It was to have been the star lot in Bonhams’ contemporary art sale in February 2016. Andy Warhol’s two-metre-high painting, 14 Small Electric Chairs, was made in 1980 by reducing the scale of 14 separate paintings which he made in 1967 as part of his Death and Disaster series, and combining them in one work.

The electric chair image was taken from a 1953 news report on the death chamber in New York’s Sing Sing prison. Single 1960s examples from that series are highly rated by collectors and have sold for as much as $20.4 million.

Bonhams’ later combination work, in which each image is reversed, was billed as a rare example of an historic icon and estimated at £4 million. But the Warhol market was going through a period of self-doubt, and the painting went unsold.

Over the years, 14 Small Electric Chairs hasn’t had much luck. In its previous outing at auction at Christie’s in 1999 it also went unsold when it carried a £430,000 estimate. But now, two-and-a-half years after its last auction appearance, it is back – not in an auction room or a gallery, but as a Blockchain investment challenge where it has been valued at a virtually unchanged £4.2 million.