How Infrared Light is used to Analyze Artwork
Infrared light is an electromagnetic light that falls between microwaves and visible light (Weiner, 1998). “Infra” is a Latin word that means below and therefore the word can be translated to mean below red light. Red light represents the visible light in the electromagnetic spectrum and therefore infrared which is below it is invisible to human eyes. Infrared light is used in different ways such as; in remote control devices, night vision equipment and sensor devices. Infrared light is also used in artwork as it enables art historians to observe invisible details of ancient fragments and painting. This paper will focus on how infrared light is used to analyze artwork.
Analysis of Painting Using Infrared Light
Art historians usually encounter the difficult task of having to determine whether a piece of work is original or not. These professionals utilize various skills in performing this task. Infrared light provide a visualization tools that enables the historians to verify the originality of paintings (Kammerer, Hanbury & Zolda, 2001). It does this by comparing the surface painting of a piece of work and the under-drawing or outlines drawn by the original artisan as blue prints. This technique is referred to as infrared reflectography. In any painting, under-drawings are usually covered by painting and it is difficult to view them without spoiling the cover paint. Art historians, using infrared light are able to evaluate whether the visible layers of paints differ from the under-drawing. This deviance by paint from original sketches or outlines is termed as pentimenti.
Apart from identifying an original from non-authentic painting, art historians use this technique of comparing painting designs and background sketches to understand the creative process of the original artisan (Kammerer, Hanbury & Zolda, 2001). This is a more complex analytic aspect of art. Through infrared lights art historians are able to conduct visual inspections on painting and view all the concealed sketches made by the original artisan before coming up with the final painting. Through this process, the historians are able to get an insight concerning the genesis of the painting, the painter’s original ideas and the complexity of the final work. It also enables the art historians to identify the style, techniques of the artisan, painting creation process, conservation history and materials used in painting (Jide, 2000). Through infrared reflectography, art historians are also able to determine whether the background drawings were intended to be rigid models or loose concepts for the final artwork.
Under-drawings in paintings can be described as the preparatory drawings for the painting, which are sketched on a medium prior to the actual painting (Weiner, 1998). The under-drawings are later covered by paint such that they are no longer visible to the work observers under normal circumstances. The under-drawings vary in terms of details and the variation may be dependent on the artist, type of material used, technology used in the drawings among others. Art historians get a better understanding about a painting by evaluating these under-drawings.
Infrared reflectography enable analysis of artwork by making colors used in the painting transparent thereby giving visibility to the underdrawing (Kammerer, Hanbury & Zolda, 2001). Infrared reflectography reveals under-drawings when paintings are exposed to waves in the spectral range of 800 to 2400 nm. Functioning of infrared reflectography is usually dependent on the ability of the material used in the underdrawings to reflect the infrared radiations. Middle age painters used material such as charcoal, chalk or paint to make the under-drawings. Such materials have higher capability of reflecting infrared light.
Underdrawing made using materials such as red chalk, which have limited ability to reflect infrared light, become invisible to infrared light and hence cannot be analyzed. The functioning of this technology also depends on the type of paint used. The paint material must have limited ability to reflect the infrared rays so that they can allow as much infrared light to pass through. Many middle ages color pigments become transparent when illuminated by this light. Paint that have utilized color pigments containing large amount of energy absorbing carbons become inappropriate to analyzed as such paint absorb much of the infrared light and thus little light passes through to the under- drawing. The thickness of the paint also matters.
How this Technology Works
As mentioned in the above discussion, infrared reflectography gives visibility to the under-drawing by making the paint visible. But how does this happen? Infrared light has a way of eliminating the value component of the paint image that covers the under-drawing (Kammerer, Hanbury & Zolda, 2001). Both visible light and infrared light are part of the electromagnetic spectrum. However, visible light cannot penetrate the color pigment on the paint while infrared light is capable of penetrating most of the color pigment. This secret lies in the interaction between the color pigments and the radiation and most importantly the wavelength of the light.
According to Kubelka- Munk Theory, when the paint is exposed to any form of radiation, the radiation is partly absorbed and partly scattered (Weiner, 1998). The scattered radiation causes diffusion of light which is then reflected by the diffusing material, in this case paint. This is what makes the paint visible under normal light. The strength of the diffusion of light is dependent on the scattering power of the paint and the thickness of the paint layer. Longer wavelengths reduce the scattering by particles. Therefore, with longer wavelengths the radiations are able to penetrate through the layer of paint without much of it being diffused. After successfully penetrating the paint layer, these radiations are reflected by the under-drawings causing their visibility. Infrared light has longer wavelength than visible light and therefore the former is able to penetrate better through the paint.
Evolution of Infrared Reflectography Technology
Infrared analysis of painting can be traced back to the 19th century when there used to be the infrared photography technology (Weiner, 1998). This technology had a limitation as it was unable to penetrate most of the paints and had to pave way for the infrared reflectography technology. Infrared reflectography was first developed in 1960 by Asperen de Boer. He used lead sulfide detectors with a peak response of 2 microns. Asperen first invention utilized a Barnes T-4 infrared camera but later shifted to vidicon television system. This system enabled digital analysis of painting by connecting the vidicon tube that has a television camera to a Digital Image Processing system. This system also had a limitation as the vidicon tubes were highly sensitive and could be damaged by continued exposure. Infrared technology then progressed to the use of a silicon CCD camera. This system was found to be more stable and has remained in use to date.
Infrared reflectography has become the main technique used by historians to analyze artwork by studying the under-drawing. This is because this technique has two advantages. First is that, it does not interfere with the painting. Infrared light only serve to make the paint covering the under-drawings transparent, otherwise the paint remains intact. Secondly, infrared reflectography does not enable the viewing of the underdrawing in isolation but combines the view of the color image and the background image (Kammerer, Hanbury & Zolda, 2001). The combination of these two images has its own advantages in the analysis of art work. First, it gives the historian the ability to localize points in the under-drawn images to the corresponding points on the paint image. Second, using search a view the historian can easily identify similarity and difference between the under-drawn images and the paint image.
Apart from infrared reflectography, there are also other imaging technologies that are used to analyze artwork. These include; x-radiography and ultra violet light (Jide, 2000). However these technologies work in different ways and are used for different purposes. X-radiography is used to identify color pigments and determine color composition. Ultra violet light on the other hand, has the ability to make colors to fluoresce and therefore is used to identify original colors of different artworks.
Imaging technologies have revolutionized the ways in which analysis of artworks is conducted. The infrared reflectography is one such technology. This technology uses infrared light to penetrate color pigments on painting making the under-drawing of the painting visible to the art historians. Access to the under-writings gives the art historians the powers to determine; the authenticity of the work, creativity process, the painter’s ideals, skills and technologies, material used in the painting and the complexity of the painting.
Jide (2000). Analyzing Arts Beneath the Canvas. April 15, 2011. Available at http://researchforward.wordpress.com/2007/06/20/analyzing-art-beneath-the-canvas/
Kammerer P. Hanbury A. & Zolda E. (2001). A Visualization Tool for Comparing Paintings and Their Under-drawings. April 15, 2011. Available at citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.4.7934
Weiner C (1998). Improved Acquisition of Under-Drawings in Oil-Painting Using IR- Reflectography. Rochester Institute of Technology. April 15, 2011. Available at https://ritdml.rit.edu/bitstream/handle/1850/5811/CWeinerThesis05-1998.pdf;jsessionid=451CE08C085523040BFF7ABF26900519?sequence=1