Marcel Duchamp. Fountain.

Bought from a plumbing supplier

In spring 1917, in New York, Marcel Duchamp bought a standard urinal from a sanitary ware supplier. He later recalled the firm as J.L. Mott Iron Works. He turned it onto its back rather than standing it upright as it would hang on a wall. In black paint he wrote on the rim: R. Mutt 1917.

The urinal was then submitted to the first exhibition of the Society of Independent Artists, a newly founded society, under the name of an unknown Richard Mutt. The title was Fountain.

Duchamp called such things readymades: a mass produced object designated by the artist as a work. He had already made Bottle Rack in 1914. But no readymade caused trouble like this one.

The name was a joke too. Duchamp said Mutt came from Mott, the sanitary firm, altered after the comic strip Mutt and Jeff. Richard was added as French slang for a man with money.

Duchamp never explained why he turned the urinal. He was fascinated by the problem of showing a fourth dimension, often illustrated in mathematics books by rotating solids. And at the same time he was working on a large piece about machines and desire, The Large Glass, which very few people knew about.

A society with no jury

Duchamp had moved from Paris to New York in 1915. He helped found the society, sat on its board and headed the hanging committee. The society promised no jury and no prizes: whatever members sent would be shown. Duchamp even proposed hanging works alphabetically by surname so that no one would rank anyone.

The urinal tested that promise. During the installation at the Grand Central Palace, about ten directors discussed it and voted. By a narrow margin they excluded Fountain. The show opened on 10 April 1917 without it. In their view a piece of sanitary ware could not be art, and was indecent besides.

Duchamp and the collector Walter Arensberg resigned in protest. At the time almost no one publicly knew that Duchamp was behind R. Mutt. He later explained that if his colleagues had known, their answer might have been different, and the test would no longer have been a test.

Some read the episode as Duchamp replaying an old wound. In 1912, at the Salon des Indépendants in Paris, he had been quietly asked to withdraw Nude Descending a Staircase, No.2 days before the opening. He complied, but later called it a turning point in his life.

A photograph, an article, a vanished object

Within days of the opening, Duchamp found the urinal stored behind a partition and took it to the photographer Alfred Stieglitz. The picture was taken by 19 April 1917. An address label hangs from the urinal in the photograph, and careful reading of it shows the address of Louise Norton, one of Duchamp's close friends.

In May 1917 the second issue of the small magazine The Blind Man printed the photograph with an unsigned editorial defending Mr Mutt. Its point was simple: whether Mr Mutt made the fountain with his own hands does not matter. He chose it. He placed an ordinary article where its useful meaning disappeared under a new title and point of view.

Then the urinal itself disappeared. Photographs believed to date from 1918 show it hanging in the doorway of Duchamp's studio. After that, no one knows. Tate suggests it may have been thrown out when Duchamp left for Buenos Aires in 1918.

So Duchamp's most famous work was seen by very few people. Much of its history is the history of a photograph.

Replicas signed in 1964

By the 1950s and 1960s a new generation of artists saw Duchamp's Dada readymades as precedents for their own work. Museums and galleries asked to borrow objects long lost. Duchamp authorised replicas of Fountain in 1950 and 1963.

In 1964 the Galleria Schwarz in Milan produced Fountain in an edition of eight, based on Stieglitz's photograph and made in close contact with Duchamp. Four more were made: one for Duchamp, one for the dealer Arturo Schwarz, two for museum exhibitions. The replicas are glazed earthenware painted white to resemble the original porcelain. The R. Mutt signature was repainted in black. Duchamp signed his own name on the back.

Tate's example was bought in 1999 with help from the Friends of the Tate Gallery and was shown in the opening displays of Tate Modern in 2000. In 2004 a poll of 500 British art experts named Fountain the most influential artwork of the twentieth century.

Some felt the replicas betrayed the readymade: an object chosen at one moment, now fabricated to a model. Duchamp did not mind. He was happy to lose the aura of the unique original, as long as more people could see the work and the idea survived.