Sitter's sculpture (5)
I believe the answer is:
model
This clue is a double definition.
'sitter's' is the first definition.
(I've seen this before)
'sculpture' is the second definition.
(thesaurus)
(Other definitions for model that I've seen before include "dummy" , "Scale representation" , "Pose" , "She saunters on the catwalk" , "Possibly the last" .)