Irishman in a film (6)

I believe the answer is:

patina

'film' is the definition.
(both can mean a layer)

'irishman in a' is the wordplay.
'irishman' becomes 'Pat' (Patrick is a common Irish name).
'pat'+'in'+'a'='PATINA'

(Other definitions for patina that I've seen before include "Green gloss on old bronze" , "Sheen acquired from constant handling" , "Sheen produced by age and polishing" , "A surface gloss produced by age" , "Fine layer on the surface, laid down over time" .)

I've seen this clue in The Globe and Mail and The Telegraph.

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