aluminum
First I used a brass wheel on the bench grinder to take off the factory coating, and then used # 2 and # 3 polishing grit and polish wheel.
Then I finished the shine with mothers aluminum polish, all using the bench grinder
I then used rubbing alcohol to clean the metal and then applied a clear coat lacquer.
I did the same to the swingarm linkage and both wheel hubs.
Use a face mask and eye protection when using the brass wheel and the polish wheel because the crap that comes off the metal is not the most friendly stuff to the eyes and lungs!!!
Actually it only took a few evenings to do, once I had everything apart.