ULTRAMARINE. Thie beautiful blue pigment was originally made from the stone called lapis lazuli; and as the process was a tedious one, the price was enormously high. The lapis lazuli was analysed by Clement and Desormes ; and their analysis led Guimet to the conception of producing artificial ultramarine. Other chemists, including Gmelin and Robiquet, devised other modes of attaining the same end ; and now artificial ultramarine is a regular manufacture. The substance is made largely in Germany, but not much in England. One of the processes consists in taking equal parts of silica, sulphur, and carbonate of soda, grinding them up into a bluish-green mass, igniting them in the open air, and applying various finishing processes to the bluish powder which results. The artificial ultramarine thus produced is saleable at so low a price as 18. 3d. per lb. It is very much cheaper than real ultramarine, and though inferior to that as a pigment, is more beautiful than smelt; hence it has come largely into use. The scientific journals have lately given a description of the ultramarine factory of Messrs. Zeltner and Heyne at Nurnberg,
the chief makers of this pigment. The buildings are said to cover seven acres. The central building is a polygon of 24 sides ; it has 12 compartments, 96 furnaces, 12 high chimneys, and 12 lines of tram ways. The polygon is 136 feet in diameter. In various parts of the area are mills, steam-engines, washing apparatus, long ranges of drying rooms, and store rooms for 5000 or 6000 cwts. of artificial ultramarine. Two hundred persons are employed in this single manufacture. The best kinds of artificial ultramarine, used only by artists, pass through no less than eighty separate processes ; but the commoner kinds, which are commercially more important, are coming largely into use in paper staining, sealing-wax making, calico printing, colour printing, and dyeing.
According to the experiments of Dr. Elsner, ultramarine must con tain sulphuret of iron as well as sulphuret of sodium, and he has given the mean of several analyses of artificial ultramarine, of natural lapis lazuli, and of an artificial product by Varentrapp:—