Process for etching photoengraving copper

Claim 2

IN A PROCESS FOR ETCHING PHOTO-ENGRAVING COPPER BY CONTACTING SAID COPPER WITH AN AQUEOUS FERRIC CHLORIDE SOLUTION CONTAINING A FORMAMIDINE DISULFIDE PASSIVATING AGENT, THE IMPROVEMENT WHICH COMPRISES IMPRESSING A POTENTIAL DIFFERENCE OF FROM ABOUT 3 TO ABOUT 50 VOLTS ACROSS THE ETCHING BATH SO AS TO ENHANCE THE EFFECTIVENESS OF THE PASSIVATING AGENTS.

Claim 3

IN A PROCESS FOR ETCHING A PHOTO-ENGRAVING COPPER HAVING A PORTION OF ITS SURFACE MASKED WITH A RESISTANT COATING, WHEREIN THE ETCHING IS EFFECTED BY CONTACTING THE PHOTO-ENGRAVING COPPER WITH AN AQUEOUS FERRIC CHLORIDE ETCHING SOLUTION CONTAINING A PASSIVATING AGENT SELECTED FROM THE GROUP CONSISTING OF (1) FORMAMIDINE DISULFIDE COMPOUNDS, AND (2) AMINE COMPOUNDS SELECTED FROM THHE GROUP CONSISTING OF ALKYL AMINES AND ALKANOL AMINES IN COMBINATION WITH FORMAMIDINE DISULFIDE COMPOUNDS, THE IMPROVEMENT WHICH COMPRISES IMPRESSING A VOLTAGE DIFFERENTIAL OF FROM ABOUT 3 TO ABOUT 50 VOLTS ACROSS THE ETCHING BATH WHILE CONTACTING THE PHOTO-ENGRAVING COPPER WITH THE ETCHING SOLUTION.

Claim 4

IN A PROCESS FOR ETCHING A PHOTO-ENGRAVING COPPER HAVING A PORTION OF ITS SURFACE MASKED WITH A RESISTANT COATING, WHEREIN THE ETCHING IS EFFECTED BY CONTACTING THE PHOTO-ENGRAVING COPPER WITH AN AQUEOUS FERRIC CHLORIDE ETCHING SOLUTION CONTAINING A PASSIVATING AGENT SELECTED FROM THE GROUP CONSISTING OF (1) FORMAMIDINE DISULFIDE COMPOUNDS, AND (2) AMINE COMPOUNDS SELECTED FROM THHE GROUP CONSISTING OF ALKYL AMINES AND ALKANOL AMINES IN COMBINATION WITH FORMAMIDINE DISULFIDE COMPOUNDS, THE IMPROVEMENT WHICH COMPRISES IMPRESSING A VOLTAGE DIFFERENTIAL OF FROM ABOUT 3 TO ABOUT 50 VOLTS ACROSS THE ETCHING BATH WHILE CONTACTING THE PHOTO-ENGRAVING COPPER WITH THE ETCHING SOLUTION.