Customers at a Bahrain jewellery store study displays of pearls that are, unusually, 100 percent natural -- the result of attempts to preserve a centuries-old industry.While rare elsewhere, natural pearls prised from seabed oysters by divers are the only variety produced in the Gulf kingdom, which is fiercely proud of its pearling tradition.Bahrain, a tiny island state neighbouring Qatar, is the sole country worldwide to have banned the cultivation of artificial pearls, which have flooded the market since the 1920s.