Janet H Walker on sat 15 feb 97
We just bought a new controller for our kiln, (a Paragon TnF
II) and of course now I realize that I have no idea how fast we were
firing before (degrees/hour-- how fast is too fast?)
Before I got my controller, I used to fire quite quickly (e.g. 7
hours for a bisque 08) but after I got it, I started looking into
firing schedules in detail. Now I fire quite a lot longer but it
has made only around a dollar difference in the cost of a firing.
Not big enough to really worry about, so I concentrate on worrying
about results. The problem with really fast firing for me is that
the organics etc don't have time to burn out of the brown clays and
so the finished pieces get little or big or lots of bloats or
pinholes in them. So I do it slower and let the controller worry
about getting up at 2 a.m. in order to start things...
(All temps in Centigrade)
Bisque (05 roughly)
ramp set hold (min)
50C/hr 120C 60
150 525 0
75 600 0
150 700 0
50 900 0
100 1000 60
The soak at the end of the bisque was recommended in a number of
older texts as helping ensure elimination of combustibles, vapors
etc. It certainly hasn't hurt as far as I can see.
Glaze (^6 roughly)
ramp set hold (minutes)
50 120 60 just be sure all steam etc is out
150 525 0
75 600 0 through quartz inversion point
150 1000 0 organics are gone already
50 1205 90 slowwwww, skip out of the soak when cones look right
150 900 0 control drop to let craters heal
50 700 0 control drop to let crystalline depth develop
I use 1205C as the defining temp because that is what my (Skutt)
controller has stored internally as the final set point for a slow
cone 6 firing. The self-supporting Orton ^6 cones are often perfect
arcs after a firing with this schedule. (So don't tell me I'm
firing to ^5 on the basis of the temp!! The extra soak time adds
heat work remember, although it takes about 10 times longer for the
cone to drop when the temp remains "below" the temperature where it
would fall if the rate of heat rise were constant.)
Just a few other things. For single firing, just kinda merge the
two schedules so you have the slow organic burnout phase added. I
choose to control the temperature drop because without that, the
temperature drops 240C/hr in the first hour after you turn off the
kiln and continues to drop, though less quickly, down to about 700C.
Trouble is, cooling fast through those temperatures interferes with
development of nice colors and surfaces in many of the glazes that I
like. So being able to fire down is essential to getting the
results I want.
Have fun with the controller.
Jan Walker
Cambridge, MA USA
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