The Sooty-Flakey-Mottled Patina Again

This coin in next CNG eAuction ( 326, Lot: 5) certainly has an interesting patina, doesn't it?

ETRURIA, Uncertain inland mint. Circa 300-250 BC. Æ Aes Grave Dupondius (97mm, 371.20 g). Wheel / Anchor; I–I (mark of value) across upper field. ICC 146; HN Italy 65b. VF, green patina. Estimate $750. Closing Date And Time: May 07, 2014 at 10:01:40 a.m. ET. 

Now, where have we seen this before, a sooty black underlayer with thin flakey mottled off-green upper layer? Where did this come from? Can we see an analysis or at least an SEM or two of that patina?

UPDATE
Oh dear, just a few hours later and it's gone. Withdrawn for some reason, wonder why?  Perhaps they took the hint and decided it would be nice to let the purchaser have some SEMs of that extraordinary corrosion together with the collecting history.