Hi,
That would depend on the method of plating that was used. Old Sheffield Plate products were made from ingots of copper with an applied layer of silver that was rolled out to a workable thickness. Close plating entailed soldering a thin sheet of silver onto a premade, usually steel, item.
The photos used in this post give a good idea of the thickness of silver that was used in the close plating process:
viewtopic.php?t=12627See also:
http://www.925-1000.com/silverglossary.html Close Plate/Sheffield Plate
The application of a magnet to your skewer could eliminate Old Sheffield Plate.
Trev.
.