27.4 parts of crude perylenetetracarboxylic dianhydride in the form of the potassium salt of perylenetetracarboxylic acid are dissolved in aqueous potassium hydroxide solution as described in Example 1. To this solution are added 2 parts of stearic acid, dissolved in 60 parts by volume of 1% potassium hydroxide solution. With stirring, the alkaline perylenetetracarboxylic acid/stearic acid solution is added dropwise in the course of 15 minutes at 60° C. to a suspension consisting of 1.4 parts of MgCl2.6H2O, 0.7 parts of stearylamine, 35 parts by volume of about 37% aqueous hydrochloric acid and 60 parts by volume of isopropanol. The formation of the anhydride imide is brought to completion by stirring the acid suspension for 31/2 hours at reflux temperature. The red pigment suspension is then filtered at about 70° C. The filter cake is washed neutral with cold water and dried in a vacuum cabinet at 80° C., affording 29.8 parts of a perylene pigment with properties as good as those of the pigment of Example 1.
