Coin Silver And Tarnish

Thanks @andrew. I'll grime up a coin and send it to you, and you can do whatever you like with it. The nice thing about SEM/EDAX is being able to test deposits right on the surface. I used to have access to it but am retired now.

This week I received from OP, the following coin





For the purpose of analyzing the black spots that recur over carrying of the coins. There are three other coins as well, but all have similar spots.

The coin was placed in a scanning electron microscope, first to take an image of what we are looking at. This is a 15x image of the three spots on the neck with the head pointing down



This is a 50x image of the middle spot.



Note that the spot has some structure and depth to it, more as if something is raised off of the surface than something changing color on the surface.

Switching to EDXA, which will give an elemental breakdown of all elements contained in this middle spot




Note the major component is silver, a significant amount of Carbon, some Oxygen, some chloride. The silver oxide is expected of course, but there is a lot of carbon in that spot. The Chloride is likely from body sweat as it was in a pocket.


Now lets go off the spot and look at the non-spotted surface



Ok, so we still see the silver, much less Oxygen, much less carbon.

So far, I can only conclude something organic from the environment is adhering to the coins, perhaps via a reaction with the silver.

I tried to remove the spots with a razor blade and got not much of anything. I'll try with a toothpick and see if I can take off enough to do an FTIR.

If a silver coin is below Fine condition, and not very rare,
I don't think it matters much if it is cleaned or not.

So, go for it, if you think it will look better.

I love the full analysis Andrew! Nice work.

I started carrying old coins around partly because of cc's question "What's in your pocket?" I expected for the coins to get shiny, the way silver did back in the 1960's in my dirty Levis pockets. I didn't expect these grimy spots. I think there's something happening to the coin silver as it ages beyond 100 years. I didn't see the spots develop on 1960's silver when I carried it in the same way two weeks ago.

I'm curious; why do you carry junk silver coins around in your pants pockets?

@aron because they're old and I like having old stuff around. Better in the pocket than in a cigar box in a drawer. Also because they jingle.

@tesla here's my preferred way to carry a coin

@coinfrog not so far. It's not like having a concho belt made of Buffalo nickels or silver dollars. It seemed like a good use for a coin with obverse damage. The best coin buckles I've seen were made by Wades using gold coins and hand chasing on the solid silver.

http://www.ebay.com/itm/191939460810

I'm not going for the showy gold though. I'd rather wear something that looks like an ordinary rodeo buckle. Why advertise? I know what it is.