From 1959 until his death three years later, Yves Klein sold non-existent spaces for gold. It wasn’t an entirely new concept for the performance artist, who in the previous year had staged the exhibition The Void at a gallery in Paris, where visitors glimpsed nothing but a large cabinet in an empty room. The piece from 1959 — <i>Zone de sensibilite picturale immaterielle (Zone of Immaterial Pictorial Sensibility)</i> — elevated this concept, with the French artist inviting guests into a gallery where empty spaces (the Immaterial Zone) were sold in exchange for pure gold. In return, buyers received a receipt that documented the sale. Klein then gave them the option to burn the receipt, after which the artist would throw half of the gold into the Seine River. As instructed by Klein, the participants would engage in the ritual with an art critic or dealer, an art museum director and at least two witnesses present. During the three years that he conducted this performance, eight spaces or “Zones” were sold, and at least three buyers engaged in the ritual. A number of others, however, kept the receipt, one of which is up for sale with the auction house Sotheby’s. It is expected to sell for €300,000 to €500,000 ($331,000 to $552,000). The piece is part of the Loic Malle Collection, which will be auctioned in Paris on April 6. Art advisor and curator Loic Malle bought one of Klein’s “Zones” more than three decades ago from art dealer Jacques Kugel, who had chosen to keep it after participating in the performance. Malle has kept the receipt for years, at times exhibiting it in various cities, including Paris, Madrid, Stuttgart and Moscow. Malle’s receipt is one of four surviving ones known to remain. Describing Klein’s performance, Sotheby’s have compared the “Zone” transactions to NFTs, as both involve “the exchange of immaterial works”. The marketing angle is likely linked to the auction house accepting crypto payments for the receipt. Apart from his self-described immaterial works, Klein was also known for his monochromes, where he painted canvasses a singular colour. His most recognisable series from this era is his blue paintings, for which he used an ultramarine pigment that has come to be known as International Klein Blue.