Direct identification of alizarin and lac dye on painting fragments using surface-enhanced Raman scattering

A surface-enhanced Raman scattering (SERS) based procedure was investigated for potential applications in the direct identification of selected anthraquinone dyes on works of art objects. The simplicity and effectiveness of this procedure was demonstrated in a proof-of-concept experiment. A microscopic fragment containing alizarin or lac dye was removed from a painting. A layer of silver nanoparticles was thermally evaporated directly on the fragment to induce SERS effect. SERS spectra were collected directly from the Ag-nanoparticle-coated sample fragments with a Raman microscope. Based on their characteristic SERS spectra, the presence of alizarin or lac dye in the sample fragments can be detected. The applicability of this procedure for potential applications in minimally invasive analysis of color layer from artwork objects is discussed. Finally, the thickness of the Ag nanoparticle layer was optimized.