Valuable pictures of workers in revolution? (7)

I believe the answer is:

turners

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'valuable pictures of workers in revolution?' is the definition.
I can't judge whether this definition defines the answer.

'valuable pictures of workers in' is the wordplay.
'valuable pictures of' becomes 'r' (I can't explain this - if you can you should give a lot more credence to this answer).
'workers' becomes 'tuners' (tuner is a kind of worker).
'in' is an insertion indicator.
'r' placed inside 'tuners' is 'TURNERS'.

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I've seen this clue in the Evening Standard.

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