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Lū′minousness, Luminos′ity.—Luminous paint, a phosphorescent powder, such as sulphide or oxysulphide of calcium, ground up with a colourless varnish or other medium, and used as a paint.

Columbium oxysulphide, CbOS3, is obtained as a dark bronze coloured powder when the pentoxide is heated to a white heat in a current of carbon bisulphide vapour; or by gently heating the oxychloride in a current of sulphuretted hydrogen.

It is a white amorphous infusible powder, which when strongly heated in sulphuretted hydrogen, yields an oxysulphide.

Sometimes it occurs as the pure metal, and rarer in a state of oxidation as an antimonious acid and as the oxysulphide.