Cleaning Disney Medals

[DisneyDudet]

Today I was putting my most recent Disney medals in my shoebox (sad, I know!), and noticed some have some spots that look like water spots. When attempting to clean with my hand, dry cloth, and damp cloth, nothing has cleaned them. It is only the ones from 2009, odd, isnt it?

I was wondering if there is anything I can try to get these spots off with? You can see them with direct light, but in low light you can.