Chris trabka on tue 11 mar 08
This past weekend I had my first "winter" firing. I have been able to
avoid firing my kiln while there is snow on the ground until this year.
While I was loading the kiln the temperature did not have a lot of degrees
in it and the morning of the firing the temps could only muster single
numbers (at least it was positive numbers). The kiln is a wee bit of a
snob when it comes to a glaze firing. It allows the oven and the gas water
heater to be used. Unfortunately she doesn't put up with the furnace! When
the furnace runs the kiln is quite happy to go from a nice soft reduction
firing to a pure oxidation firing (even if she is loaded with copper reds
and celadons). So the only cure is to turn the furnace OFF when the kiln
gets to cone 06. It takes 7 hours to get from cone 06 to cone 10. The
house was a bit chilly, and we were all wrapped in double blankets waiting
for the kiln to finish. She did, right on schedule, and the furnace was
put back into service (what a potter will put up with for a firing!).
Three days later I could open her up. What a glorious firing!! The copper
reds have never been as deep and ritch! I'm not sure if it was the temps
or the dew point. I won't have another firing day like the last one for
quite some time.
Have any of you experienced a positive firings in the winter months with
cold temperatures?
Chris
Paul Borian on thu 13 mar 08
hard to tell if the cold weather helped get those reds.
My waste oil kiln fires incredibly fast on cold days - i got several of
them in this winter and my 70 cu.ft. kiln can handle somewhere around
900,000 btu's without too much smoke. If i fired with that much fuel
pressure in mid summer on a hot humid day i would get totally smoked out
and the temperature would drop instead of rise.
But, back to your question, you may be able to learn something here -
either your reds came out nice because the kiln reduced less than normal,
and this would be because the very cold air, which is more dense and
therefore has more oxygen, helped create a less reducing atmosphere and
that improved the color response. I have heard that too much reduction can
be bad for reds but i never proved this to myself and gave them up a few
years ago in favor of other glazes. But it is definitely possible that the
more oxidizing atmosphere helped them.
OR, the other possibility, which is kind of the opposite scenario, is that
the cold air made you have to turn up the fuel pressure more in order to
get the reduction you wanted, and this in turn helped even out the temps
and the atmosphere throughout the kiln, and that can definitly be good for
reds. This theory is based on my experiences, in that ever since i figured
out how to get the absolute max btu's out of my kiln i have found the
temps have evened out considerably - and the top of the kiln, which used
to be cooler, is now right up to temp with everywhere else and in some
cases hotter. The flames in my kiln travel clear across the flame trench
right up to the very top of the arch - i know this because i can see the
way they color the bricks up there, leaving some kind of residue from the
oil.
At any rate, you should be able to get reds like that regardless of the
ambient temp outside. But hopefully you can use this experience to figure
out how to adjust the firing schedule for next time to get them again. You
should let us know how the next firing goes...
Paul
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