NiO. A powerful glaze colorant (<4%) typically producing browns but also pinks, blues and greens depending on glaze chemistry. Zinc crystalline glazes containing it yield striking turquoise blue zinc silicate crystals on a clear mustard yellow background. Nickel oxide can be used in combination with other colouring oxides to produce good blacks. Many of the best black stains contain nickel oxide.
For more information on nickel oxide, see the Digitalfire.com Reference Library of ceramic materials.