In 1959 the French artist Yves Klein first performed "Zone de Sensibilité Picturale Immatérielle". The work involved the sale of documentation of ownership of empty space (the Immaterial Zone), taking the form of a cheque, in exchange for gold; if the buyer wished, the piece could then be completed in an elaborate ritual in which the buyer would burn the cheque, and Klein would throw half of the gold into the Seine. The ritual would be performed in the presence of an art critic or distinguished dealer, an art museum director and at least two witnesses.