A few months ago in New York, a private collector handed over a small fortune to buy a white canvas on which four letters had been stencilled in black ink: FOOL. The painting, by an American artist namedChristopher Wool, had changed hands three years ago for $8m. Its new owner paid nearly twice as much.

Prices have been rising in other markets, too, in large part due to quantitative easing. This tool for central bankers was forged in the aftermath of the financial crisis, and involves buying assets with newly created money.

Mario Draghi, president of the European Central Bank, is this week widely expected to follow in the footsteps of his American and British counterparts by announcing that the eurozone, too, will embark in earnest on a programme of asset purchases. Many economists say this is the only way of avoiding a depression. They may be right. But alternatives have never seriously been considered, and QE has had profound effects, not all of them welcome.