McGill chemists using a technique known as photoacoustic infrared spectroscopy say they can  identify the composition of pigments used in art decades or even centuries old.

Pigments give artist's materials color and they emit sounds when light is shone on them, and Fourier-transform photoacoustic infrared spectroscopy is based on Alexander Graham Bell's 1880 discovery that showed solids could emit sounds when exposed to sunlight, infrared radiation or ultraviolet radiation.

More recent advances in mathematics and computers have enabled chemists to apply the phenomenon to various materials.   The McGill team is the first to use it to analyze twelve inorganic pigments that most artists use - cobalt blue, ultramarine blue, Prussian blue, azurite, malachite, chromium oxide, viridian, cadmium yellow, chrome yellow, iron oxide, yellow ochre and Mars orange - by the infrared spectra they exhibit (the range of noises they produce) and they hope the technique will be used to establish a pigment database.    

"The chemical composition of pigments is important to know, because it enables museums and restorers to know how the paints will react to sunlight and temperature changes," explained Dr. Ian Butler, lead researcher and professor at McGill's Department of Chemistry.

Without a full understanding of the chemicals involved in artworks, preservation attempts can sometimes lead to more damage than would occur by just simply leaving the works untreated.

"Once such a database has been established, the technique may become routine in the arsenal of art forensic laboratories," Butler said.

The next steps will be to identify partners interested in developing standard practices that would enable this technique to be used with artwork.

Citation: Eleanor L. von Aderkas, Mirela M. Barsan, Denis F.R. Gilson and Ian S. Butler, 'Application of Photoacoustic Infrared Spectroscopy in the Forensic Analysis of Artists’ Inorganic Pigments', Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy(in press) doi:10.1016/j.saa.2010.08.027