Historians estimate that more than 5 million artworks illegally changed hands during the Second World War in Europe. But despite the dimension of the crime, the question of works that were looted from Jewish owners remained the elephant in the room for much of the 20th century.

It was only in 1998 that representatives of 44 countries convened in Washington D.C. to establish a set of principles to help descendants reclaim their family's art. The goal of the non-binding Washington Principles on Nazi-Confiscated Art was "to complete by the end of this century the unfinished business of the middle of the century," declared Stuart Eizenstat, the US official who hosted the conference.

The guidelines were praised as revolutionary at the time.

Read more: Nazi-looted artwork in Gurlitt collection belonged to French resistance politician

Undue optimism?

Twenty years later, the promise of restitution has still not been realized. "The Washington Principles have been a failure," says historian Marc Masurovsky, co-founder of the Holocaust Art Research Project (HARP).

Masurovsky established HARP in 1997 to focus on archival research, and unwillingly became a restitution activist through this work. He says he can name a dozen cases off the top of his head of claimants who are still seeking justice.

Eizenstat's vision proved over-optimistic. More than 100,000 paintings remain lost to this day. Some of the cases brought by heirs seeking the return of works by artists like Picasso and El Greco from museums have been going on in court for decades.

The dream of every provenance researcher: an inventory of looted art. Hitler's last known personal art album lists works stolen by the Nazis during the war

Before 1998: 'Don't mention the war'

"The glass is maybe slightly more than half full," Eizenstat admitted in a recent interview, however adding, "Just think of where we were before 1998. We would not be anywhere without the Washington Conference."

For most of the second half of the 20th century, the trajectory of works between 1933 and 1945, or their so-called provenance, was a topic that curators all over Europe aptly side-stepped.

"When I started working for the auction house in the mid-90s, the motto was 'Don't mention the war,'" Lucian Simmons, the head of provenance research at Sotheby's, said at a recent conference in Berlin, "and if one object had once belonged to Goering, you'd be encouraged to leave that out and write 'formerly owned by senior Nazi official.'"

Read more: 80 years ago: How 'degenerate art' purges devastated Germany's museums

The legal context was also adverse to restitutions. In Europe, private claims were almost universally time-barred under national property laws, which meant that a rightful owner's claim to looted items simply elapsed after a given period of time, 30 years in Germany, after the theft. In the pre-internet era, that period was far too short to trace an object that could have been anywhere in the world. In some countries like in France, cultural property laws forbade the removal of any art from the state's collection.

The most important contribution of the Washington Principles was that it stated a moral principle. It said: "Of course property law should be applied, but the issue of looting of art that happened during the Holocaust was out of the ordinary." In the declaration, the signatories also formulated the goal of total transparency of museums' collections and unrestricted access to archives. The declaration encouraged governments to create structures to allow pre-war owners to find their art and achieve what they called a "just and fair solution."

"Winter Garden," a Manet painting discovered in a salt mine vault in 1945

'The smallest common denominator'

Every time the phrase "just and fair solution" is mentioned, Masurovsky gets agitated. There is nothing just and fair, he claims, about the Washington Principles. For him, the declaration disregards the claimants' perspective. "Stuart Eizenstat admitted that he used the guidelines published by American museums for his draft. Just imagine! It is precisely American museums who have historically fought against restitution the most relentlessly!"

But the crux of the issue for Masurovsky is that the principles were non-binding. "Everyone went home satisfied — they hadn't committed to anything but the smallest common denominator."

As detailed in a report by the Claims Conference in 2014, the majority of nations who signed the Washington Principles have since done next to nothing. Only five countries out of 44 — Germany, France, the Netherlands, Austria and the UK — have fulfilled the request to provide "alternative dispute resolution mechanisms for resolving ownership issues." Because statutes of limitation mean that claimants have very little chance of recovering family property in court, such bodies are absolutely vital.

Read more: 'Suspicious' art from Nazi dealer to go on show in Germany

Where do Germany and the US stand?

In the US, attempts to create such a panel failed, leaving heirs at the mercy of an expensive court system when making a claim. And yet, the US remains one of the most favorable jurisdictions for claimants, in part because of the Holocaust Expropriated Art Recovery Act (HEAR Act) signed in 2016. Since then, judges have recognized the principles as part of US policy and turned down foreign governments seeking to dismiss cases against them.

In Germany, it was more the discovery of thousands of artworks in Cornelius Gurlitt's apartment than the Washington Principles that prompted a nationwide debate about looted art.

Where did the Gurlitt collection artwork come from? Max Beckmann, Zandvoort Beach Cafe, 1934 The watercolor by the Jewish painter Max Beckmann entered Gurlitt's collection only in 1945. Held by the allied occupation forces at the Central Collecting Point in Wiesbaden from 1945-1950, it was returned to Hildebrand Gurlitt in 1950. Before working for the Nazi regime, Gurlitt had collected and exhibited modern art, curating Beckmann's last exhibition in 1936 before the artist fled Germany.

