Firing

Electric Kiln

Most of my work is fired in my electric kiln. Once dry, pieces are initially bisque fired to 1000 - 1050ºC. Then glazes are applied, and the pieces fired again. Earthenware is typically fired to 1000 - 1150ºC - the higher temperatures giving a darker, stronger and less porous clay, as well as affecting the glazes. Stoneware is fired to 1200 - 1300ºC depending on the glaze primarily, but the higher temperature also gives a darker colour to some of the clays. Some of the glazes may need the piece to be held at top temperature for 2 or 3 hours for the effects to develop fully. Additional firings may be required, for example if adding a low temperature glaze onto a high temperature fired piece, or adding lustres or decals. After the main glaze firing, each subsequent firing has to be at a lower temperature than the previous one, so that glazes already applied don't melt again.

The kiln is computer controlled, so a very fine degree of control can be exerted over the firing. The downside of an electric kiln, though, is that it can only fire in oxidation. It cannot use those glazes designed for reduction firing in a gas or wood kiln, where the air supply to the flames is throttled back and the amount of oxygen in the kiln is reduced, so oxygen is sucked out of the glaze to feed the flames. However there are more than enough other routes to follow to produce attractive work.

Anagama Kiln

The anagama kiln is a large, wood fired kiln that is managed by Oxford University as the Oxford Anagama Project. In fact they have not just one, but two! They are run in conjunction with Jim Keeling of Whichford Pottery as a community project - potters can pay to have their pieces fired in the kiln, making a contribution to the cost of the timber fuel, and helping out with the firing itself. At present they are fired a couple of times a year.

The kilns are modelled on Japanese kilns from Bizen. There is a single firing chamber on a slope, fired at the downhill end and the chimney at the other end, the slope helping increase the draw. They are fired slowly, about a week of continuous feeding with timber, 24 hours a day, to get up to a top temperature of 1200 - 1250ºC, and then the best part of another week to cool down before the kiln can be opened and the results examined. Bizen ware is traditionally unglazed, allowing the heat, flames and ash to create a thin surface glaze on a red/brown clay, with variations depending on how the piece was exposed to the flames, the level of ash deposition, and the top temperature in that part of the kiln. Whilst there is no requirement for pieces to follow the Bizen style, and many do put slips or glazes onto their wares, there is an attraction to the simplicity of just using clay and fire, without the decorative veneer of the glaze.