I have painted many hubcaps for my 1966 230SL (Five in one day)
(1) Scuff area to be painted with brass wool.
(2) Clean entire hubcap with lacquer thinner.
(3) Mask with blue tape as close as possible do not worry if chrome area is not completely mask.
(4) Clean one more time with lacquer thinner.
(5) Spray paint using self etching primer.
(6) Spray paint color coat.
(7) Remove masking tape.
(
Using a smooth cotton rag clean up over spry from chrome surface. I spend my time been careful in cleaning the over spray than masking, with perfect results.