An X-ray – as used on the Millet picture – is the most common method of uncovering hidden paintings. Long wavelength X-rays are used because they are easily absorbed by paint. The degree of absorption depends on the type of paint. For instance, lead and cadmium-based paints are more absorbent than those containing chromium or cobalt. Thicker layers of paint will absorb more than thinner ones.
Photographic film is placed behind a suspect painting, and X-rays are passed through it from the front. When the film is developed, the ghostly outlines of earlier pictures may be seen.
In the early 1980s, for instance, two art restorers in Glasgow – both of them superintendents radiographers in a local hospital – X-rayed Rembrandt’s Man in Armour. They discovered what appeared to be a white plume blowing in the wrong direction from the top of the helmet. However, on turning the X-ray picture around, the ‘plume’ was seen to be part of an abandoned work by Rembrandt: a lady in a flowing white dress and headdress. Man in Armour is in the Glasgow Art Gallery and Museum.
Similarly, a painting by the 16th century Italian painter Paris Bordone – Saints Jerome and Antony Abbot commending a Donor – was found after X-ray to have two donors, one of them by an unknown artist. The painting is also in the Glasgow gallery.
X-rays are also used to study pentimento, the changes an artist makes while producing a painting. Alterations to the compositing, changes in the angle of an arm or a head, will all show up under X-ray, and are useful to art historians and restorers. (The word pentimento comes from the Italian word pentersi, ‘to repent’, suggesting a change of mind by the artist.)
Charcoal outlines
Infrared light is also used to discover paintings beneath paintings. When infrared light is shone on the picture it penetrates the surface paint and it reflected. The reflection is recorded on a camera. The effect is to make the thin, upper paint levels transparent, so revealing the charcoal outlines of the artist’s preliminary drawing. The technique has been used by New York’s Metropolitan Museum to study Flemish Renaissance paintings.
In some cases it reveals details not apparent on the final painting, and helps in understanding the artist’s technique.
Picture Credit : Google