Coin is rusting

[alvarof27]

I have a big problem with a coin... I do not know why but it is starting to rust...
What can I do? What material is this?

[Victor]

Your coin is bronze, but iron is a commonly found trace element in bronze alloys. You probably have a bit of humidity making the coin rust. Is the green stable or is it soft and powdery-- if soft, it is bronze disease, which is also associated with higher humidity. Dessicant packs can be a quick fix for the humidity.

[livingwater]

I have used a product called Verdi-Care I bought from Wizard Coin Company to stop coin disease.  I've also seen it for sale on ebay.  It has worked for me, does not change the appearance of the coin much, and it can be washed off if you no longer want it.