Only mark is 962 on white metal.

by Elizabeth
(NY)

I have a pin/pendant that was my grandmother's. I know it dates pre-1960's, but that is the best I can do on the date. I was told it is platinum by my father. The only marks on this piece is the #962 stamped in two places on the back. I have attached photo.
I have looked everywhere and can not find that number connected to any metal. It is definitely not silver. No tarnish in the 20+ years I have had it. No reaction to magnet.
Any ideas?