Noninvasive Methods in Examining Valued Artwork and its Preservation
Noninvasive Methods in Art Conservation
The field of art conservation deals with expensive and irreplaceable artwork, and thus requires noninvasive methods of examination, or minimal sampling at most. Specifically, the preservation of paintings requires knowledge of paint layers and pigments in order to fully analyze the artwork and determine how it will age over time. In order to accomplish this, conservators utilize noninvasive methods such as Raman spectroscopy and reflectance spectroscopy.
Raman Spectroscopy
Raman spectroscopy was discovered by physicist C.V. Raman in the 1920s and has applications in a large range of science fields, from biomedicine and forensics to art conservation (L’Heureux). Raman spectroscopy (in addition to Raman microspectroscopy) analyzes inorganic pigments used in paintings, which is important because all colors age, decay, and react to chemicals in different ways. Raman spectroscopy also proves useful when determining what a painting looked like in its original state versus its present state, which can change the way people view the art. A downfall of Raman spectroscopy is that it does not work with fluorescent colors like yellow and red – upon encountering fluorescence, the Raman spectrum of these colors is obscured and cannot be analyzed.
In terms of detecting organic pigments and analyzing fluorescent colors, conservators can utilize surface-enhanced Raman spectroscopy, though this requires minimal sampling (Mukhopadhyay).
Reflectance Spectroscopy
Reflectance spectroscopy also identifies pigments in oil and watercolor, in addition to monitoring how these colors change over time. Specifically, fiber optics reflectance spectroscopy is helpful in identifying the normally hard-to-pinpoint organic dyes, most commonly found in East Asian art. These natural pigments are extremely difficult to identify because they absorb light strongly and thus appear very diluted in paintings. Reflectance spectroscopy works in spite of this, and can even identify pigments in thin washes or mixed with other colors. Downfalls of this technique include poor wavelength and “fingerprinting” ability (Leona and Winter).
Note: I am following the format of the L’Heureux article.
Small-scale fiber optic reflectance spectroscopy, for low budget art conservation. This is a chart for pigment identification and comparison. (Source: http://chsopensource.org/2014/11/10/fors-reflectance-spectroscopy-for-pigments-tested-bwtek-mini-spectrometer/)
References
Bacci, Mauro, Picollo Marcello, Trumpy Giorgio, Tsukada Masahiko, and Kunzelman Diane. “Non-Invasive Identification of White Pigments on 20th-Century Oil Paintings by Using Fiber Optic Reflectance Spectroscopy.” Journal of the American Institute for Conservation 46.1 (2007): 27-37. Web.
Leona, Marco, and Winter John. “Fiber Optics Reflectance Spectroscopy: A Unique Tool for the Investigation of Japanese Paintings.” Studies in Conservation 46.3 (2001): 153-62. Web.
L’Heureux, Megan. “Analysis of the state of the art: Raman Spectroscopy.” Spectroscopy June 2015: 44+. Academic OneFile. Web. 25 Sept. 2016.
Mukhopadhyay, Rajendrani. “Spectroscopy in Art.” Chemistry World Jan. 2010: 44-47. Print.
Pouyet, Emeline, et al. “Thin-sections of painting fragments: opportunities for combined synchrotron-based micro-spectroscopic techniques.” Heritage Science 3 (2015): 3. Academic OneFile. Web. 25 Sept. 2016.
