What are Pottery Glazes made of?

Pottery glazes are made from raw materials which generally include Silica, Flux and Alumina. Also included are Metal Oxides, which provides the color.

Silica(SiO2)

Silica, commonly referred to as Silicon Dioxide in chemistry, is a natural compound of Silicon and Oxygen. Silica has three main crystalline varieties: quartz, tridymite, and cristobalite. Silica bonds with the silica found in the clay when fired.

Flux

Flux is a metal oxide that lowers the melting temperature of a mix of materials. Fluxes often melt poorly on their own but react strongly with materials like Al2O3 and SiO2 which have high melting points on their own.

Alumina

Alumina or Aluminum Oxide, on its own, is a white, dense powder. Alumina Oxide in its crystalline form is extremely durable. It is one of the strongest, hardest and abrasion resistant material. The Alumina in the glaze helps the glaze stay on the clay.

Color

Transition Metal Oxides are added to a glaze to create color. Generally, the first row of the Transition Metals is used. The most common of the Transition Metals in Oxide form are Cobalt Oxide, Chrome Oxide, Iron Oxide, and Copper Carbonate.

Chrome

Chrome Oxide (Cr2O3) is regularly used to make greens. With Zinc, it can produce brown. When combined with Tin Oxide the result would be pink.

Cobalt

Cobalt is generally used in its Oxide (Co2O4) form in glazes. When combined with most Fluxes, it makes blue colors. However, when Magnesium is present, it can become purple, pink or reddish blue.

Iron

Iron Oxide (Fe2O3) is commonly used to make earthy reds and browns. With Barium, the result may be a yellow-green. When combined with Calcium, it will produce a pale yellow, amber or green.

Copper

Copper carbonate (CuCO3) is mainly used to produce greens, turquoise, and copper reds. With Barium present, the result would be greenish blues. When combined with Alkaline Feldspar, it can make an ox-blood or copper red.