Why diamonds are losing their allure

The appeal of a diamond, for a ring on a finger or to string on a necklace, rests on its sparkle. Its precise value is determined by how well the stone is cut, its colour, its size (also called its “carat”) and whether it contains flaws. The clearer, heavier, closer to colourless and more perfectly cut the rock, the better.The appeal of a diamond for an investor is that, in addition to being nice to look at, it has historically offered a steady return on investment. Given the opacity of the market, and the broad variety of gems that are available, long-run price data are scarce. But a paper by Luc Renneboog of Tilburg University, which was published in 2015, analysed thousands of auctions each year, finding that the average return between 1999 and 2012 rivalled those of stocks and property. Holders of diamonds would have earned a handsome 8% or so a year.