Nero Tetradrachm And Green Blobs

I agree: removing the green corrosion will reveal pitting underneath.
I have read that in humid conditions, such coins that are not isolated from the rest of the collection can lead to verdigris corrosion spreading to nearby copper based alloy coins.

Optional to physically remove most of the verdigris, but you need lots of patience to do this reasonably well.

Somewhat of a pity: pictured coin is in better than average condition for which these coins are normally found.

My policy to prevent verdigris affecting other coins
is to put the affected coin in a close fitting non PVC album pocket, and seal that inside a standard / cardboard Mylar flip.

Thank you for the replies, @louisvillekyshop, @sel_69l and @JohnConduitt. The situation with the encrustation is as I had thought, but it is always better to hear the assessment of those with much more experience.


In hand it does indeed appear to be stable, and looks to have been on the coin for quite some time. I did wonder about the pit on the lower right, and I agree that it doesn't do anything for the coin.


Indeed, and on the bright side, if it weren't for the encrustation I probably wouldn't have been able to afford it. The encrustation was highlighted by the dealer, and the coin priced accordingly. I do like the portrait of Nero.


I have not seen this encrustation on any other silver/billon coin, and had assumed that it may have been caused by bad storage. If the person who originally cleaned the coin stopped there, it would be unwise for me to try and take it further.

I am content to leave the coin as it is, and take the preventative measures to ensure that the growth is not transmitted to other coins. Thanks again for the replies.
Jim