Jeff Lawrence on fri 11 may 01
Hi,=3D20
=3D20
I usually rely on Clayart to explode myths, but this thread is shaking =3D
my faith.=3D20
=3D20
Vince Pitelka, from whom I have learned a great deal about pottery in =3D
this forum, asserts that dampering in makes the top of a kiln heat up, =3D
not the bottom. He demonstrates this with compelling theoretical =3D
accounts of what actually does happen.=3D20
=3D20
Unfortunately, Vince, my kiln just doesn't get it -- over several =3D
hundred firings, it has cantankerously and consistently done exactly =3D
what you have so elegantly proven it cannot do.=3D20
=3D20
Perturbed near Pojoaque,
Jeff
PS the kiln in question is for sale -- email me for brochure: Very =3D
efficient downdraft 100 total cu feet (80 usable), monolithic fiber =3D
block construction with inside coated with ITC 100, natural gas fired =3D
MFT type with Ward power burners and too big a flue -- which may be the =3D
culprit. Aside from its scofflaw behavior, it's a good kiln.
vince pitelka on sat 12 may 01
Jeff Lawrence wrote:
"Vince Pitelka, from whom I have learned a great deal about pottery in th=
is
forum, asserts that dampering in makes the top of a kiln heat up, not the
bottom. He demonstrates this with compelling theoretical accounts of what
actually does happen.
Unfortunately, Vince, my kiln just doesn't get it -- over several hundred
firings, it has cantankerously and consistently done exactly what you hav=
e
so elegantly proven it cannot do."
Jeff -
Thanks for the kind words. I think it is all a matter of how MUCH you
damper the kiln. If you close the damper too much, the top will be reduc=
ing
while the bottom is still in neutral or partial reduction, and the top wi=
ll
stall out while the bottom will continue to climb. We are talking about
very subtle adjustments. If it were not possible to close the damper
slightly and concentrate heat towards the top, we would never be able to =
get
the upper part of a downdraft kiln to temperature, unless we just slowed =
the
firing down so much as to insure even heat through simple convection. Mo=
st
of us do not have time for that, so it makes sense to control heat
distribution through a symbiosis of burner and damper settings.
Before we reach body-reduction temperature we usually fire a downdraft in
neutral or slight oxidation, and yet the top still reaches body-reduction
temperature first. That is due to the natural inclination of heat to ris=
e,
especially before the chimney is hot. Once the chimney is really hot the
stack draft becomes much more intense, and later in the firing it becomes
more of a challenge to even out the top and bottom temperatures. I have =
had
best luck by maintaining a light partial-reduction atmosphere after body
reduction. This usually gives very even temperatures top to bottom by th=
e
time we hit cone 10, and usually eliminates the need for any glaze
reduction.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
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