It was Jackie's. Who cares if it's fake?

Only Jacqueline Kennedy Onassis could make a simulated pearl necklace valued on the market at about $65 worth $211,500 at auction. Estimated at a high of $700, it was the triple strand made famous in the 1962 photograph of a young John-John in his mother's arms, pulling one strand of the three over her chin as she tosses back her head and smiles. It is one of the most seductive photographs in American memory: the innocence of the era exposed as vulnerably as Jackie's smooth neck.

The Jackie O auction in New York last week was astonishing throughout. Some would call it grotesque. The highlights: the $702,500 golf clubs. The $2.6m diamond engagement ring from Aristotle Onassis. The $85,000 high chair. Anything that got close to the sex appeal of the century's most glamorous couple earned the highest bids. Rumours were circulating that the gay community was particularly interested in Jackie's saddles.

But nowhere was the added value of the Jackie factor more exponential than in the category of costume jewellery. Worth nothing in and of itself, it became the sale's biggest per-lot earner, garnering 61 times its presale estimate, a Sotheby's record. The way she wore her hat, the ineffable Jackiness of her, made a banal pair of Liz Claiborne ear-rings that anyone could buy at the counter of Saks Fifth Avenue worth a fortune. Instead of the estimated $54,795, this session brought in over $2m.

"People wanted to buy anything that she wore," said John Block, executive vice-president and jewellery expert at Sotheby's, of the "pearl", "diamond" and even "coral" and "turquoise" fakes that Sotheby's described in quotes. "There's nothing more personal than the fashion jewellery. People wouldn't have paid one dollar more if they were real pearls. They were buying the dream. They were buying the history."

Indeed, one could argue that bidders got more of Jackie per dollar from her hippie beads and Saint Laurent gilt metal belts than from her precious gems. Fashion jewellery has always been a measure of a woman's poise, her grace under pressure, her power to turn the fake into fortune simply by the way she moves. Coco Chanel popularised its chimerical value, its je ne sais quoi. And, like her, Jackie had no qualms about mixing the fake and the fine.

"The actual inherent value of most of this jewellery was incredibly small. We wouldn't even sell this jewellery if it weren't a name you can count on 100 per cent for the history or the magic," explained Block. Previous names include Diana Vreeland and the Duchess of Windsor.

Auctions put humanity on the block. They are unchristian places that define social worth. They evaluate the moment with 20/20 hindsight and put price tags on relics that only an elite few can possess. Traditionally, they perpetuate class and privilege. But the big buyers at the Jackie sale were not, ultimately, the privileged few. They were the masses, and the merchants who market to them.

The fake pearl necklace, that of the sublime photograph, was bought by The Franklin Mint, a direct-response marketer to the lowest common denominator of American taste: those who buy "instant heirloom" kitsch collectables, from porcelain dolls to collector plates with cartoon characters on them, from the ad pages of Sunday supplements. (Carolee Friedlander, designer of Carolee, purveyor of simulated pearls and other jewellery priced from $75 to $250, bought a strand of Jackie's glass pearls at the sale, "to share the excitement of how Jackie wore them" in a travelling display in department stores across the country. "Fashion is aspirational. That's what it's about," said Friedlander.) One can only hope Jackie is laughing, breathily, from her grave.

"Of all the pieces in the auction, this was the only one we were interested in," says Jack Wilke, vice-president of communications and marketing at The Franklin Mint, speaking by cellphone from an aeroplane about the triple strand necklace, "it was jewellery that Jackie wore every day ... in Bermuda shorts or attending coronations. It really reflected her sense of style, her elegance and grace. Her rhinestones became diamonds because she wore them."

A peculiar, large and successful company, The Franklin Mint has earned international fortunes by minting nostalgia from "heirloom quality collectables", crammed with Americana, and prices from $29 to $8,000. The company intends to enshrine the Jackie pearls at the Franklin Mint museum outside Philadelphia - simultaneous, of course, to mass marketing them as precious limited edition fakes. In 1987, they bought the Duchess of Windsor's panther bracelet at auction for $90,000 and "re-created" it as fine jewellery (for $4,800 a piece) and "fashion" for $195.

