Abstract: Red iron oxide pigments having a lower metal impurity content and enhanced purity of color are disclosed as being comprised of clusters of spherical particles.

Abstract: A process for the production of iron oxide yellow pigments by the Penniman-Zoph process from the raw materials iron (II) sulfate, sodium hydroxide and metallic iron, is disclosed in which iron (II) is oxidized to iron (III) by gassing with air in the presence of goethite nuclei, the iron (III) sulfate is dissolved to form iron (II) and the goethite nuclei are built up to iron oxide yellow pigments, characterized in that the gassing with air and dissolving of the metal are carried out in separate vessels.

Abstract: Iron oxide black pigment with improved color intensity is produced by subjecting finely divided pigment obtained from reaction of metallic iron with aromatic nitro compounds to a heat treatment of 200.degree. to 800.degree. C. under a non-oxidizing atmosphere for a time of 2 minutes to 5 hours.

Abstract: Iron oxide black pigments useful as coloring pigments for lacquers and plastics are prepared by an improved process wherein finely divided iron oxide black suspensions obtained from the precipitation processor the aniline process are filtered, washed, dried and ground with the improvement in the process comprising grinding the dried iron oxide pigment in a jet mill with air as the grinding medium and with a water content of from about 1 to 6% by weight based on the iron oxide black pigment input to the process.

Abstract: Iron oxide red pigments comprise clusters of a plurality of pigment particles, preferably at least five intergrown spherical particles, are prepared by conducting nuclear formation of iron oxide yellow .alpha.-FeOOH in the presence of compounds of the elements, B, Al, Ga, Si, Ge, Sn or mixtures thereof in quantities of from 0.05 to 10% by weight, calculated as tri- or tetravalent oxides and based on the arithmetically calculated precipitated .alpha.-FeOOH nuclei, separating brine from the resulting yellow slurry to isolate an iron oxide yellow paste, drying and annealing the paste to form iron oxide red pigment and grinding the red pigment, which pigment is useful in coloring foodstuffs, lacquers, plastics and building materials.