Ferrioxalates physical development

Other iron-based photographic systems have been devised. For example, the complex (119) can be coated with a suitable binder. Exposure reduces Fe to Fe . Treating the coating with water produces intensely colored Fe bipy complexes in exposed areas and washes unreacted salt out of unexposed areas.A system in which a fenioxalate complex is photolyzed to form Fe which is then selectively complexed with a dye indicator, was discussed in Section 59.4.2. An obsolete palladiotype process relied on the photolysis of ferrioxalate complexes to produce Fe, which in turn reduced a Pd salt to produce an image in Pd. More economical and sensitive processes today are based on amplifying a weak image in Fe or palladium nuclei by physical development. 

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