mel jacobson on mon 4 dec 06
the most difficult part of firing the iron saga pots to
cone 13, with high iron clay was keeping the atmosphere
of the kiln in oxidization. if we even got a little bit
of reduction we would see bloating.
it was a very good test of bloating theories. high temperature,
high iron clay, and high iron glaze.
first, i mixed the clay very well. joe sent the clay
from laguna, but i added grog and sand...so the
mixing was critical so we did not get layers.
when i fired the kiln, i removed the damper, and filled
the slot with kaowool. i wanted the stack to pull
freely. no obstruction.
the gas pressure was kept low. this added about
two hours to a typical full load firing. but, for sure,
i could not creep up the gas pressure. i too, added a bit
more primary air. (opened the bell closure)
all cooling was done with down firing....at least three
hours...in two sessions.
if my firing was kept at least nothing more than neutral,
the pots did not bloat. any reduction at all and we would
find very fine bloat marks..if the kiln got away from me,
well it was a mess...bloats as big as quarters.
it still amazes me that we were able to fire that high,
with very runny glazes, and high iron clay and the
pots did not warp or collapse.
it indicates that reduction does a lot a bad things to
clay and glaze when done without control. the older
and more experienced i get, the more i hold back reduction.
that old saw of black coated kilns, smoke and flame from
the stack....well, it all leads to very poor pots. (and a terrible
waste of fuel.) it is like
taking pain medicine...`well, if one of these vioxx pills makes
me feel a bit better, i am going to take ten. bingo.
the oxyprobe taught me some great lessons. i do not use
it much anymore...no need. but for sure, it let me see, first
hand, how reduction could overpower a kiln, and i did not even
know it. that damper can be moved a quarter of an inch and
the reduction skyrocketed.
reading the back pressure of your main peep hole is critical
with fuel firing. i like to use a front of the kiln, half way down
peep hole. i never let more than 2.5 inches of flame come from
the kiln. ( you know i do not measure it...it is observed.) that peep
is in the kiln, not the door...it never changes position...and the
cones in front of that peep are my `main readers`.
i have worked with potters, art centers where the flame coming
from the kiln was three feet...yes, 36 inches...and they
wanted to add more gas pressure when the kiln stalled.
the kiln stalled because of the back pressure, not the lack of it.
makes me crazy.
(crazier)
mel
from: mel/minnetonka.mn.usa
website: http://www.visi.com/~melpots/
Clayart page link: http://www.visi.com/~melpots/clayart.html
Kathy McDonald on mon 4 dec 06
Mel if ya don't want that oxyprobe...send it my way ....
Kathy
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of
mel jacobson
Sent: Monday, December 04, 2006 6:03 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: bloating/iron saga study
the most difficult part of firing the iron saga pots to
cone 13, with high iron clay was keeping the atmosphere
of the kiln in oxidization. if we even got a little bit
of reduction we would see bloating.
it was a very good test of bloating theories. high
temperature,
high iron clay, and high iron glaze.
first, i mixed the clay very well. joe sent the clay
from laguna, but i added grog and sand...so the
mixing was critical so we did not get layers.
when i fired the kiln, i removed the damper, and filled
the slot with kaowool. i wanted the stack to pull
freely. no obstruction.
the gas pressure was kept low. this added about
two hours to a typical full load firing. but, for sure,
i could not creep up the gas pressure. i too, added a bit
more primary air. (opened the bell closure)
all cooling was done with down firing....at least three
hours...in two sessions.
if my firing was kept at least nothing more than neutral,
the pots did not bloat. any reduction at all and we would
find very fine bloat marks..if the kiln got away from me,
well it was a mess...bloats as big as quarters.
it still amazes me that we were able to fire that high,
with very runny glazes, and high iron clay and the
pots did not warp or collapse.
it indicates that reduction does a lot a bad things to
clay and glaze when done without control. the older
and more experienced i get, the more i hold back reduction.
that old saw of black coated kilns, smoke and flame from
the stack....well, it all leads to very poor pots. (and a
terrible
waste of fuel.) it is like
taking pain medicine...`well, if one of these vioxx pills
makes
me feel a bit better, i am going to take ten. bingo.
the oxyprobe taught me some great lessons. i do not use
it much anymore...no need. but for sure, it let me see,
first
hand, how reduction could overpower a kiln, and i did not
even
know it. that damper can be moved a quarter of an inch and
the reduction skyrocketed.
reading the back pressure of your main peep hole is critical
with fuel firing. i like to use a front of the kiln, half
way down
peep hole. i never let more than 2.5 inches of flame come
from
the kiln. ( you know i do not measure it...it is observed.)
that peep
is in the kiln, not the door...it never changes
position...and the
cones in front of that peep are my `main readers`.
i have worked with potters, art centers where the flame
coming
from the kiln was three feet...yes, 36 inches...and they
wanted to add more gas pressure when the kiln stalled.
the kiln stalled because of the back pressure, not the lack
of it.
makes me crazy.
(crazier)
mel
from: mel/minnetonka.mn.usa
website: http://www.visi.com/~melpots/
Clayart page link:
http://www.visi.com/~melpots/clayart.html
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