The official unveiling of the restored exterior panels of The Adoration of the Mystic Lamb, an altar piece painted by the Van Eyck brothers in 1432, at Saint Bavo Cathedral in Ghent. [Photo/Agencies]

At the heart, or interior, of the work, there are three vibrant scenes, each one made up of four painted panels. The two outer scenes can be closed, meeting in the middle to cover up the central scene. On the reverse, or exterior, these panels are painted with more somber imagery.

Begun in 2012, restoration work has so far been completed on the exterior panels, which worshippers saw most often as the altarpiece would have been kept closed, except for major holy days and festivals.

In relatively muted tones－compared with the splendor and richness of the interior－they show the Annunciation, John the Baptist, the patron saint of Ghent－and the wealthy merchant and church warden Joos Vidjt and his wife Lysbette who donated the work to the cathedral.

But even these external panels show newfound life after the removal of a yellowish sheen which had drained the colors of their vibrancy.

The painting is complex, densely detailed and full of symbols relating to passages in the Bible and daily life at a time when Ghent was ruled by the Dukes of Burgundy, whose court was among the most flamboyant and refined in late medieval Europe.

Restoring space, light, color

During the work, the team of 10 restorers have had to very delicately chip away, centimeter by centimeter, at layers of discolored varnish and the "repainting" of early preservation efforts, some of which may date back to the 1500s.

"Nowadays, we would not cover over the original work but then, restorers would really have been painters themselves who would have repainted the whole thing, rather than just minutely retouch it bit by bit," Postec said.

"Before, there was just a uniform black background but we have found space, light," she said.

"We have also found folds (in the clothes) from the 15th century which were simply painted over and (this sort of detail) really changes how you see the picture."

Restoration work will now begin on the internal panels at the nearby Ghent Fine Arts Museum with the aim of finishing by 2020, when there will be a celebratory year dedicated to Van Eyck paintings.

Until then, reproductions will have to suffice for the thousands of visitors who come to Ghent to see a painting many consider second only to Leonardo da Vinci's Mona Lisa in artistic achievement and cultural importance.