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Most important thing about aluminium paint previously article overlooked (7)

Ross

I believe the answer is:

capital

I'm a little stuck... Click here to teach me more about this clue!

'most important' is the definition.
(I've seen this before)

'thing about aluminium paint previously article overlooked' is the wordplay.
I cannot quite understand how this works, but
'thing' could be 'it' and 'it' is found in the answer.
'about' could be 'ca' (abbreviation for 'circa') and 'ca' is found in the answer.
'aluminium' could be 'al' (Al is the chemical symbol for aluminium) and 'al' is found within the answer.
A single letter 'p' remains which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for capital that I've seen before include "Upper-case letter" , "Seed money" , "city such as London" , "Metropolis" , "Havana, say" .)

I've seen this clue in The Telegraph.
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