Cobalt glass is a deep blue colored glass prepared by adding cobalt salts of alumina to the molten glass. It is appreciated for its attractive color. It is also used as an optical filter in flame tests to filter out the yellow flame caused by the contamination of sodium, and expand the ability to see violet and blue hues. Under fluorescent light, cobalt glass has twice the effect. It used in flame tests because of it’s tinted hue.

Powdered cobalt glass, called smalt (or also simply cobalt glass), has been historically important as a pigment in painting, pottery, for surface decoration of other types of glass and ceramics, and other media. It is colored to a deep powder blue hue using cobalt ions derived from cobalt oxide. Cobalt aluminate can be used in a similar way, and is now more common, often known as “cobalt blue”.Cobalt glass and smalt are made from silica and are not the same as cobalt blue, which is colored by cobalt ion in a similar way, but using a melting process with alumina. Read More

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