So fine art hewn, if sculpted (5,4)
I believe the answer is:
wafer-thin
'so fine' is the definition.
'art hewn if sculpted' is the wordplay.
'sculpted' indicates an anagram.
'art'+'hewn'+'if'='arthewnif'
'arthewnif' is an anagram of 'WAFER-THIN'.
(Other definitions for wafer-thin that I've seen before include "Very narrow" , "Warn thief stealing slim biscuit - very slim" , "Having very little width or substance" , "Very fine" , "Having little thickness" .)