Painter’s way of working with black to speed up task (9)
I believe the answer is:
brushwork
'painter's way of working' is the definition.
I can't tell whether this defines the answer.
'black to speed up task' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'to speed' becomes 'rush' ('rush' can be a synonym of 'speed').
'up task' becomes 'work' (I am not sure about this - if you are sure you should believe this answer much more).
'b'+'rush'+'work'='BRUSHWORK'
'with' is the link.
Can you help me to learn more?
(Another definition for brushwork that I've seen is " Painter's technique".)