John McCain on sat 5 jul 97
Julie,
My wife and I have fired our Olympic Updraft Propane Kilns (3 of various
sizes) to Cone 10 frequently for the past 10 years. More gas is
generally not the answer when they stall, and they do stall
occasionally. I have several suggestions as follow:
1. Adjust the height of the top baffle. If the baffle is too high, the
kiln may stall, too low and it may go to temperature too fast in full
oxidation. Our kilns have one or two holes in the lid. I place the
baffle (an octagonal kiln shelf about 18" diameter) centered below the
hole about 3 inches from the bottom of the kiln lid. The placement of
this baffle is the key to even firing in an updraft kiln in my opinion.
2. Do not flood the kiln with gas. This can cause extreme reduction
and can actually bring down the temperature of your kiln. I sometimes
reduce the gas flow to the kiln to get the kiln up to maturation
temperature. As the kiln approaches Cone 10, the flame is generally
only licking out the vent hole in the lid of our kilns, maybe 3 or 4
inches and it might be coming out the top bung hole (about 4 inches
below the lid bottom) a little bit.
3. Closing the damper increases the amount of reduction in your kiln
and can reduce kiln temperature. I like to soak our pots at maturation
and sometimes I fire down using the damper to cause reduction, then burn
out for a few minutes at the end. We adjust the damper (a piece of kiln
shelf) to cause light reduction from about 1800 deg. F to Cone 10;
however, this is nowhere near 1/3 closed. We get fairly heavy reduction
at that percent closed.
Keep us posted on your firing.
Regards,
John & Judy McCain
Palo Pinto Pottery
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