Blue
Pigments for painting and glass

Blue pigments were once produced from minerals, especially lapis lazuli and its close relative ultramarine. These minerals were crushed, ground into powder, and then mixed with a quick-drying binding agent, such as egg yolk (tempera painting); or with a slow-drying oil, such as linseed oil, for oil painting. Two inorganic but synthetic blue pigments are cerulean blue (primarily cobalt(II) stanate: Co SnO) and Prussian blue (milori blue: primarily Fe (CN)). The chromophore in blue glass and glazes is cobalt (II). Diverse cobalt(II) salts such as cobalt carbonate or cobalt(II) aluminate are mixed with the silica prior to firing. The cobalt occupies sites otherwise filled with silicon.
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