It’s night on the top floor of an anonymous tower block in the Qatari capital, Doha. Outside, the alleys of the souk buzz with nocturnal commerce, but in here an air-conditioned hush prevails. All around are bowls and baskets lined with red cloth, filled with translucent globules graded according to size. At a glance the smallest might pass for lentils or even rice. Yet the contents of any one of these receptacles would be worth several hundred thousand pounds, at the very least. These are pearls. Not your common or garden cultured pearls, which nowadays are mostly farmed in China using mussels, but natural pearls of the most valuable and sought-after kind, hand-picked from the bed of the Persian Gulf using processes that have barely changed in 3,000 years.