More Artex mixture! (5)
I believe the answer is:
extra
'more' is the definition.
(thesaurus)
'artex mixture' is the wordplay.
'mixture' indicates an anagram.
'artex' with letters rearranged gives 'EXTRA'.
(Other definitions for extra that I've seen before include "Ancillary" , "on top" , "wide? It could be" , "Another" , "Minor actor in crowd scenes" .)