Chinese HPHT press grows a one-carat diamond chemically identical to a mined stone in about two weeks, collapsing a price the cartel defended for 137 years

Inside a steel cylinder the size of a household refrigerator, in a factory in Henan province, a sliver of graphite the width of a pencil lead is pressed between two anvils until it experiences about 50,000 atmospheres of pressure and 1,500 degrees Celsius.

Two weeks later, a one-carat diamond emerges that is chemically, optically and structurally identical to a stone pulled from a kimberlite pipe in Botswana. The wholesale price of that stone has fallen sharply in recent years, ending a price discipline the De Beers cartel had maintained for more than a century.

The machine is called a cubic press. China now operates thousands of them. The slogan “A Diamond Is Forever,” written by N.W. Ayer copywriter Frances Gerety in 1947 and named the advertising slogan of the 20th century by Advertising Age in March 1999, still appears in jewellery store windows.

However, the economics it built no longer hold.