Process for dyeing hair by the sequential treatment of hair with metal ion-containing composition and with a dye composition containing 5,6-dihydroxyindole-2-carboxylic acid and certain derivatives thereof

A process for dyeing human hair a brown color, the process consisting of the steps set forth below:

• (a) applying to the hair an aqueous buffered hair dye composition having a pH of from about 3 to about 10, said hair dye composition consisting essentially of from about 0.01 to about 5% by weight of a colorant having the structure:
• ##STR2## wherein R.sub.1 is hydrogen, benzyl or an alkyl of from 1 to 6 carbon atoms and R.sub.2 is hydrogen, benzyl or an alkyl substituent group;
• (b) applying an aqueous composition consisting essentially of a transition metal ion selected from the group consisting of Cu.sup.+2, Fe.sup.+2, Fe.sup.+3, Co.sup.+2, Mn.sup.+2 and Ti.sup.+2 to the hair for a period of time sufficient to deposit on the hair an amount of said metal ion effective to promote the conversion of the colorant of structure I to a melanin-type pigment,
• said step (a) being conducted before or after the conduct of step (b), and
• (c) optionally rinsing the hair with water following steps (a) and (b),
• the hair following the completion of the process having a brown color tone.