How to clean coins?

[stefs]

I collect this for years, but i dont know how to clean and see what they is.
Some are from beaches, some from forests...
Advices?

 

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[Robinb]

If those are euro copper cent coins, the core is iron, once they eat through the copper clad you cannot clean them.

fit for bin only.

If there is no rush them put them in a tumbler.