Art Deco Platinum, Cabochon Sapphire, Diamond and Black Onyx Brooch

The modified rectangular openwork brooch highlighted by 16 buff-topped cabochon sapphires, decorated with numerous small old European-cut diamonds, accented by a stylized key-fret motif set with calibre-cut buff-topped black onyx, with French assay mark, circa 1920, approximately 7.8 dwt.