n (barites, blanc fixe, heavy spar, permanent white, terra ponderosa) BaSO4. A white powder obtained from the mineral barite or synthesized chemically. One of the synthetic varieties, blanc fixe, is made by mixing aqueous solutions containing sulfate and barium ions. As a filler in plastics and rubbers, barium sulfate imparts opacity to X rays but only a low order of optical opacity. Thus it is useful as a filler when it is desired to increase specific gravity without adversely affecting the tinctorial power of pigments. (Ash M, Ash I (1998) Handbook of fillers, extenders and dilutents. Synapse Informtion Resources, Inc., New York).