how to clean old coins

How to clean old silver coins?

I dug up a 1956 half crown in my garden. I have tried every caustic substance know to man, but it remains the colour of an old penny (ie brown). Can anyone tell me how to restore it to its shiny original self?
Thanks in advance.

It sounds as if your coin is already beyond restoration, but try the methods at the link below. Never use acids or abrasives on coins. I hope that helps.

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Cleaning Silver Coins & Old Nickles Part 1 of a 3 Part Series