The seas were high and the fog was thick in December 1746 when the Prince de Conty, a French frigate returning home from China with tea, ceramics and roughly 100 gold ingots, foundered in the Atlantic, just 10 miles from shore.
Its bounty sank beneath the waves and laid untouched for 228 years until 1974, when treasure hunters located the wreck and illegally scavenged its remains.
On Wednesday, five of the gold ingots, embossed with Chinese characters and valued at $231,000, were returned to the French Embassy in Washington, ending an odyssey of 48 years that involved underwater detectives, international diplomacy and an appearance on “Antiques Roadshow.”
Patience, said David R. Keller, a special agent with Homeland Security Investigations who oversaw the American side of the case, is critical when pursuing stolen cultural items as they travel through the marketplace.
“Objects like these have a way of showing up in unexpected places years later,” he said.
His counterpart on the French side of the case, Michel L’Hour, the former chief of France’s Underwater Archaeology Research Department, agreed.
“Wreck looters are often very discreet at first,” said Mr. L’Hour, who remains on the case after more than four decades and vows to keep hunting for the rest of the bullion. “But there is always a moment when they tell someone about their discovery and especially about their desire to sell something.”
Mr. L’Hour believes many of the ingots have been melted down and others remain secreted in what he calls someone’s “woolen sock,” and he says one that France intends to claim was sold to the British Museum.
The tale of the missing ingots begins with the shipwreck of the Prince de Conty, homeward bound from Nanjing, China. It went down in rocky shoals near the small coastal island of Belle-Île-en-Mer, France, according to French and American officials and legal documents, and only 45 of its 229 hands survived. Salvage efforts were thwarted by the dangerous waters. The vessel was soon forgotten.
In 1974, a group of amateur treasure divers from nearby Brittany, acting on local lore, found the wreck in roughly 30 feet of ocean. The divers did not report the find to officials as required under French law that says shipwrecks and their cargo in territorial waters are the property of the state. Instead they kept the site secret, and revisited in 1975 to recover its bounty.
One of them took a picture of the ingots as they laid on the sea floor, a photo that would prove crucial during the investigation.
Mr. L’Hour caught wind of the find in the late 1970s and traced his way to the treasure hunters, who had divvied up their 100 or so ingots but later fell out amid disputes.
“When you have a large network of informants,” Mr. L’Hour said, “there is always someone who owes you something or who wants to get back at the seller by passing information on to you.”
By 1983, French prosecutors had filed charges against more than a dozen people in connection with the shipwreck, yet most of the accused testified that they knew nothing of the ingots. But in 1995, Mr. L’Hour was able to track down a copy of the underwater picture of the ingots taken by one of the divers in 1975. It showed the gold nestled among two sea creatures, a starfish and a sea urchin — useful evidence if the ingots ever surfaced.
Some of them did, in 1999, on an episode of PBS’s “Antiques Roadshow” in Tampa, Fla., when a French woman presented a set of five Chinese ingots and an underwater photo of the bars.
She said the ingots had come from a different shipwreck off Western Africa, but the accompanying photo she had would later prove to match the one Mr. L’Hour had already acquired. (It, too, showed the ingots beside the starfish and sea urchin, which are indigenous to French, but not African, coastal waters.)
The five ingots would not surface again until 2017, when a Florida woman who had acquired them sometime after their “Roadshow” appearance consigned them for auction with a rare coin dealer in California. It was then that Mr. L’Hour received a call from someone in his “network of informers” — people who scour the internet looking for looted cultural items put up for sale — and began to make inquiries.
The auctioneers argued that there were many similar Chinese ingots traveling by sea in the 1700s. As part of their argument, they referenced the “Antiques Roadshow” episode that had featured the ingots in question.
Mr. L’Hour studied a clip of the episode, which was still posted on the PBS website. He noticed right away, he said, that the photo of the ingots presented by the French woman on the show matched the one that had been taken by the diver in 1975. In an affidavit, Mr. L’Hour declared that the French woman, in fact, was the sister of the photographer’s wife.
Armed with that evidence, in 2018 the French government petitioned American officials to seize the ingots from the auctioneer.
In an interview, Joe Lang, a representative of the auction house, Stephen Allen Rare Coins in Santa Rosa, Calif., said, “I don’t think their argument is conclusive,” but added that his company always withdraws items “right away” when presented with reasonable claims.
Each bar weighs about 13 ounces, so as a matter of gold, by weight, the five ingots are worth about $125,000 on the precious metals market. But officials said they had increased the estimate of their value because collectors will often pay a premium for ingots recovered from a shipwreck.
The return to France likely would have occurred earlier than Wednesday, but for a claim filed by Chinese cultural heritage officials with United States Customs and Border Protection. The Chinese argued that the ingots were in fact their cultural heritage property, but the agency determined that the ingots were more accurately viewed as “a common form of currency” distributed throughout various markets by Chinese traders at the time of the Conty’s voyage.
Mr. Keller said there are “always unexpected complications” in cultural restitution cases.