Paulette Carr on wed 22 aug 01
Marianne and Snail and others interested in uneven kilns,
I have been following the behavior of my small (3.5 cu. ft.) top-loading,
electric kiln with a kiln vent very closely while I test glazes. What I find
is that my temperature gradient is reversed from that which Snail observes:
my lowest shelf is fires to exactly the cone set by entering temperature and
soak into the controller, the next shelf up (usually 3", the cone bends to 3
o'clock rather than the complete 6 o'clock, and subsequently higher shelves
are fired to the next lower Orton cone. From here to the top shelf on which
I load objects, the cones are all bent the same, seemingly regardless of the
density. I use a blank shelf at the top as a baffle to prevent cool air from
being drawn directly across any objects. I also fire exceedingly slowly to a
top temperature of cone 9 and down again. This is completely reproducible
for me, and, thankfully, my elements have not changed enough to begin to
alter things. To me, the pattern of the heat gradient that I observe makes
sense, since I am bringing air into the top of the kiln. I have another,
larger kiln with a vent (again, air drawn in through the lid) and controller,
and will also take a look at the gradient here. I would expect it to behave
in a similar fashion, but I could always be surprised. I remember Ian Currie
mentioning a few weeks ago, that as he traveled around for his workshops he
observed a 2-cone difference in any given firing between the top and bottom
shelves. Like all things, I think it depends upon your equipment, and how it
is configured. As Snail suggested as long as you know what you are working
with you can use that to your benefit. Like everyone tells you, don't guess,
use cones!
Paulette Carr
St. Louis, MO
Snail Scott on wed 22 aug 01
At 12:38 AM 8/22/01 EDT, you wrote:
>I have been following the behavior of my small (3.5 cu. ft.) top-loading,
>electric kiln with a kiln vent very closely while I test glazes. What I find
>is that my temperature gradient is reversed from that which Snail observes
>Paulette Carr
I'm guessing that the vent is making the
difference; I don't use one. Also, my
kiln is a bit gappy, which I expect
allows for an exchange of hot and cold
air, resulting in the opportunity for a
temperature gradient.
-Snail
Arnold Howard on thu 23 aug 01
Paulette's 3.5 cubic foot kiln is firing one cone cooler in the top
than near the bottom.
Paulette, I would suggest that you eliminate the top blank shelf
that you have loaded near the lid.
The top and bottom of an electric kiln are more difficult to heat
than the center. This is because the top and bottom firebrick mass
absorb so much heat. By eliminating the top blank shelf, your kiln
will have much less mass at the top. That shelf is absorbing
energy, lowing temperature.
If incoming air from the vent is affecting the glaze on the top
shelf, you could reposition the ware or plug holes with fiber and
allow the air to enter through a peephole.
When I test fire 8-sided kilns, the temperature is ordinarily very
uniform--usually half a cone from top to bottom. A 2 cone
difference is unusual.
With best wishes,
Arnold Howard
Paragon Industries, Inc.
--- Paulette Carr wrote:
> Marianne and Snail and others interested in uneven kilns,
>
> I have been following the behavior of my small (3.5 cu. ft.)
> top-loading,
> electric kiln with a kiln vent very closely while I test glazes.
> What I find
> is that my temperature gradient is reversed from that which Snail
> observes:
> my lowest shelf is fires to exactly the cone set by entering
> temperature and
> soak into the controller, the next shelf up (usually 3", the cone
> bends to 3
> o'clock rather than the complete 6 o'clock, and subsequently
> higher shelves
> are fired to the next lower Orton cone. From here to the top
> shelf on which
> I load objects, the cones are all bent the same, seemingly
> regardless of the
> density. I use a blank shelf at the top as a baffle to prevent
> cool air from
> being drawn directly across any objects. I also fire exceedingly
> slowly to a
> top temperature of cone 9 and down again. This is completely
> reproducible
> for me, and, thankfully, my elements have not changed enough to
> begin to
> alter things. To me, the pattern of the heat gradient that I
> observe makes
> sense, since I am bringing air into the top of the kiln. I have
> another,
> larger kiln with a vent (again, air drawn in through the lid) and
> controller,
> and will also take a look at the gradient here. I would expect
> it to behave
> in a similar fashion, but I could always be surprised. I
> remember Ian Currie
> mentioning a few weeks ago, that as he traveled around for his
> workshops he
> observed a 2-cone difference in any given firing between the top
> and bottom
> shelves. Like all things, I think it depends upon your
> equipment, and how it
> is configured. As Snail suggested as long as you know what you
> are working
> with you can use that to your benefit. Like everyone tells you,
> don't guess,
> use cones!
>
> Paulette Carr
> St. Louis, MO
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