vintage BSK silver tone leaf brooch

Detailed leaf shaped brooch in a brushed/matte silver tone metal with a shiny finish around the edges. Has some discoloration that may be removable with some focused polishing, but didn't come off in a sonic jewelry cleaner - see pictures for the brownish spot. In otherwise good shape. Measures approximately 2.5" long. BSK was in business from the 1940s to the 1970s or 80s, but I'm not sure the exact decade of this brooch.