The street is a long line of hole-in-the-wall shops. From the sidewalks rises a babble, mostly in the English peculiar to New York, but also in Russian, German, Yiddish, Hungarian, Flemish and Dutch. Plainclothesmen unobtrusively roam the block, and inside the buildings armed guards watch passers-by through bulletproof windows. But for all its crowded and wary atmosphere, Manhattan's West 47th Street is the most sparkling street in town because it is the hub of the U.S.'s $500 million annual diamond market.
Through the hands of West 47th Street's 400 dealers, 200 cutting firms and scores of sawyers, brokers and retailers,...