AMSTERDAM (Reuters) - Rembrandt’s 17th century masterpiece “The Night Watch” begins restoration work on Monday in Amsterdam where visitors will be able to watch every step of the Rijksmuseum’s biggest ever project.

The 3 million euro ($3.4 million) effort is expected to take about a year, museum director Taco Dibbits said.

That is due not only to the fame of the painting, which dates from 1642, but also to its size, as the canvas measures 3.63 by 4.37 metres (11.9 feet x 14.3 feet) and weighs 337 kg (742 pounds).

The painting will remain in its usual spot at the end of the Gallery of Honour in the Rijksmuseum and visitors will be able to watch from behind a glass wall as experts restore it.

Painted over several years, “The Night Watch” was commissioned as a group portrait of an Amsterdam city militia and broke new ground by showing its subjects in action rather than as a static portrait.

Experts argue over whether it was intended as a night scene or whether it is simply perceived as such because of Rembrandt’s use of shadows pierced by light.

Restorers will begin by taking thousands of high-resolution photos of the work from every angle and scanning it with lasers.

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“Those you have to stitch together so you get one image and then we will be able to see which changes Rembrandt made” as he worked, Dibbits said.

Restorers want to learn “which pigments were used, so which paint he basically used, and also how we can treat it.”

The painting was most recently restored after a man attacked it with a knife in 1975.

($1 = 0.8907 euros)