I took a propane torch to it, the bulk of the build up came off with a pop, exploded when it got hot the rest of it started to crumble when I put more heat to the coin and just scraped it off with my finger nail.
Finish it off with hot peroxide.... also, if the dimes are held in by pressure, you may first want to see if there is anything concealed between them. RickO
Go to Wallie World a nd get a can of Never Dull...that stuff is awesome! Shouldn't cost much a one can lasts a LONG time...I've had mine for about a year and it's still almost full....really shines up metal....just be sure to keep it off the table or it'll eat the varnish