If ... repeat IF ... they turn out to be not valuable and you really do want them shiny, then soaking in vinegar or brown sauce for a couple of hours should bring them up.
But I repeat what Vagrant says - get them valued first. I'm in touch with a fair few archaeologists and metal-detectorists, and they all say that cleaning coins beyond 'finger clean' (ie rubbing off the worst of the muck in warm water with your fingers) can corrode and devalue them. Same goes for any other metal 'finds'.
As a test ... get a dull 2p coin...put a spot of ketchup on the end of your finger.
Just spread it across half of the coin... Get a cloth and wipe it off after 10 seconds.
It's quite impressive.!
When I first tried this, my immediate thought was ...what does ketchup do to your stomach ?
Have a look on eBay before you go to the expense of getting them valued or trek off to a dealer - if they are worth anything they are probably on sale there (although probably at silly prices). Whatever you do, don't clean them up, half the value is in the forlornness!