On 12 April, 70 ceremonial masks used by the Hopi, Zuni and Jemez tribes in the south-western United States will be sold at the Drouot auction house.
"This sale is very emotional for me," says appraiser Daniel Dubois, who researched and wrote the catalogue for the auction.
He has been studying Native Americans since the late 1950s, when he says no one in France was interested in the subject.
In the Paris offices of the auctioneers in charge of the sale, Néret-Minet Tessier & Sarrou, Dubois takes one of the masks out of a cardboard box: Kana Kwe from the Zuni tribe in New Mexico.
A leather dome with a wooden beak, it's painted white with a rainbow above the eyes and dragonflies and tadpoles on the back.
Most of the objects for sale are from the Hopi tribe in Arizona. Made of colourfully painted leather or fabric, decorated with fibres or feathers, the Hopi do not call these objects masks. They are called friends, considered to embody the Katcina spirits of the Hopi religion.
Unlike the Katcina dolls made by artisans for sale even today, these are ceremonial objects, used in rituals and dances closed to outsiders.
These particular objects are old, dating back to the late 19th and early 20th centuries. They were collected in the 1940s, eventually making their way into the hands of the current seller, who has been identified by the auctioneer with the initials LS.
Eric Geneste, another of the auction's appraisers, says the collector comes from a French family and the 70 masks are part of a much larger collection of some 3,200 Native American objects.
It's such collections that has kept these objects in existence, he says.
"This collection is a gift to humanity and to the Indian people, because over 30 years the collector has preserved these masks," he says. "The European and American collectors play the role of saviours: they preserved these objects, which will allow future generations of Hopi Indians to rediscover them in museums or institutions."
But the Hopi say that these objects were never intended to leave the tribe.
"These items...were never meant to have any kind of commercial value," says Leigh Kuwanwisiwma, the director of the Hopi Cultural Preservation Office on the phone from Arizona.
He wrote a letter to the auction house in March protesting against the auction.
"These are spiritual people," Kuwanwisiwma says of the masks. "They hear, they talk, they listen and they have emotions."
The auction catalogue lists starting bids ranging from 2,000 to 40,000 euros. It is vague about the origins of the items. Like the seller, previous collectors are listed only with initials and there is no indication of where or when they were originally acquired.
Kuwanwisiwma believes they are authentic, though he disputes the appraisers' claim that they were acquired legally. He says there was a rush to collect Native American objects in the late 19th century.
"We know that many items were taken from holding areas, what we call clan homes. These are ceremonial places where these items are kept. They were broken into, in many cases. Some were also stored in caves outside the villages," he says.
Kuwanwisiwma concedes that these may have been taken by Hopi looking to make some money and that they may well have sold them to collectors. But that, he says, would have been illegal.
"No Hopi, under traditional law or under our modern law, has any right or authority to alienate these items. So, quite frankly, we have stated the position that these items have been collected illegally; they left the Hopi reservation illegally."
Kuwanwisiwma wants France to treat these objects like art looted art by the Nazis during World War II.
In the United States the Native American Graves Protection and Repatriation Act, passed in 1990, allows tribes to reclaim their sacred items. Sales in France are not subject to this law.
Ethnohistorian Joëlle Rostkowski, who specialises in Native American art and artefacts, says France has a tendency to hold on tight to its collections.
"French law is very strict. Whatever is in our museums belongs to the French state," she explains. Even non-French objects are considered part of the French patrimony, which makes it difficult to agree to return anything.
But times are changing. Rostkowski points to the Quai Branly, the French national museum of non-European art, which returned several sacred Maori warrior heads to New Zealand last year, something she says would have been unthinkable just five years before.
"Until now this hasn't been the museum's policy, but now they're probably more open to working with native people and more sensitive now than they were 10 years ago," says anthropologist Marie Mauzé, who worked on the return in 2003 of a headdress owned by French surrealist André Breton to the Kwakwaka'wakw tribe in British Columbia.
French institutions need to learn more about native objects in order to work with tribes on the best way to preserve and display them respectfully, she says.
"It depends on the good will of people and the understanding of each other's culture," she says. "There is a trust relationship that has to be built between native people and museums."
The auctioneers of the Hopi objects hope the Quai Branly museum will buy the whole collection but Rostkowski says the museum might be wary, as it has no established contact with the Hopi.
"They would be taking a risk, unless they talked to the people concerned, because afterwards there might be problems," she says. "If public museums think it's too tricky, they won't buy those pieces."
The auction appraisers dismiss any claims the Hopi of today have on these objects that are over 100 years old.
Dubois says it would be problematic for France to return all sacred objects in French hands.
"At the Quai Branly we have African objects that are interesting because they are religious," he points out. "So we would have to return everything."
Geneste says that France lost a lot of its own heritage during the revolution.
"Will France ask for all the Versailles furniture back from the British Royal collection?" he asks rhetorically, pointing out that French institutions like the Louvre have been buying back certain objects.
But for Lee Kuwanwisiwma buying these masks is out of the question for the Hopi. It would be like buying a person.
"These are people, spiritual people," he insists. "There’s a very strong heartfelt desire for the family that currently possess these objects to provide a good gesture to the Hopi people, and talk about returning these Katcina friends to their rightful home."