Yves Klein covered postal stamps with his signature IKB (International Klein Blue) pigment to send on invitations for the openings of his double exhibitions in Paris in 1957 (May 10 at Gallerie Iris Clert and May 14 at Gallerie Colette Allendy). This portion comprising over 6 complete stamps is from those executed during the period 1957 - 1959, when Klein continued to use the stamps while he exhibited with Iris Clert - unused and archivally stored since execution.

Nan Rosenthal, in her essay, "Assisted Levitation: The Art of Yves Klein," which is included in the 1982 Rice University catalog, Yves Klein, writes, "The postcards which announced the double exhibitions suggest another attempt by Klein to attract an audience beyond the art world. The postage on these cards consisted of Klein's own blue stamps: ultramarine stamp-size paper rectangles with perforated edges. It was an effort by Klein to widen the dragnet for his art - in this instance to include and co-opt the government. Each postmark was an official validation, a stamp of approval on top of Klein's stamp of blue, and each postman who carried one of these postcards had briefly to become the deliverer of Klein's blue, as the addressees had to become on some level receivers of it." "Klein's stamps were also a spurious self-decoration: like stamps issued by the French government in reproduction of well-known paintings or in commemoration of nationally significant cultural figures, Klein's stamps proposed that his ultramarine paintings were important. However, like the pasted papers in Klein's 1954 booklet, the stamps are best understood as original monochromes which belong to an extremely large series.

Each stamp measures 2 ½ by 2 centimeters, like the proportions of so many of Klein's serial panels, a proportion of height to width of 5 to 4." In her 1994 book, Yves Klein, Sidra Stich, writes that "In many ways, the stamps conformed with the usual ones: they were small, regulation-sized rectangles with perforated edges. Unlike official stamps, however, they were totally blue, imageless, and devoid of any signifying information. They were thus a telling reversal of the commemorative stamp that features a depiction of someone or something, as well as a contrast to the pragmatic prerequisites of philatelic design practiced by modern governments. Quite like the old-fashioned, personalized wax seals that were used to fasten envelopes, Klein's blue stamps were 'stamps' in the traditional sense - emblems, insignia. But in the most modern sense, they were also logos, instantaneous signs, advertisements, components of a spectacle." The use of the blue stamp arose perfectly from Klein's art. It should not be construed as a promotional device, rather as a commemoration of the blue void of his work. His art had worth, and having it franked by the French government was the ultimate approval.