Artist, after good argument, mounted current painting on the wall (8)
I believe the answer is:
graffiti
'painting on the wall' is the definition.
(artwork on a wall)
'artist after good argument mounted current' is the wordplay.
I cannot quite understand how this works, but
'artist' could be 'ra' (Royal Academician, member of Royal Academy of Arts) and 'ra' is located in the answer.
'good' could be 'g' (abbreviation) and 'g' is found in the answer.
'current' could be 'i' (symbol for electric current) and 'i' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for graffiti that I've seen before include "Scribblings on public buildings" , "Writing on the wall" , "Unauthorised public writings" , "Wall scribblings" , "Unauthorised public writing" .)