Why do we only worship 'real' works of art? Generations stand in wonder at the cast courts of the Victoria and Albert Museum in London. The east court reopens next week, burnished and refurbished, with Michelangelo's David buffed up and every monument cleaned of darkening decades of dirt. In the west court, Trajan's column is next to have its reliefs sharpened with a dusting and its marble colouring restored. The courts are a breathtaking Victorian spectacle, so even the child who usually crumples at the door of a gallery is awestruck. Allowed in this week for an early look, I stood remembering visits here as a child, bringing my own children, and now finding my grandchildren just as amazed by the grandeur and the towering magnificence of these sculptures. Opened in 1873, these high glass-roofed courts were built to house gigantic casts of Europe's greatest monuments, an array of the gothic, the classical and the renaissance, incongruously hugger-mugger. A huge Celtic cross, a Pisano pulpit, an intricately carved Norwegian doorway, knight crusader effigies from English churches, a lion from Brunswick, the gates of paradise from Florence, Byzantine mosaics from Ravenna, centuries and nations apart. This was a high Victorian artistic education, an aristocratic grand tour all within the precincts of South Kensington, without Florentine sun or gothic gloom of a German cathedral. What's striking is that none of these are "real." They are copies, reproductions, images, simulacra, not genuine. As if to emphasise the point, there is even, high up on the wall, a good 18th-century copy of Raphael's School of Athens with Plato and Aristotle, looking, at least to my non-expert eye, much like the real fresco in the Vatican. A cast has at least touched the authentic sacred original, but a copy is just a mere copy. Does it matter? What's wrong with modern perfect reproductions of the world's greatest art that we could display in any gallery, virtually identical to the original? You can feel the frisson of shock at such iconoclasm, undermining the religion of art and the art market. But if the authentic experience is to gaze with the eye, not worship at the altar of a relic, why does it matter if a painting or an object is the "real" thing? If Duchamp's urinal isn't the original, wasn't that the point? What matters is the image you look at, as created by the artist. It's a miracle the V&A's casts survived the 20th century revulsion against the vulgarity of reproduction. Similar great collections of casts in museums around Europe were broken up and destroyed: fashions changed, led by Berlin's director of museums, who declared a real fragment of Chartres cathedral was worth an entire replica. British art schools that owned great profusions of casts for their students to copy threw them out in disgust at such inauthenticity. The V&A's casts survived mainly, says their curator, Marjorie Trusted, because there was no other use for the museum's great courts. Now they are safely passed the danger zone because they have turned old, rare and precious in themselves. A few serve practical purposes: casts of effigies of knights are better than their originals bombed in the Temple church. The V&A cast of Trajan's column preserves what has since worn and perished in Rome's polluted air. But these casts are now treasured not just as copies but as fine Victorian artefacts in their own right, turned into respectable and valuable art objects, which is perverse. They were meant to bring the glories of Europe to those who would otherwise never see them, a noble idea. But by the same token, there is no reason why we shouldn't have a lot more of them. Minor local museums treasure minor randomly donated works, when they could show reproductions of anything their curators dared imagine. So why not? Many have contemplated this, from Walter Benjamin to Pierre Bourdieu, considering the infinitely reproducible art of photography and prints. Does Mona Lisa on a million tea towels dilute the power of the painting, or is it pure snobbery to think so? On one thing everyone agrees, and that's honesty: the viewer needs to know what they are seeing. Trusted resents a visit to the Albertina Museum in Vienna, spending a long time looking in delight at the most famous Dürer drawings - the hare among them - only to find at the end a note saying these were photographic reproductions, the originals too delicate to display. Though they were perfect, on the right paper, "I felt I'd been tricked," she said, as you would. But why should it matter, if they look exactly the same? Art descends to fetish if the only value is to worship at the actual spot where Turner put his brush. Much art looks better on television than in life. I rewatched Kenneth Clarke's Civilisation series, and even in 1969 TV colour, he makes you look and see better. So can Andrew Graham-Dixon in his many TV series. Johanna Puisto, sculpture conservator at the V&A, works on the David statue The Fighting Temeraire looks magnificent in the film Mr Turner, as Mike Leigh makes you look intently. These are all reproductions, so why such contempt for reproductions elsewhere? The art market exists on the principle of rarity, unique objects, relics of the artist, where authenticity is a matter for the courts. The only point of limited-edition prints is to jack up the price: the artist's signature and number of the print become its intrinsic value, not the art itself. Trusted remembers a lecture by the great art historian EH Gombrich recalling his parents' unashamed photographs of great works on their walls, things no longer socially tasteful. Reproductions are seen as vulgar among the cognoscenti - except as posters for exhibitions, regaining authenticity as "real" posters. All this is snobbery or cultish fetishism that sets up barriers between the preciousness of the art world and those outside it. "But there is a magic about the real thing," says Trusted - and, since we are not entirely rational creatures, she's right, because we all feel it. That shudder at standing inches from the actual canvas where Van Gogh laid down layers of paint that no one valued at the time has an aura of its own - though of the same ilk as a fragment of the true cross or the drop of Mary's milk you can see in a vial in Bethlehem. A ticket to the V&A's Constable exhibition costs £14. The National Gallery charges £16 to see Rembrandt's late works. Late Turner at Tate Britain costs £16.50. All these are splendid - and the price has to cover transporting and insuring wildly valuable works. They remind us to be grateful that our national collections are free again, despite some Tory calls to bring back charges. But in the spirit of the reopening of the V&A's cast courts, I'd like to suggest an experiment to the Art Fund, the Arts Council or any other funder. Why not curate a magnificent exhibition of the 200 greatest works of art in reproduction? Choosing would be an enjoyable controversy in itself. Present them spectacularly in a marquee to take to any town that wants it, a travelling art circus of the very best. And if you must have "authenticity," add one real work, without revealing which.