my late father in law was a chemist assistant, he told me a mixture to get rid of bronze disease on coins and so far I have had pretty good results. you take sulfur powder and Vaseline and make a paste, take a Q tip and apply to infected area, let set 4-6 hours and take clean cloth and wipe away, repeat if necessary. once the bronze disease is gone soak coin in trisodium phosphate for an hour or 2 then rinse in distilled water. dry and or put a protecting coating on coin (I use renaissance wax) sometimes the coin will have a pit or be smooth where the disease was. if paste comes in contact with copper it will darken the coin. I will be going through my coins in a few weeks of some I treated.
I have been using a lite oil such as peanut, or sesame. I often just let them sit for months on end. I have a 1850s IHC thats been in some for about 2 years. Ill find it and post pics. Also dig up my b4 pics as well....
I suspect he meant 1850s as in the decade, not the specific year, and Indian Head Cents were first struck in 1859 .