If you intend to send it in for melt you can use a propane torch to test. Heat it red hot and if it is plated you will see the plating 1. flow away from the heat. 2. When it cools the base metal will show. 3. a thick silver area like the handle will be very hard to heat up with a propane torch. Base metal of copper turns green and there is green in the torch's flame surrounding the heated area, pewter turns a light white, nickel silver turns black. One other thing. If heavily oxidized, the torch's flame will turn the oxidation back to a nice silver color.
I use this method on old silverware I am sending in for melt. I also use an acid test but felt both tests make my results more predictable.