The wood-fired kiln
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Below the floor of the kiln are two fire boxes running the full length of the kiln. These are 50cm high and have as lids the bottom kiln shelves. The lids do not run the full distance and the flames and ash are allowed upwards. Between the 2 fireboxes is a 13 cm gap (the flue) leading to the metre tall chimney. The kiln has a stacking space of approx 40 cubic feet. The flame and smoke passes over and around the pots so that they are effectively bathed in the fire. This shows up mainly on the unglazed pots which pick up the flying ash as it goes through the kiln.
The ash in the bottom of the fireboxes is raked vigorously from about 1150 degrees Celcius onwards to accentuate this effect. When the kiln is stacked and ready for firing it is warmed overnight with 2 gas torches to a temperature of about 100-120 degrees celcius. The firing proper starts with wood at about 5 a.m. slowly raising the temperature to 1300 degrees over about 14 hours, and then 'soaked' (i.e temp held) for a further half an hour. When the temperature reaches approx 1100 degrees the pots are 'reduced' for 1 hour. This involves the kiln being starved of air so that oxygen is removed from the clay and glazes. This markedly changes the character of the finish and gives a 'softer' colour to the pots. |
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