The Kiln
The mainstay of production rejoices in the name of Bathsheba. She is a two chambered, catenary arch design, fuelled by a combination of wood and propane gas. The propane gas provides a short, very hot flame that can be easily controlled during the first phase of firing, and helps to ensure a much cleaner combustion of the wood. We could easily fire the kiln on wood alone, but for this size of kiln, the relatively small amount of propane makes everything work much more efficiently.
Bathsheba started out as a single chamber kiln, built with mainly high-temperature insulating bricks, covered with ziron wash on the inside, and two inches of Rockwool on the outside. A fairly high ratio of fire box to stacking space (1:3) ensures fast firing times.
Bathsheba started out as a single chamber kiln, built with mainly high-temperature insulating bricks, covered with ziron wash on the inside, and two inches of Rockwool on the outside. A fairly high ratio of fire box to stacking space (1:3) ensures fast firing times.
This 38 cubic foot space shot to 1300 C in under four hours the first time she was fired (the pyrometer went out early on) with no problem at all. For the most part, we have to work at 'breaking' the kiln rather than struggling to achieve temperature.
Realising there was plenty of 'power' in the beast, a second chamber was added to use the hot exhaust gases. This chamber is approximately 31 cubic feet, and the floor is about 6” higher than the preceding chamber. This addition no way detracted from the performance of the first chamber and achieved 1300 C with only a few more hours additional stoking, and the transfer of the propane burner.
We really can't recommend this style of kiln highly enough; it is
Realising there was plenty of 'power' in the beast, a second chamber was added to use the hot exhaust gases. This chamber is approximately 31 cubic feet, and the floor is about 6” higher than the preceding chamber. This addition no way detracted from the performance of the first chamber and achieved 1300 C with only a few more hours additional stoking, and the transfer of the propane burner.
We really can't recommend this style of kiln highly enough; it is
- Highly fuel efficient. Over 70 cubic feet fired on 20 small sacks of wood and less than 16kg of propane for Cone 02 (1100 C) terracotta firing. A 1300 C stoneware firing use roughly doubles this.
- Sensitive, larger pots can be fired in the second chamber.
- The second chamber cleans up the exhausts from any 'dirty' fuel encountered.
- Having to slow the firing in the initial phases so as not to damage the ware as we pass various quartz and cristobalite conversions. This was eased by the addition of an external firebox for prefiring.
- Temperature variation – cold spots are a natural consequence of all cross draught kilns. There is about a cone to a cone and a half variation. Not a problem with terracotta and earthenware glaze firings, but when packing a stoneware firings you've got to use your noggin.
