In 1974 Rotraut Klein-Moquay wrote to Tate saying that she was fairly certain that 'IKB 79' was one of about four monochrome paintings Klein made when they were together at Gelsenkirchen, West Germany in 1959. The letters IKB stand for International Klein Blue, a distinctive ultramarine which Klein registered as a trademark colour in 1957. He considered that this colour had a quality close to pure space and he associated it with immaterial values beyond what can be seen or touched. The announcement card for his one-man exhibition at the Galleria Apollinaire, Milan in 1957 described IKB as 'a Blue in itself, disengaged from all functional justification' (quoted in Stich, p.81). By this time Klein had arrived at a means of painting in which the incandescence of IKB could be maximised. First he stretched his canvas or cotton scrim over a wooden backing, which had been treated with a milk protein called casein. This assisted the adherence of the paint when it was applied with a roller. Then he applied an industrial blue paint, similar to gouache, which he mixed with a highly volatile fixative. When the paint dried the pigment appeared to hover over the surface of the canvas creating a rich velvety texture and an unusual appearance of depth.

Many of Klein's artistic activities, such as selling zones of 'immaterial' space for the price of gold, trod a fine line between shamanism and commercialism. Like other artists of the Nouveau Réaliste movement in France, or the Italian artist Piero Manzoni, Klein's practice was strongly influenced by the originality, irreverence and wit of the French artist Marcel Duchamp. The production of monochrome paintings was probably conceived by Klein as both a spiritual and a marketable activity. At his 1957 exhibition in Milan, he displayed a series of 11 ostensibly identical blue monochromes, each with a different price which he claimed reflected its unique spirit. As he explained: 'Each blue world of each painting, although the same blue and treated in the same way, presented a completely different essence and atmosphere. None resembled any other – no more than pictoral moments resemble each other – although all were of the same superior and subtle nature (marked by the immaterial) … The most sensational observation was from the "buyers". They chose among the eleven exhibited paintings, each in their own way, and each paid the requested price. The prices were all different, of course.' (quoted in Stich, pp.86–87.)

Further reading: 'Yves Klein, 1928–1962: Selected Writings', Tate Gallery, London 1974 'Yves Klein 1928–1962: A Retrospective', exhibition catalogue, Institute for the Arts, Rice University, Houston 1982 Sandra Stich, 'Yves Klein', exhibition catalogue, Hayward Gallery, London 1995 Sophie Howarth April 2000