Hiro Matsusaki on tue 25 feb 97
Reduction firing extends the artistic range of a studio potter. An attempt
to convert an electric kiln into a gas fired one is one manifestation of such
an ardency. Only gas (occasionally wood) firing is conducive to reduction.
An electric kiln, commonly available at a very reasonable price, is
oxidizing (or neutral, it does not matter how you may call it--it's a moot
question, it does not change a single bit how I use it), and cannot be used
for reduction firing the way it is set up. A commercially available gas
kiln, on the other hand, is usually bulky and quite pricy, actually way too
expensive, compared to the electric one. Sacrifice one electric and make it
into a gas kiln using its shell is not necessarily a bad idea, especially an
old useless one, but it takes far more than putting some combustibles in it,
I believe, and hence it is not practical. It is better to build one from
scratch. It is much cheaper. But we are not all engineers. At any rate,
sometimes it costs a lot to modify the power supply for a proper hoolup to an
electcric kiln. It costs far more to modify the domestic gas supply for a
proper hookup to a gas kiln. Propane is less costly in the short run, but
the risk that accompany its use are varied and greater.
Smaller gas kilns exist in the form of a raku kiln. We are more or less
accustomed to propane use in barbecues, and if lucky, RVs equipped with
propane to go camping and do cross-country skiing in the middle of winter.
A small fibre raku kiln, properly constructed, should be able to handle
most reduction fire, but their drawback is its relatively small size. A word
of caution here. Propane used to be cheap. Not any more. We no longer heat
our house with propane in the winter. We use natural gas. Natural gas is
cheaper, but we don't know what will happen to the price in future. I never
took the low propane price for granted, anyway. A dosen years of heating the
house at sub-zero weather and a routine use of RVs gave me a lot of
experience on propane. ... ...
A reduction kiln is simply a box into which a heated mass of gas (flame) is
introduced, so that the interior, which is full of clay can be heated to the
temperature we desire. Needless to say, larger the box and higher the
temperature, the more heat or gas becomes needed or required. Strangely,
larger the box, it takes far less gas per pot, or less heat value per unit of
clay to be fired. The larger the kiln, the more economical it gets as far as
the gas usage goes. Incidentally, the cheapest and the most abundant source
of heat on earth is the sun. Natural gas is but what stayed underground for
ages after the sun had converted a mere fraction of its heat (infinitesmal
amount, as it turns out) into a sort of fire hazard.
In the olden days, when wood was used as fuel, as with the climbing
multi-chambered kiln in Japan, the fuel was a determining factor. Firing
once a year by an itinerary kiln master, a communal kiln was a logical
conclusion. This sort of firing frequency and dependence on unreliable fuel
(quality of wood vary from year to year, supply not always guaranteed) is
sustainable today only by the top studio artist who has a bunch of disciples
who follow the instruction faithfully. A smaller wood kiln is not an
economical proposition. The cost (time spent) is prohibitive for the mild
learning curve achieved.
We are fortunate in North America. Gas is cheap and abundant. It is
therefore of seconday consideration to the studio potter. The first, as
always, is the aesthetics. One beautiful piece, the entire firing cost of
fuel is recovered. This is not so for a commercial operator. Anything that
keeps the fuel cost down is of primary importance. Anything to lower the
production cost, including labor, must be looked into. Foreign competition
where fuel is dear but labor is cheap (the opposite of ours) will make sure
that this is so. To me, a small gas kiln the size of a large electric kiln
is not a good idea, but for different reasons other than the fuel
consideration.
What size gas kilns do you think is ideal for a studio potter/artist? Since
fibre is far more fuel efficient (higher insulation value) than bricks,
should it be used all the time? If the fuel is of secondary importance, the
material may not matter much, but where do we draw the line. For what type
of firings?
HM
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