The "sales of the century" in the last decade - the estates of the Duchess of Windsor, Andy Warhol and Jackie O - have deconstructed the material world much in the way that Derrida did the novel. They share the Warhol factor: the perspective of pop culture that makes a Campbell's soup can precious by celebration of its ordinariness. Photographic images of the life become a kind of provenance, as good as gold, a stamp of credibility where there is none. Mere "black beads", as Sotheby's catalogue described a necklace sold for $101,500 to a French designer, Gerard Darel, "known" by a 1961 photograph in which Jackie wears them alongside a smitten De Gaulle.

"In the past, provenance from a distinguished gallery or collector was a warrant of a work's quality," stated Bruce Wolmer, editor-in-chief of Art & Auction magazine recently. "Increasingly, we're seeing celebrity provenance of minor and even utterly inconsequential pieces as a guarantee of their value. So, associational value replaces real value and associational value becomes value in itself."

In London, Steinberg and Tolkein, the fashionable second-hand and vintage couture clothing store on the King's Road, is selling clothes that probably belonged to Jackie, but so what. They haven't been through the accrediting media mill. Pearls just like hers, the same vintage, can only go for pounds 300. They haven't had Cindy Adams, the gossip columnist, interview the highest bidder live in front of Sotheby's. The same goes for the luxury mini-van purchased by an innocent on Martha's Vineyard: Jackie's vacation car quietly traded in for a new model by her daughter, Caroline. (Her sexier BMW concluded the Sotheby's sale, selling for $79,000.)

What Jackie's adoring public values - then and now - is the grand illusion, even as they yearn for the spot of breath against the glass. When Kenneth Jay Lane made a costume copy of her Indian-style necklace of rubies, emeralds and diamonds - another gift from Ari - he gave her a break on the fee in exchange for the right to sell it in quantity from his store. Later, she would tell him, "I saw our necklace again on Dynasty!"

At auction, the fake, with matching earclips, sold for $90,500. Jackie got the discount, and the last laugh. Pearly gates, W1 and elsewhere A brief guide to buying the perfect heirloom faux pearl necklace.

Steinberg & Tolkein, 193 King's Road, SW3.

This vintage couture clothing emporium stocks original pearls from the Twenties to the Fifties, from pounds 30 to pounds 300. It has necklaces made by Gripoix, the company that made Chanel pearls and closed last year after 100 years. Its faux pearls, of the finest quality, were made from glass beads coated in ground sea shells up to 12 times.

Accessorise, 293 Oxford Street, W1, and branches nationwide

The range includes very simple one strand pearls from pounds 3.99 and goes up to more elaborate chokers, made from glass-coated beads, which are heavier to handle, making them feel more like the real thing. They also have stronger clasps, decorated with diamante detailing, at pounds 17.99.

Butler & Wilson, 20 South Molton Street, London W1

Pearl necklaces start at pounds 38 for synthetic beads with gold-plated clasps or graduated chain fastenings which make it easier to adjust the length.

Fenwick, 63 New Bond Street, London W1, and Northumberland Street, Newcastle upon Tyne.

Fenwick's own range starts at pounds 6.95 for a thin pearl choker and goes up to pounds 29.95 for a long pearl rope, threaded on to a chain or with gilt beads, and pounds 34.95 for a Baroque four-string choker. Their most exclusive range is designed by Cobra & Bellamy, whose baroque faux pearls start at pounds 62 and go up to pounds 230 for a 16in necklace which can be wrapped around the neck and fastened at any desired length.

At their counter in Fenwick, New Bond Street, this week to Saturday from midday to 3pm, Vicki Smallwood will be in the store demonstrating the art of pearl stringing, and inviting customers to bring in their old or damaged pearl necklaces to be restrung. Prices start at pounds 9 for unknotted (when the string is not knotted after each bead) and go up to pounds 49 for knotted strings.

JILL WANLESS