Dale Neese on tue 7 aug 07
I purchased an Olsen updraft kit that I built in 85 and I am still firing it
regularly today. First I used the recommended firing chart provided with the
instructions. As hard as I tried with this cycle to achieve even reduction I
was always getting "cold spots" in certain areas in the stack. Sides of pots
or half a plate were reduced and the other half just blandly cold. With
following the provided firing chart and burner turn ups I was reaching my
beginning reduction of cone 09 before finishing the gas pressure increase
for one set of burners. (there are 10 burners on the 24cu.ft). I surmised
that not enough heat was being introduced by the second set of burners at
the time cone 09 was going down. From then on I made sure that all burners
are operating at full pressure before cone 09. The reasons I like to start
body reduction at 09 is that one of the two clay bodies that I use will
bloat and my Shino glaze will heavily carbon trap if I start reduction
earlier. Some people will like all the carbon trapping but for my aesthetic
value I don't care for the overly reduced Shinos. God bless Malcolm Davis.
With all the burners roaring at full turn up and damper wide open, cone 09
in the top of the kiln softens first followed closely by 09 in the bottom.
Then achieving even reduction is just a matter of sliding in the damper
until back pressure brings a nice strong, flickering orange flame out of the
bottom peep. I don't have any more "cold spots". All the ware is nicely
reduced. With cone 7 softening in the bottom first, I pull out the damper
only 1/2 inch, keeping reduction but allowing more heat flow to the top.
Again at cone 9 in the bottom I pull the damper out 1/2 inch more. Once cone
10 is down in the bottom there is nothing else you can do so I seal off the
bottom peep and pull the damper out for oxidation. Probably the bottom part
of the stack has reached cone 11. I stack the porcelains and iron reds in
the bottom cause they can take the extra heat. It's only a matter of a few
minutes that you can see clearly cone 10 in the top dropping in the clean
atmosphere. I do a short "soak" period of about 5-7 minutes then shut the
kiln down. Earlier I posted that this is what works for my kiln and glazes
after some tweaking. Now I usually fire easily, consistently with what I
have learned over the years from the glazes and the kiln, the same marks on
the damper, same burner turn up intervals without messing with the shutters
on the burners. Rarely do I have to use a hammer anymore.
Dale Tex
"across the alley from the Alamo"
San Antonio, Texas USA
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