Wendy Keeler on sun 7 nov 99
I have recently fired a ^10 reduction downdraft kiln (with 2 burners on each
side, bagwall, and flue in the back), not very successfully, and have some
questions I hope to put to rest.
We used longer shelves than usual, which touched the back or the kiln and
stopped only an inch or so from the door. I did not notice the height of
the first shelf to the damper (I think it was an inch or so higher than the
flue opening). We used a hard brick in the center of the flue to fit the
shelves lengthwise since they would not fit the width between bagwalls. The
work we had was all low, the first 6 shelves where half brick height,
tightly packed. The last shelf was 9" with tall pieces on the top shelf.
Damper was open 3" (normal for this kiln) and assume the air/gas is good.
The kiln seemed to take longer than usual to reach ^010. For body reduction
the damper was closed to 1". There was backpressure with flames coming out
of the peeps and the carbon monoxide smell, everything appeared normal, but
15 or 20 minutes later ^08 was down and ^06 was right behind it. Obviously
we can assume that reduction was gone (and after opening the kiln it was
confirmed). When discussing this with my professor, he felt the biggest
problem was probably the height of the first shelf. To be honest I have
never thought about the first shelf height as a big variable. Can someone
explain the role that it plays and things to consider regarding it?
-Wendy with a "bad firing migraine" on the Cape
Marcia Selsor on mon 8 nov 99
I always (or almost always) stack a 9" shelf for the first level in our
downdrafts. It just works better for a more even firing. The best thing
is an even density throughout. You should also have more space between
the shelf and the back and door wall. Could you put the shlves the side
way somehow rather than block the flu?
Marcia in Montana
Wendy Keeler wrote:
>
> ----------------------------Original message----------------------------
> I have recently fired a ^10 reduction downdraft kiln (with 2 burners on each
> side, bagwall, and flue in the back), not very successfully, and have some
> questions I hope to put to rest.
>
> We used longer shelves than usual, which touched the back or the kiln and
> stopped only an inch or so from the door. I did not notice the height of
> the first shelf to the damper (I think it was an inch or so higher than the
> flue opening). We used a hard brick in the center of the flue to fit the
> shelves lengthwise since they would not fit the width between bagwalls. The
> work we had was all low, the first 6 shelves where half brick height,
> tightly packed. The last shelf was 9" with tall pieces on the top shelf.
> Damper was open 3" (normal for this kiln) and assume the air/gas is good.
>
> The kiln seemed to take longer than usual to reach ^010. For body reduction
> the damper was closed to 1". There was backpressure with flames coming out
> of the peeps and the carbon monoxide smell, everything appeared normal, but
> 15 or 20 minutes later ^08 was down and ^06 was right behind it. Obviously
> we can assume that reduction was gone (and after opening the kiln it was
> confirmed). When discussing this with my professor, he felt the biggest
> problem was probably the height of the first shelf. To be honest I have
> never thought about the first shelf height as a big variable. Can someone
> explain the role that it plays and things to consider regarding it?
>
> -Wendy with a "bad firing migraine" on the Cape
--
Marcia Selsor
selsor@imt.net
http://www.imt.net/~mjbmls
http://www.imt.net/~mjbmls/spain99.html
http://www.silverhawk.com/ex99/selsor/welcome.html
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