Old brooch restoration - which gems to choose

A friend of mine told me that when he was in the service in Korea, which was much later than this brooch of course, that the Koreans rounded up the spent brass shells and made items like this to sell to the GI's. Could this have been done in Europe, too, during one of the earlier skirmishes in those countries. Or did they have plenty of material already mined in those countries? Also, does anyone else see in an enlargement of the back what looks to me to be a ribbon-like marking from just above the hook that curves down and toward the center of the pin? Also it looks to me as if there are 2 "NN"s almost in the center of the area just above the center of the pin. i am new at identifying antique items and I sometimes find myself looking too hard!

 

Hi,
Scrap metal was used for all kinds of things. My little brother had a Japanese friction car made in 1952. It came apart and the bottom of the car was cut out of a Rediwhip can. Rediwhip was a whipped cream that came in an aerosol can.
greg

 

I've searched this brooch with a loupe and there is a faint mark that Davey pictured but so vague that it could be something or nothing. Good spot though.

 

My granddad did that during the Depression and WWII. My dad had, we still have most of them somewhere, railroad stations and the like made from boxes and cans. Sometimes you use what you can get instead of what you're supposed to work with.