It is possible for “immaterial” artists to make money off the performance itself, of course. In the late 1950s and early ’60s, French conceptual artist Yves Klein sold a series of “immaterial zones,” or empty spaces within Paris, in exchange for gold. His patrons would then watch as he threw half of the payment into the Seine; the transaction was completed when the purchaser burned a certificate of authenticity confirming the amount of gold transferred. Contemporary British-German artist Tino Sehgal has sold several performance pieces to museums, including MoMA and the Guggenheim. He provides no written contracts, insists that the directions for reenacting his works be delivered via word-of-mouth, and requires that collectors never photograph or film his “constructed situations.” Online auction house Paddle8 last year sold a one-time performance by Icelandic artist Ragnar Kjartansson for more than $36,000. - www.bloomberg.com