According to London's National Gallery, where the painting is on display, the picture was painted on a wooden panel, which is very reactive to changes in humidity and climate. As a result, the altarpiece had already undergone several major structural changes before the Gallery acquired it in 1867.
In 2011, the gallery undertook one of its most intricate structural conservation projects to conserve the altarpiece for future generations. The gallery terms the conservation treatment as one of the longest and most complex in its history.
The treatment included removal of old varnish and re-paints done earlier on the altarpiece.
"Paint flakes that had been dislodged and stuck in wrong places during previous treatments were realigned. The hundreds of splits in the wood were levelled using pressure from above and below, then repaired with adhesive," the gallery said.
Severe woodworm damage, which happened before the painting entered the gallery's collection, along with wide compound fractures, required that missing wood to be built up.
A reinforcing structure was given in form of an auxiliary support.
"Finally, the losses to the paint were filled and retouched, and the panel was framed to ensure it could still move if it needed to."
The altar's biblical type of painting, called a "sacra conversazione" (holy conversation) between the Virgin Mary, Christ Child and Saints became increasingly popular over the course of the 15th century.
( With inputs from IANS )