Answer:
Unfortunately, Pewter is a common name describing several very similar metal alloys. It is important to know if it is lead-pewter (the kind the Romans used to use for drinking--causing madness; this is till used for small statues, trinkets, etc.) or silver-pewter or tin-pewter (the kind now often used in drinkware and jewellery). I would suspect it is silver-pewter and will be safe, but it is not necessarily wise to do so without checking.