Types of Glaze Mixing
- Most glaze mixtures are designed for oxidation, and are done in electric kilns between temperatures of 1,623 to 2,530 degrees Fahrenheit. Oxygen reacts with the materials in the glaze, turning them into ash. Metal pigments like iron, oxidize, giving the glaze its color. Glaze mixtures that are made for reduction are generally used in gas kilns, at temperatures between 1,600 to 1,900 degrees Fahrenheit. Oxygen is limited, resulting in an environment that is high in carbon dioxide and carbon monoxide. Reduction glaze mixtures include copper red and milky white "shinos."
- A raw glaze mixture is made by combining natural and synthetic substances like quartz and minute pieces of clay, which are suspended in a water-based liquid and brushed onto the pottery. When heated, these pieces oxidize. A fritted glaze mixture is made from pieces of previously melted glass, which are also suspended and brushed onto the pottery. Compared to raw glazes, fritted glazes are more expensive to make, but can create more effects on the pottery, including bright colors and different textures, depending on the materials used.
- Different mixtures of materials react differently when fired, and react at different temperatures. To create bright colors, low-fire glazes are used, which react at temperatures between 1,623 and 2,048 degrees Fahrenheit. Medium-fire glazes oxidize at temperatures between 2,167 and 2,264 degrees Fahrenheit. These are less colorful than low-fire glazes. For very light, and sometimes transparent, glazes, high-fire glazes are used. These oxidize between 2,305 and 2,530 degrees Fahrenheit. With multiple coats, however, high-fire glazes can have very deep colors.
- Underglaze mixtures are generally used to create a base coat of glaze on the pottery. These are often light, or even transparent colors, with very little or no texture. Overglazes are used to highlight portions of the pottery with deep or bright colors, or different textures, on a piece that has already been fired using an underglaze. When fired a second time with the overlgaze, the kiln can be set at a lower temperature.