be etched the unshielded portions of the copper surface are etched by being sprayed with etchant which may be passed in a continuous spray through nozzles in the etchant supply line the above etching apparatus has not been illustrated other than by general designation of a schematic system block 10 since the instant invention is not dependent on the equipment configuration for that component rather the instant invention is directed to the nature of the fluid utilized in the etching apparatus and to the manner in which the fluid is supplied thereto the etchant utilized in this system may be a solution of ferric chloride in water when the ferric chloride solution is sprayed onto the copper surface the ferric fe ions react with the copper and are reduced to form ferrous fe ions and cuprous cu ions according to the equation fe cu u00b0 fe cu as a cuprous ion dissolves into solution it immediately reacts with another ferric ion as shown by the following equation as the reaction continues the concentration of the ferrous ions increases at the expense of the ferric ions the effect of this reaction is to decrease the oxidation potential of the etching solution where the prior art has tried to solve the problem by the recycling or regeneration of the etchant the system embodying the instant invention rejuvenates the solution by the selective dumping of the spent.