Raku-temporary kilns
     The the kilns pictured here are the ones I used during raku ceramics classes at Bradford College. It takes about an hour to an hour and a half to assemble them after the materials have been brought to the site. Disassembly takes about half as much time after they have cooled.
             
 
             
     As can be seen in the above photographs, a base of eight cinder blocks is set up on the ground. Care must be taken to ensure a smooth, flat, reasonably level surface for the soft kiln brick firing box to be built on. The kiln floor consists of eighteen soft fire bricks laid tightly together over the cinder block base. Two courses of soft fire brick make up the walls of the fire box. The first course has half brick space(s) left open as burner port(s). The reason for having two ports in one kiln is to allow the use of inexpensive weed burners as raku firing guns while the kiln with a single port uses a gun designed specifically for raku firing. Weed burners are designed to throw a long narrow intense flame whereas the raku gun is designed to throw a soft short flame. The raku burner can be used to put a much higher BTU/H level without burning out the back of the kiln or causing hot spots which would cause the pieces to crack. In the fire boxes, you can see fire bricks placed about two thirds of the way back in the line of the gun(s) firing path to divert the flame from the back of the kiln and to distribute the heat more evenly throughout the kiln.
             
 
             
     The kiln shelf is supported by kiln furniture one half to one inch taller than the diverted bricks. The shelves used in these kilns are either eighteen inches in diameter or fifteen inches square. An extra shelf should be available in case of an overfiring which has caused the glaze to flow onto the shelf. The cinder block(s) set away from the kiln act as rests for the rear of the firing guns. Below, the double burner kiln is shown during a firing.
     The kiln hood which creates the firing chamber is constructed from welded wire fencing or expanded metal mesh and lined with one inch thick kiln blanket. The exhaust port is a hole in the top approximately three inches in diameter. The kiln blanket is attached to the wire with a loop of nichrome wire holding one and a half inch ceramic buttons.
     Although the burners may be controlled with a simple needle valve it is better to use a regulator at the propane tank. The regulator provides a consistent flow of gas to the burner as the pressure in the tank drops (the vaporization of the liquid propane causes tank pressure to drop about fifty percent) and in case of a rupture of the hose, the pressure of the escaping gas is less than ten percent of what it would be with a control valve at the burner. The pressures used vary not only with the particular gun being used, but also with the weather conditions (temperature, wind, humidity etc.), typically they max out at one and a half to ten PSI while tank pressures are over a hundred PSI.
             
 
raku • wabi • ceramics • firing techniques • kiln design • glazes • history      
         
To contact me with any questions or for more more information e-mail me or phone me at (603)772-1512
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