Barium sulfate (barytes / blanc fixe)
Barium sulfate is the heavyweight of coating fillers: dense, chemically inert and low in oil absorption, so it adds body and resistance without thickening the paint much.
Barium sulfate (molecular weight 233.4 g/mol) is a white, highly insoluble mineral salt with a density of about 4.5 g/cm³, a Mohs hardness of 3–3.5 and a refractive index of about 1.64. It is supplied as barytes (ground natural barite) or blanc fixe (synthetic precipitated barium sulfate, finer and brighter).
It is used as an extender in primers, putties, industrial and protective coatings, high-build systems and powder coatings, and in some floor and sound-damping coatings for its density. Fine blanc fixe is valued in powder and industrial coatings for gloss retention, smoothness and chemical resistance.
Because it is so insoluble, barium sulfate has low toxicity and is generally not classified as hazardous, unlike soluble barium salts. Control dust when handling powders and follow the SDS and occupational dust limits.
Barytes is ground natural barite, coarser and lower cost. Blanc fixe is precipitated synthetic barium sulfate: finer, whiter and more consistent, used where gloss and smoothness matter.
Its low oil absorption and inertness let it fill the film without hurting flow, gloss or chemical resistance.
It is very insoluble, so it has low toxicity; it is even used as an X-ray contrast medium. Soluble barium compounds are toxic, which is a different matter. Avoid breathing the dust.
