Abstract: The invention relates to a process for the preparation of a melanic pigment, comprising the polymerisation of a compound corresponding to the formula: ##STR1## in which: R denotes a hydrogen atom, an alkyl, alkoxy, hydroxyalkyl, SiR.sub.4 R.sub.5 R.sub.6 or aminoalkyl radical, or an aryl radical which is unsubstituted or substituted by OH, NH.sub.2, alkyl, alkoxy or NO.sub.2 ;R.sub.1 and R.sub.2 denote alkyl groups or together form a methylene or ethylene group which is optionally substituted by one or more alkyl groups, and R.sub.2 denotes hydrogen or COOH, in the presence of an oxidizing medium and of an enzyme with (per)oxidizing activity or of a compound which has a similar activity, and to powders which make use of them and to their cosmetic use.