The brightest colors: A Fourier-transform Raman, surface-enhanced Raman, and thin-layer chromatography-surface-enhanced Raman spectroscopy study of fluorescent artists' paints

Among the so-called special effect pigments, fluorescent ones play an important role, thanks to their application to a wide range of objects in everyday life. Also in the artistic field, they have been exploited since 1950s by several painters (among others Andy Warhol and Frank Stella), thus representing a particular class of materials with which conservators must confront themselves. Not much information is available about the complete composition of commercial fluorescent paints that are based on fluorescent dyes dispersed in a transparent and brittle resin. Herein, Fourier-transform Raman spectroscopy and surface-enhanced Raman spectroscopy (SERS) were used to recognize the main dye components of the paints, whereas thin-layer chromatography was coupled with SERS to better distinguish further chromophore mixes responsible for the color and/or the fluorescence emission due to the presence of optical brighteners. This methodology results suitable to more fully define the composition of such fluorescent paints originally used by artists in their works, thus providing valuable information to conservators for restoration and retouching efforts.