Cleaning with olive oil...

[Chilli]

I recently found a knife buried in sand while metal detecting. I soaked it in WD-40 for several days and was amazed at the amount of encrustation that it removed from the aluminum sides. Haven't tried on a coin but might be worth a try.

Agree. Have used WD-40 on a number of things in the past. The new one is almost odourless too.
My go to initial clean for small relics, coin and gold nuggets is the microwave technique.
Coffee cup 3/4 full, in the microwave for 4 to 5 minutes on high.
Take it out, put on a bench and stand back, wear glasses and drop your coins or whatever in it. The reaction is full on and the water literally erupts as the cold item drops in. The reaction often lifts things instantly like baked on hardened clays and can even dislodge quartz fragments and hard coatings on nuggets. You'll be amazed at not having to lift a finger to clean, what can come off at times in the bottom of the cup/mug.

 

Amazon Forum Fav 👍

Diving for Pleasure and Treasure - Grab it through Amazon!