Polish, perfect (6)
I believe the answer is:
refine
I believe this clue is a double definition.
'polish' is the first definition.
(I know that polish can be written as refine)
'perfect' is the second definition.
(I've seen this in another clue)
(Other definitions for refine that I've seen before include "Get rid of impurities" , "Purify or improve" , "Remove impurities as from oil" , "Remove impurities from (eg, metals)" , "Remove impurities or make cultured" .)