Lajos Kamocsay on mon 27 jan 03
Hello,
I've fired my small downdraft gas kiln to cone 6, and did not want to reduce
at all.
When cone 5 started to bend in the middle of the kiln I've noticed that the
top of the kiln was cooler, cone 5 was not even soft. Then I've closed the
flue a little bit to keep more heat in the top. I've noticed some flame coming
out of the peephole, so I've turned the burner down, but this only lasted for
probably a minute.
When I unloaded the kiln today, I've found that the glazes containing cobalt
turned grey on the top of the kiln, another containing copper turned purple.
I've seen this effect more closer to the walls.
The further down I got unloading, the better color I saw on the pots.
What am I doing wrong? Am I firing with too much gas and the flue open too
wide so that heat can't build at the top? Why do I get reduction on the top
and not at the bottom?
Any ideas welcome.
Thanks,
Lajos
Ron Roy on wed 29 jan 03
Hi Lajos,
The one rule I found most helpful in a fuel burning kiln is - direct flame
to cold areas. Sounds like the flame in your case is being drawn out too
soon - does not get to the top before it is pulled down.
Two ways to go - bag wall so the flame has to travel up further to get out
- and or reduce chimney pull (damper in) so the flame is not sucked out too
soon. So - if you don't want reduction you will have to reduce gas. This is
assuming you have atmospheric burners. If you have blowers on your burners
- forced air - it is different in that you reduce draft and then balance
air and gas for oxidation.
The more you slow down the flame the more chance you will get carbon
monoxide if you are reducing - can be deadly - make sure you have a CO
monitor going when firing fuel burning kilns in a confined space. CO is
insidious - it will travel well - into adjacent rooms - best to know it is
around whenever it is.
RR
>I've fired my small downdraft gas kiln to cone 6, and did not want to reduce
>at all.
>When cone 5 started to bend in the middle of the kiln I've noticed that the
>top of the kiln was cooler, cone 5 was not even soft. Then I've closed the
>flue a little bit to keep more heat in the top. I've noticed some flame coming
>out of the peephole, so I've turned the burner down, but this only lasted for
>probably a minute.
>When I unloaded the kiln today, I've found that the glazes containing cobalt
>turned grey on the top of the kiln, another containing copper turned purple.
>I've seen this effect more closer to the walls.
>The further down I got unloading, the better color I saw on the pots.
>
>What am I doing wrong? Am I firing with too much gas and the flue open too
>wide so that heat can't build at the top? Why do I get reduction on the top
>and not at the bottom?
>
>Any ideas welcome.
>
>Thanks,
>Lajos
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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