The backmark, Art Metal Works, dates from 1902-1930's. Prior to 1923 Great Seal buttons had a black finish, which I can't tell if this originally had, but would determine the range of when it was produced. AMW was owned by Ronson, the cigarette lighter folks. During WWII they still made stuff for the military, but they were better known for things like flame throwers and ordnance. I think they left buttons to the multitude of others manufacturers.