In the belly of the National Gallery of Victoria, in a room usually dedicated to 18th and 19th century British painting and sculpture, curator Katie Somerville dons a pair of cotton gloves. She is showing me the feats involved in making a 1956 Christian Dior evening dress, embellished with gold sequins.

“This piece demonstrates the peak of the mid-50s silhouette,” she says, pulling up the hem to reveal the structure beneath. Under seven layers of tulle is a corset, fastened to the exterior with a few scant threads – it’s as if the dress sort of floats around it.

“It’s delicate, and lined in silk,” says Somerville, “but there’s this rigid metal boning structure underneath. Once you’re in this, it’s not going anywhere.”

It’s early August, and Somerville is overseeing the preparation of more than 200 pieces for The House of Dior: Seventy Years of Haute Couture. A temporary workshop – chosen for its size and light – has been set up on the second level of the gallery ahead of the opening. Invaluable paintings still adorn the walls, but they’re obscured by naked mannequins, rows of clothing racks, shelves of hat-boxes, and benches piled high with fabrics, measuring tapes, pin cushions, thimbles and dozens of Dior gowns. It’s somewhere between a makeshift atelier and a construction site.

A couture garment does not exist unless a client commissions it, so each piece here is unique and poses its own conservation challenges. Across the room, Bronwyn Cosgrove, NGV’s senior conservator of fashion and textiles, is stitching padding to the thighs of a mannequin. Each mannequin will be customised specifically for the ensemble it’s going to wear, and this one will be hosting a pink silk-crepe and wool ensemble with coral-like, metal-thread embroidery inspired by a lobster shell.

“We have to think in three dimensions,” says Cosgrove. “You could pad out a mannequin perfectly well and it still wouldn’t look like Dior,” she says. “It’s about elegance.”

Each couture piece is one-of-a-kind and has been designed for a specific body. Gowns in this show, for example, have been worn by actors Nicole Kidman and Marion Cotillard. The padding that Cosgrove is attaching helps bridge the gap between the mannequin and its original wearer.

“It’s about working up the mannequin, which is tiny, to reflect the body shape of the dress,” says Cosgrove. She works from a reference image of the pink gown, which shows it on the catwalk. Cosgrove’s challenge is to make this inanimate figure emulate a model’s poise – in this case, the grace of Canadian model Jessica Stam, who wore the gown on the runway in Autumn 2006.

“It’s incredibly heavy,” says Cosgrove. “At least four kilos. It gives you a new respect for models, knowing they have to carry this while looking elegant.”

This exhibition has been three years in the making, and the NGV has worked closely with Dior Heritage every step of the way. The process for transporting each item is meticulous, and begins in France. Each garment is checked over and packed into crates at Dior headquarters at 30 Avenue Montaigne in Paris, then undergoes the same process here in Melbourne. Each piece is taken from its crate and its condition scrutinised by Dior staff. Some crates contain dozens of pieces, others, like the one carrying a 1997 John Galliano gown with a four-metre train, contain just one.

The small team from Dior Heritage in Paris is still here two weeks after delivery to oversee the preparations. Across the room I watch a very stern, bespectacled Frenchman in a white Dior-embroidered lab coat thread petticoats onto a mannequin, and then dress her in a peach gown with an extravagant organza silk floral arrangement on the right shoulder.

One of the things you see when the dresses are lain out on the table, Somerville explains, is that while some of the internal construction is ingenious in its simplicity, others are extremely technically accomplished.

“In those days it was about providing a dress that you could literally step into and it would take the desired form.”

She reminds me of the 1956 evening gown – the one with the suspended internal foundation.

“Undoubtedly as a designer he was inspired by architecture,” she says of Dior. In fact, architecture was his first career choice, though after school he opened a contemporary art gallery before making his way into couture. By the time he set up his own fashion house he was 41.

“In that post-war period, people had been trained not to think about things like fashion,” says Somerville. “It was all about survival. But people were ready for optimism.”

There’s a great deal of nostalgia in his designs, particularly in the masculine, broad-shouldered silhouettes he favoured earlier in his career, but he presented his vision in a way that spoke to people’s yearning for something new, going against the trend of austerity.

“He made fashion newsworthy,” says Somerville. “We’re used to the cycle of seasons and trends now [but] he created that dynamic of looking to Paris for what’s coming next.”

As each garment is fitted to its mannequin and deemed ready for display, it’s moved into storage and wrapped in a dramatic red cape. “The catwalk is part theatre,” says Somerville.

As I leave, I notice a crowd of them in the darkened room adjacent to the workshop: blank-faced, caped figures, waiting in the wings before their encore performance.

The House of Dior: Seventy Years of Haute Couture is at NGV from August 27 to November 7.

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