ISO 4621:1986

Specifies three grades, which shall not be in admixture with other colouring matter of organic or inorganic nature and shall be free from extenders. The pigment consists essentially of chromium(III) oxide (Cr2O3) in the form of a dry powder. Grade 1, these pigments shall contain a residue on a sieve of 45 nm mesh aperture of not more than 0,01 % (m/m); grade 2, under the same conditions, shall contain a residue of more than 0,01 % (m/m) and not more than 0,1 % (m/m) and grade 3 shall contain a residue of more than 0,1 % (m/m) and not more than 0,5 % (m/m).