Recently I have been experimenting with a different firing pan — a simple, cheap, stainless steel mixing bowl, available everywhere, including $1 stores.
The mixing bowl will wear out sooner than the rectangular firing pan, but the bowl has a lot of advantages over the rectangular pan.
1. The cost.
2. The thickness of the walls. Both stainless steel and carbon are poor heat conductors. The walls of the mixing bowl are thinner and allow better penetration of heat into the bowl.
3. The shape. The narrower bottom of the bowl (where the carbon is useless anyway and interferes with the heat flow) holds less carbon.
4. The top of the bowl, where the temperature is the highest, has a larger area than the rectangular firing pan.
5. Availability in different sizes. The mixing bowl that I use for both FireFly and Caldera kilns (and which also fits in front loaders from the Paragon SC series), is 7″ in inner diameter and 2½” tall. In bigger kilns you can use bigger mixing bowls and place the pieces close to all heating elements.
Here is how I place pieces in the mixing bowl:
All these pieces are fairly big: 2″ x 2″. In the rectangular firing pan I would fire them horizontally; if I were to fire vertically, their bottom would be too close to the bottom of the box, where the temperature is lower. Here they are positioned at an angle roughly parallel to the walls of the bowl.
The following drawing may bring my point across.
All the pieces sintered beautifully, including the one in the center.
I used the mixing bowl to fire a thick piece that sometimes would not sinter at first firing in the rectangular box. It is a copper circle, ¾” in diameter, ¼” thick.
Placed close to the wall of the bowl, it sintered perfectly.
Worth a try!