Metal oxides are used in ceramics to produce color and effect

The Difference Between Oxides and Stains in Pottery? What is metal oxide in pottery? How do you use oxides on ceramics? How to add to glazes for amazing effects

The Metal Oxides powder produced is a completely new form of matter with new properties, it fits comfortably into the ceramic world. 

In ceramics, metal oxides impart color to glazes, bodies, engobes, and stains (however not all colorants). The most common glazes used in pottery are a composite of a base transparent with a metal oxide added to color it (with optional opacifier and variegator). If added to an effect glazes, stunning effects are produced.

Common metal oxide materials are iron oxide, cobalt oxide, chrome oxide, copper oxide, manganese dioxide, nickel oxide. Some of these have carbonate forms (e.g. cobalt, copper, nickel). Some are stable and predictable in their color contributions (e.g. cobalt, chrome). Some, although named "oxides", are actually a mix of the oxide and hydroxide forms of the metal (e.g. copper oxide). Some metal oxides can exist in multiple colors depending on the metal:oxygen ratio.

Zinc, lead, and tin do not produce color by themselves but interact with others to develop unique effects. Some metal oxides contain larger particles that produce effect spots in glazes

Many people avoid stains and continue to use metal oxides in order to save money.