One of history’s most frequently stolen artworks, Hubert and Jan van Eyck’s “Adoration of the Mystic Lamb” — also known as the Ghent Altarpiece — is receiving a massive restoration, the AFP reports. With its tumultuous history of being looted, hidden, burned, and torn apart, the large, multi-panel, oil-on-wood altarpiece is expected to take five years to restore, but the process will be visible (from behind glass) to visitors at the Ghent Fine Arts Museum.

Conservationists hope that the in-depth study of the panels, which included infrared macrophotography and X-radiography, will help to answer persistent questions as to the duration of time the panels took to complete, and which areas were painted by the brothers and their assistants.

“We have noticed huge differences in painting technique,” art historian Helene Dubois told the AFP. “There are very big differences in quality not only between the panels but also between different parts of one panel.”

Despite the many hands the panels have passed between and the many hardships to which they have been subjected, conservators are making progress on the remaining eleven panels — the panel entitled “The Just Judges” remains missing since its theft in 1934. A web project from Lasting Support and the Getty Foundation, “Closer to Van Eyck: Rediscovering the Ghent Altarpiece,” documents the original testing and assessment of the “Adoration of the Mystic Lamb.”

“All in all there are no catastrophic gaps, no faces or key elements have been badly damaged or attacked,” project leader Livia Depuydt-Elbaum told AFP. “With time, colors fade, materials alter. But we can get closer than has ever been possible before.”