Portable Raku Kiln
This kiln is powered by a propane weed burner we picked up at the local farm store for about $50. A few used bricks serve to keep the burner in place, although we do have to be careful not to kick the burner and gas hose when walking around. We also have to be careful to plant our tomatoes and peppers in a much sunnier spot next year. Poor things. And do you see our flamingos? They are made of plastic! They migrate to the tool shed for winter.
The burner port is about 4 inches wide. The weed burner is capable of delivering far more fuel than the kiln can handle, and does not need to be turned up very high to get a good temperature rise in the kiln. This kiln probably takes a bit longer to reach temperature than similar kilns because of the relatively small burner port and flue, but it seems to be quite fuel efficient.
- Update -
Experimentation revealed that the quickest temperature rise occurs when the burner nozzle is positioned a bit further away from the burner port - roughly 2 inches away.
Here you see some glazed pieces prewarming on top of the lid, and the reduction buckets in the background. Note the wet concrete: the nearby shrubbery and woods are watered down with a lawn sprinkler before firing, just to be on the safe side.
Glazed pieces - some handbuilt candle holders - prewarming on top of the lid.
Just after removing the lid.
The reduction buckets contain wood shavings and newspaper.
Here is one of the finished pieces. In fact, this is one of the candle holders that you can see prewarming on top of the kiln, before it was fired.
The flame enters the burner port at the bottom of this photo. A firebrick serves to hold the shelf and also deflect the incoming flame. Broken firebrick pieces on either side of the burner port complete the shelf support. These bricks distribute the weight of the shelf so the fiber doesn't compress too much. To the right you can see where we miscalculated when cutting the fiber blanket, and had to add a piece about 2 inches wide to fill the gap. After several firings it seems to be staying in place nicely.
Five homemade ceramic "buttons" positioned near the top hold the fiber blanket to the sides of the drum. The fiber blanket is not pulled tightly against the metal, but just held snugly, as the fabric should not be compressed.
The ceramic buttons also hold the insulating fiber against the lid's underside. The buttons were bisque fired, and we have several in reserve in case any need to be replaced.
Homemade "stilts" made from metal scraps keep the lid from touching the ground when it is removed. Here you can also see the wire that holds the buttons in place. It's just twisted and flattened a bit. Not fancy at all. Thanks to Brent Jay for the nifty handle!
The high temp wire came from our local ceramics shop. The buttons are made so that the wire is not exposed directly to the flame, and they have gone through several firings with no problems. In fact, after more that a year, not one of them has failed. Installing them is a bit tricky, as the wire has a tendency to meander when pushed through the fiber blanket.
The drum was cut down to 23 inches height. It is lined with 2 layers of 1 inch thick ceramic fiber blanket - although the blanket is generally thicker than an inch, so it's greater than 2 inches thick in most places. The seams are offset for maximum insulation.
Thanks to Brent Jay for his acquisition and fabrication of the 55 gallon drum.
Thanks to Linn Hower for his assistance in building the kiln.
- It is absolutely essential to wear gloves and some sort of protective breathing mask when working with ceramic fiber!
- Safety glasses and long sleeves would also be a real good idea.
- I also wear a respirator when I am near the kiln while it's firing, as it gives off nasty fumes from the paint that is gradually burning off both the barrel and the fuel nozzle. Nasty, nasty fumes.
