Natural as an empty gallery (7)
I believe the answer is:
artless
This clue is a double definition.
'natural' is the first definition.
(I've seen this in another clue)
'as an empty gallery' is the second definition.
(I've seen this before)
(Other definitions for artless that I've seen before include "Without guile or affectation" , "Free from cunning" , "Ingenuous" , "Natural - uncontrived" , "Natural like slaters" .)