Conversion of crude copper phthalocyanines into pigments

A process for converting copper phthalocyanine into a pigmentary form, wherein finely divided crude copper phthalocyanine, which has crystallized irregularly and is heavily agglomerated, is finished in the presence of basic copper phthalocyanines of the formula WHERE CuPc is an n-valent copper phthalocyanine radical, R1 is hydrogen or alkyl, A is alkylene of 2 to 6 carbon atoms, R2 is alkyl, alkoxyalkyl or cycloalkyl and R3 is hydrogen or alkyl, or the group is a saturated 5-membered, 6-membered or 7-membered heterocyclic ring and n is from 1 to 6, in from 50 to 75% strength by weight sulfuric acid at from room temperature to 100 DEG C.