How did Mt Rushmore get covered with green gunk?

notwilight

I had my 1802 cent thread last night so here is the modern crap thread for balance. This coin is in the original mint capsule but the history for the past 15 years is unknown so it may have spent some time out of the capsule. I didn't know gold turned like this and what could cause it?


Thanks,
Jerry

notwilight

No opinions? I rescued this from the 4th page (already) because I really do need help understanding this stuff. Under a microscope it looks like green lichens growing on the coin. --Jerry

RichieURich

It could have been stored in a humid location or a location with temperature and humidity changes. I often see this type of situation with proof sets. Now as far as what to do about it, I don't know. For a proof set, I just wholesale it, but noting the problem, it gets discounted a bit. With a gold coin of higher value, it is probably worth restoring it/conserving it/removing the gunk.

Pentimento

I am having a hard time telling gunk from reflection. Is it only on the fields?

BillJones

I'd say the coin was stored in a hostile environment in which it was subjected alternate periods of extreme heat and cold. The copper in the coin, which may have been in a thin layer on the surface, reacted this by corroding to its natural green color.

I’ve seen commemorative gold sets down here in Florida that have been “cooked” in the extreme heat. A careless former owner stored the coin in an unair-conditioned house or more likely stored it in one of the storage attics that are often included in Florida houses. The summer temperatures in these attics can reach 150 degrees or higher in the summer down here. As a result the gold coins had a hazy dull look them, which made them very undesirable IMO.

When I was collecting my wooden box set of modern commemoratives, I remember when dealer asked me if I was interested in buying a six piece Mt. Rushmore set at “bid.”

“Sure,” I said, but when I saw the coins I had to pass because all of them had been “cooked.” I had a similar situation with a 1988 four piece Olympic set. The owner had left the padded shipping sheet with the set, and it had melted on the coins and scared the interior of the wooden box.