Quinacridone mixed-crystal pigments of the gamma phase

A process for preparing a quinacridone mixed crystal pigment wherein the quinacridone mixed crystal pigment consists of

• a) from 82.5 to 99% by weight of unsubstituted γ-phase quinacridone of formula (I)
• in which R1 and R2 are hydrogen atoms and
• b) from 1 to 17.5% by weight of one or more 2,9- or 3,1-substituted quinacridones, or of a combination thereof, of the formula (I) in which the substituents R1 and R2 are identical or different and are chlorine, bromine or fluorine atoms or C1-C4-alkyl, C1-C4-alkoxy or carboxamido groups which can be substituted by C1-C6-alkyl groups, and R1 can additionally be a hydrogen atom;
• the process comprising:
• cyclizing 2,5-dianilinoterephthalic acid of formula (Ia)
• and substituted terephthalic acid(s) of formula (Ib)
• in a ratio of from 82.5:17.5 to 99:1, in the presence of polyphosphoric acid, a polyphosphoric ester, or a mixture thereof, hydrolyzing the ring closure mixture which is present after cyclization, at a temperature of at least 110° C., by metering the ring closure mixture into an amount of at least 70% strength by weight, of aqueous orthophosphoric acid which is such that at the end of the metered addition the concentration of aqueous orthophosphoric acid in the hydrolyzed mixture is at least 85% by weight, and then isolating the mixed crystal pigment, directly or following a fine division step, a finish treatment or both.