Although the economic downturn of the past 12 months has seen many auction categories suffer, jewellery has remained a robust performer, notably at the high end despite a significant fall in the market value of diamonds. In May, for example, Sotheby’s Geneva achieved a record price per carat for any gemstone at auction when it hammered down a 7.03 carat blue diamond for $9.4m. But it is the mid-range sector that is proving especially buoyant, where pieces in the $8,000 – $165,000 bracket are attracting stiff competition...