Building a Raku Kiln
It is fairly easy to make the metal frame yourself but if you think it beyond you, you will probably be able to find a local metal worker to do it for you. I used mild steel strip and pop rivetted the pieces together except for the handles and the strips around the top vent which I welded for strength.
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| Fig 1 |
Make two identical rings, mine are about 20 inches in diameter, using a strip of metal and two rivets to join the ends of the piece of strip metal. These are the top and bottom of your kiln. Also make a smaller ring, about 4 inches in diameter. This will be the burner port. Do not make it smaller than this otherwise you may find you do not get enough air mixing with your gas flame to get your kiln up to temperature quickly enough. see fig_1.
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| Fig 2 |
Make a number of clay buttons using stoneware clay with small lugs on the back which will need to be fired to Cone 8 (about 1260 degrees Celcius) when they are dry. You will need twenty or so of these. You will also need some Nichrome wire to thread through these buttons after they are fired, see fig_2.
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| Fig 3 |
fig_3. Use four strips of metal, mine are 20 inches long, equally spaced around the circumference to join the top and bottom rings. Attach four strips of metal as shown across the top of the kiln. The square made in the centre of the top by the strips will form the 'flue' of the kiln and it is important that this is about 5 inches square so that you will get sufficient air flow through the kiln to ensure efficient burning of the gas flame. I welded the crossing points of these strips for strength. Attach the burner port at a point where one of the uprights is fixed to the bottom ring. I welded this as well. Fix on a pair of handles so that you can easily and safely lift the kiln when it is hot. If you have used rivets the whole structure is probably pretty floppy at this stage but don't worry. The next stage will make it rigid.
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| Fig 4 |
fig_4. Cut strong wire mesh to size and wrap it around the inside of the frame, fixing it to the frame by twisting Nichrome wire tightly through the mesh and round the frame at several points. Cut a circular piece a little larger than the top of the kiln and push into place inside the top. Again secure it with twisted loops of Nichrome wire. Cut the wire mesh from inside the flue hole and the burner port. The whole structure should now be very rigid and look like a drum with an open bottom.
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| Fig 5 |
fig_5.
Line the inside of the mesh with aluminium foil. I used turkey size cooking foil. Don't forget to cut away the foil covering the flue and burner port. Cut two circles of ceramic fibre blanket, I used Carborundum's Durablanket S (Thick), and fix these to the inside top of the kiln so that they form a double layer. Fix the blanket by threading Nichrome wire through the hole in your stoneware buttons, pushing both ends of the wire through the blanket and foil (one each side of the mesh wire) and twisting the two ends together firmly to pull the blanket tightly onto the mesh. Cut away the blanket where it covers the flue hole.
Warning! Ceramic fibre is an irritant and should be handled carefully wearing gloves and a mask.
Wrap two layers of Ceramic Fibre blanket round the inside of the sides of the kiln, fixing them in the same way as the top. It is important that you get a very snug fit between the side layers and the top layers to prevent heat loss. Cut away the blanket where it covers the burner port and if you intend to use a thermocouple to monitor the temperature poke a hole through the foil and fibre towards the top of kiln side.
When you have finished it is best if you coat the inside surface of the Ceramic fibre with a rigidiser which should be available from your ceramic fibre supplier.
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| Fig 6 |
fig_6 Shows the 'sandwich' of two layers of fibre blanket, the foil and the wire mesh fixed together with a stoneware button.
I find that a kiln of these dimensions made in this way will reach raku temperature in about twenty minutes using an ordinary propane gas blowlamp with a one and a half inch diameter burner nozzle.
The kiln stands on a base of insulating material. You can build a platform of insulating fire brick but I find it convenient to stick two layers of ceramic fibre which are larger than the diameter of the kiln, using the rigidiser as a glue, to a metal platform mounted on wheels, which makes it easy to move the kiln around even when hot!