Your compiler’s beyond taking on old painting technique (7)
I believe the answer is:
impasto
'painting technique' is the definition.
(I've seen this before)
'your compiler's beyond taking on old' is the wordplay.
'your compiler's' becomes 'im' ('your compiler' refers to the crossword compiler).
'beyond' becomes 'past' (I've seen this before).
'taking on' says to put letters next to each other.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'im'+'past'+'o'='IMPASTO'
(Other definitions for impasto that I've seen before include "Thickly-applied painting technique" , "Thick painting technique" , "Thick coat required" , "Slapping paint on" , "Sort of paint" .)