Writing material I expanded for radio - essentially unkind somehow (6,3)
I believe the answer is:
indian ink
'writing material' is the definition.
The definition suggests a singular noun which matches the answer.
'i expanded for radio essentially unkind somehow' is the wordplay.
'i expanded for radio' becomes 'india' (I can't explain this - if you can you should believe this answer much more).
'essentially' says to take the centre.
'somehow' indicates an anagram.
The central letters of 'unkind' are 'nkin'.
'nkin' is an anagram of 'nink'.
'india'+'nink'='INDIAN INK'
Can you help me to learn more?
(Other definitions for indian ink that I've seen before include "Deep black writing fluid" , "Writing fluid containing carbon particles" , "black pigment" , "Draw with this" , "Maybe part of squid" .)