Soda firing is a captivating ceramic technique that emerged in the 1970s as an alternative to traditional salt glazing, offering artists a unique way to achieve varied surface textures and subtle nuances of color. Instead of salt, soda firing introduces sodium compounds like soda ash (sodium carbonate) or baking soda (sodium bicarbonate) into a kiln at high temperatures. These compounds vaporize and interact with the silica and alumina in the clay, resulting in distinctive glaze effects. The unpredictable nature of soda firing leads to finishes that are highly valued by ceramic artists, with each piece boasting its own character and charm. Soda firing provides a wide array of possibilities for creating unique and interesting effects.
Historically, soda firing is closely related to salt firing, a method that dates back to 13th-century Germany. However, unlike salt firing, which releases hydrochloric acid and poses environmental concerns, soda firing produces carbon dioxide, making it a more eco-friendly option. Traditionally, soda firing is conducted at high temperatures, typically around cone 10, approximately 2350°F (1287°C). At this temperature, the soda vaporizes and reacts with the silica in the clay bodies and glazes, forming a sodium-silicate glaze that results in varied surface textures and colors. There has also been exploration into low-temperature soda firing, conducted in the cone 1 to 4 range (approximately 2124°F or 1162°C). This approach uses less energy and offers new opportunities in color, texture, and finishes for ceramic work. For more on firing temperatures, check out this article. Additionally, to understand kilns better, read this guide to kiln care.
Low-temperature soda firing offers a unique method to reduce energy costs while still creating interesting and unique pieces of pottery.
Safety is paramount when soda firing. Always wear personal protective equipment (PPE), including a NIOSH-approved respirator, chemical safety goggles, and impervious rubber gloves to protect against the inhalation and skin contact with soda ash, which can cause respiratory and skin irritation. A well-ventilated kiln area is essential to disperse harmful gases like carbon monoxide and sulfur oxides produced during firing. When preparing soda ash solutions, handle all chemicals with care to avoid accidental spills or contact. In the event of skin or eye contact with soda ash, rinse the affected area immediately with plenty of water and seek medical attention if necessary.
The choice of clay body is also crucial for successful soda firing, as it must withstand the aggressive soda atmosphere and contribute to the desired aesthetic outcomes. High-alumina stoneware bodies, porcelain bodies, and stoneware bodies with added grog are popular choices, each offering unique properties and visual effects. Remember to test clay body recipes to ensure compatibility with your specific firing conditions and desired aesthetic outcomes. It’s also important to consider ventilation, employing downdraft or hood systems to maintain a consistent atmosphere within the kiln, which is essential for achieving uniform glaze effects and preventing defects such as blisters or pinholes.
- High-Alumina Stoneware Bodies: Known for their durability and ability to withstand high temperatures, these bodies are a reliable choice for soda firing.
- Porcelain Bodies: These offer a smooth, translucent surface that can beautifully showcase the subtle color variations achieved through soda firing.
- Stoneware Bodies with Added Grog: The added grog enhances the body’s thermal shock resistance and creates a more textured surface, which can interact uniquely with the soda vapor.
Soda firing has been embraced by contemporary ceramicists who value the element of surprise and the interaction between clay, soda, and fire. Notable ceramicists such as Lisa Hammond and Jack Doherty have significantly contributed to the development and popularity of soda firing. Whether you’re drawn to the glossy or matte finishes, or the unique textures like orange-peel, soda firing offers a world of possibilities for creating one-of-a-kind ceramic art.
