Marcel Duchamp labored in secret for 20 years to produce what the painter Jasper Johns has called "the strangest work of art any museum has ever had in it." He might be right: The diorama known by its abbreviated French title Étant donnés is spectacularly bizarre, enigmatic, mysterious, disturbing, captivating, and, perhaps to some observers, repellent.
None of those attributes is obvious, because Étant donnés is also as secluded as a cloistered nun. It has been one of the Philadelphia Museum of Art's cherished masterpieces for 40 years, yet I'll wager that - Duchamp partisans excepted - most visitors have not seen it or even been aware that it exists.
Étant donnés doesn't attract crowds because it can be viewed by only one person at a time. Furthermore, Duchamp restricted what the solitary viewer could see: He or she must stand in one spot and peer through two peepholes in an antique wooden door, like watching a baseball game through a knothole in the outfield fence.
What do the peepholes reveal? A lifelike female nude lying on a bed of twigs and leaves, legs splayed, shaved pudenda lasciviously exposed, and holding an archaic gas lamp in an outstretched hand. Behind her stretches a bosky landscape enlivened by a twinkling waterfall.
What to make of it? Duchamp, who completed the assemblage in 1966 and died in 1968, didn't provide a single clue. Art historians and critics have debated its meaning since it was installed at the museum in July 1969.
Even the exhibition devoted to this career-capping bombshell that opens this weekend at the museum doesn't try to resolve the puzzle. Curator Michael R. Taylor says this is intentional, to preserve the "open-ended" character Duchamp preferred.
However, the show of about 100 objects does relate the story of Étant donnés' creation in fascinating detail.
Duchamp himself, one of the two most influential artists of the 20th century (Picasso being the other), was himself an enigma.
For instance, he once told the late museum director Anne d'Harnoncourt that "whether you paint or not, it is the same thing," meaning that works of art coalesce in the artist's mind before they are realized materially.
Gnomic remarks like that provide useful clues to his intentions for his art, although this one doesn't seem to apply to Étant donnés (Full title - Étant donnés: 1. la chute d'eau, 2. le gaz d'eclairage . . ., which translates as - "Given: 1. the waterfall, 2. the illuminating gas. . .").
One other famous construction by Duchamp, The Bride Stripped Bare by Her Bachelors, Even, also called The Large Glass, which is part of this exhibition, is more helpful, as well as more arcane and less shocking. The Large Glass is about frustrated sexual desire, expressed symbolically.
As other small sculptures in the show confirm, eroticism as a prime motivator of human behavior is a major component of Étant donnés, but not its only facet. The unusual configuration of the assemblage forces each viewer to become a voyeur who completes the picture.
The diorama also can be read as a parody of Renaissance visual conventions (all those Madonnas against landscape backdrops), a pointed critique of an art that is mainly visual and emotional rather than intellectual.
The fact that Duchamp was an intellectual is the most important thing to remember when one is peeping through the door. He began to think about the piece some years before he began to construct it, then spent two decades working on it in a small Manhattan studio, in absolute secrecy. This is not consistent with a superficial, and salacious, interpretation, or with an elaborate prank.
In any case, Étant donnés is low-wattage eroticism (the antique gas lamp, converted to electricity, implies sexual energy). The spread-eagle female more resembles a corpse or a rape victim than a seductress.
The show explores every fact and circumstance connected with the conception, creation, and ultimate disposition of Étant donnés, which came to the museum - already possessor of the world's largest Duchamp collection - as a gift from the Cassandra Foundation in 1969. The foundation was formed by artist and dealer William Nelson Copley specifically to transfer the assemblage from his friend Duchamp to the museum.
Organized by Taylor, the exhibition consists of about 100 objects related to the assemblage - drawings, small sculptures called erotic objects, documentary photographs, and partial body casts used to construct the nude. Duchamp took plaster casts from the body of Maria Martins, a Brazilian sculptor who was his lover for a period during the 1940s.
Taylor has also produced a 450-page catalog that tells us, for instance, that Duchamp learned a plaster-casting technique so he could take impressions from Martins' nude body and translate them into realistic body sections molded in parchment.
The parchment panels are fastened to an armature made of metal, wood, wire, and putty. The body as seen through the peepholes is not complete; it lacks feet, a right arm, and a head. These parts are cropped by a ragged oval hole in an interior brick wall that serves to restrict the scene to a single point of view.
Duchamp constructed the figure first, then turned to the elaborate landscape backdrop, which he composed collage-style from fragments of photographs he made himself. The photocollage was transposed into an editioned collotype print, which in turn was cut up and assembled to make the final hand-painted panorama.
The tiny waterfall is a piquant touch. Duchamp made it from solidified transparent glue, then simulated flowing water by placing behind it an illuminated perforated disc that rotates. This is the only animated feature of an otherwise eerily static tableau. It's unexpectedly whimsical, but to me it symbolizes male genitive effusions, a counterpart to the female sexual energy of the gas lamp.
These elements, combined with the nearby presence of The Large Glass, suggest a plausible reading of the tableau as an elaboration in naturalistic terms of a primal force - sexual desire, sometimes frustrated. It's possible that this expression is in part personal to Duchamp as well. He was deeply attached to Maria Martins, whose body he immortalized in parchment. But she eventually broke off their affair and moved back to Brazil with her husband.
There's one other clue to the personal dimension. Viewers can see a tiny section of a blond wig. Originally, the wig on the dummy head was dark - Martins was a brunette. But about the time Duchamp married the blond Alexina "Teeny" Sattler in 1954, he changed the wig.
Besides celebrating 40 years of Étant donnés, the exhibition also serves as a tribute to d'Harnoncourt, who died unexpectedly in June 2008. She was a Duchamp expert; as a 25-year-old curatorial assistant, she helped to install the assemblage, in what is now Gallery 183, after it arrived at the museum in early 1969.
In a 2006 interview with the Swiss writer Hans Obrist that appears in his recent book A Brief History of Curating, she recalled interviewing Duchamp about six months before he died in the fall of 1968.
She said that when Étant donnés became public knowledge, she considered it not a conclusion, even though it was Duchamp's last documented work, but "more like a picture puzzle that you are putting together; it's a network, there are many strands and many pieces, and you can make as many themes, you can make as many connections.
"I have always found it dangerous to categorize, to say Duchamp is only interested in this or only interested in that, because the minute you say it, something else pops up," she continued.
"I don't think I thought of [Étant donnés] as explosive. I thought of it as a really important and fascinating piece that had infinite numbers of connections with a lot of other artists."
All this is still true, which makes the exhibition a splendid opportunity to engage one of the most confounding and obscurantist artists of the 20th century at his most provocative.
"Étant donnés" continues in Galleries 181, 182 and 183 of the modern-contemporary wing at the Philadelphia Museum of Art, 26th Street and the Parkway, through Nov. 29. Hours are 10 a.m. to 5 p.m. Tuesdays through Sundays and to 8:45 p.m. Fridays. Admission is $16 general, $14 for visitors 65 and older, and $12 for students with ID and visitors 13 to 18. Pay what you wish first Sunday of the month. Information: 215-763-8100, 215-684-7500 or www.philamuseum.org.