Hi. Some answers after this beuatifull presentation. I was in Mesa Verder myself some years ago. Awesome. Answers: Numismatic coins loose there extra value when cleaned but I have looked at internet and these bars do not much above spot so some cleaning is not an issue if you want to get them clean. The paper should go off in a bath with some soft soap added (we call it green soap here and it has no chemicals added) and you then wash them off a little without rubbing. Blow dry. As for the dirt it can be removed either in the same soap bath (no rubbing) or if you wanna see spectecular result : put alufoil on the bottom of a bowl (a bit wrinkled first) , put bakingsoda in the bowl on the foil, put the bars on top and poor hot water on top of it; turn the bar after some time. Flush when clean.The first layer of silveratoms is dissolved by het electorns and baking soda. Toning will remain (the blue). Just have fun!