Conservation departments
'Pieta' by Ercole de' Roberti from the Walker Art Gallery
Accession number WAG2773
Although this looks like an ordinary painting it actually has a hidden secret. The back of the painting, pictured below, reveals a keyhole at one side which was skilfully filled in before the painting was started.
The x-ray of the painting clearly shows how the keyhole originally went right through the panel, to the left of where the figures now are.
This seems to be an example of a door becoming a painting, possibly the thrifty recycling of a good piece of wood. In contrast, 'St Michael and the Dragon', from the Lady Lever Art Gallery's collections, was originally a painting that was converted into a door and later changed back.
Detail of an x-ray of the painting, showing the keyhole,
and a close up view of the filled-in keyhole on the back of the panel