Abstract: Apparatus for use in developing diazo emulsion media (e.g. plates, films, etc.) for use as integrated circuit masks wherein a developing gas is utilized; the apparatus including a developing chamber for housing the media and containing the gas during developing; an accumulator and reservoir for storing the gas when developing is not taking place; a pump for evacuating the developing chamber of air and the developing gas and for pressurizing the gas in the accumulator reservoir; a plurality of solenoid valves for regulating gas flow between the developing chamber, the pump, and the reservoir; and a control unit for automatically controlling the developing process.