John Post on sun 2 may 04
Several years ago I was having some discussions with Jan Walker about iro=
n=20
red glazes. I began experimenting with controlled cooling in order to g=
et=20
a redder color and more metallic sparkle in the glazes.
I found that many of my glazes benefited from a slow cooling especially a=
=20
high calcium matte glaze base that I use frequently=20
I fire to cone 6 with a computer controller in my studio. After I reach=20
cone 6, I let the kiln drop to 1800 degrees F. Then I use the computer t=
o=20
drop it 150 degrees per hour until I hit 1300 degrees F and then I let th=
e=20
kiln cool on its own again. =20
As an elementary school art teacher, I wanted to duplicate this firing=20
schedule at my school. The problem was that the kilns I have do not have=
a=20
computer controller on them. =20
I have found a work-around method that I have been using all year.
I have a 6 cubic foot paragon kiln with a kiln sitter and two switches th=
at=20
are the low-med-high type. I noticed that when both switches were set to=
=20
medium the kiln would reach red heat, but not get hot enough to reach con=
e=20
6. When I leave the building for the day, I turn both switches to medium=
=20
and the limit timer to the max setting. When I come in the next morning =
the=20
kiln is at red heat. Then I turn both switches to high. It takes about =
3-4=20
hours for the kiln to reach cone 6 and for the sitter to drop.
Then I lift the sitter plunger, push the button in again and lower the=20
plunger slowly.
I turn both switches DOWN TO MEDIUM and set the limit timer for 4 hours. =
=20
This gives the kiln a four-hour soak in the red heat range. The calcium=20
mattes look as good as they do at my home studio with the controller. =20
For my glazes it appears as though it is not that important that they go=20
from 1800-1300 F at a controlled rate=85as long as long as they are somew=
here=20
in that red heat range for 4 hours during cool down they turn out fine.
I have a smaller 3.3 cubic foot kiln with the on-off type switches and wh=
en=20
3 out of the 5 switches are turned on I can maintain red heat in that kil=
n=20
and get the same kind of effect with it.=20
I am sharing this information for those that may wish to try the slow=20
cooling technique.
A computer controller is the way to go, but if you don=92t have one, this=
=20
method yields similar results for me. =20
Cheers,
John Post
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