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kiln shelf placement help please

updated tue 19 mar 02


Lajos Kamocsay on mon 18 mar 02


I've built a small ~7 cu ft downdraft gas kiln. I've fired it for the =
first time this past weekend with a bisque load.
I put cones that I could see through peep holes at about mid level, and =
at the top of the stacking space. I've also placed cones all over to =
check how even the firing is. The cones that I was watching bent at the =
same time, so I was really happy. However when I opened the kiln, I saw =
that on the sides of the bottom shelf none of the cones bent.
I was reading through several books on kiln building, but none of the =
ones I have talk about shelf placement, and I think that's where I've =
messed up. I made a quick sketch, here's the link:

The bottom shelf is the box in black, the blue represents the walls of =
the kiln (2300 IFB, with 2600 on the floor and in the flame path).

The inside of the kiln is 22.5" x 22.5". I use a 500,000 BTU propane =
burner, and I have a 5 ft tall 8" diameter stack on a Nils Lou type flue =
box. With this burner and the flue about 3/4 closed I had no trouble =
getting the kiln to just above 2000 degrees (Cress pyrometer), when the =
cone 06 bars melted.

There was one more shelf on top of this on 4" stilts, positioned as the =
bottom one. The kiln was not stacked too tight.

The possibility is that I've fired too fast. At the end I was going at =
about 50 degrees every 10 minutes (that's 300 per hour).

Any comments welcome.