Setter's beyond old painting technique (7)
I believe the answer is:
impasto
'painting technique' is the definition.
(I know that impasto is a painting technique)
'setter's beyond old' is the wordplay.
'setter's' becomes 'im' (referring to the person who set the crossword).
'beyond' becomes 'past' (to go beyond something is to go past it).
'old' becomes 'o' (abbreviation).
'im'+'past'+'o'='IMPASTO'
(Other definitions for impasto that I've seen before include "Sort of paint" , "Painting with pigment laid on thick" , "Technique of laying on paint thickly so that it stands out from a surface" , "Thick painting technique" , "Thickly-applied paint" .)