It’s a trade any dealer would dream of: Koopman Rare Art, silver dealers from London, bought an 18th-century tureen at Sotheby’s on Saturday for $740,000 and have put it on display in their booth at the International Fine Art and Antiques Fair at the Park Avenue Armory, with a price tag of $3 million.

The International Fair, which opens to the public on Friday, is always full of rare, opulent, and expensive items. But the markup is not always so dramatic (nor as well-known) as on the Koopman tureen.

“It’s probably the greatest piece of Rococo silver to survive in its original form,” a partner in the firm, Lewis Smith, said. “The queen has an identical one, but hers was altered in the 19th century.” As for the “knocked-down price” at Sotheby’s, Mr. Smith said he couldn’t explain it. “It’s the most important find we’ve ever had,” he said.

The tureen was made in 1786 for John Fitzgibbon, the 1st Earl of Clare. It was one of a number of pieces copied from the Marine Service, a famous service with marine motifs made for Frederick, Prince of Wales, in the 1740s and ’50s. The Fitzgibbon Centerpiece, as it is called, is topped with a reclining figure of Neptune, and decorated with mermaids, fish, and shells.

Outside of Koopman’s booth, the major trend at the fair is mixing old and new art, furniture, and design to create a modern and eclectic decorating style. The attractive booth of Axel Vervoordt, a firm that has always been good at blending old and new, has everything from Bronze Age objects from southern Turkmenistan — carved stone disks, columns, and other abstract sculptural forms, all of whose function is unknown — to a colossal hand broken off a monumental Roman statue, to a monochrome white painting by Lucio Fontana. Compared to the Fontana, which is priced at $2.5 million, the Roman hand, which could pass for a contemporary sculpture, is a relative bargain at $300,000.

Vervoordt, which is based in Belgium, also has a piece from its own home territory: a life-size dog carved in oak by the early Baroque Flemish sculptor Artus Quellin. “It’s very unusual to have an individual portrait of a dog,” a gallery director, Robert Lauwers, said. The coat of arms on the dog’s collar identifies with the household of Roose, an important Antwerp family.

The booth of Antoine Chenevière from London is also a dramatic mix of antique and contemporary. Besides a pair of rare English oil lamps from 1830, there is a pair of teal Venetian glass chandeliers from the 1960s, and an industrial-looking floor lamp made in Milan in 1952, which would be a perfect addition to any modernist apartment. The furniture and design pieces are set off by works of contemporary art, including several large color photographs by Candida Höfer.

Mallett, which deals primarily in pairs, has a pair of black-and-white photographs, in frames designed by the artist, of Gene Kelly and Le Corbusier. The photographer, Willy Rizzo, worked for Paris Match in the 1950s and ’60s. Later he moved to Rome with his Italian actress wife, Elsa Martinelli, and designed much of the furniture for their apartment there. Mallett has a pair of lipstick-red lacquered commodes and a pair of very large stainless steel lamps, all from Mr. Rizzo’s apartment.

Looking for the perfect gift for the SAT tutor who helped your mathematically-challenged scion get admitted to Yale? Mallett has a pair of enormous English globes, which were commissioned from James Wyld in 1863 by a wealthy young man to give to his tutor, who got him into Oxford. The inscription reads: “Presented to Dr. Eagleton, In Grateful Acknowledgment of His Continual Kindness, Unremitted Attention, and Valuable Services, By His Pupil, Reginald Bray.” The globes are priced at “around $1 million,” a director of Mallett, Henry Neville, said.

Vallois, which specializes in Art Deco furniture and design, has several pieces by Diego Giacometti, the brother of Alberto, the sculptor. These include a bronze valet (a piece of furniture on which one hangs coats, hats, or blankets) with a lovely dark patina and a dramatic hanging light fixture. The latter is a rather delicate-looking bronze triangle, along the base of which Giacometti sculpted one of his favorite motifs, called “Promenade des Amis,” which shows a horse and three dogs around a tree. The Giacometti brothers grew up on a farm in Switzerland, and Diego frequently depicted animals in his work.

Bernard Goldberg has a set of leaded glass windows by the architect George Washington Maher, a contemporary of Frank Lloyd Wright. Maher designed the set, which includes a top arched window and two side rectangular panels, for the home of Charles and Helen Winton in Wausau, Wisconsin. The set is $850,000. Mr. Goldberg also has a table and four chairs from another Maher house called Rockledge, and a rare Gustav Stickley tea table topped with tiles designed by William Grueby. They are known as elephantine tiles, for their cracked, leathery texture.

For those who like to daydream about battlefields, Peter Finer has his usual excellent selection of arms and armor, including a pair of French flintlock pistols that were presented by Napoleon Bonaparte, when he was First Consul, to a Spanish captain named Coronado. They are in their original case with an inscription describing the gift. Mr. Finer refused to put a value on them, saying only that they would go for “lots.”

The pistols may be pricier, but a couple of extremely long swords, once born by the bodyguards of the Duke of Brunswick, are more intimidating. The swords, dated 1574, are $60,000 each.

“As I was saying to Mrs. Thatcher the other day at Grosvenor House,” Mr. Finer said — referring to the major London art and antiques fair — “I said: ‘When you go out, you go out in an armored car with a bunch of men on motorbikes. When the Duke of Brunswick went out, he had two hundred men, all bearing these.’ And she got a twinkle in her eye and said, ‘How many have you got?'”