This New York Times article points out a serious problem in the art world that has been created as a result of the new AAM (American Association of Museums) collecting guidelines. Collectors that started after 1970 that are now downsizing as they enter their 60s are finding that they have limited options for passing on their collections. The options are pretty clearly limited for most to giving them to the family or selling them. The wealthiest collectors are creating trusts or foundations to circumvent issues where museums could be compelled to return objects that had been donated and had become part of the museum's collections. The UNESCO convention and UNIDROIT will in my opinion in the future exert increased pressures on governments to infringe on the property rights of private citizens. The new AAM guidelines are just one manifestation of this movement that creates some problematic precedents for the future. So far no one has given me an adequate answer to the rationale for creating one standard for objects being considered for acquisition and another standard for those objects aleady in the collection. Understandably no one wants to talk about this but it really is the 10,000 pound gorilla in the room. There is no intellectual honesty in maintaining two standards.

"In the three decades since David Dewey of Minneapolis began collecting Chinese antiquities he has donated dozens to favored museums, enriching the Institute of Arts in his hometown as well as Middlebury College in Vermont, where he studied Mandarin.

David Dewey bought these Yuan dynasty artifacts from a dealer 15 years ago, but many museums now seek a more extensive provenance for gifts.

“Antiquities collecting destroys far more than it saves,” said Ricardo J. Elia, a Boston University archaeology professor on a field study in Spain.

This Olmec-era statuette owned by the Metropolitan Museum of Art has a provenance dating to 1972 — not early enough for current guidelines for donations.

Amid the artifacts with undisputed provenance in the home of Alan M. Dershowitz, there is a sarcophagus for which there is no proof of when and how it left Egypt.

But his giving days are largely over, he said, pre-empted by guidelines that most museums now follow on what objects they can accept. “They just won’t take them — can’t take them,” Mr. Dewey said.

Alan M. Dershowitz, the Harvard law professor, is in a similar bind. An antiquities collector, he is eager to sell an Egyptian sarcophagus he bought from Sotheby’s in the early 1990s. But he is stymied, he said, because auction houses are applying tighter policies to the items they accept for consignment. “I can’t get proof of when it came out of Egypt,” Mr. Dershowitz said.

Across the country measures taken to curb the trade in looted artifacts are making it more difficult for collectors of antiquities to donate, or sell, the cultural treasures that fill their homes, display cases and storage units. Museums typically no longer want artifacts that do not have a documented history stretching back past 1970, a date set by the Association of Art Museum Directors, whose guidelines most institutions have adopted. Drawn up in 2008, the rules have been applauded by countries seeking to recover their artifacts and by archaeologists looking to study objects in their natural settings.

But the sweeping shift in attitudes has left collectors stuck with items they say they purchased in good faith many years ago from reputable dealers. One study found that as many as 100,000 privately owned ancient Greek, Roman and related Classical objects in the United States would be unable to pass muster with most museums. “Objects are guilty until proven innocent,” said James J. Lally, a Manhattan dealer in Chinese art and antiquities.

Collectors and their advocates predict that museums, cultural scholarship and the items themselves will suffer as important gifts are disallowed. Kate Fitz Gibbon, a lawyer with the Cultural Policy Research Institute, warned at a March forum that museums, long reliant on the generosity of collectors, may come to regard the guidelines as a “self-administered slow poison.”

“This may sound like an exaggeration,” she said. “But if we continue on this path, there may not be a next generation of collectors, donors and patrons of ancient art, not in the United States of America anyway.”

There are many on the other side of the question who view Ms. Fitz Gibbon’s perspective as hyperbolic. “Antiquities collecting destroys far more than it saves,” said Ricardo J. Elia, an archaeology professor at Boston University who specializes in the global art market. “Looting is driven by the art market, by supply and demand.”

For centuries collectors have helped define artistic taste, and their collections, whether assembled for vanity, beauty, profit or some combination thereof, have been the backbone of museums. But the antiquities trade begins, at its source, with an act of appropriation: the removal of artifacts from a native site to one where, in the case of museums, they can be more accessible to scholars and the public.

Whatever air of nobility once attached to that effort has dissipated recently as antiquities collectors are increasingly depicted as the beneficiaries of a villainous trade.

Collectors and their advocates insist the depiction is unfair, particularly when it recasts acquisitions made decades ago, when cultural sensibilities were different, as the illicit booty of indifferent rascals.

“Even objects that entirely lack history are also not necessarily smuggled or looted,” said William G. Pearlstein, a New York lawyer who advises collectors and dealers in the antiquities trade. “Many owners simply failed to keep records of their objects, which they treated like other household possessions.”

Archaeologists scoff at the suggestion of naïveté, since collectors are typically educated, wealthy people who understand the relationship between provenance and value and are not likely to let important documents fall behind the couch.

“Collectors know that without provenance it is impossible to know whether an object was first acquired by illegal or destructive means,” said Neil J. Brodie, an archaeologist and former director of the Illicit Antiquities Research Centre at the University of Cambridge.

Momentum for stricter guidelines has been building since a United Nations convention on looted antiquities in 1970 led to international protocols. It accelerated several years ago in the aftermath of major acquisition scandals at the J. Paul Getty Museum in Los Angeles and other institutions that ultimately led to the new policies drawn up by the museum directors. They strongly discourage museums from buying or accepting objects that cannot pass the 1970 test or lack an export permit from the country of origin.

