This is a very old Corocraft pin and certainly style and age wise looks to be from the 1930s after Coro began making jewelry under that mark in Great Britain in 1933.
The pin is a slightly pewtery grayish silver color and I'm not sure what it is made of. I don't think it is plated or silver tone over base metal. Feels solid whatever it is. It is lightweight like pewter but the only mark is Corocraft.
The pin is made by backing 4 sets of 2 arcs into a cross shape. It has a safety clasp on the back and is 2 inches square. Condition is excellent for its age. Needs cleaning which I will do if you request it before mailing.