ULTRAMARINE

(Lat. ultra, beyond, and mar in us, belonging to the sea.) The blue colouring matter of the lapis lazuli. This substance is much valued by painters, on account of the beauty and permanence of its colour, both for oil and water painting. In its preparation the finest lapis lazuli is selected, heated to a dull red heat, and quenched in water; it is thus rendered friable, and is ground down into an impalpable powder. This is then mixed with a tenacious paste made of linseed oil, wax, resin, turpentine, and mastic; and the mixture being kneaded in warm water gives out the blue particles, which are afterwards collected by subsidence. Chemists have long in vain endeavoured to imitate this colour, but till lately its nature even had not been determined. It appears from the experiments of Gmelin that sulphuret of sodium is the principle to which the blue colour is owing, and he has succeeded in preparing an artificial ultramarine by heating sulphuret of sodium with a mixture of silica and alumina, {^ee the Annates de Chimie et Physique, vol. xxxvii. p. 409.) ULTRAMONTANE, or [s. 1286]