Goldish Patina : Do You Have An Explanation?

Hi all,

I recently acquired this distater from Thourioi (the new Sybaris) struck in late classic age (350-300 BC) and one of the reasons, beside its splendid classic style, was its extraordinary goldish patina. It is now 5 or 6 years that I look at all the greek coins in the main Auction Houses, and it is excessively rare to find such a patina. Actually, the only other exemplar I can remember is precisely from the same type (see below)...

Does anyone have an explanation for this strange phenomenon?

One of the things I like the more with numismatics is that every specimen carries with it its own fate, its own history, that it is a contingent encounter between art, as intentional, and accident. As wrote the Greek poet Agathon (quoted by Aristotle) : "Art loves hazard, and hazard loves art".