Countries such as Germany, Austria, France, the United Kingdom and the Netherlands all have national commissions that act as arbitrators in cases of allegedly Nazi-seized art. These commissions take only the merits of a given case into account – not individual laws of the host country.
The creation of the commissions stems from the 1998 Washington Conference Principles on Nazi-Confiscated Art, a non-binding international agreement that the United States and dozens of other nations have signed that calls for openness and transparency in the recovery of Holocaust-era art.
The pact says that "consideration should be given to unavoidable gaps or ambiguities in the provenance in light of the passage of time and the circumstances of the Holocaust era" and that parties to the agreement are "encouraged to develop national processes to implement (the conference's) principles."
The United States has not created a commission to handle the claims. Most U.S. museums are private rather than government-owned, so they don't have to make public what they have if they don't want to.
People who suspect a U.S. museum of having looted art must go through the courts, which usually support the claims of the possessors of the artwork, experts say.
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"Our museums in the U.S. are much more secretive and don't really research or publish the knowledge about their collections," said Raymond Dowd, a New-York-based lawyer who has represented the Groszes and other families trying to reclaim art. "The Germans are much more open, and they have the additional pressure of national commissions that were agreed to by the Washington principles."
In the Grosz case, his heirs seek return of three works. Self-Portrait With a Model portrays the artist painting a voluptuous model standing in front of a mirror. The Poet Max Herrmann-Neisse is a portrait of the writer, aged and slumped in a chair. Republican Automatons is a watercolor depicting clockwork automatons standing on a city street, one of which is holding a German flag.
George Grosz was a German artist whose drawings of Berlin life in the 1920s often depicted its seamier side. He was anti-Nazi and fled to America before Hitler came to power out of fear that he would be persecuted as a degenerate artist. He left behind with his art dealer artworks that eventually turned up at MoMA in the 1940s and 1950s – two from private purchase and one that was donated.
Grosz himself saw The Poet Max Hermann-Neisse hanging in MoMA in 1953. He wrote his brother-in-law that the museum was displaying a painting stolen from him, but he made no effort to have it returned and died in 1959.
His son, Martin, and his daughter-in-law, Lilian, investigated the paintings and made their first formal request to have them returned in 2003. They argued that Grosz's Jewish art dealer had been coerced into selling or abandoning the paintings and that subsequent paperwork was falsified to make the provenance of the paintings appear legitimate.
MoMA's experts concluded that the sales had been made fairly. The Groszes sued.
Lilian Grosz said their lawyers had warned them that the case would face an uphill battle. When a court dismissed the lawsuit in 2011 on grounds that they had been too slow to file their claim, it nonetheless came as a surprise to the family.
"You know the song, 'Whatever Lola Wants, Lola gets'? Whatever MoMA wants, MoMA gets," Lilian Grosz said.
In an e-mailed statement, the MoMA said it has proper ownership and did nothing wrong.
"After years of extensive research, including numerous conversations with Grosz's estate, it was evident that we did, in fact, have good title to the works by Grosz in our collection and therefore an obligation to the public to defend our ownership appropriately," the museum stated.