Jeff Tsai on fri 25 jan 02
Hi Martin,
Sounds like you got a good little pit there.
Temperature control is real tricky with pits, and to be frank, I highly doubt
glazes are going to work exactly as planned.
Well, let me rephrase. Don't expect a perfectly lovely glaze coating on the
inside of a piece that is in the pit. You might get one corner of the piece
where the glaze is fully melted and another corner with almost no melt. This
is because pit fires have very variable temperatures, even in areas with just
a few inches of separation.
What you might achieve, if you got the pit hot enough, is something odd like
spots of glazed areas (with chunchs of charred wood and sawdust stuck to it)
and unglazed areas where the glaze could still be washed of peeled off.
I won't say don't do it, cause I did it once, but I did it by building a
saggar box in an old outdoor kiln and filling that like it was a pit fire. I
then used the kiln's gas to achieve the temperature I wanted with little con
packs to check how hot I got, in hopes the inside of the saggar would be
around that temperature, but even then, the stuff in the kiln came out
looking like it had reached varied temperatures.
If you decide to do it, I'd be careful not to try it with my favorite piece.
As far as temperatures, I'd say most pits range anywhere from 1200 degrees F
to 1700 degrees F depending on several factors:
Thin, small pieces of wood will burn hotter than large firewood.
If you light the pit, get the fire going good, then dump a whole lot of wood
in at once, the temperature will flare very high very quickly and then die
down.
If you put all the wood in first and light the pit; or put wood in, light the
pit, and slowly add wood little by little, the temperature will not go as
high, but will stay more consistent throughout the firing process.
Deeper pits tend to get hotter, especially if you can get some air
circulating down near the bottom, or start with only half the pit full and
then add the rest once the fire gets going well down below.
Wide shallow pits tend to stay a little cooler.
A pit that is covered during large portions of the burning by a piece of
steel will retain heat and stay a little hotter.
The kind of wood, hard vs. Soft, will also change temperature (though I
forget how now)
if you channel air into the bottom of the pit through pipes (an annoying but
sometimes helpful method) the pit might get hotter.
It's a bit of work really.
There are two really good books that I recently read with articles showing
different kinds of pits. One was "Barrel, Pit and Saggar" which is a
colloection of ceramics monthly articles over the last 30 years and "Smoke
Fired Pottery" By Susan Peterson. I think these could be possible sources of
info that might inspire or help.
I think they can be found for sale on this website:
Pottery Books S
Luck to ya,
Jeff
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