Janet H Walker on wed 29 oct 97
For Joan Warren (and anyone else getting going with controllers.)
Here's my ^6 firing schedule just so you can compare (warning! I
ALWAYS use degrees centigrade because I like small round numbers.
Please, Please if you copy this down write CENTIGRADE all over it
and enter the program in centrigrade. If you are going to convert
to Fahrenheit, be sure to get the exact conversion formula, not
something that is close enough for low temperatures.)
Ramp Target Hold
40 120C 1:00
135 525C 0
75 600C 0
100 700 0
50 900 0
60 1200 0:25
150 900 0
50 700 0
I should put the "6" in quotes because cone 6 never actually falls
for me but the ^7 is starting to bend just a bit. Cone 5 is
definitely flat. So according to Tony Hansen's treatise on reading
cones, this is probably a ^6 firing. I use 1200 as the end point
because 1205 is the temp that the controller would go to when toldto
do a slow ^6 firing. I just rounded down a teeny bit. I decided on
the soak time after a lot of tinkering and eyeballing of cones
during longer soaks. I found that a soak of 40 minutes with this
schedule caused the ^8 (yes, that's eight) in the sitter to melt and
shut off the kiln. So I now use 20 to 25 minutes so that I don't
lose control over the cooling.
There's no point that i can see in an overnight preheat. If I've
put things in with wet glaze on them, I will sometimes put in a
delay of several hours before the firing starts. Having the vent
fan on during the delay will clear the humidity and let the pieces
dry as far as I can tell. Overnight preheats are leftover from
pre-controller days when people had to switch manually and preferred
to do it during 9 to 5 workdays.
Note that Orton cones are calibrated for 60C ramp during the final
two hours of firing. If you go slower than that, you should lower
the final target temperature.
For crystalline glazes, I remember from my reading that fast cooling
from top temp to the critical temp for crystals is how people do it.
(Egad, what a clumsy sentence.) Don't bother programming in a temp
drop. On my controller, you just tell it to drop at 9999 degrees
per hour to the point where you wantto take over again. I
understand from my reading that some intrepids actually open their
kilns as a way of getting them to cool really fast. But wear your
asbestos suit... My underinsulated kiln cools plenty fast without
that kind of drastic action so I have to control its fall in order
to give glazes time to heal over their bubbles.
So have fun.
Jan Walker
Cambridge, MA USA
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