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How to make a simple 'medieval' kiln
Capable of producing good earthenware pottery, by using readily available, inexpensive modern materials. It will fire to 1100-1150C, but best at 900-1000C. The kiln is smokeless and can be used in built-up areas.
The kiln is a brick cylinder laid without mortar on a concrete and/or brick plinth separated from the ground by a polythene sheet. The height and width of the kiln is determined by the dimensions of the firing chamber, roughly 2-3 feet in diameter, or larger, always keeping height and width the same.
Fire is provided by a propane tank, with hoses from the regulator leading to two blowtorch burners inserted through openings opposite each other at the base of the kiln. The pottery is placed on a pedestal of brick or kiln shelving with brick support. The kiln walls and floor are lined with a 1or2 inch thick ceramic fibre blanket (2 inches is preferable) backed by aluminium foil (kitchen foil), held in place by wire ties inserted through the blanket into the brickwork. The ceramic fibre is necessary if the kiln is to function well; most pottery supply establishments will stock it.
The top of the kiln is covered with pre-fired insulating slabs placed directly on the pottery stacked inside. The slabs, roughly 8" square, can be made from a mix of clay and sawdust or chopped straw, and fired in the first kiln firing. A circular vent can be placed in the centre, and two or three layers will suffice.
firing the kiln
With modifications to the flues the kiln can fire wood instead of propane, but the gas version is given here. As in a medieval kiln, the pottery is stacked on the pedestal, mainly inverted, up to the top of the firing chamber, The pre-fired slabs cover the pottery at the top, closing the kiln. Three layers will give the best insulation.
The kiln fires easily in both oxidation and reduction. An oxidising atmosphere is created by firing with a full draught through the kiln; restricting the draught, severely or completely if necessary, will produce reduction. The draught can be regulated by using a tile to cover the vent in the kiln capping, and/or by restricting air entering at the burner ports. A spy hole through the brickwork in the side of the kiln may be helpful in assessing the state of the ware during firing. A pyrometer is useful, but with experience accurate judgements can be made on the basis of colour and the history of the firing.
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