under them
and to simplify escape of moisture. You can stack several leather-hard
plates on top of each other that way - separate them with wads or shims,
with the wads or shims lining up vertically just as you would line up kiln
posts supporting shelves.
We generally program a preheat into our bisque-firings, and that takes care
of any pots that are still damp. On our L&L kilns I select slow-bisque, and
then program in a preheat up to 12 hours, depending on the dryness of the
ware.
I can't see that bisque-firing damp pots now and then has appreciably
shortened element life. But it is just an occasional thing. If you did it
regularly, it might shorten the element life, but it might still be worth
it.
As Leti said, if you are bisque-firing leather hard ware, during the preheat
period, leave the spyhole plugs out and keep the lid propped up two or three
on a piece of softbrick.
- 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/
Lee Love on fri 13 apr 07
Japan is usually damp, except in winter when you are running heat
inside. Traditionally, you try to make use of the sun and wind
whenever possible, setting things outside for their final drying. As
long as the rain does not prohibit it.
--
Lee in Mashiko, Japan
Minneapolis, Minnesota USA
http://potters.blogspot.com/
"To affect the quality of the day, that is the highest of arts." -
Henry David Thoreau
"Let the beauty we love be what we do." - Rumi
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