A process for the preparation of a vat dye of the dianthraquinone-azine or dianthraquinone-N,N'-dihydroazine series, or a higher cyclic homologue thereof, which comprises reacting a primary amine selected from the group consisting of amino anthraquinones, their substitution products and higher cyclic homologues, with an alkaline condensing agent, wherein reaction is effected in the presence of at least one oxide of an organic derivative of a metalloid element of Group 5B of the Periodic Classification of the elements.
