Some blue material from jeans initially caught in frame under muck (5,4)

I believe the answer is:

dirty joke

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'some blue material' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'jeans initially caught in frame under muck' is the wordplay.
I cannot quite understand how this works, but
'muck' could be 'dirt' (I've seen this before) and 'dirt' is found in the answer.
This may be the basis of clue (or it may be nonsense).

'from' acts as a link.

Can you help me to learn more?

I've seen this clue in The Independent.

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