badges

Those things are made of the cheapest material possible & they'll eventually start to oxidise.
Usually it's the pin that goes first.
You could try treating them, but it'll be more trouble than they're worth really &, in any case, you'll only be able to treat the visible surfaces. The ones underneath the picture will still oxidise.
You can slow down the process. If you get hold of sachets of silica gel (like the type you get in the box when you buy a new electronic device or other moisture sensitive gadgets) & put those in the bag you keep the badges in, they'll absorb the moisture.
Alternatively, silica cat litter (sounds silly but really works*) also absorbs moisture.






*When my car's windscreen blower broke I filled a sock with the stuff, put it on top of the dash board & it stopped the windscreen misting up

It won't make any difference really. They'll still be exposed to moisture wherever you keep them.
At least in bags they are all together & you can minimise the exposure. & if you drop some silica in, then they'll be better protected so as to slow oxidisation.
Outside a container there'll just be more exposure than inside

The silica absorbs a lot of moisture.
Yep, take them out every now & then or change the silica from time to time.
That's all I can think of that's relatively cheap.
I've never tried it, but rice might also work. Often people put one or two grains in a salt cellar to stop salt from getting moist & sticking together