Up until a few months ago, traditional diamond engagement rings were a staple for Tara Silberberg, owner of The Clay Pot, a jewelry boutique with locations in Brooklyn, N.Y., and the Nolita neighborhood of Manhattan. Lately, however, Silberberg has noticed a change in what customers are requesting. “We have four engagement rings in production now with lab-grown diamonds because the girlfriends want an ethically sourced stone,” she says. Silberberg has been selling Canadian diamonds, which come with guaranteed conflict-free sources, since the 1990s. But after reading a recent New York Times article about lab-grown diamonds, she began to consider the man-made products. The lower cost of lab-grown stones—they sell for about 30 percent less than natural mined diamonds—makes them especially appealing to young couples in the market for wedding jewelry. Silberberg has become such a be