How does cobalt oxide affect the color of pottery glazes and enamels?

Cobalt oxide is a versatile compound used extensively in the ceramics and glass industries to influence color and appearance. Its primary effects include:

• Coloration: Cobalt oxide is famously used to impart a blue color to glazes and ceramics. A rich blue is achieved by adding 5 percent cobalt oxide to a high-lead glaze. Additionally, cobalt silicate produces a unique violet-blue shade, while cobalt aluminate creates a turquoise color known as Thenard’s blue.1
• Neutralization: In pottery, sanitary ware, and tiles, small amounts of cobalt oxide are employed to neutralize the yellow tint caused by iron, resulting in a cleaner appearance.1
• Enamels: In white enamels, cobalt oxide neutralizes yellow tones caused by iron. When used in larger quantities, it produces a blue or black color. Furthermore, in concentrations of 0.2–2 percent, it is used in enamel coats on steel to promote better adherence to the metal.1