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Scanning for Secret Images

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1366622.  Sat Nov 28, 2020 9:45 am Reply with quote

Paintings, and art works in general, can often be more complicated than they appear at the surface. Scanning techniques based on infrared light and x-rays can be used to reveal more about what lies beyond the visible surface of an art work.

The oldest of the scanning techniques used is x-radiography, which came into use within the art world early in the twentieth century. An X-ray of a painting can show where heavy element pigments, such as lead white or vermillion which contains mercury, are found within a painting. It creates a black and white photograph which is often used to determine the condition of a work of art as well as elements of the painting process. Using this technique in 2017, a hidden image was found in a painting of Sir John Maitland (1589, by Adrian Venson). A depiction of Mary Queen of Scots became recognisable in the x-ray image. Caroline Rae, who conducted the research, stated that the reason Mary had been overpainted may well have to do with the political tensions that arose after Mary's execution in 1587. It could have been dangerous to have an image of the queen on display during this time.

X-radiography has also revealed the re-use of a canvas when the initial painting was not profitable or a new commission came in. Sometimes in an x-ray image, the image of the painting is visible as well as an upside down or turned previous composition. Furthermore, smaller, but significant changes to a final composition can be identified in an x-ray image. Finding these previous compositions or compostion changes can tell us a lot about an artist's working process as well as about the history of an art work (the support for instance a panel or canvas and stretcher, as well as evidence of conservation/restoration treatments). Sometimes, eveidence can be found in x-rays of the cutting down of the original canvas, or the attachment of another strip of canvas. Arthur Melville's 'Audrey and Her Goat' has been manipulated both in compositon as well as in size and shape of the canvas. X-radiography of the painting allowed for the identification of these alterations.

X-ray techniques have been in continuous development since its first use within the art world. Nowadays a separate x-ray technique is used that allows for the identification of elements in a specific spot of a painting. This technique can be used in a handheld version, which allows for the reading of elements in a specific spot. But this technique is also used on a macro scale in which an entire painting is carefully scanned, allowing for the generation of element maps. Element maps can show where in the painting a specific element can be found. This can be useful for determining which pigments were used.

A separate technique is Infrared Reflectography. This technique uses infrared light and its reflection of the paint surface to create a black and white photograph. The longer wavelength of the infrared light allows it to penetrate further through the paint layers than our normal visible light. The light is then either absorbed by pigments, often carbon containing, or drawing materials such as charcoal. This technique is often used to identify underdrawing, a step within the traditional painting process in which the artist lays out their composition in charcoal or chalk after which they paint the composition. Underdrawings can consist of a few lines or can be very extensive, delineating the entire composition. It can occur that the underdrawing does not quite match the painting visible to the naked eye. This often relates to changes in the composition. However, it is also possible that initially the artist meant to create a different composition but changed his mind. This can result in there being two compositions overlaying each other in this underdrawing.
Infrared reflectography can also be used to determine changes in the composition made during the painting process as certain pigments also absorb the infrared light.
Not every painting has an underdrawing and not every painting with an underdrawing can be identified with infrared reflectography due to the interference of the paint layers or the drawing material used.

A final technique that is often used on paintings is Ultraviolet light photography. A photograph is made of a painting exposed to ultraviolet light. Varnish layers as well as some pigments emit a fluorescence in uv light. This technique can be used in the identification of varnish used on a painting as well as to determine potential previous restoration/conservation treatments.

All of these techniques can be used without taking microscopic samples from a painting. These samples can exist out of only a few or over more than ten different paint layers. They can be rather beautiful to look at as well as providing crucial information about the painting process of an artist and the materials they used. Sampling of art works is a delicate process that can reveal lots about an art object. But that's something for another post maybe.


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