Firing pottery is a transformative process, turning fragile clay into durable ceramic ware. The heart of this transformation lies within the kiln, a specialized oven designed to reach the high temperatures necessary to consolidate the clay and melt glazes. Understanding the different types of kilns and their characteristics is essential for any potter, as the choice of kiln significantly impacts the final outcome of the ceramic piece.
The choice of what to fire pottery in is a crucial one that can significantly impact your work. You’ll need to consider many factors, including the size, heat source, insulation, and much more.
Electric Kilns: User-Friendly and Versatile
Electric kilns are a popular choice, especially for home-based potters and beginners, due to their affordability and ease of use. These kilns use electric heating elements, typically coils embedded in the walls of the kiln, to generate heat. Electric kilns are known for producing bright colors, and their reliability and simplicity make them a wonderful choice for any ceramist, regardless of skill level. They are very easy to load and fire and many of them have programmable controllers and preset cycles, which further adds to their convenience.
However, electric kilns have some limitations. They typically reach a maximum temperature of around 2350°F (1288°C), which is suitable for earthenware, stoneware, and lower-temperature porcelain firings. They also can’t produce as wide a range of glaze colors due to their inability to create a reduced atmosphere. Electric kilns are typically made of 3” brick and are side-fired with elements in their walls only.
Gas Kilns: Achieving Unique Glazes and Atmospheres
Gas kilns offer more control over the firing atmosphere, allowing potters to achieve unique glaze effects. These kilns use natural gas or propane as fuel, and the firing atmosphere can be adjusted to be either oxidation (oxygen-rich) or reduction (oxygen-deprived). Reduction firing results in a beautifully rich array of glaze colors as the oxygen-deprived molecules latch onto the oxygen in clay, such as brilliant copper reds. Gas firing tends to result in earth like colors such as dark browns, giving the end piece a more rustic, aged look. Learn more about oxidation vs reduction firing and discover which is the potter’s choice.
However, gas kilns are typically more expensive than electric kilns, and they require permits for fire safety, which can add additional barriers for use. They also require more skill and experience to operate, as the potter must manually control the fuel-to-air ratio to achieve the desired atmosphere. However, gas kilns will likely cost less to run for each firing since propane/natural gas fuel usually costs less than electricity.
Wood-Fired Kilns: Embracing the Unpredictable
Wood-fired kilns are the oldest type of kiln, and they offer a unique and unpredictable firing process. These kilns use wood as fuel, and the ash from the wood interacts with the clay and glazes to create distinctive surface effects. Wood firing can also create reduction atmospheres, and the results from this type of firing are very visually distinct from electric kilns.
Raku Kilns: Rapid Firing and Dramatic Effects
Raku kilns are designed for a rapid firing process that involves removing the pottery from the kiln while it is still glowing hot. The hot pottery is then placed in a container with combustible materials, such as sawdust or newspaper, which ignite and create a reduction atmosphere. This process results in dramatic and unpredictable glaze effects, including crackle patterns and metallic sheens. Read up on kiln care 101 with maintenance tips for potters.
Bisque Firing and Glaze Firing: The Two-Step Process
Most pottery is fired in two stages: bisque firing and glaze firing. Bisque firing is the first firing, which hardens the clay and makes it porous enough to absorb glaze. The kiln is heated gradually to a lower temperature than the glaze firing, typically between Cone 06 (1830°F) and Cone 04 (1940°F).
Glaze firing is the second firing, where the bisqued pieces are coated with glaze and fired to their final temperature. As the temperature rises, the glaze ingredients melt and form a glass-like surface. The surface becomes glossy, matte, or textured, depending on the glaze used, and the piece becomes waterproof and functional.
Choosing the Right Kiln: Balancing Budget, Space, and Artistic Vision
Selecting a kiln involves considering several factors, including budget, space, and desired artistic effects. Small kilns can be ideal for testing pieces and for beginner potters. For those just starting out, a small electric kiln or a home kiln is a good option. These kilns are easy to use, regardless of size.
Pottery Firing Temperatures
Different types of pottery require different firing temperatures to reach maturity. Earthenware, also referred to as low-fire clays, contains iron and other minerals which cause it to reach optimum hardness between 1745℉ (950℃) and 2012℉ (1100℃). The average firing temperature at which low-fire materials reach maturity is 1940℉ (1060℃). Mid-fire earthenware should be fired between Cone 2 and Cone 7. For mid-range material, a kiln should be firing at a temperature between 2124℉ and 2264℉ (1162-1240℃). The average firing temperature for high-fire stoneware is 2381℉ (1305℃). While pure kaolin fires to maturity at 3272℉ (1800℃), most porcelain should be fired between 2381℉ and 2455℉ (1305℃ and 1346℃) for best results.
Safety First: Essential Precautions for Kiln Operation
Operating a kiln involves working with extremely high temperatures, so safety precautions are crucial. Proper ventilation is essential to remove toxic fumes released during firing. Protective gear, such as kiln mitts, dark glasses, and a dust mask, should be worn when handling the kiln and working in the studio. It is also important to follow all manufacturer’s instructions and local safety codes. Always be sure to unplug the kiln before working on the electrical components.
Firing pottery is both a science and an art. Understanding the different types of kilns, the firing process, and the safety precautions involved is essential for achieving successful and beautiful ceramic creations. Whether you choose an electric kiln for its convenience, a gas kiln for its atmospheric effects, or a wood-fired kiln for its unpredictable nature, the kiln is the key to unlocking the full potential of your clay.
