Writers were aware of extremes (4,4)

I believe the answer is:

felt tips

'writers' is the definition.
(a felt tip pen is something which writes)

'were aware of extremes' is the wordplay.
'were aware of' becomes 'felt' (feel can mean to be aware of).
'extremes' becomes 'tips'.
'felt'+'tips'='FELT TIPS'

(Another definition for felt tips that I've seen is " writers?".)

I've seen this clue in The Guardian.

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