His work usually has to be nude to be this notorious

Paul Gauguin abandoned his family in France and sailed around the world seeking paradise in Polynesia. He married a 13-year-old Tahitian girl. “Are you not afraid of me?” he asked.

That type of thing is frowned upon today, and the placard next to one of Gauguin’s paintings in the Art Institute of Chicago dispatches the issue thus: “Gauguin’s predatory behavior toward young girls was a well-documented and integral aspect of his self-fashioned artistic persona.”

OK then. Gauguin’s paintings are still on display, as they should be. Qualms over the personal lives of artists are so random. The Medicis were bad guys, too.

Yet time mediates their excesses. As does fame. No matter how badly Picasso treated his mistresses, his big rusty baboon — made of the same COR-TEN steel as the building behind it — will still be on display at the heart of Chicago.

Art is a window into the past, and the past is often a terrible place. The Art Institute is being vigorously reminded of this over a small pencil drawing — 17 inches by 12 — tinted with watercolors, “Russian War Prisoner.” An undistinguished sketch by Austrian artist Egon Schiele, possessing none of the raw sexuality for which he was infamous.

Schiele died at 28 of the Spanish flu, and the drawing came into the possession of Jewish cabaret star Fritz Grünbaum, whose art collection was mostly snatched by the Nazis after he was shipped to Dachau concentration camp.

Except this drawing, the Art Institute insists. The Nazis missed this one. Maybe they were careless.

His heirs disagree, and have been suing to get the collection back. Nine of 10 works have been returned. My colleague Emmanuel Camarillo has been documenting the lawsuit, which accuses the museum of “willful blindness.”

Given in memory of Gloria Brackstone Solow from Dr. Eugene A. Solow and Family/Art Institute of Chicago

The Art Institute claims it legally owns the work, insisting that, unlike its unfortunate owner and his larger collection, the Nazis never got their hands on that particular drawing and Grünbaum’s sister-in-law sold it after the war.

Art has trends like anything else, and the latest rage is for treasures to find their way home. Nigeria is hoping to draw tourists with the Benin bronzes, scattered across the world after being looted by British troops in 1897, now flooding back. The Smithsonian returned 29 bronzes; the British Museum refused, no doubt thinking of the Elgin Marbles. The Greeks opened a museum at the foot of the Acropolis in 2009, with plaster stand-ins for the friezes pried off the Parthenon.

The Brits have yet to take the hint, but they should, whether Lord Elgin got a receipt from a nearby goatherd or not.

It’s easy to give other people’s possessions away, and if the Art Institute indeed owns the thing — as has been ruled previously in court —then it’s hard to fault them for keeping it. The art world is not for the squeamish.

That said, this may be a situation where being right, legally, is secondary to the terrible optics. It might be easier if the Art Institute gives it to the heirs, then later buys back the doodle with the $1 million they won’t be losing from donors who won’t become disgusted and stop supporting the museum for keeping tainted goods. They’ll surely make money on the deal.

Bottom line: Whoever ultimately gets the sketch, the media is highlighting Egon Schiele, and how cool is that? How would that be possible otherwise? We don’t give the role of notoriety its due in art.

Paul Chabas’ “September Morn” was anonymous soft porn kitsch in a Wabash Avenue shop window in 1913 when Chicago’s mayor at the time, Carter Harrison Jr., sent the city’s official art censor to buy a copy. Now the original is owned by the Met.

The “Mona Lisa” is by no means the best Da Vinci in the Louvre, never mind the greatest painting in the world. Yet tourists hurry past better paintings to jam a room — crowded as an L car and smelling like a high school locker room — to take selfies before it. Why? Because the “Mona Lisa” was stolen in 1911 — when it was so obscure the Louvre didn’t realize it was missing for a day. The painting became famous, a notoriety that continues to this day.

Schiele, by the way, gave Gauguin a run for his money in the bad man department, between incest with his 12-year-old sister, and his arrest for seduction of a 13-year-old. I suppose the Art Institute will explain all that on a card when it puts the work on display and visitors flock to see it.