Barthélémy Pedotti - Fire madness
I filled you with this longtime work, kiln, give it back!
Potter chooses his kiln according to the clay used, his production and the available energy.
Outside cities, wood is readily available (as above, edging slabs). With wood one can reach 2550°F (if dry and with a well designed kiln!) and it gives "sensitive and living" glazes; an obvious choice if you're ready for the extra work involved. - the firing kiln reaching 1500°F, side flues opening will be reduced, wood ignites as soon as put on the grate.
The kiln must have a compact volume - like a cube or a sphere - of about 1m³ (35ft³) for a self employed potter - to ensure that the heating is uniformly distributed; constraints are such at these temperatures that the kiln needs to be strapped like a barrel, or even set in a metal cage - Catenary arch kiln plan - Front View
The catenary arch (from the curve obtained by hanging a string hold at both ends) is an exception, its stability allows no reinforcement - Profile View
It is called a reversed flow kiln (flames go under the arch, then down into the charge and out by the chimney flue at the bottom), a technique to equalize the temperature and make the most of the hot gases before they escape out of the chimney - Plan View
The onset of the building of the arch on its form; first, the sequence of bricks (flat and angled)
is determined to follow the curve the best possible.
It is then built in alternate layers.
The inside is partitioned by two bagwalls, burners and ash pits on the sides, in the middle the main shelf above the level of the chimney flue (clearly visible at the bottom) The inside is made of high heat resistant bricks.
The increase in temperature should be gradual; the constituent water, what was used to wheel and for the glaze vats, the humidity, must evaporate before 212°F: then the composition water (H2O linked at molecular level) goes off at 392°F; around 1060°F a change in the spatial arrangement of silica molecules occurs.
Finally at the end of firing a plateau is set to help the isothermie, the maturation of the glazes and the control of oxidation / reduction. As for the cooling process, with somewhat like 5,000 bricks, it is always longer than the patience of the potter is great.
- Firing; 8 to 12h, cooling: 2 days
The dismantling of the kiln (to move from house to house it experienced three major versions) shows the power of fire by the deformation of materials yet designed for that purpose...
Another view. The chimney at the bottom is lined with "ordinary" bricks
Daniel Rhodes plans, my inspiration source. These sketches are quite sufficient, one always has to adapt to the collected materials, wether purchased new or not...
Wood is the perfect fuel for primitive kilns as for the "slope-kiln"; you see here the fire place and the begining of a long and narrow chamber following a gentle slope for the draw - on top of the trench a rudimental chimney ends the device; you place the pieces in the trench from above, closing with bricks and soil - from D. Rhodes