Why De Beers makes 'not for sale' diamonds

London

SCIENTISTS at De Beers can make near-flawless diamonds in a lab, but they will never sell you one. The 127-year-old mining company's Element Six unit, named for the carbon atom's rank on the periodic table, makes gems that are as perfect as any found at Tiffany & Co stores, yet their destination is a 1980s office complex on the edge of London. There, a team of 62 studies their creations and develops machines for diamond buyers trying to spot synthetic stones being peddled as the real thing.

While still a small part of the market, man-made diamonds are now being mass produced, and retailers such as Walmart Stores Inc sell them to c…