As I understand it the dark toning found on silver coins is primarily silver sulfide. When the coin is a Au-Cu alloy some of the dark material may be copper oxide. On Au-Cu alloy coins you can sometimes see green spots which is copper chloride. As has been pointed out many times you shouldn't clean valuable silver coins! However, toning (patina) is a corrosion process and corrosion can be progressive. Corrosion products are usually cracked or porous so that corrosion will proceed if not stopped. I have searched the coin literature to find something on stabilizing the toning so it doesn't get progressively "worse". I haven't found anything. Some time ago I put some silicone sealant (type used to seal tile) on some bright coins to see what would happen - so far nothing. I haven't tried it on toned coins but I have tried the silicone sealant on cleaned silver bullion coins and so far they haven't corroded. Anyone have any comments??
Quote: VacdepmanAs I understand it the dark toning found on silver coins is primarily silver sulfide. When the coin is a Au-Cu alloy some of the dark material may be copper oxide. On Au-Cu alloy coins you can sometimes see green spots which is copper chloride. As has been pointed out many times you shouldn't clean valuable silver coins! However, toning (patina) is a corrosion process and corrosion can be progressive. Corrosion products are usually cracked or porous so that corrosion will proceed if not stopped. I have searched the coin literature to find something on stabilizing the toning so it doesn't get progressively "worse". I haven't found anything. Some time ago I put some silicone sealant (type used to seal tile) on some bright coins to see what would happen - so far nothing. I haven't tried it on toned coins but I have tried the silicone sealant on cleaned silver bullion coins and so far they haven't corroded. Anyone have any comments??
Do you mean Ag-Cu? Au is gold. Anyway silicone sealant...sounds like fun but not sure whether it is such a good idea BUT it is your collection: so sure why not?
Of course slabbing will protect the coin but it also prevents you from handling the coin and you have to look at it through a plastic window. I don't like particularly like slabbed coins since I collect old coins that have a lot of nuances that can only be seen by looking (or photographing) at the surfaces from various angles. Also it is much harder to detect a counterfeit coin (cast, weight, etc.) through a plastic window. I guess if you collect to just say "I have one of those" slabbing is fine but I like to look and study a coin and learn about the story behind the coin as well as the mint. For example the "Muera Huerta" coin of the Mexican Revolutionary period. Why would someone mint a coin with "Death to Huerta" on it? A lot of history there. Or the Mexican Zacatecas mint which minted a lot of silver coins but comparatively few gold coins. Also the features of some older coins can only be detected by looking at them from various angles. This may be due to problems and variations in the minting process. Some features may best be seen in photographs taken with various lighting angles.
I stand corrected in my first post the symbol for silver is Ag not Au - thanks.
I keep my AU and BUNC US silver coins out on my shelf. I dunno if tarnishing is good or bad on coins but they just sit there, including a BUNC 1945 Mercury dime, 10 BUNC Peace dollars and two AU Morgan dollars, all which I bought for only $10 from a friend.
Should they be sealed? I was never really sure about sealing silver coins, and the only one I do have sealed is a Polish proof 10 Zloty.
Kenny
- Verifying your Asian and British-territorial coins everyday with the best quality photos and the best information.
a little plastic sealable bag or plastic coin folder will protect them and are cheap
but if you have silver proof unc the round coin cases are good but you can get the coin out if you want to handle it,, but only by the edges of coin...i would definately not use silicone when a littlr plastic bag will do
In that long topic I wrote (with pictures) on 24-Dec about Copper-nickel v. plastic
Results were not good - but that was copper-nickel, not silver. So I think I should put a silver coin in a bag, and carry it around in my pocket, and see the results in a few months, for comparison.
P.S. I guess I should take 'before' pictures for comparison ...
