amines in aqueous solution or as an aqueous slurry preferably naoh is employed suitable oxidizing agents include atmospheric oxygen oxygen ozone h 2 o 2 chlorine nitrates of the alkali or alkaline earth metals or nh 4 no 3 atmospheric oxygen is preferred if the iron ii chloride solution that is used contains relatively large amounts at ph values of less than 4 of chromophoric metals that can be precipitated then these can be precipitated up to ph 4 by adding an alkaline component to the iron ii chloride solution the solid that is formed can be removed by sedimentation filtration or centrifugation from the supernatant clear purified solution in addition to the undesired chromophoric metals fe iii which has a significant undesirable influence formation of black magnetite on the reaction to form the u03b1 feooh crystallization nucleus is also thereby removed the reaction can be carried out batchwise or continuously in stirred vessels in cascades of stirred vessels in recycle reactors or in stirrer less reactors using twin feed nozzles as mixing devices after production of the u03b1 feooh crystallization nuclei according to the invention the latter are converted into a pigment which is effected by a coarsening of the nuclei particles known per se pigment build up since the u03b1 feooh crystallization nuclei according to the invention are however not used as such it is necessary to describe the pigment build up and the annealing to form an iron oxide red pigment the al containing crystallization nucleus produced by the process according to the invention is pumped into a solution of fecl.