Two decades later, Duchamp embarked on an even grander project: a room-sized installation enigmatically entitled Étant donnés: 1° la chute d’eau, 2° le gaz d’éclairage (Given: 1° The Waterfall, 2° The Illuminating Gas) (1946-1966). The ensemble is currently the focus of an astonishing show at the Philadelphia Museum of Art, a contextual display launched under the cautionary epigram, "the strangest work of art in any museum" -- a remark by one of Duchamp’s famous admirers, Jasper Johns.

This year marks the 40th anniversary of the museum's permanent installation of Given which, like the Large Glass in the adjacent room, has remained obdurately immovable, impervious to changes in curatorial choreography. Unlike the Glass, it has not been the subject of exhibition copies, nor has it inspired anything approaching the same amount of voluminous commentary. Perhaps now, deep in the age of installations, of which it is clearly an ancestor, its time has come.

The numerous revelations of the exhibition for Duchamp enthusiasts include over 20 previously unknown sculptures and studies. These unpublished works include erotic objects, body casts, prints and notes, plus more than 70 Polaroid photographs snapped by Duchamp to document Étant donnés in his New York studio. The most immediately striking pieces related to the work are the unused body casts, which were part of a long and complex experimental process. Four large casts are grouped together: an arrangement of fragments that has something of the air of an incomplete Classical pediment. Two body parts are casts in beige parchment, a medium that curator Michael Taylor associates with the bookbinder Mary Reynolds, Duchamp’s companion from 1924 to the early ’40s. The medium privileges surface -- suggestive that Duchamp thought in terms of the skin of the nude, as he wrote in a 1949 letter, "the surface produced by the plastilene gives me more or less what I am looking for, namely, the epidermis and not the sculpture of the bones or the volumes."

This comes from one of 35 letters that Duchamp wrote in the 1940s and early 1950s (except for the last one) to his then-lover, the Brazilian sculptor Maria Martins. They contain his only written commentary on Étant donnés, albeit in mostly brief allusions. And they differ in tone and are more revealing than his other correspondence.

The unveiling of these and other works and documents, given to the museum after Duchamp’s death, offers present-day viewers something approaching the shock experienced by those first peepers in 1969 -- when the reconstituted diorama was quietly placed on view and made its own contribution to the "Summer of Love."

At the time, such an environmental installation resonated for many with tableaux by Edward Kienholz and George Segal, not to mention the body casts found on occasion in works by Jasper Johns. As Taylor persuasively argues, however, Étant donnés was a product of the 1940s. It continues the modern fascination with the mannequin, in particular Hans Bellmer's more illusionistic second suite of Poupée photographs, as well as late-Surrealist exhibition installations.

Work on Étant donnés began in 1946, and is linked to Duchamp’s relationship with Martins, a self-described "torturer" of men, yet also his sculpture consultant. The first part undertaken was the female nude, based on her torso. The technical, even academic details of its production are clarified here, as both Marcel and Maria took lifecasting lessons from Ettore Salvatore, a specialist in the procedure. Salvatore was also commissioned to make a plaster cast of the figure, which Duchamp then reworked. Duchamp produced a number of cast body parts in the 1950s, most frequently versions of the Female Fig Leaf. Technical examination confirms what the title suggests, that these are molds of the mannequin’s vagina, or "chat ouvert" as the artist termed it.

Duchamp’s path after the war may be seen as parallel with Salvador Dali's return to the Classical, perhaps helping account for their improbable yet growing friendship in the late 1950s. Dali had turned polemically academic, praising Ernest Meissonier and blasting modern art. To our knowledge of his friendship with Duchamp we can now add that in 1959 Dali himself assisted in the process of enlarging and printing the photographic landscape backdrop for Étant donnés in collotype, for further cutting and collaging. Dali was thus one of only a handful of people who knew that Étant donnés was being created. Indeed, its final form is more Meissonier than modernist -- opposing the informel and abstractionist avant-garde of the era. It could be seen as closer to veristic Surrealism: especially Dali’s own nudes of the mid-1940s, or the bright skies of Magritte.

Duchamp’s tinkering was done off the main room of his apparently bare studio at 210 West 14th Street. He had become a kind of secular hermit or monk, following his own advice to "go underground," as Taylor emphasizes, rather than risk being besieged with visitor requests. From the mid 1950s, he proceeded with the collaboration and mutual amusement of his wife Teeny. Part of the mannequin was ruined when stored in the summer of 1958, and Teeny became the model for replacement-part casts. The nude thus became a figurative palimpsest reflecting the change in Duchamp’s personal life, as his affections moved from Maria to Teeny. As a final touch, the hair color was altered from brunette (Maria) to blonde (Teeny).

At the time of Duchamp's death in October 1968, the exterior bricks selected in Cadaques had not yet arrived. (Thus in the end, it too could be considered slightly "unfinished.") The following year the whole room was packed, shipped to Philadelphia and re-erected following the precise instructions of Duchamp's second manual, a binder filled with hand-written pages, here exhibited. The bricks surrounding the door we admire today were installed by museum masons. Funds were provided by a foundation Duchamp had arranged for the purpose. Thus, Given’s rebirth nine months later as the artist’s own posthumous show, which has always been one of its piquant aspects.

For me one of the important features of the scenario -- somewhat overlooked in the attention to the nude -- has been "given #2," The Illuminating Gas: the outdated Bec Auer gaslight redundantly held up in the bright sunlight. We learn that in the first version, the nude was to have held a mirror instead, reflecting back the viewer’s gaze, similar to Andre Masson’s 1938 exhibition mannequin, which has a mirror covering its sex (in contrast to the "light of truth" trope, in which a woman holds up a light, as in Picasso’s Guernica). It was instructive to study a sheet of yellow lined paper entitled Lumières, where Duchamp listed details like General Electric bulbs. Antique gaslight is to be simulated "inside the round glass a small bulb painted green giving illusion of gas light." The number 75 watts is crossed out and 150 penciled in, as Duchamp presumably experimented and opted for a dazzlingly bright, even overlit room. The light of truth affords us no shadowy respite from the naked facts presented. And the glow diffusing from the two small peepholes into the dimly lit antechamber ("in the dark," per another note) is the main clue to the spectator that something is there behind the handle-less, old wooden door.

The show dispels any vestige of the notion that Duchamp had retired from making art. Projecting an easygoing life in the public sphere, he can now be imagined as meticulous and hard at work, behind the scenes. If Guillaume Apollinaire had remarked as early as 1913 that Duchamp was the only modern painter who seemed concerned with engaging the tradition of the nude, he can scarcely have anticipated this final outcome: a labor-intensive, life-like, almost pornographic nude, viewed in the form of a peep-show. It still disturbs, both the public morality, and the prior image of the artist-philosopher of the readymades and The Large Glass. This statement of Eros, c’est la vie bites the hand of his admirers, posthumously, and though one might not like the tableau, one can at least respect his refusal to repeat himself.

"Marcel Duchamp: Étant donnés," Aug. 15-Nov. 29, 2009, at the Philadelphia Museum of Art, 26th Street and Benjamin Franklin Parkway, Philadelphia, Pa. 19130

LEWIS KACHUR is associate professor of art history at Kean University in New Jersey. He is author of Displaying the Marvelous: Marcel Duchamp, Salvador Dali and Surrealist Exhibition Installations (2003). The author wishes to thank Stephen Brown, Catherine Craft and Charles Stuckey for their comments on this essay.