Diamond and onyx brooch, circa 1930; designed as an openwork plaque, centring three millegrain-set early round brilliant-cut diamonds together weighing approximately 0.15 carats, flanked by a pair of modified rectangular-shaped onyx upon a pierced surround accented with rose-cut diamonds, mounted in platinum with an 18ct white gold brooch pin, length 48 mm, total gross weight approximately 5 grams.