William IV/Early Victorian cannetille diamond and emerald unmarked yellow metal brooch

William IV / Early Victorian cannetille diamond and emerald unmarked yellow metal brooch, the old cushion cut diamond measuring approx 5.20mm x 4.23mm (depth inaccessible) calculated weight approx 0.60 carat, four small mixed cut emeralds, rubover claw settings, tapered coils, granulation and flower head detailing, glazed panel verso containing woven hair, hinged pin and simple loop brooch fittings, dimensions approx 4cm x 3cm, weight approx 12g