Identification of Organic Colorants in Fibers, Paints, and Glazes by Surface Enhanced Raman Spectroscopy

• NCJ Number: 304209
• Author(s): Francesca Casadio ; Marco Leona ; John R. Lombardi ; Richard Van Duyne
• Date Published: 2010
• Length: 10 pages
• Grant Number(s): 2006-DN-BX-K034
• Agencies: NIJ-Sponsored
• Award: Development of Advanced Raman Spectroscopy Methods and Databases for the Evaluation of Trace Evidence and the Examination of Questioned Documents

Annotation

This article reports on a project with the objective of developing practical approaches to the identification of dyes in works of art from samples as small as 25 μm in diameter with surface-enhanced Raman scattering (SERS).

 

Abstract

The article first explains the difficulty of identifying dyes in cultural heritage objects, since the techniques routinely used in the identification of inorganic pigments are generally not applicable to dyes often used in works of art. In SERS, however, the Raman scattering signal is greatly enhanced when organic molecules with large delocalized electron systems are adsorbed on atomically rough metallic substrates; fluorescence is concomitantly quenched. Recent nanotechnological advances in preparing and manipulating metallic particles have afforded staggering enhancement factors of up to 1014. SERS is thus an ideal technique for the analysis of dyes. Indeed, rhodamine 6G and crystal violet, two organic compounds used to demonstrate the sensitivity of SERS at the single-molecule level, were first synthesized as textile dyes in the second half of the 19th century. The current project examined the practical application of SERS to cultural heritage studies, including the selection of appropriate substrates, the development of analytical protocols, and the building of SERS spectral databases. It also considered theoretical studies on dyes of artistic interest. Using SERS, the project successfully documented the earliest use of a madder lake pigment and the earliest occurrence of lac dye in European art. It also found several examples of kermes and cochineal glazes, as well as madder, cochineal, methyl violet, and eosin lakes, from eras ranging from ancient Egypt to the 19th century. The ability to rapidly analyze very small samples with SERS makes it a particularly valuable tool in a museum context. (publisher abstract modified)