Silver rusting?

[Rotsco]

Hi everyone, hoping you can shed some light on what I'm seeing here.

This is just a little piece I recently made for a friend, but I'm confused as to what looks like rust showing up in some sections.
I'll attach an image to explain, it's pretty obviously discoloured.

Could it be from the Steel Wool I used to give this a rougher finish?

Any and all advice appreciated!