Antique Old Mine cut diamond plaque pendant brooch

Antique Old Mine cut diamond plaque pendant/brooch. Centred with a cushion shape Old mine cut diamond in a millegrain setting, set to the cross section with four cushion shape Old Mine cut diamonds in millegrain settings, further set to the corners with four cushion shape Old Mine cut diamonds in collet settings, highlighted throughout with twenty rose cut diamonds in grain settings, to a truncated rectangular design with pierced openwork, scrolling motifs, millegrain borders and open linear gallery, fitted to top with a tapering diamond set bale flowing with movement and fitted to reverse with a screw mechanism to allow manual removal of the bale, also fitted with a secure hinged pin and safety latch.