Silver Art Nouveau

I have been given a lovely old pewter candlestick, but it us a horrible dull grey-how do I get it shiny again?
This is an Art Nouveau candlestick bought by my great-grandparents in 1890. It is worth around £500 and worth restoring to its original silver appearance. I have tried about 12 commercial products for cleaning pewter, but none of them has worked, also tried petrol, half a lemon dipped in salt, vinegar and talc and turpentine- no success!!! Help; I have quite a few bits of pewter, and the rest are all shiny, so whats wrong???
Try a paste made of baking soda and water.
Pewter used to be made with lead, which is a different alloy from modern pewter.