On the auction side collectors and their advocates say the nation’s two largest houses, Sotheby’s and Christie’s, have tightened their policies in recent years, though Sotheby’s is currently embroiled in a dispute with Cambodia over a 10th-century Khmer statue.

Antiquities dealers say their clients feel boxed in. Randall Hixenbaugh, a Manhattan gallery owner and appraiser, said he knew a donor with good paperwork who was turned away by a museum because his dossier lacked a pre-1970 photograph showing the item in the United States. “The intention is good,” he said. “Museums are not buying objects of dubious provenance. But there are unintended consequences for objects that were here for 150 years but not documented as such.”

Several years ago the Cultural Policy Research Institute, based in Santa Fe, N.M., surveyed American collectors and museums and estimated that as many as 111,900 ancient objects from Greek, Roman, Etruscan and related cultures are in private American hands and “unprovenanced.”

Arthur A. Houghton III, president of the institute, said that if rejected by museums, these “orphaned” items will likely end up in private hands outside the country.

Mr. Houghton is a former acting curator of the Getty who resigned his post there in 1986 after accusing the museum of willfully accepting illegally excavated antiquities. Now he says the pendulum has swung too far back in a way that places significant objects “at risk of damage or destruction.”

Professor Elia dismisses talk of “orphaning” as patronizing “mythology.”  “It ignores the fact that dealing and collecting are causing looting in the first place,” he said from Spain, where he is overseeing a field study. “For every object ‘rescued’ by looters, dealers and collectors, there is a trail of destroyed sites, lost knowledge, broken artifacts and broken laws.”

Lawrence Rothfield, founder of the Cultural Policy Center at the University of Chicago and a member of Saving Antiquities for Everyone, said the study wrongly suggests the entire lot of privately owned, unprovenanced artifacts are museum worthy. “Even if the objects in question were not excluded from acquisition,” he said, “most of them would not be acquired anyway.”

What is clear is that collectors are uneasy. They worry that placing undocumented items for auction exposes them to litigation from foreign nations or perhaps a seizure effort from United States authorities acting as their agent. Many expressed their concerns at a forum in March, hosted by the Asia Society in New York and titled “The Future of the Past: Collecting Ancient Art in the 21st Century,” where collectors spoke of a “climate of fear.”

Mr. Dewey, the antiquities collector, said in an interview that he contemplated giving the Minneapolis museum an eighth-century ceramic horse from the Tang dynasty that he had bought from a Hong Kong dealer 20 years ago. But he decided not to do it because even with the paperwork from the sale, he said, he knew he would run up against the museum directors’ guidelines.

“Everybody just got scared,” he said of the museum world. One former museum director suggested that when a museum declines a gift, it can strain relations with a longstanding benefactor. Marc F. Wilson, who oversaw the Nelson-Atkins Museum of Art in Kansas City, Mo., from 1982 to 2010, said museums must be more careful but ought not leave benefactors feeling, in effect: “You can’t take my items? So you can’t take my $30 million either?”

Dougald O’Reilly, founder and director of Heritage Watch, a nonprofit that focuses on preserving Southeast Asian cultural heritage, sees it differently.

“In many cases collectors donate antiquities to museums for a tax break, hardly a completely altruistic act,” he said. “Why would it be objectionable to return the items to their country of origin? The oft-quoted reason is the ‘inability’ of developing countries to care for their antiquities. Surely it is time people stopped using this condescending argument.”

Despite the rhetoric, professionals on both sides are exploring ways to bridge the gulf. At the Asia Society forum Julian Raby, director of the Freer Gallery of Art and the Arthur M. Sackler Gallery at the Smithsonian Institution in Washington, urged a system under which American museums might provide funds for archaeological excavations and benefit by sharing the discoveries with host nations.

Mr. Houghton suggests creating an amnesty of sorts for collectors who post facts and photos about potentially contested artifacts on a “credible and neutral” database. If the item is not claimed after some number of years, he said, its ownership could no longer be contested. The museum directors’ association actually hosts such a Web site and asks that museums taking in an undocumented artifact post photos and other data that can be reviewed around the world.

Patty Gerstenblith, director of the Center for Art, Museum and Cultural Heritage Law at DePaul University in Chicago, said that four years after the Web site went up the number of items posted, more than 550 this week, seems small. (Two museums account for 418 of the items.) “This raises a serious question as to whether museums are failing to post their acquisitions on the registry,” she said.

Mr. O’Reilly said he did not believe that heightened scrutiny by museums or dealers threatens to orphan a large set of objects that were lovingly collected by people with a passion for antiquity. “That implies the collectors no longer want them if they can’t give them away, which surely is not the case,” he said.

Mr. Dershowitz said that while he is disappointed, he is not distraught about his inability to sell the wooden Egyptian sarcophagus he purchased from Sotheby’s. He had sent it to Christie’s several months ago for auction, but Christie’s demurred.

“They told me it was perfectly legal to keep or sell it,” he said, “but it was not their policy to sell it unless it was absolutely documented that it left Egypt before 1970,” something he and both auction houses are unable to establish. So for now it’s in limbo.

Meanwhile, he said, he had another Egyptian sarcophagus at home in Cambridge, this one of granite, that he bought for about $35,000 from Christie’s about the same time. He isn’t even trying to sell that one. “I’m keeping that in the house,” he said, “in the hall.”