Self portrait of Max Liebermann. Photo: wiki commons.

The great-granddaughters of Max Liebermann, a renowned German-Jewish Impressionist painter, are asking the Berlin Museum to return two drawings their family lost due to Nazi persecution.

Liebermann was a major collector of pieces by other artists, including works by Edouard Manet, Edgar Degas, Claude Monet, Auguste Renoir and the two paintings in question by Adolph Menzel. Most of Liebermann’s collection disappeared in the Nazi era, and the Menzel paintings eventually found their way to the Berlin Museum.

Post-World War II laws stated that any art sales by Jews after 1935 likely came under duress and were therefore invalid. In 1998, the U.S. and 44 other nations required public museums to find “just and fair solutions” for the original owners of such lost art. The two Menzel paintings remained in the family until 1938. The family most likely had to sell them for food or medicine, supplies that were often restricted to Jews at the time.

Menzel was one of the most prominent artists of 19th-century Berlin. One of the pieces the family is demanding back is a pre-sketch for one of his famous paintings,  “Floetenkonzert” (Flute Concert), that shows Frederick the Great playing to an audience at Sanssouci Palace. The other sketch, “Koenigshuette,” shows a mining scene.

“The Prussian Cultural Heritage Foundation has been brooding over these drawings for more than three years,” said Monika Tatzkow, a researcher of Liebermann’s collection on behalf of the great-granddaughters, according to Bloomberg Businessweek. “It is completely incomprehensible. We know they were lost due to Nazi persecution.”

Stefanie Heinlein, a spokeswoman for the Prussian Cultural Heritage Foundation, the organization that runs Berlin’s museums would not release an official comment on the issue, but the foundation did recently return four other Menzel drawings to the Liebermann family.