I have found two nice coins (seated quarter and barber dime) that I am having trouble cleaning. They have a thick black junk on and I have tried every

[Chris1]

n/t

 

[Craig in Alabama]

n/t

 

[CampPollardC.S.A.]

n/t

 

[RichardSATX]

This method is posted on the PCGS website and does no physical damage to the coins. It involves a soak in household ammonia and then vinegar. I have done this on many coins including a 1923 Peace Dollar with black staining that I just finished. It worked great. I just started a couple of mercs last night with good detail left but are stained. Most ways will either stain the silver or leave fine scrub marks that can be seen under magnification that will devalue the coins.
http://www.pcgs.com/articles/article616.chtml

Rich

 

[Dave Z]

Rub it with a baking soda and water paste.I found a few like that before.The gunk felt like glue.Dave

 

[Chris1]

I can see spots of detail coming through but I still would like to get the dull grey off. Thanks for all the suggestions.

 

[Bavaria Mike]

Consider buying a silver cleaner from a coin dealer, liquid dunk the coin type. I use it on my blackened or dirty silver coins here in Germany for just a few minutes, brush lightly with a soft toothbrush under running water afterwards. Repeat several times if necessary. I once forgot an 80% silver coin over night soaking, it could use a buffing but still looks good. HH, Mike

 

[RichardSATX]

I don't think there is a way to get rid of it.