Creating your own pottery glazes at home is an adventure that allows for endless customization and a deeper connection to your craft. It starts with understanding the fundamental ingredients and how they interact during the firing process. This exploration into glaze making can be both rewarding and challenging, but with patience and experimentation, you can achieve unique and beautiful results.
Glaze Ingredients and Their Functions
The three primary components of any glaze are silica, alumina, and flux. Silica, in the form of quartz or flint, is the glass former. It’s the backbone of the glaze, providing the glassy surface we see after firing. However, silica alone requires extremely high temperatures to melt, which is where alumina and fluxes come into play. Alumina, typically introduced through clay or alumina hydrate, acts as a stabilizer, preventing the glaze from running off the pot during firing and increasing its hardness and durability. Fluxes are the melting agents; they lower the melting temperature of silica, allowing the glaze to mature at kiln-friendly temperatures. Common fluxes include feldspar, calcium carbonate (whiting), and various frits, which are pre-melted glass compounds that offer more predictable and consistent results. More information on glaze composition can be found at South Texas College.
Beyond these basics, other ingredients can be added to achieve different effects. Colorants, such as metal oxides (cobalt for blue, copper for green, iron for brown), create a wide spectrum of hues. Opacifiers, like titanium dioxide or tin oxide, make the glaze opaque, while other additives can create textures, speckles, or specialized effects like crackle glazes. Understanding how each ingredient influences the glaze’s final appearance is crucial for developing your own recipes. All clays and glazes are created to mature at specific temperatures, and any variance can lead to unsatisfactory results in ceramic durability or color. Soul Ceramics has a guide to Kiln temperatures to help you. 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.
This video shows a great example of someone glazing ashtrays. It’s a good visual guide to the glazing process:
Formulating and Testing a Basic Glaze Recipe
Creating a glaze recipe from scratch can seem daunting, but starting with a simple base recipe is a great way to begin. A typical starting point is a 3-2-1 glaze, consisting of 3 parts feldspar, 2 parts silica, and 1 part clay. This provides a balanced combination of flux, glass former, and stabilizer. From there, you can make adjustments to achieve specific qualities. For example, increasing the silica content will generally result in a glossier glaze, while adding more clay can create a matte finish. More information on this can be found at The Little Pot Company.
The key to successful glaze development is thorough testing. Before applying a glaze to a finished piece, create small test tiles using the same clay body you intend to use for your pottery. Apply the glaze to these tiles using different application methods (dipping, brushing, spraying) and in varying thicknesses. Then, fire the tiles in your kiln according to your usual firing schedule. The results will provide valuable information about how the glaze looks and behaves under different conditions. Based on the test results, you can make adjustments to the recipe, such as adding more flux to improve melting or increasing the alumina to prevent running. Keep detailed notes of your recipes, firing schedules, and test results, as this will help you track your progress and learn from both your successes and failures. More information on glaze testing can be found at PotteryGeek. You can find more information on glaze defects at Digital Fire.
Mixing and Applying Glaze
Once you have a glaze recipe you’re happy with, the next step is to mix and apply it. Start by accurately measuring out each ingredient using a digital scale. It’s important to be precise, as even small variations can affect the final result. Combine the dry ingredients in a container and mix them thoroughly. Then, slowly add water while stirring, until you achieve a creamy, paint-like consistency. The amount of water needed will vary depending on the specific ingredients and desired application method. A good practice is to start with water in the bucket already before adding dry materials. Sue Mcleod Ceramics recommends this to wet the powder right away so it’s can’t float back into the air.
There are several methods for applying glaze, each with its own advantages and disadvantages. Dipping involves immersing the pottery into a container of glaze, providing a quick and even coating, but it’s best suited for smaller pieces. Brushing allows for more control and detail, but it can be time-consuming and may result in uneven coverage. Spraying, using an airbrush or spray gun, is ideal for large or complex pieces, but it requires specialized equipment and a well-ventilated spray booth. More information on this topic can be found at South Texas College. Regardless of the method you choose, it’s important to apply the glaze evenly and avoid drips or thick spots, which can cause problems during firing.
Safety, Firing, and Troubleshooting
Working with glaze materials requires caution, as some ingredients can be hazardous. Always wear a respirator when handling dry materials to avoid inhaling dust, which can cause lung damage over time. More information on safe glaze practices can be found at South Texas College. Wear gloves to protect your skin from irritants and avoid ingesting any glaze materials. Work in a well-ventilated area to minimize exposure to airborne particles and vapors. It is good practice to wipe the soles of your shoes after a messy round of mixing so you don’t track dust and raw materials around your studio where they could later be hazardous to yourself and others. More safety advice can be found at Sue Mcleod Ceramics.
The firing process itself has a dramatic impact on the final appearance of the glaze. Different firing schedules and temperatures can influence the color, texture, and overall look. For example, a slow cooling cycle can promote the growth of crystals in the glaze, creating a matte surface. More information on firing can be found at Ceramic Arts Network. It’s important to carefully control the firing process to achieve the desired effects. Additionally, the type of clay you use significantly impacts the glazing process and the final result. Soul Ceramics has a guide to help you understand the Kiln temperature ranges for pottery. Earthenware clay typically reaches maturity (or optimum hardness) between 1745° F and 2012° F, although some low-firing earthenware clays can be fired in temperatures as low as 1200° F. Stoneware reaches maturity between 2000° F and 2400° F – hotter than lava! Porcelain typically reaches maturity between 2381° F and 2455° F – however, pure kaolin reaches maturity at 3272° F! Additional kiln firing information can be found at Kiln Control.
Even with careful planning and execution, glaze defects can occur. Crazing, characterized by a network of fine cracks in the glaze surface, is often caused by a mismatch in the thermal expansion rates of the glaze and clay body. Pinholing, tiny holes in the glaze surface, can result from gases escaping during firing. Crawling, where the glaze pulls away from the clay surface, is often due to a dusty or oily bisque surface.
Example Glaze Recipes
To get you started, here are a few beginner-friendly glaze recipes for different effects:
Clear Glaze (Cone 6):
Feldspar: 45%
Silica: 30%
Whiting: 15%
Clay: 10%
White Glaze (Cone 6):
Feldspar: 40%
Silica: 25%
Whiting: 10%
Clay: 15%
Zirconium Oxide: 10%
Blue Glaze (Cone 6):
Clear Glaze (above): 98%
Cobalt Oxide: 2%
These recipes are just a starting point, and you can adjust them to suit your own preferences and firing conditions. Remember to test each glaze thoroughly before applying it to your finished pottery.
