Cleaning pewter items is one of the more rewarding tasks you can undertake when trying to bring shoddy-looking items back to their former glory. That's because removing tarnish from pewter is relatively easy, and once the tarnish is gone, the piece will look as it did when it was first sold, whether that was ten years ago or a hundred years ago.
Of course you can clean the tarnish from pewter using a commercial pewter cleaner/polish. However, if you want to get even better results, and clean your pewter the way folks have done it for centuries, get some rotten stone.
You can buy rotten stone at a home supply store like Home Depot, or you can order it online.
"Rotten stone" is powdered limestone you can mix into a paste by adding boiled linseed or olive oil. Rotten stone is abrasive enough to remove all tarnish, but it will not scratch the pewter's surface. The oil gives your pewter a beautiful luster.