Crossword Genius

Film I presented in rice production centre (6)

Ross

I believe the answer is:

patina

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

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

'i presented in rice production centre' is the wordplay.
I cannot quite understand how this works, but
'i' could be 'a' and 'a' is found in the answer.
'in' is found in the answer.
The remaining letters 'pta' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for patina that I've seen before include "Developing surface film; sheen" , "A surface gloss produced by age" , "Sheen acquired from constant handling" , "Surface film formed by age" , "Gloss or colour produced by a paint" .)

I've seen this clue in The Independent.
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