The Science of Pottery: Understanding Clay and Glaze Formulas

Pottery is both an art and a science, and understanding the science behind it can help potters create better, more consistent pieces. One of the most important aspects of pottery science is understanding clay and glaze formulas. In this article, we'll take a look at what clay and glaze formulas are, how they work, and how to use them to create beautiful and functional pottery.

First, let's talk about clay. Clay is a natural material made up of minerals such as kaolin, feldspar, and quartz. The specific types and amounts of these minerals determine the properties of the clay, such as its plasticity, shrinkage, and color. Potters use this information to create clay formulas, which are recipes for specific types of clay. For example, a porcelain clay formula would have a high percentage of kaolin and a low percentage of feldspar, while a stoneware clay formula would have a higher percentage of feldspar.

Next, let's talk about glaze. Glaze is a glassy coating that is applied to pottery before it is fired. It can change the color, texture, and surface properties of the pottery. Glaze formulas are similar to clay formulas in that they are recipes that specify the types and amounts of materials needed to create a specific type of glaze. For example, a glossy glaze formula would have a high percentage of feldspar, while a matte glaze formula would have a lower percentage.

Using clay and glaze formulas can help potters create more consistent pieces and troubleshoot problems when they arise. For example, if a potter is having trouble with a glaze that is not sticking to the pottery, they can check the glaze formula and adjust the percentage of silica or the firing temperature. Similarly, if a potter is having trouble with a clay that is cracking, they can check the clay formula and adjust the percentage of feldspar or the amount of water used.

It is important to keep in mind that creating pottery is not only an art, but also a science. By understanding clay and glaze formulas, potters can create better, more consistent pieces and troubleshoot problems when they arise.

If this seems all very confusing to you then don't worry you can also buy glazes in premixed or powered form. Check out our blog post about applying glaze.

Questions and answers about glazing

Q: What is glaze and why is it used in pottery? A: Glaze is a glassy coating that is applied to pottery before it is fired. It can change the color, texture, and surface properties of the pottery. Glaze is used to protect the pottery from liquids, making it more functional, and to add color, design, and texture to the pottery, making it more decorative.

Q: What are the main ingredients in a glaze formula? A: The main ingredients in a glaze formula are typically silica, alumina, and a flux. Silica provides the glassy surface, alumina gives the glaze hardness and durability, and the flux lowers the melting temperature and helps the glaze to fuse to the pottery.

Q: How do I apply glaze to my pottery? A: Glaze can be applied to pottery in several ways, including brushing, pouring, or dipping. It is important to apply the glaze evenly and to avoid leaving any unglazed areas, as these areas may be more prone to cracking or breaking during firing.

Q: Can I mix my own glaze? A: Yes, you can mix your own glaze. It is important to use a glaze formula and carefully measure out the ingredients to ensure consistency. You can also experiment with different ingredients to create your own unique glazes.

Q: What happens to the glaze during firing? A: During firing, the glaze melts and fuses to the pottery, forming a glassy coating. The temperature and time of firing, as well as the composition of the glaze formula, will affect the final appearance and properties of the glaze. High firing temperatures and long firing times can cause glazes to become more glossy and transparent, while lower temperatures and shorter firing times can cause glazes to be more matte and opaque. Some glazes will also change color during firing due to chemical reactions between the glaze ingredients and the kiln atmosphere.

Three basic glaze recipes

Clear Glaze:

50% silica
25% feldspar
25% kaolin

Cone 10 Oxidation Matte Glaze:

50% ball clay
25% feldspar
25% kaolin

Cone 6 Reduction Glaze:

50% silica
25% feldspar
25% whiting

Keep in mind that these are basic recipes, you can also add small amounts of colorants and other materials to create different effects and colors, also you can use different types of clay and fluxes to achieve different results. It's important to test the glaze by applying it on small test pieces before applying it to your final piece. Also, the firing temperature and time will also play a big role in the final outcome of the glaze.

Here are a few resources that offer a wide variety of glaze recipes:

These websites offer a wide range of glaze recipes for different firing temperatures and techniques, and provide detailed instructions on how to mix and apply the glazes. Some of them also have a section for glaze calculation and materials substitution which may be helpful for the potters. It's important to keep in mind that the final outcome of the glaze may vary depending on the specific kiln and firing conditions.