ULTRAMARINE

• Ultramarine is a deep blue color and a pigment which was originally made by grinding lapis lazuli into a powder.[1] The pigment consists primarily of a zeolite-based mineral containing small amounts of polysulfides.
• It occurs in nature as a proximate component of lapis lazuli. The pigment color code is P. Blue 29 77007. Ultramarine is the most complex of the mineral pigments, a complex sulfur-containing sodio-silicate (Na8-10Al6Si6O24S2-4) containing a blue cubic mineral called lazurite (the major component in lapis lazuli).
• Some chloride is often present in the crystal lattice as well. The blue color of the pigment is due to the S3- radical anion, which contains an unpaired electron.

COMPOSITION

• The raw materials used in the manufacture are:

1. Iron-free kaolin, or some other kind of pure clay, which should contain its silica and alumina as nearly as possible in the proportion of SiO2:Al2O3 demanded by the formula assigned to ideal kaolin (a deficit of silica, however, it appears can be made up for by addition of the calculated weight of finely divided silica),
2. Anhydrous Na2SO4,
3. Anhydrous Na2CO3,
4. Powdered sulfur, and
5. Powdered charcoal or relatively ash-free coal, or colophony in lumps.

• The mixture is heated in a kiln, sometimes in brick-sized amounts. The resultant solids are then ground and washed as per any other insoluble pigment manufacturing process.
• The chemical reaction produces large amounts of sulfur dioxide meaning that Flue gas desulfurization is an essential part of its manufacture to comply with pollution regulations. Large chimneys were used to disperse sulfur dioxide produced in the process, resulting in ultramarine tinting the surrounding ground surfaces and roof vents with a blue color.