How One Ceramic Studio Tests Glazes at Volcanic Temperatures

At the Archie Bray Foundation in Helena, Montana, resident artists fire ceramics in a wood-burning anagama kiln reaching temperatures exceeding thirteen hundred degrees Celsius, comparable to the base of a lava flow. At these temperatures, conventional glaze chemistry gives way to physics of molten rock, producing effects no laboratory furnace can predictably replicate.

The anagama kiln, a Japanese design with fifth-century origins, is a single-chamber tunnel fired exclusively with wood. Stoking continues around the clock for five to seven days, with teams feeding wood at intervals of five to ten minutes. The labour is enormous, making each firing a communal event bonding participating artists.

At peak temperature, wood ash carried by the flame melts onto pottery surfaces creating natural ash glaze. The composition depends on wood species, kiln atmosphere, and the pot's position relative to flame. Pieces near the firebox receive heavy deposits flowing and pooling like volcanic glass.

The kiln atmosphere fluctuates between oxidation and reduction as fuel is added and burns. This produces colours impossible in electrically fired kilns. Iron-bearing clays shift through a spectrum from red to brown to black, sometimes within a single vessel, each shift recording a moment in the firing.

Cooling is as important as firing. The anagama takes five to seven days to cool. During extended cooling, crystalline structures develop within the glaze, producing textures from rough crusts to smooth pools. The slowest-cooling areas produce the most complex and desirable surfaces.

To experience wood firing, attend an anagama kiln opening at a ceramic art centre. The moment the kiln door is removed and first pieces revealed, still warm, surfaces recording days of fire in geological detail, is one of the most exciting events in contemporary craft. Follow at https://www.archiebray.org