The striking shade of Yves Klein’s Timbre Bleu, more vibrant than any earthly postage, is I.K.B. itself – International Klein Blue, the legendary pigment Klein invented with the help of a chemist to create the purest form of blue possible. Klein first created these stamps in advance of his dual 1957 gallery shows in Milan and Paris, attaching them to exhibition invitations to be used in the place of official postage. Klein achieved this effect by persuading (and likely bribing) postal workers to authenticate the stamp with a cancellation mark, allowing his facsimiles to travel in the mail – and making unmarked examples such as these exceedingly rareⁱ. By using his artwork as stamps, Klein placed himself in a lineage of famous artists whose artwork has appeared on official government postage and secured at least the appearance of validation from the French government.

Klein’s stamps combine a variety of Klein’s artistic impulses and bear an outsized importance in his oeuvre. Timbre Bleu communicates Klein’s engagement with the monochrome and the color blue, as well as his legendary skill for generating buzz. With the public appeal of Klein’s work was intimately tied with the fervor it generated, much of which Klein whipped up himself. Among the first truly social artists, Klein’s 1957 exhibition opening would also feature the headline-worthy release of 1,001 blue balloons and an audacious one-note soundtrack of Klein’s own creation. The stamps themselves functioned as daring advertising, enticing the public to come and investigate the cutting edge of modern art. As a promotional device, they were effective enough that Klein would continue to use them for future exhibition mailers, including for his scandalous exhibition Le Vide (The Void), which featured an entirely empty gallery, two French Republican Guards serving as bouncers, and the infamous Cointreau and methylene cocktail Klein served at the opening, which dyed the urine of unwitting visitors bright blue. 

These stamps are from the collection of Claude Parent, the famed French architect and longtime collaborator of Klein’s. Together, they drew up atmospheric designs for architecture unbounded by convention or physics, formally embracing one of Klein’s favored concepts: the void. After Klein’s death in 1962, Parent was asked by the artist’s mother and wife to design the artist’s mausoleum – a yet-unbuilt structure in Saint-Paul-de-Vence that perfectly captures the formal experimentation the two brought out of each other.