Nondestructive Identification of Natural and Synthetic Organic Colorants in Works of Art by Surface Enhanced Raman Scattering

Abstract

We present a new method based on surface-enhanced Raman scattering (SERS) for the nondestructive identification of organic colorants in objects whose value or function precludes sampling, such as drawings, prints, historic and archeological textiles, handwritten or printed documents, and forensic evidence. A bead of a polymer hydrogel loaded with a solution containing water, an organic solvent, and a chelating agent is used to extract minimal amounts of the colorants from the work of art for SERS analysis. Using a gel as a medium for the solvent mixture confines its action only to the areas of the work of art covered by the gel bead. The gel bead is then removed from the work of art, covered with a drop of Ag colloid, and examined with a Raman microscope. Transfer of the dye from the substrate to the gel does not require removing a sample from the work of art, therefore preserving the physical integrity of the object. Spectrophotometric color measurements confirm that color change is below the limit perceivable by a human observer. Finally, the size of the polymer bead can be reduced to a fraction of a millimeter in order to further minimize any impact on the work of art, without detriment to the effectiveness of the method. The technique has been successfully used for the analysis of a mordant dye on the 15th century Netherlandish tapestry, “The Hunt for the Unicorn”, and of a synthetic lake pigment on a Meiji period Japanese woodblock print.

Marco Leona†, Peter Decuzzi‡, Thomas A. Kubic‡, Glenn Gates§, and John R. Lombardi

^† Department of  Scientific Research, The Metropolitan Museum of Art, 1000 Fifth Avenue, New York, New York 10028, United States

‡ John Jay College of Criminal Justice, CUNY, 445 West 59th Street, New York, New York, 10019, United States

^§ The Walters Art Museum, 600 N. Charles Street, Baltimore, Maryland 21201, United States

Department of Chemistry and Center for Analysis of Structures and Interfaces (CASI), The City College of New York, New York, 10031, United States

Anal. Chem., 2011, 83 (11), pp 3990–3993   DOI: 10.1021/ac2007015                           Publication Date (Web): April 28, 2011      Copyright © 2011 American Chemical Society

E-mail: marco.leona@metmuseum.org Phone: (212) 396-5476. Fax: (212) 396-5466