Visitors to the exhibition, “In Search of Matisse,” which runs until Dec. 13 at the Henie Onstad art museum near Oslo, will not be seeing one of the museum's prized Matisses. The 1937 painting “Blue Dress in a Yellow Armchair" was returned last year to the heirs of French art dealer Paul Rosenberg, whose collection was plundered by the Nazis more than 70 years ago.

London-based Art Loss Register records showed that Rosenberg purchased the work directly from the artist and kept it in his bank vault until Nazis stole it in 1940. After spotting "Blue Dress" on loan to Paris's Centre Pompidou in 2012, Rosenberg's granddaughter, Anne Sinclair, contacted the museum for the painting's return.

A three-year provenance research project by the museum ensued after the restitution of the Matisse. Discoveries about the collection were then compiled into a 160-page report. One surprise was a Paul Klee painting titled “Um Sieben über Dächern” (At Seven Above the Roofs) that documents revealed was hanging sideways in the museum's galleries. (The Klee was found to be legally transported before the war years.)

Details from the curators' sleuthing and the 19 paintings that were investigated are displayed in the exhibition along with other modern art that gives a picture of provenance during the World War II-era.

Much of the museum's holdings were formed from the private collection of shipping magnate Niels Onstad who married Olympic ice skater and Hollywood star Sonja Henie in 1956.