Pigment preparations based on PY 155

A process for producing a pigment preparation comprising C.I. Pigment Yellow 155 and 0.1% to 50% by weight, based on the weight of C.I. Pigment Yellow 155, of at least one pigment dispersant selected from the group consisting of monoazo and disazo pigments, wherein the at least one pigment dispersant is substituted with at least one sulfonic acid group, wherein the pigment preparation has of a chroma C greater than 35 in the CIELAB system in an aqueous base vamish system in a white reduction comprising a 0.2% by weight concentration of the pigment preparation in white reduction said process comprising the step of heating a PY 155 crude pigment in a mixture of water and an organic solvent having a boiling point of above 100° C., at an alkaline pH, and in the presence of 0.1% to 50% by weight, based on the weight of C.I. Pigment Yellow 155, of the pigment dispersant to a temperature of above 60° C.