Clockwise from top left: the Hope Spinel; Christie's 16.08-carat pink diamond; the ring and earrings from Leonard Joel's record-breaking emerald and diamond suite; Leonard Joel's Tiffany ring; Sotheby's 12.03-carat Blue Moon

Jean Ghika, Bonhams director of jewellery for the UK and Europe

John D'Agata, Leonard Joel national head of jewellery