This is a stunning and very large Mikimoto Japanese akoya saltwater cultured pearl grape brooch.

The pearls are 4.25-5.50mm and round. They have great luster with rosy pink overtones. They are set into a grape leaf design with vine accents. The leaves have a delicate hammered texture to simulate real grape leaves. 

It is made of solid sterling silver with a bright gold plate. It is stamped "<CPO>" "SILVER" "950" "M (in a clamshell)" "GPLATE". The CPO stands for "Central Processing Office" which was in charge of regulating metals export after WII. This brooch was probably produced for export right after the war was over.  It measures 2 3/4 inches long. From Japan 1940's-1950's.

All pearls are truly vintage and have only been lightly cleaned. Some dark patina on the back.