Cleaning Coins with Electrolysis - A Detailed Illustrated Tutorial, page 22
7. Effects of Coin Electrolysis on Dug Copper Coins with Verdigris Coating & Crust
Electrolysis can not damage a coin and only disclose the damage that has been inflicted on the dug coin by corrosion and oxidation. The more severe the damage, the uglier the coin's appearance after the electrolytic cleaning. Electrolysis can damage the coin only if the coin is attached to the wrong electrode - anode. Given below are three examples of what the verdigris-damaged copper coins and a non-dug clad coin may look like after electrolysis.
• Results of Cleaning Coin #1 with Electrolysis Only
The dug copper coin #1 shown below had been badly damaged by verdigris and corrosion crust. First it was brushed with a nylon brush to remove as much corrosion coating as possible in order to establish good electrical contacts with both a cathodic power connector and electrolyte.
Badly Corroded Dug Copper Coin #1 Before Electrolytic Cleaning
During the electrolytic cleaning session using the "Classic" setup, all the coating was removed, and the badly pitted surface was revealed. The coin's details are almost impossible to read. Whatever details were visible prior to electrolysis, they are gone now because they had become a part of verdigris layer during the process of corrosion in soil.
Severe Corrosion Damage Is Revealed After Electrolytic Treatment