mel jacobson on mon 26 sep 11
at the farm this past week we fired my small
stoneware kiln three times in three days.
we have nils lou burners and a great deal
of propane pressure. (five hundred gallon tank.)
the firing time for all three firings was 4 1/2 hours.
yes, four and a half. all three firings had my bright
red glazes present. we did temmoku from the chinese
study....it was all perfect.
i tried to follow my own instructions perfectly.
it works.
start the kiln with as much gas as it can take. damper open
kick it in the butt. as soon as there is back pressure
at the peep, back off on the gas. get the back pressure
to about 3-4 inches. hold it there.
when cone 9 starts over we back off even more on the gas.
cone ten would fall over in about twenty minutes.
we fired these kilns to cone 11. that is cone ten flat.
we fired with bob anderson, bill burgert and tim frederich. (tim
is the past editor of pmi/ceramics monthly. he also worked for
orton for years and wrote the section on cones for our book.
we had good critics with us, for sure. we all agree...this is the
way to fire a kiln for efficiency and quality of glaze.
we had wonderful crystal growth in the temmoku. it has that
gold lustre crystal that most like.
the reds had that deep purple/red variegation that is so nice.
so many argue that glaze depth is compromised when you fire
too fast. sorry, not the case. it has a great deal to do with
hitting the right temperature on the way up, and slowing the
cooling. these glazes are dirty and flat at cone 9. they improve
a bit at cone 10, but get glorious at cone 11.
and that means firing for about twenty minutes extra.
18 hours in the kiln would not improve these glazes a bit.
just waste gas.
we burn wood scrap all during the cool down cycle.
we could use gas, but our wood kiln piles have mountains
of scrap wood in small pieces. we just chuck it in.
this kiln holds about 40 average sized pots. it is the perfect
back yard kiln. bill burgert has this same kiln in denver and
fires with natural gas, low pressure....and fires to cone 7.
(six flat over.) he has wonderful results.
my apprentice colleen, loaded and fired the last firing all by
herself. she hit the same timing and got the same result.
she was thrilled. (you know how young potters fret when they
first fire kilns alone. you know...those dreams at night.)
anyway. a great firing schedule.
unload at 8 in the morning. cool down, load at noon. fire
until almost 5 pm. do the same next day.
mel
from: minnetonka, mn
website: http://www.visi.com/~melpots/
clayart link: http://www.visi.com/~melpots/clayart.html
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