Those are some excellent reference points, thanks for the useful pics @paddyman98. Yeah, they're technically gross but look at the bright rust...
Awesome feedback, thanks everyone!
Seems like water damage? I think I can see some nickel peeking through on the relief but I can't see any on the edge. Maybe a combo of water...
Provided to investigate the type of damage involved to create this look.
Separate names with a comma.