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I get something similar, if I forget coins in my ultrasound machine. The coins are laying on a plastic plate with holes in it. Where the holes are, the liquid seems to be able to do some damage (acid). I hardly use the machine any longer because of the liquid. If I do use it, just with water from the tap….
Globetrotter
Coin varieties in French:
https://monnaiesetvarietes.numista.com