The completed ceramic piece must be slowly fired to the proper maturing temperature of the clay. Generally each piece is fired twice. The first firing, the bisque, is to approximately 1000° C. This hardens the work so that glaze can be applied. Then the glaze firing brings the clay and applied glazes to maturity.
Different kilns and kiln atmospheres are used for different results.
Atmospheres
Oxidation
- A plentiful supply of oxygen during the firing process.
- Will produce green glazes from copper and honey colours from iron.
Reduction
- The amount of oxygen in the kiln is deliberately reduced, drawing oxygen from the clay and glazes.
- This causes copper in glazes to change from green to red and iron to turn green.
Kilns
Electric Kiln
- Uses electricity to produce heat
- Most commonly used
- Produces an oxidized atmosphere
- Firing takes about twelve hours
- Can be fired to different temperatures but most suited for earthenware and medium fired stoneware
- Electric kilns are precise, controllable and easy to use
Examples of electric fired work: Barbara Balfour, Ken Chernavitch, David Krindle, Merilyn Kraut, Judith Marchand, Kevin Stafford, Anne Fallis Elliott
Gas Kiln
- Uses natural gas as its fuel for heat
- A reduction atmosphere is created by controlling the amount of oxygen in the combustion
- Most suited for firing stoneware and porcelain to 2400 degrees fahrenheit
- Firing takes about twenty-four hours
- Firing a gas kiln takes care and experience
Examples of gas fired work: Marusia Foster, Kathryne Koop, Valerie Metcalfe, Steve Jorgenson
Wood Kiln
- Uses wood as its fuel for heat
- Provides a reducing atmosphere
- Most suited for high firing to 2400 degrees Fahrenheit
- Firing takes about twenty-four hours and uses over a cord of wood which is stoked every few minutes throughout the firing
- Wood firing is labour-intensive but it produces a rich patina on the pots
Examples of wood fired work: Alan Lacovetsky, David Krindle
Raku Kiln
- A fast firing process fired to earthenware temperatures, around 1800 degrees Fahrenheit
- A dramatic process where the pots are taken out of the kiln at peak temperatures using tongs, and placed in a closed container with combustible materials for post firing reduction
- While the claybody is blackened, the glaze will often appear crackled, and/or metallic
- Generally, this process is best suited for decorative pieces, and not food related items
Examples of raku fired pieces: Steve Robinson