TiO2. A dense, white, opaque powder often used as a pigment. Titanium dioxide occurs naturally in three crystalline forms: anatase, rutile and brookite. It is a very stable compound with a high refractive index. Titanium white pigment was prepared from ground rutile as early as 1870. Synthetic titanium dioxide was first prepared in 1906, was manufactured commercially in Norway and the United States in 1916 and sold under the name of Titanox. It contained 25% titanium dioxide co-precipitated with 75% calcium or barium sulphate. Both pure titanium and barium base titanium pigments have a very fine texture. Prior to 1938, only anatase was produced. However, white paints with anatase were subject to chalking and yellowing, so manufacturing shifted to the use of rutile in 1938 and rutile white pigments were first commercially produced in 1940. Currently, titanium pigments are usually sold as admixtures with zinc oxide. In addition to paints, titanium dioxide is used as an abrasive. Synonyms: titanium white; rutile; anatase; brookite; Titanox; titania; Pigment White 6; CI 77891; titanic anhydride; titanic acid anhydride; titanic oxide; Unitane; titania; oxyde de titane (Fr.); Titandioxid (Ger.); bianco di titanio (It.); dióxido de titanio (Sp.); titandioksid (Nor.). Museum of Fine Arts, Boston (2000). [J. Cassar, R. de Angelis]