You can mix Coke with rum, rye, or even vodka, just don't mix it with your coins. I'm not a chemist, but I've heard that if you leave a coin soaking in Coke long enough, the phosphoric and carbonic acids will strip away its natural shiny surface, leaving behind discoloration, pitting, corrosion, and even dissolving the metal itself. The 1977 Kennedy half dollar in these photos looks like it may have been the victim of exactly that. The copper core appears to have partially dissolved, the cupronickel layers have turned all kinds of strange colors, and the whole thing looks like a commemorative vanilla Oreo. Could Coke really do this to a Kennedy half dollar, or is something else responsible? I'd love to hear from the coin chemists and metallurgists out there.
I've seen the rim cut like that for pendants. I know Coke is acidic, so I assume a coin sitting around in it wouldn't help the overall appearance! We could start a whole new realm of errors on eBay called "the ultra rare Coke Error" for all the "I'm gonna get rich quick" people to gawk at. It has been a very long time since I drank Coke.
This is always a little confusing to me. Nickel is a more reactive metal than copper, so I'd expect acids to attack the outer layers (making them more copper-colored) and spare the pure copper core. But it's a lot more complicated than that. Nickel can form a protective layer that prevents further corrosion, and copper is less inclined to do that (passivation) - but it depends on what's doing the attacking. I've seen this "Oreo effect" many times before. But what I haven't seen is the inner layer looking silvery like this. It's usually dark, or copper-colored. It almost looks like this was dipped in something that deposited silver on the copper layer. ... which I think is exactly what would happen if you dropped a coin like this into a silver dip that had been used on a number of silver coins first. But this speculation is getting pretty deep, and I'm not going to have time any time soon to start playing with chemicals again...
I've used a can of coke to dissolve car battery terminal corrosion successfully on several occasions. I try not to drink that stuff.
