Editor’s Note: This article was updated to reflect the item’s sale price at auction.

CNN  — 

In 1958, artist Yves Klein famously opened an exhibition called “The Void,” which saw him place a large cabinet in an otherwise empty room. Thousands of paying visitors turned up at a Paris gallery to catch a glimpse of nothing at all.

Following the show’s success, the French artist then took the idea one step further – by giving collectors the chance to purchase a series of non-existent and entirely conceptual spaces in exchange for a weight of pure gold.

A handful of buyers took him up on the offer. And on Wednesday, almost 60 years after Klein’s death, one of the receipts he wrote to prove ownership of his invisible artworks sold for more than 1.06 million euros ($1.16 million) at Sotheby’s auction house in Paris.

Measuring less than 8 inches wide, the receipt grants ownership of one of Klein’s imaginary spaces, which he dubbed a “Zones of Immaterial Pictorial Sensibility.” Designed to resemble a banker’s check, it is signed by the artist and dated to December 7, 1959.

A receipt for 'invisible' art could fetch half a million dollars.

The receipt was originally given to antiques dealer Jacques Kugel, and is among one of the few thought to have survived, Sotheby’s said in a press release prior to the auction. This is not simply because Klein struggled to sell many of the imaginary works, but because he offered his customers a choice: to keep their receipt or burn it in a ritual.

Should they have chosen the latter, they would be considered the conceptual artwork’s “definitive owner.” As part of Klein’s performance art, he would then burn the receipt in the presence of witnesses before dumping half the gold he was paid into the Seine River.

Kugel opted to keep his, and it has since been displayed at major art institutions across Europe, including London’s Hayward Gallery and the Centre Pompidou in Paris. The item is being put on sale by art advisor and former gallery owner Loïc Malle, who is putting over 100 items from his private collection up for auction.

In its auction catalog, Sotheby’s had likened Klein’s idea to NFTs, writing: “Some have likened the transfer of a zone of sensitivity and the invention of receipts as an ancestor of the NFT, which itself allows the exchange of immaterial works. If we add that Klein kept a register of the successive owners of the ‘zones,’ it is easy to find here another revolutionary concept – the ‘blockchain’.”

Members of the public admire Eduardo Basualdo's artwork 'TEORIA' at the Frieze London art fair on October 16, 2013 in London, England. The annual Frieze Art Fair takes place in London's Regent's Park and runs from October 17 to 20. The exhibition comprises of the Frieze Masters exhibition and Frieze London which aim to showcase historic and established art as well as contemporary works.
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Sotheby’s confirmed prior to the sale that the successful bidder would not only “become the custodian of this historic receipt, but also of Klein’s invisible work of art as well.”

Klein, who died in 1962, was a key figure in the nouveau réalisme (new realism) movement, which used art to subvert viewers’ perceptions of reality. In 1957, he opened an exhibition in Milan consisting of 11 blue canvases, identical in shape, shade and size. His best-known work, however, is the 1960 photograph “Leap into the Void,” which appeared to show the artist jumping from a high wall, though it was in fact a composite of two separate images.