How is cobalt oxide used to produce blue glass and ceramics?

Cobalt oxide is a gray to blue-black powder used primarily as a colorant in the glass and ceramics industries. It functions by being added to these materials to impart a distinct blue hue or to neutralize unwanted yellow tints caused by iron impurities.123

In the production of glass, cobalt oxide is added in varying amounts depending on the desired effect:
* Coloring: Adding 140 to 4,500 grams per ton of glass creates a blue color in structural glass, bottles, and optical filters.3
* Neutralizing: Small quantities (1 to 45 grams per ton) are used to counteract the yellow tint of iron in plate and window glass.3

In ceramics and pottery, the compound is used similarly:
* Neutralizing and Coloring: Approximately 454 grams per ton of dry clay is used to neutralize iron discoloration in sanitary ware, tiles, and pottery, while larger quantities produce a blue color.3
* Glazing: A rich blue shade is achieved by adding 5 percent cobalt oxide to high-lead glazes. Specific shades can be achieved through chemical combinations, such as cobalt aluminate for turquoise (Thenard’s blue) or cobalt silicate for a violet-blue.3