Hydrogen Peroxide Etching Rate of Developed Silver Halide-Gelatin Films.

An explanation is presented for the etching chemistry of developed silver halide-gelatin films using acid hydrogen peroxide containing halide and cupric, stannic or ferric ions. The effects of etch bath composition on the etching and bleaching rates were measured. The results are consistent with reduction of the cupric ion by developed silver, which is favored by the removal of silver ion by halide ion. Cuprous ion can then react with hydrogen peroxide to form hydroxyl radicals which degrade the gelatin in the vicinity of developed silver. Ferric ion can react in similar fashion except that oxidation of hydrogen peroxide to oxygen is an important side reaction. Stannic ion produced slower etching than either cupric or ferric ions.