Glazing pottery can seem daunting at first, but with a bit of knowledge and practice, it’s an achievable and rewarding skill for beginners. Glaze is essentially a thin layer of glass that is fused to the surface of the pottery during firing. Its purpose is multifaceted: it seals the porous ceramic surface, making it waterproof and food-safe; it adds color, texture, and visual appeal; and it strengthens the pottery. There are various types of glazes, each with its own firing temperature range and characteristics. Low-fire glazes are typically used for earthenware, maturing at lower temperatures, generally between Cone 015 and Cone 1, with an average of Cone 04 (1940℉ or 1060℃). Mid-range glazes, often used with stoneware, fire between Cone 2 and Cone 7, needing temperatures between 2124℉ and 2264℉ (1162-1240℃). High-fire glazes are designed for stoneware and porcelain, maturing between Cone 8 and Cone 12, or around 2300°F to 2381°F (1260°C to 1305°C). It’s crucial to choose a glaze that matches the firing range of your clay body to achieve the desired results. When selecting a clay for your project, consider starting with earthenware due to its forgiving nature and lower firing temperature. Alternatively, a white or off-white stoneware is a popular choice for beginners, as it’s structurally strong and suitable for both wheel throwing and hand building. To choose a clay body, it is helpful to understand clay types.
Essential Tools and Materials
Before you start glazing, gather the necessary tools and materials. These include a variety of brushes, such as large flat brushes for covering larger areas and small, round-tip brushes for detailed designs. Hake brushes and fan brushes are also excellent for achieving smooth, even coverage. Sponges are useful for creating textures and cleaning up drips. Dipping tongs are essential for safely submerging your pottery into the glaze. A banding wheel can help with even glaze application when brushing or spraying. Safety equipment is paramount. Always wear a NIOSH-approved respirator, especially when mixing dry glazes, to prevent inhalation of harmful particles. Gloves protect your skin from irritation and absorption of toxic materials, and safety glasses shield your eyes from splashes. A plastic or vinyl apron is preferable to a cloth one, as it prevents glaze from soaking through to your clothes. Remember, working with glaze materials poses long-term health risks if proper safety measures are not followed.
This video from MyClayCo gives a great overview of different ways to seal polymer clay. It’s a helpful resource for anyone working with this material.Glazing Techniques
There are several glazing techniques that beginners can easily learn. Dipping is often considered the easiest way to achieve an even coat. Submerge the piece into the glaze, hold for a few seconds, and then remove it slowly and steadily. Pouring involves flowing the glaze over the piece, allowing it to coat both the interior and exterior. Brushing is versatile for both base layers and decoration. Apply multiple thin coats, alternating the direction of brushstrokes to avoid streaks. Splattering is a fun, carefree way to add texture. Dip a stiff brush into the glaze and flick it onto the piece. Stippling involves applying glaze to the tip of a soft brush and painting the pottery, creating shadow effects or a painted look. Sponging can add texture; wet the sponge before applying glaze and use it to create various designs. Wax resist is used to repel glazes, allowing you to create patterns by preventing glaze from adhering to specific areas. Before glazing, ensure your bisque ware is clean and free from dust, grease, or other dirt, as these can cause crawling.
Troubleshooting Common Glazing Problems
Even with careful application, glazing problems can arise. Crazing, characterized by fine cracks in the glaze surface, occurs when the glaze has a higher coefficient of expansion than the clay body. To correct this, you can add materials with low expansion, such as boron, or reduce high-expansion materials like feldspar. Shivering, the opposite of crazing, happens when the glaze expansion is too low, causing pieces of glaze to peel off. Correct this by adding high-expansion materials like alkaline frit or feldspar. Crawling results in bare patches on the pottery surface, often caused by dust, grease, or over-application of glaze. Ensure the bisque ware is clean and apply glaze in thinner layers. Pinholes, tiny holes in the glaze surface, are caused by gases escaping from the clay body during firing. A longer firing cycle with a soak at peak temperature can help, as can a thinner glaze coating or a glaze with more flux. Blisters, which look like small craters, can result from too thick a glaze layer, insufficient drying, or a dense clay body. Be sure to apply glaze evenly, allow pieces to dry thoroughly before firing, and ensure your clay body is not too dense. See more information on glaze chemistry here.
Firing Considerations
The firing process significantly affects the final appearance of the glaze. All clays and glazes are created to mature at specific temperatures, and any variance can lead to unsatisfactory results in ceramic durability or color. If fired too high, clay can deform or even melt and can result in glaze runoff; if fired too low, your pieces will be dry, rough, and potentially unsolidified. The atmosphere within the kiln—oxidation or reduction—also impacts glaze color and effects. Oxidation firing results in bright, vibrant colors, while reduction firing produces more muted colors and earthy tones. A well-designed firing schedule is crucial for achieving consistent results and preventing defects. This includes controlling the rate of temperature rise, soaking time at peak temperature, and cooling curve. Slow cooling can help ensure a glossy, even glaze finish. Always conduct test firings with small tiles to observe how glazes react at different temperatures and schedules. Keep a detailed log of your firing schedules, glaze recipes, and results to refine your process over time.
