Plasmonic colloidal pastes for surface-enhanced Raman spectroscopy (SERS) of historical felt-tip pens

Abstract

Surface-enhanced Raman spectroscopy (SERS) has been identified as a suitable technique for the analysis of colorants in works of art. Herein, the application of SERS to the identification of dye compositions in historical felt-tip pens is reported, which is of paramount importance for the development of appropriate conservation protocols for historical drawings. In this study, three pens (pink, green, and blue colors) belonging to the film director Federico Fellini were analyzed. SERS measurements were performed directly on the pen lines drawn on a commercial paper by the deposition of Ag colloidal pastes, which allowed fast in situ dye identification without the need for extraction or hydrolysis treatments. Eosin Y was identified as the only dye present in the pink pen ink, whereas erioglaucine was found to be the main dye component in green and blue pen inks. SERS also resulted in highly efficient identification of the individual dyes erioglaucine, crystal violet, and rhodamine present as a mixture in the blue pen ink.The high SERS sensitivity was ascribed to the plasmonic effects and efficient quenching of the fluorescence interference of dyes. A comparison with contemporary pen inks highlighted minor differences in the chemical composition. These results prove that SERS can be used as a fast and sensitive analytical tool for ink analysis that provides invaluable support for the general assessment of the date, provenance, and originality of the historical drawings as well as for the development of preventive conservation protocols.

Handheld surface‐enhanced Raman scattering identification of dye chemical composition in felt‐tip pen drawings

“…This could be due to the fact that slightly different blues were compared (Caran D'Ache 555 against Fellini Caran D'Ache 100) or that the composition of the blue Caran D'Ache used by Fellini in 1960s has changed with time. The comparison of results obtained with benchtop Raman instrumentation previously carried out in our group showed that comparable results were obtained under the two experimental conditions (benchtop illumination wavelength 514 nm, resolution 3–5 cm −1 , spot size 2–5 μm, laser power <2 mW, handheld illumination wavelength 514 nm, 10–12 cm −1 , resolution, 1 mm spot size, laser power 50 mW). In blue Fellini, additional traces of rhodamine were detected by benchtop Raman illumination.…”

“…SERS was also used by our group and others for the identification of dye content in ballpoint pens . Recently, SERS was also used in combination with other analytical techniques for the identification of dyes in commercial felt‐tip pens and used to identify colorants in colored inks used by artists such as Lucio Fontana and Federico Fellini . As an increasing number of modern artworks are already entering a state of high degradation, the inherent noninvasiveness, high sensitivity, and efficient quenching of interfering fluorescence signals could make SERS the analytical technique of choice to support the development of long‐term conservation methods for modern artworks.…”

Identification of dye content in colored BIC ballpoint pen inks by Raman spectroscopy and surface‐enhanced Raman scattering

“…From previous work carried out in our group, it is known that green inks are often constituted by a mixture of blue and yellow dyes and that blue phthalocyanine Solvent Blue 38 pigment (C.I. 74180) is used in BIC pen formulations . Therefore, presence of CuPh Blue 38 was hypothesized.…”

“…74180) is used in BIC pen formulations. [27] Therefore, presence of CuPh Blue 38 was hypothesized. Clearer indication of Blue 38 occurrence in green pens was obtained by SERS analysis at 532 nm (see Figure S3) where Medium, Crystal and Medium Crystal green pens showed diagnostic bands at 1,541, 1,453, 1,341, and 712 cm −1 .…”

“…[26] Recently, our group has successfully applied Raman and SERS, in combination with bench and handheld instrumentation, for the identification of the major dye constituents of felt tip pens. [27,28] The application of SERS allowed circumventing fluorescence interference and provided high intensity spectral profiles of fluorescent dyes under visible wavelength illumination. [29] In this paper, we report on the application of Raman and SERS spectroscopies to the identification of dye mixtures in colored BIC ballpoint pens.…”