Firing temperatures play a critical role in the outcome of your pottery, influencing everything from the durability of the piece to the vibrancy of the glazes. Understanding the nuances of different firing ranges is essential for any potter looking to master their craft. Let’s explore the typical cone numbers for various clay types and the effects of temperature on the final product. Firing temperatures are important!
Earthenware, often chosen for its versatility and bright color potential, is typically fired at lower temperatures. Specifically, earthenware firing generally ranges from Cone 06 to Cone 04, which corresponds to temperatures between approximately 1,828°F (998°C) and 1,945°F (1,063°C).
Ginna’s Art Café notes that Cone 06, around 1,840°F (1,005°C), marks the beginning of earthenware firing. It’s fascinating to note that the rate of temperature increase can affect when a cone bends; a slower rate like 108°F per hour sees Cone 06 bending at 1,828°F (998°C), while a faster rate of 270°F per hour results in bending at 1,855°F (1,013°C). This sensitivity underscores the importance of consistent and monitored firing schedules.
Moving up the temperature scale, stoneware firing typically ranges from Cone 4 to Cone 10, each cone corresponding to temperatures that ensure proper vitrification and glaze maturity. Cone 6, at approximately 2,232°F (1,222°C) at 108°F per hour, is a favorite among potters for its balance between strength and glaze development. For higher-fire stoneware, Cone 10, reaching about 2,345°F (1,285°C), is traditionally used to achieve maximum strength and glaze maturity. Kiln types can also affect temperatures.
Again, the heating rate matters; for example, Cone 6 bends at approximately 2,165°F (1,185°C) at a slower rate of 27°F per hour, but at around 2,269°F (1,243°C) at a faster rate of 270°F per hour. Choosing the right cone is crucial for achieving the desired properties in your stoneware pieces.
Porcelain, known for its translucence and delicate nature, demands even higher firing temperatures. Typically, porcelain is fired at cone 9 (approximately 2336°F or 1280°C) and cone 10 (approximately 2381°F or 1305°C). As with other clay types, the final temperature at which a cone bends is influenced by the rate of temperature increase during firing; at a heating rate of 150°F per hour, cone 10 bends at approximately 2381°F (1305°C).
The numbering system for cones might seem a bit backwards at first—cones with a leading zero (like 06) are cooler than those without (like 6). To ensure accurate firing, many potters use a three-cone system: a guide cone one number below the target, the firing cone at the target temperature, and a guard cone one number above. This setup helps monitor temperature uniformity and kiln performance.
It is important to remember to always monitor your kiln and firing schedules!
What happens if your firing goes awry? Underfired pottery often results in a dry, scratchy glaze surface. You might also notice crazing, where fine cracks appear on the glaze surface because it hasn’t properly bonded with the clay.
On the flip side, overfiring can cause glazes to run, potentially ruining the piece and damaging kiln shelves. In severe cases, bloating can occur as gases trapped within the clay expand, creating blisters on the surface. Being able to recognize these issues will help you adjust your firing schedules and techniques for better results.
