Discolored coins...anybody got any science on why they turn various shades?
nickelsciolist
Posts: 196 ✭✭✭
Okay, not a post for most avid collectors. I've taken an interest in common circulated cupro-nickel coins that turn different shades. I see 4 primary types that I call: flat black, flat red,flat gray, and gloss bronze.
Anybody got some metallurgical insight as to what causes these (to me) interesting changes?
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Comments
It is called tarnish... and depending on the coins environment (temperature, moisture, surrounding materials such as envelopes, plastics etc) the coin will react accordingly. Silver loves sulfur..... many people store their coins in Taco Bell napkins or other paper and set in sunlight to achieve tarnish colors ..... then sell them at a premium. Intent to tarnish (and achieving it) is called artificial tarnish and abhorred by dedicated collectors - but others still pay a premium. No matter if it is natural or artificial, it is still environmental damage to the coin. If TPG's do not reject it, it is termed 'market acceptable'. Cheers, RickO
...thanks RickO. I've heard "toned" used as well. Seems to me telling natural from intentional tarnishing would be challenging.
I wonder about some of the cool ones I get in rolls...like why is this one red and that one black?
So...in your opinion, would really cool toning add premium to a coin that has no real numismatic premium...say a post 1970 Lincoln half ? I've found some that are really unique, and they look beautiful in a nice carved setting...