We recently replaced our soda kiln at the Craft Center, and I plan to post some images of that kiln very soon, but for now, here are images of the previous kiln. It is a 24 cubic foot (total volume) downdraft/crossdraft IFB (insulating fire brick). The kiln was almost five years old when these photographs were taken, shortly before it was replaced. That may seem a short life, but averaging through the year, the kiln was fired about once a week, and thus survived around 250 firings. Most firings were to cone 10, but I am excited by the results of cone 6 soda firing, and have been encouraging my students to experiment with this temperature. The results are good, the colors and graphics are crisp, and the kilns last a lot longer.
I fire my own work to cone 6 in this kiln, using 1 1/2 pounds of soda dissolved in several gallons of hot water, sprayed in fifteen-second bursts with a pump-up garden sprayer into the burner ports as cone 6 softens, fanning the spray back and forth against the bagwall. I alternate back and forth between burner ports two or three times, wait five or ten minutes, pull a draw ring to gauge soda deposition, and repeat this process several times until I get the surface I want. While spraying soda I close the damper most of the way in order to get a more even deposition over the colored clay surfaces.
The first incarnation of this kiln was a flat-top, designed and built by Meagan Kieffer and Mel Jacobson, and it was Mel who wisely suggested spraying the interior with ITC 100. Four years ago we rebuilt the kiln with a sprung arch using new IFB in the arch. The walls are constructed with a combination of new and recycled IFB. The used bricks were placed with the good face inwards, and if there was no good face then one face was cleaned down to fresh surface, or else they were placed in less vulnerable locations. The floor, the area around the firebox and burner ports, and the door sills are hardbrick. There is a 2" layer of AP Green insulating castable on top of the arch.
As mentioned, the kiln interior was sprayed with a thin coat of ITC 100 before it was fired the first time. The door is bricked up with a single thickness of hardbrick each time, and on such a small kiln that isn't much trouble. After 100 firings we are starting to get some exfoliation on the inside of the arch, and we simply scrape it every few firings to knock off any loose material.
The kiln is fired with two MR-100 GACO venturis on high-pressure propane with an adjustable regulator and high-pressure Baso valves. We rarely turn the pressure above 5 lbs. The kiln has about 18 cubic feet of stacking space.
Normally I always build kilns up off the ground on a concrete block foundation, in order to make it easier on the back when loading and unloading. This kiln had to fit under the overhead ventilation hood, with enough chimney height to make it work as a downdraft. There is a length of iron pipe on top of the brick chimney, and it points directly up into the flue, which minimizes corrosion of the hood itself.