So, i really like this coin, the patina really sets it off...but my question is can this kind of patina be damaging to ancient coins? I know that if this were on, say, an early U.S. large cent, people would run for the hills! Please, tell me your thoughts. Image courtesy of CNG.
Looks fine, typical of the type. Bronzes do need to be carefully stored though. I generally give all of mine a light coat of Verdicare if there is any verdigris at all, and of course store in a low humidity environment. The mere presence of hard dark green deposits generally not something that devalues an ancient coin. Most people much prefer their bronze coins to have a patina!
When you see green deposits on Ancient coins, it is good to be cautious. If it's hard, it is most likely safe. If it's fuzzy and kinda soft, it is more likely bronze disease and can eat away at the metal till you have nothing left.
The question is more whether the coin is already damaged under the green. Removing it may work but it may reveal something less good looking. Leaving it would be the choice of most.
In addition to what others have said, I would point out that CNG is quite good about pointing out bronze disease if a coin is suffering from it, and they rarely sell coins with bronze disease - only if they're types of considerable rarity.
I agree with @Bing and @dougsmit. In my opinion, this coin was already cleaned, and his patine is in new process of development. The green hard deposits are older, and wasn't removed before. Under these deposits, if removed can it show corrosion areas. Personally, don't touch this.
