Still damaged but now a bit younger than originally thought, Edvard Munch's The Scream will return to public display at Oslo's Munch Museum on Friday.

Restoration experts hope that they will be better able to repair moisture damage to Edvard Munch's The Scream sometime in the future, when better technology exists. (Stian Lysberg Solum/Scanpix Norway/Associated Press)

Despite extensive restoration efforts, The Scream — one version of Munch's masterpiece — and another piece called Madonna still show some of the physical damage the two canvases suffered after they were snatched from the city-owned museum in 2004 and passed around by the thieves for two years after that.

"There has been an extremely comprehensive process to restore the paintings. There was significant damage," Gro Balas, chair of the Munch Museum board, told reporters on Wednesday.

For instance, rips in both canvases were repaired by meticulously gluing back each torn fibre individually.

"There is still a moisture stain on The Scream that cannot be repaired," Balas added, citing the damage on the painting's lower left corner.

Restorers chose not to proceed for fear of further damaging the two paintings, said Mette Havrevold, head of the Oslo art conservation department.

"Maybe more reliable technology will enable us to erase it in the future," she said.

Shortly after the two works were retrieved by police in 2006, they were briefly displayed to the public under protective glass before being transferred to conservation experts.

During the restoration process, however, the experts found evidence that pointed to this version of The Scream having been completed in 1910, rather than in 1893 as previously believed.

Munch, an Expressionist pioneer, created several versions of his key works, including four of The Scream, an iconic piece depicting an anguished subject screaming under a luridly coloured sky.

The original is in Oslo's National Gallery, while the stolen work — considered the main reproduction — and another version were given to the Munch Museum after the artist's death. A private collector owns the fourth.

After the theft, the Oslo museum underwent major security upgrades, with valuable works now displayed behind glass and all visitors passing through metal detectors.

With files from the Associated Press