When the Hutton–Mdivani jadeite necklace comes to Sotheby’s Magnificent Jewels and Jadeite sale in Hong Kong on April 7, it is expected to set a new world record for jadeite at auction. Considered the most important known piece of jadeite jewelry, the necklace comprises 27 enormous jadeite beads (15.40 to 19.20 mm in size) of exceptional color and luster. It once belonged to a member of China’s Qing imperial court, and its estimated value is $12.8 million. The necklace, with a Cartier-designed clasp, was given…