The photochemical behaviour of four reactive‐azo dyes, (two dyes with poor wet light fastness and two dyes with normal wet light fastness) was examined to elucidate the mechanisms by which some reactive azo dyes, applied to cellulose, fade more rapidly when wet.
In one case it was found that the major primary photochemical reaction is photoejection of electrons, which is enhanced in the aqueous environment, while in the second case, a back reaction between hydroxyl radicals and dye molecules is facilitated by the aqueous environment.