Infrared Reflectography (IR)

The top layers of a painting become transparent when viewed in infrared light. The INOA scanner is a remarkable device which exploits a technique called infrared reflectography to harness this property of infrared light and produce very high resolution images, called reflectograms, compared to the usual reflectograms that can be obtained by standard equipment.

By capturing an image of the painting under these conditions, it is possible to reveal the drawings, or underdrawings, made by Leonardo as he composed his picture. The result of the scan has proved to be most fascinating. Not only are there significant changes in the composition of the work, suggesting that Leonardo was experimenting as he went along, it also revealed a number of small changes, or pentimenti, which occurred as the work was painted, suggesting that the great Leonardo may have felt the need to revise his composition as he went along.

Key among the changes revealed by the INOA scanner are:

· An architectural structure that once stood on the left of the painting, with an additional arch within the arched doorway. (There is another, smaller archway to the left of the Madonna’s head.) There is also a group of three or four people in front of the structure. · The Madonna’s headdress originally had a slightly different fold, higher up along the top edge.
· The profile of the upper part of a donkey can be seen to the right of the upper part of the yarnwinder.
· In the underdrawing, the Madonna’s left thumb curls upward against the chest of the child.
· There are a number of corrections, or pentimenti, to the child: the fingers around the yarnwinder have been moved, as have his arms; the left leg was once closer to a kneeling position and the right leg was originally more outstretched.
· The yarnwinder was originally positioned with the upper strut turned slightly towards the viewer while the lower strut was once much further up the winder.
· There were originally four or five spindles wound with possibly wool at the base of the cross.
· There is the suggestion of a mountainside directly behind the upper part of the yarnwinder.
· There seems to be an element resembling a rectangualr shape (perhaps a basket?) by the Virgin's left knee.

INOA scanner: technical specification
· The scanner acquire the image according to three colour channels (red, green and blue) and one infrared channel. In different combinations they are able to produce a colour image (RGB), a false-colour image (a type of optical analysis that allows the detection of pigments) and an infrared image (which exposes the underdrawings).
· The spatial resolution is 4 points per millimetre (16 points per millimetre squared).
· The scanner has a 12-bit range and is able to differentiate up to 1,000 grey levels.
· The maximum scanning size is 100cm squared.
· The scanning rate is 600hz.
· The “safe” working distance of the scanner from the painting is 150mm.