C 8082 (OTTO) Cobalt(III) oxide, ≥70% Co basis, black Cas 1308-04-9 - used for buffing and polishing. C 8082 (OTTO) Cobalt(III) oxide, ≥70% Co basis, black Cas 1308-04-9 - used as a precursor to the magnetic pigment viz., chromium dioxide, it is used in inks, glasses, and pigments (viridian).