Wheel polishing troubles

[Commissar]

Over winter I bought my last two wheels to polish up, did my first 2 last fall/winter.  Throughout sanding these I have been seeing some discoloration areas on the wheel.  When I got to 1500 grit it was pretty apparent that it wasn't getting removed.  I proceeded to remove a spoke back to 80 grit until most of what I was seeing was gone.  Sanded back up to 1500 grit and the discoloration was still there.  See the pictures, I need some suggestions on what to do.  I have about 8-10 hours into these things, would hate for them to not be able to polish up to a nice shine.

 

[Team Adam's]

Thats really strange... I wonder if its some kind of staining thats worked its way deep into the surface so you haven't sanded "past" it yet. 

[Rich B.]

That's a lot of work, think if you sandblasted would change the finish texture. Use to have good luck sandblasting curbed hub caps and respraying but wheels are different. Usually by first sandblasting and then lightly wire brushing with drill motor the satin finish can be brought back on metal. But who has a sandblaster?