This etching process was first described by Cedric green on his website and by Alphonso Crugera in his recently published Handbook. In this process the cell becomes a self etching battery.
When two metals with different potentials are placed together in electrical contact in an electrolyte, one metal will act as anode and the other as cathode. The electro potential between the metals is the driving force for the corrosion of the anode. Zinc has a potential of -0.762v on the index and copper +0.340v giving a difference of 0.422v. The anode becomes vulnerable when the difference is over 0.15v. Making the copper zinc coupling ideal for etching. This form of corrosion is also known as dissimilar metal or sacrificial anode corrosion. In a corrosive environment the metal with the lowest electrical potential (the zinc) becomes the anode in the cell and sacrifices itself for the more “noble” metal (the copper).
The etch on the plates is very deep and is great for viscosity inking.