Green’s Dictionary of Slang

oral sex, fellatio, cunnilingus.

1969		F. Norman in Fashion July in Norman’s London (1969) 251: ‘Plating makes your face smell nasty,’ a young whore giggles.
1998		K. Sampson Awaydays 131: Tongue-plating, good. Dobber, bad.
2002		Fabian & Byrne Out of Time (ms.) 31: ‘Last time I asked you to suck me off you said you wouldn’t because you didn’t like that expression. And after you wrote the book, you wouldn’t accept blow-job.’ ‘It became plating,’ I explained. ‘But Jay says that’s something only welders do, so it’s blow-jobs again.’.