Passion of artist turning grim (6)
I believe the answer is:
ardour
'passion' is the definition.
(ardour is a kind of passion)
'artist turning grim' is the wordplay.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'turning' says the letters should be written backwards.
'grim' becomes 'dour' (synonyms).
'ra' in reverse letter order is 'ar'.
'ar'+'dour'='ARDOUR'
'of' is the link.
(Other definitions for ardour that I've seen before include "Love and enthusiasm" , "Eagerness, zeal" , "Intense eagerness" , "Fervency" , "Emotional warmth" .)