Here in Surat, dirt-cheap wages and loose regulations have created a dream environment for the global diamond industry. It has turned a sleepy provincial town into a new megacity within a single generation, a business center where more than 90 percent of the world's unpolished diamonds are now processed and polished. Individual stones can change hands up to a dozen times over a matter of weeks in polishing houses that grab from piles of legal and illegal stones like mix-'n'-match candy bins. Deciphering clean from dirty becomes nearly impossible. Once the Gujarat Mail [train] reaches the end of the line in Mumbai, the stones have had their damning histories washed away, and buyers ship more than $40 billion of certified merchandise annually out of a country that international authorities say is clean. But if you own a diamond bought in the 21st century, odds are it took an overnight journey on the Mail. Odds are too, you'll have no idea where it really came from.