Black Coin Coating [gelöst]

Hello! I currently have a problem with some coins, and help would be greatly appreciated . They have a black layer on their faces, and I can't seem to get them out. I have tried vinegar and baking soda and it seems to have worked for the nordic gold coins, but the copper coins remain resilient. I have tried soaking them in hydrogen peroxide for six hours, but it seems to have failed. Thanks in advance! 

Environmental exposure  issues - going to be hard and or impossible to remove it unfortunately.  

 Agreed. Looks like it was in a fire, so the composition 

of the metal may have changed, so is more than surface damage 

and may not be possible to remove. Will see what other members think. 

Thank you very much for the help! 

ZacUK

 Agreed. Looks like it was in a fire, so the composition 

of the metal may have changed, so is more than surface damage 

and may not be possible to remove. Will see what other members think. 

Hello.  I wouldn't draw fire to it, it really is the environment.  Here is a sample of cent coins with gas stations.  the entire bottle was delivered to me by a truck driver neighbor somewhere from a gas station in Europe.  Coins in diesel, gasoline and dust were thrown into the can.  She showed: I have them Momo reach collection for research purposes under the microscope.