If pressed to mark the change exactly, Mr Stella dates it to the moment when a museum wall could no longer take the weight of one of his increasingly turbulent reliefs.
The rest it sucks into its system through contracts made with other diamond producers, and by dispatching its buyers, whose clipped British accents and pressed cotton shirts mark them out as the sort who might otherwise be employed by Her Majesty's secret service, to vacuum up diamonds that seep onto the market in such places as Angola and Congo-Kinshasa.