Rocker Arm....
People have parts like this polished not for beauty, but to reduce the chances of stress crack related failures, by polishing out surface imperfections 
GALLERY
Before and after of 1907 American "underslung" wheel holders
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1957 BSA valve & primary covers
These poor things looked like they were found at the bottom of the "Great Salt Lake" when I got them.
  "High-rise" intake for a flat-head Ford
  "Eddie Meyer" flat-head intake
1907 American "Underslung" Wheel holder  Before....
BEFORE & AFTER......
Misc. parts for 1907 American "Underslung"
1969 Sand-cast Honda CB750 
valvecover BEFORE......
AFTER........
Some very old pots & pans done for display at Paris Gourmet.