When Picasso’s “Boy with a Pipe” fetched a record $104m (£53m, €79m) at a Sotheby’s New York auction in 2004, it was the talk of the town. Never before had an artwork commanded more than $100m and the deal made news outside the art world.

Two years later David Geffen, the entertainment mogul, sold almost half a billion dollars’ worth of paintings within a few months – one, Jackson Pollock’s “No.5, 1948”, for $140m – and few blinked.