Ive been doing pottery now for a few years and recently bought an old small ‘test’ up draft kiln with a capacity of 2 cubic feet and a single gas burner coming in from the side at the bottom ( an Australian Port-O-Kiln ‘Chameleon’ made about 1975)
The problem I am finding is that of uneven temperature, something which I know is not uncommon in updraft kilns.
Bricks are used as a floor but the rest is ceramic fibre.Two shelves can fit in to accommodate the height of tall mugs or two cereal bowls stacked rim to rim.A third top shelf is used as a baffle to help draw through the heat.
The shelves have been placed at the same height (zig-zagging from back to front – again for heat flow )for three bisque and one glaze firing .The bottom shelf is sited just above the burner port opening. the second shelf up is approximately in the middle.
I have a pyrometer monitoring the kiln located in the upper part of the kiln with the only spyhole also located in the upper part too.
Reaching the projected target of ^10 (for the glaze firing) proved very difficult and concerned at my previous bisque firings which showed overbisqueing in the lower half of the kiln I stopped at 1214 Celsius.
Cones on the two useable shelves showed ^9 starting to fall on the middle shelf and ^12 starting to fall on the bottom shelf ! -so approximately a 40 to 50 degree Celsius temperature disparity.
Between the last Bisque and the latest Glaze firing I had reduced the size of the shelves along the sides and under the bottom shelf placed a small fire brick with it’s corner angled to split the flame. These measures were again designed to even out temperatures.
If the shelves are reduced further this would obvious decrease the amount of ware I can fire in this very small kiln.
Any suggestions to even out temperature ?