Fred Paget on mon 18 aug 97
I'm just back in California from British Columbia where I participated
in the recent firing of the TOZAN kiln, and I have a ton of e-mail to go
through. Apparently I was the only person from USA to attend this firing.
I was surprised at how developed British Columbia is. I thought I was
going to the ends of the earth and was ready for lots of rain and chilly
weather. Expected the locals to have web feet, etc. However the weather was
just like California at this time of year. Dry and warm. The locals were
all going around in shorts and T shirts. No web feet seen. There was no
rain while we were there except one brief shower.
Nanaimo, site of TOZAN, is a growing city with lots of new development.
TOZAN is located on a hillside in what was formerly a remote area
surrounded by woods. However they have just built a new road just behind
and uphill from TOZAN- what we in the States would call a freeway except it
has traffic lights at each interchange instead of overpasses . There are
some houses above the freeway. Just downhill they have cut down the trees
and built a new baseball stadium. To the right of the entrance road there
is a new college dormitory and more dorms are even now being built to the
left of the entrance road. Civilization is crowding in on the dragon.
TOZAN is a reproduction of an 18th century Japanese multichamber (5)
climbing kiln, a noborigama. The firebox is called the doggi and is the
first chamber. It has ware stacked at the rear above the grates. Above the
doggi are four chambers about 5 by 8 feet each with small firegrates at the
front of each that are used late in the firing to heat the upper chambers
to cone 10 after the doggi reaches cone 11 or 12 and is sealed up.
TOZAN is big, it is hungry for wood, and it smokes . The TOZAN Kiln
Cultural Society is trying to cut down on the smoke but it is difficult to
do that without destroying the medieval character of the kiln. It is a
marvelous kiln and does a beautiful job of firing as designed.
Notice the word "Cultural" in the Society name. Many of the members have
been trained in the far east or imbued with the philosophy of the eastern
potters and they do not want to do things that might change the mystique of
the kiln.
As a retired engineer, when I first saw the kiln start to smoke my brain
went into high gear and I thought of numerous high tech solutions to the
problem of the smoke. As the kiln heated up I began to see that it was not
that easy a problem. Some members are afraid that a great lessening of the
smoke will change the atmosphere in the kiln over to oxidation and their
glazes will not work . Installation of oxygen probes and pyrometers are
anathema to others, Firing is by observation of the color and cones if they
can be seen through the stoke holes. (We lost the cones in the top chamber
somehow - apparently somebody knocked them into the ash pit when stoking.
After an initial warm-up of 1 day with a small campfire size fire in the
doggi we began to put in more wood, in smaller pieces than the previous
firing. We were using 2 by 3 by 18 inch pieces, 6 pieces every five minutes
at first. Later the quantity and frequency were increased. Toward the end
it was about double the initial rate with a couple of larger pieces at each
stoke. Firing went on for about 5 days and nights in 3 shifts. Around 10
cords of fir and pine were used with a great quantity of lath like scrap
strips from a planing mill used in the side stoking the last day.
To stoke, the firebox door is opened and the wood thrown in to spread it as
evenly as possible on the grate. Instantly upon being thrown in to the
yellow hot doggi the wood belches into flame. Fire begins to shoot out the
door and it is almost like throwing gasoline onto a fire. The volatiles are
immediately driven out of the wood and the pressure in the kiln rises above
atmosphere. Black smoke seeps out of every hole and crack in the kiln and a
mighty cloud of black smoke goes up and out the chimney. Slowly over a
period of several minutes it clears up and it is time to stoke again. Why
smoke does not also come out of the primary air intake holes in the front
of the doggi is a mystery to me. Probably the draft is just strong enough
that it does not happen. The fact that the pressure goes up so much sort of
rules out introducing secondary air at the doggi. And if you tried to blow
it in with a blower system it probably would blow smoke out through the
primary air holes.
We experimented one day with a sort of continuous stoking. One or two
pieces of wood every minute and it did not smoke that way. This would wear
down the crew in short order however, and is impractical late in the firing
when it would take about three people to open the door and stoke a larger
amount about every 30 seconds.
There is a sort of afterburner in the short vertical chimney at the end of
the long tail-pipe that goes up the hill. It is running on a lot of
expensive propane and it seems to do very little. One day it quit and we
could see no difference in the amount of smoke. It looks like to make it
work right you would have to cut the tail off the dragon and ram a
stovepipe 50 feet high up his fundament with the afterburner at the bottom.
This radical surgery is not in tune with the culture of the Society.
Perhaps the flues can be opened up a little more for the next firing and
some sort of a system of ropes and levers can be connected to the damper
(which is 50 feet uphill) to control it to get more draft at the time right
after stoking when the volatiles come off the wood. In spite of opposition
I think that an oxygen probe is essential to settle the argument as to
whether the kiln is in oxidation when it is not smoking.
Toward the end of the firing my busy little brain gave out and they gave me
the honor of stoking the last piece of wood as I had traveled the
furthermost to come to TOZAN.
A week later we gathered at the still luke-warm kiln to remove about a
thousand beautiful pots . It was the best firing yet.My 20 pots came out
beautifully. Got my TOZAN T-shirt and I made a lot of new friends.I had a
great time.
Fred Paget---Mill Valley,CA,USA
Never try, never win!
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