Practical Magazine 22, 1876
(Chemistry applied to the Arts, Manufactures, &c.)
Articles in black glass made in Venice are distinguished from all similar products by the intensity of their black colour. What is the matter employed to give the glass this colour? M. KAYSER, a chemist of Nuremberg, in order to discover this, made an analysis of a glass known to have been made in Venice, and compared it with black glass, such as is used in the manufacture of Venice beads. This comparison brought out the fact that manganese is the matter employed to give the black colour to glass in which it exists. In fact, while white glass contains only 1.80 of manganic oxyde, black glass contains 11.39, and that is the only notable difference that the two analyses present. To confirm this result, M. Kayser melted in a small furnace a mixture of sand and sulphur, in which he introduced fifteen per cent. of peroxyde of manganese. He thus obtained a glass of a deep black colour; in very fine threads or thin splinters it was of a sombre violet. In one word, it exactly presented, in respect to colour, the same properties as black Venetian glass.
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