the subject matter of this invention relates to a process for removing the soluble metal cations contained in iron oxide pigments comprising washing said iron oxide pigments with a ligand compound having a ph greater than 6 . 0 . the pigments can be used as colorants for substances ingested by man and animals , and they can also be used to stabilize plastics against ultraviolet degradation , and as pigments in base - coat clear - coat automotive finishing operations .