3Na2O.3Al2O3.6SiO2.2Na2S. Natural ultramarine blue pigment is the ground, separated blue particles (lazurite) from the gemstone lapis lazuli. Lapis has been mined since the 3rd millennium BCE in Afghanistan at the Badakhshan mines. Ancient trade routes distributed the lapis throughout Europe and the Far East. To prepare ultramarine pigment, lapis is powdered then kneaded in a wax/resin mixture in a dilute lye solution; the blue particles disperse into the alkaline water while the extraneous minerals (e.g., calcite, pyrite, silicates) are retained in the putty. This was a time consuming process that produced varying shades of blue. The purest, deep blue was extracted in the first batch and sold for very high prices. As the process was continued, the subsequent batches of pigments were slightly less pure; the final batch was a transparent blue grey called ultramarine ash. In all the fractions, some transparent material is present (calcite) which aids microscopically in the distinguishing the natural from synthetic ultramarine pigments which were first made in 1828. Ultramarine blue is used as a pigment in paints (oil, tempera, watercolour, fresco) and wall paper. The natural product was extremely expensive and thus rarely used for decorative painting, except occasionally for works such as a royal commission or for touches of colour. Ultramarine is listed among the pigments used for colouring stucco marble in the nineteenth and twentieth century. Synonyms: lapis lazuli blue; natural ultramarine blue; bleu d'Azur; Armenian blue; lazuline blue; ultramarine ash; mineral blue; Ultramarinblau echt (Ger.); outremer lapis (Fr.); oltremare genuino (It.); ultramarino verdadero (Sp.); Pigment blue 29; CI 77007. Museum of Fine Arts, Boston (2000); Wittenburg (1999); Trench (2000). [J. Cassar, R. de Angelis]