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A single Bourry box kiln |
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A single Bourry box kiln |
This is the plan of a kiln with a bourry firebox. At the suggested scale it is easily built using standard 9ins x 4.5ins x 3ins bricks, and easily fired. If made with dense firebricks it would be good for salting. More diagrams and comments will be added later. The flashy colors are not just for show as some of these areas need to be identified. The plan can be modified provided certain proportions are maintained. The diagrams below are based on the plan set out by Janine King and Steve Harrison in their useful booklet Layed Back Wood Firing, the third edition of which is now available . Photos of a similar kiln being built can be seen here (external link).
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Stoking is done through the area covered by the firebox lid. The firebox door is used in the initial stages of firing while the fire is very small. It is also necessary for cleaning out ash and for maintaining the mousehole system. The mousehole has to be protected by some sort of structure to avoid clogging and to distribute the air into the bed of embers. The number and total area of the exit flues (fig 5) are significant and must be kept in proportion to the other critical areas if the plan is modified. |
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A =
cross sectional area of exit flues (fig 5) |
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Here
are some critical proportions which have been successful
in moderately sized kilns, where in both cases E = 100 To make sensible use of these figures it should be kept in mind that the part of the kiln where the pots are stacked should be approximately in the shape of a cube. In
practice, the throat arch area is easily diminished by a build-up
of embers with some woods, and in small kilns it could be made
proportionally larger. Link here
to
see a small double bourry box kiln where I have successfully used
the ratios |
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Figure 6 shows how the chimney is tapered above the exit flues. The damper can be made from an old kiln shelf. A sheet of metal will do but will tend to warp and get stuck in position. |
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