Roman Silver? [solved]

Hello dear Numista members,
I recently acquired some Roman coins. I also got a coin that has a silver-ish tone, however the whole coin looks bronze, and after a search I did, the coin may indeed be silver. I can detect at the obverse a radiated bust of a man, and on the reverse two victories and a palm tree(?) between them. On the left side, I can read VOTA. Could you identify the coin. Moreover, how can I know it is silver but oxidised, or just another bronze?

Diameter: around 22mm

PS: How could I clean it?

The radiate crown makes it an antoninianus. When first introduced in the early 3rd century these coins were silver however with time they were debased to bronze with minimal silver content (around 5%). I don't think cleaning it is possible.