'Earth', the artist said (4)
I believe the answer is:
clay
'earth' is the definition.
(clay is a kind of earth)
'the artist said' is the wordplay.
'the artist' becomes 'klee' (Paul Klee).
'said' shows a homophone (sound like).
'klee' sounds like 'CLAY'.
(Other definitions for clay that I've seen before include "Brick/pottery material" , "Pigeon target" , "Court surface" , "Soil used in pottery" , "Earth suitable for modelling" .)