Sestertius with green incrustations - BD or verdigris?

[Miguel P]

Hi everyone,

I recently purchased a nice Antoninus Pius sestertius with this kind of green copper compoud in some areas around the edge. Does it look like stable incrustations or should I worry?

They are pretty hard and they are raised above the surface of the metal. However, I'm still concerned so I would like to know your opinion.

Thank you very much in advance!

[Akropolis]

Looks mostly stable, but poke light green areas with a wooden toothpick. If powdery green comes off, you have BD.
PeteB

[Miguel P]

Thanks for your reply!

I poked a little and brushed it gently with small (unused) toothbrush, but couldn't see any powder come off. Should it still be recommended to remove these incrustations though?

[Akropolis]

If stable, and I think they are, do NOT remove them. You will probably destroy the coin in the process.
PeteB

[Miguel P]

Thanks, I will not attempt to remove it.

I took another shot  with better lighting and it seems to confirm that they are stable malachite/copper hydroxi-carbonate crystalline incrustations (they are also very hard) I used gloves to prevent any chloride ions present in my sweat from coming into contact with the coin.

[SC]

Typical malachite for such a coin.  It similar deposits were likely cleaned off the main surfaces in the past but no one bothered to clean the edges.

SC