The prodn. system has a transparent electrically conductive film applied to a transparent mask substrate (1), which is then immersed in an electrolyte soln. (5) and displaced relative to the front end of a working electrode (2) in 2 dimensions. The required mask pattern is formed in the mask substrate by the electrochemical reaction obtained when a given voltage is applied across the electrode and the transparent conductive film. Pref. the 2-dimensional mask pattern is formed with a given voltage applied between the electrode and the transparent conductive film, with subsequent electrochemical deposition of an opaque material onto the latter from the electrolytic soln.