Where did the Gurlitt collection artwork come from? Otto Griebel, Veiled Woman, 1926 This work was owned by lawyer and art collector Fritz Salo Glaser. Artists of Dresden's avant-garde scene were his guests in the 1920s — as was the young Hildebrand Gurlitt. It is not known how Gurlitt came to possess the painting. It was confiscated in 1945 and later returned. Of Jewish heritage, Glaser only narrowly avoided deportation to the Theresienstadt concentration camp in 1945.

Where did the Gurlitt collection artwork come from? Claude Monet, Waterloo Bridge, 1903 This painting by the famous impressionist is not suspected to have been looted. The artist sold it to the Durand Ruel Gallery in 1907. The Jewish art merchant and publisher Paul Cassirer is said to have given it to Marie Gurlitt as a present, and she left it to her son Hildebrand Gurlitt in 1923.

Where did the Gurlitt collection artwork come from? Thomas Couture, Portrait of a Seated Young Woman, 1850 This work by the French painter was only recently identified as a looted work of art. A short handwritten note was the clue for the provenance researchers. The picture was quite likely in the collection of the Jewish politician Georges Mandel, whose family stakes a claim to the work. It is not known how it came into Gurlitt's possession.

Where did the Gurlitt collection artwork come from? Auguste Rodin, Crouching Woman, approx. 1882 Hildebrand Gurlitt must have acquired this work by the French sculptor between 1940 and 1945. Previously belonging to the Frenchman Eugene Rudier, it entered circulation in 1919 at an auction by Octave Henri Marie Mirbeau, who is said to have received it as a present from the artist.

Where did the Gurlitt collection artwork come from? In Gurlitt's apartment Cornelius Gurlitt hoarded the sculpture along with many other artworks for decades in his Munich apartment. Before his death in 2014, he consented to have his stocks researched and — should they include articles of stolen art — have them returned to their rightful owners in accordance with the Washington Principles on Nazi-looted art.

Where did the Gurlitt collection artwork come from? Albrecht Dürer, Knight, Death and Devil, 1513 This copper engraving by Albrecht Dürer once belonged to the Falkeisen-Huber Gallery in Basel. It is not known how it got there or how long it was there however. In 2012 the engraving turned up in Cornelius Gurlitt's collection. "Old masters" like Dürer were very important to the National Socialists' view of art and were often exploited for propaganda.

Where did the Gurlitt collection artwork come from? Edvard Munch, Ashes II, 1899 The provenance of this drawing is completely unknown. It is certain, however, that Hitler considered Norwegian artist Edvard Munch's work "degenerate art." Some 82 pieces by Munch were confiscated in German museums in 1937.

Where did the Gurlitt collection artwork come from? Francois Boucher, Male Nude, undated Hitler venerated 18th century French painting. He secured exceptional paintings for his own collection by targeting the collection of the Rothschild Family after the annexation of Austria. Hildebrand Gurlitt supplemented them with drawings by renowned French painters. He acquired this work by Boucher from a Parisian art merchant in 1942.

Where did the Gurlitt collection artwork come from? Carl Spitzweg: Alpine Valley with Dairymaid, 1871 This painting was probably Hitler's personal property from 1934 onward. Not a part of the Gurlitt collection, it has been on loan from the Federal Republic of Germany since 1973 and shown in Dusseldorf's Kunstpalast Museum. The image reflects Hitler's taste in art, and he wished to have such works at the "Führer Museum."



Provenance research has massively increased ever since. The Lost Art Internet Database currently lists more than 34,524 items from public museums with a suspicious provenance. Fifteen years ago, it listed only a few hundreds.

Yet Germany's litigation system has been regularly castigated.

For one thing, the country does not have a restitution law like Austria, which some say would significantly accelerate restitution claims.

Secondly, the so-called Limbach Commission, a panel convened by the German government to give recommendations on restitution claims, can only intervene if both sides agree to sit at the table. Several museums have unsurprisingly refused to do so in the past.

Lastly, no nation in the world was able to coerce private collectors or auction houses into divulging the provenance of their artworks. While some big auction houses like Sotheby's and Christie's now have sizeable provenance departments and probe every object before they sell it, many art dealers still shield behind business confidentiality. As long as this is the case, much of the looted art will remain unavailable to potential claimants, says Marc Masurovsky.

For all the declaration's shortcomings, it is still a fact that the issue of looted Jewish property has become an integral part of the public discourse related to the Holocaust. But as the last historical witnesses are dying out, experts in the field are growing restless. They know progress takes time, but it's getting late.