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Revealing the invisible: using surface-enhanced Raman spectroscopy to identify minute remnants of color in Winslow Homer's colorless skies



The fading of pigments in items of importance to cultural heritage, such as paintings, works of art on paper, and textiles, is a ubiquitous problem. Tools currently available that can detect and identify organic colorants in severely degraded works of art are rare, given the heavy deterioration and restricted availability of the sample. Recently, however, surface-enhanced Raman scattering (SERS) spectroscopy has shown great promise in detecting and identifying mass-limited samples. The art conservation field has seized upon the opportunity opened up by this powerful analytical technique to enable the identification of microscopic amounts of organic molecules used as artists' colorants in complex matrices, such as biomaterials (i.e. dyed natural textiles, linseed oil biofilms present in oil paintings, etc.), a possibility that was previously precluded due to interfering fluorescence and small sample size. Here, we report SERS spectra recorded directly on single particles of red lake pigments from an important historical watercolor by the American master Winslow Homer (1836–1910) that suffered some degree of fading. The accurate colorant identification provided by SERS, enhanced by comparison with reference samples of historical watercolors, has thus enabled important discoveries regarding the materials and intended meanings behind artworks from one of the most influential American watercolor painters. Copyright © 2011 John Wiley & Sons, Ltd.