Stoneware is a type of pottery prized for its durability and versatility. It stands between the more delicate porcelain and the more porous earthenware, offering a balance of strength and aesthetic appeal. This article will guide you through the process of creating stoneware pottery, from selecting the right clay to firing and glazing your finished pieces.
The Stoneware Difference: Clay and Characteristics
Stoneware distinguishes itself from other ceramics primarily through its firing temperature and the resulting properties. Earthenware, fired at lower temperatures (between 1745℉ (950℃) and 2012℉ (1100℃)), remains somewhat porous unless glazed. Porcelain, on the other hand, is fired at very high temperatures (between 2381℉ and 2455℉ (1305℃ and 1346℃)) and becomes vitrified, meaning it turns glass-like and non-porous. Stoneware bridges this gap, typically fired between 2000°F and 2400°F, resulting in a dense, durable, and non-porous ceramic. This makes it ideal for functional ware like tableware, as well as decorative items such as vases.
Choosing the right clay body is the first step in making stoneware. Stoneware clays are typically composed of a mix of different clays, fluxes, and fillers to achieve the desired properties. One example of a stoneware clay body recipe includes: 12 parts Custer Feldspar, 26 parts Hawthorne Missouri Fireclay, 13 parts Hawthorne Bond Fireclay, 13 parts Kentucky Stone Ball Clay, 26 parts OM4 Ball Clay, 10 parts Virginia Kyanite, and 10 parts Firebrick Grog. The addition of acetic acid (vinegar) to the water when mixing this clay body is sometimes done to improve the clay’s plasticity by neutralizing any sodium present in the water. Before forming, the clay needs to be properly prepared through wedging, a process that removes air bubbles and ensures a consistent moisture level throughout the clay mass. For more information, see this guide to wedging techniques.
Forming and Drying: Shaping Your Stoneware
Once your clay is prepared, you can begin forming your stoneware piece. Wheel throwing is a popular technique, where the clay is centered on a pottery wheel and shaped using hand pressure as the wheel spins. Hand-building techniques, such as coiling, pinching, and slab construction, offer alternative ways to create forms without the use of a wheel. Each method offers unique possibilities for shaping the clay and achieving different aesthetic effects.
Even drying is crucial to prevent cracking and warping. Drying the piece slowly and evenly is essential. Uneven drying can lead to stress within the clay, causing cracks to form. Covering the piece loosely with plastic can help to slow down the drying process, especially during the initial stages. As the clay dries, it shrinks, and if some parts dry faster than others, the resulting tension can lead to warping or cracking.
For those interested in learning more about hand-building techniques, this video demonstrates how to make a ceramic mug without a pottery wheel:
Firing: Transforming Clay to Stone
The firing process is where the transformation from clay to stoneware truly happens. It typically involves two stages: bisque firing and glaze firing. The bisque firing is the first firing, done at a lower temperature (e.g., Cone 04 glaze firing goes to 250F at 150F/hr, 1695F at 400F/hr and 1945F at 120F/hr), which hardens the clay enough to handle it for glazing but still leaves it porous enough for the glaze to adhere. A slow bisque firing goes at 80F/hr to 250, 200F/hr to 1000, 100F/hr to 1100, 180F/hr to 1695 and 80F/hr for a 13-hour firing to 1945F. After bisque firing, the piece is ready for glazing. Glazes are applied to the bisque-fired ware to add color, texture, and to make the piece watertight. There are various glazing techniques, including dipping, brushing, spraying, and pouring, each offering different effects.
The glaze firing is done at a higher temperature, typically between Cone 8 and Cone 12 (the average firing temperature for high-fire stoneware is 2381℉ (1305℃)), where the glaze melts and fuses to the clay body, creating a durable and often decorative surface. The specific firing temperature and schedule depend on the clay and glazes used. Firing schedules programmed into electronic controllers determine the rate-of-rise, soaking time and often the cooling curve. Optimal firing temperatures and schedules for different types of stoneware clays affect the final properties of the ceramic. It’s important to follow a well-designed firing schedule to ensure the ware reaches the desired state of maturity without cracking or other firing defects.
Troubleshooting: Addressing Common Stoneware Problems
Even with careful preparation and execution, problems can arise during the stoneware making process. Cracking, warping, and glaze defects are among the most common issues. Cracking in a bisque fired body can be caused by rapid or uneven drying, or firing the body too fast up to 300°C. Warping can be caused by uneven drying or uneven firing, thick and thin sections and ‘bad’ geometry of piece.
Glaze defects like crazing, where fine cracks appear in the glaze surface, can be caused by a mismatch of glaze and body thermal expansions. Crazing is due to a thermal expansion mismatch between body and glaze. Pinholes in the glaze after firing can be caused by development of gases from the body and/or glaze during firing, under firing of the body, or air trapped in the clay. Addressing these issues often involves adjusting the clay body or glaze recipe, modifying the forming or drying process, or altering the firing schedule. For more information, see this guide to troubleshooting your electric kiln.
Stoneware in History and Today
Stoneware has a rich history, with examples found from the Indus Valley civilization to medieval Europe and colonial North America. Historically, it was valued for its durability and used for storage containers, tableware, and industrial applications. Today, stoneware remains a popular choice for both functional and decorative pottery, valued for its strength, versatility, and aesthetic appeal. Modern, commercial tableware and kitchenware use stoneware, and it is common in craft and studio pottery. Some designs are subtle—others are more striking and exuberant—but what they all have in common is an underlying belief that humble, everyday objects have an important place in our lives and homes.
Making stoneware is a rewarding process that combines technical skill with artistic expression. By understanding the properties of stoneware clay, mastering forming techniques, and carefully controlling the firing process, you can create beautiful and durable ceramic pieces that will last for generations.
