Don't EVER dip any badge (coin, etc) into Coca Cola - it is VERY corrosive !
(Ld knows what it does to ones guts !!)
Mild cleaning with water and soap AND full rinsing will usually do. A rubbing with a clean cloth will get back to a good condition. However, you won't really restore a badge to the exactly same condition it was made 100 years ago.
But that's what most collectors like - good condition with a bit of history.
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