Ultramarine Blue occurs naturally in Lapis Lazuli and was formerly obtained from this mineral by a simple process of heating, cooling quickly in water and further careful washing and separation of the coarser particles. The natural ultramarine is very expensive and hence little used. Artificial ultramarine is prepared by heating together in closed crucibles, in a furnace, a mixture of china clay, silica, sodium carbonate, sodium sulphate, charcoal and sulphur. After cooling the mass slowly, it is powdered and gently roasted with the addition of a little sulphur.

The calcining or roasting process may be repeated until the proper color is obtained.

In color, it is pure blue and of brilliant tone when of good quality. It has, however, little strength. It has no influence on nor is it affected by other pigments; is not injured by heat or the alkalies, but is decolorized or modified by acids and cold alum solutions. Oriental blue is a form of ultramarine containing much silica.