I'll use Euro coins.
1, 2 e 5 Eurocent coins are made of copper covered steel and are too small, so I think they won't be a good choice.
1 and 2 Euro coin are the right size, but it seems that they are made of alloys containing nickel, that may cause allergy.
So I think I'll use a 50 Eurocent coin, that is made of Nordic Gold, an alloy (89% copper, 5% aluminium, 5% zinc, and 1% tin).
Has anyone ever made a ring out of Nordic Gold?
Did it cause allergy or stain your finger? Did it tarnish?
Is it malleable?