wondering what happened to these coins

[MakesCents]

I got these nickels from different places over the years. I am assuming that it was some kind of plating error and that there must be more out there because they are different years. Feel free to share your thoughts. Thx

IMG_20210223_112122743.jpg (819.22 KiB) Viewed 1019 times

IMG_20210223_112100345.jpg (840.01 KiB) Viewed 1019 times

[coinguy]

It can't be a plating error as 1942-43 Tombac Nickels were not plated.
Looks like some sort of environmental damage.

[momomomo]

My guesses are dipped/cleaned/polished.