The use of Raman microscopy and laser desorption ionization mass spectrometry in the examination of synthetic organic pigments in modern works of art

Abstract

Synthetic organic pigments are widely used in modern and contemporary works of art. They have been examined by a variety of techniques including spectroscopic methods such as Fourier transform infrared spectroscopy, Raman, and X‐ray powder diffraction as well as chromatographic or mass spectrometric techniques such as pyrolysis‐gas chromatography/mass spectrometry and laser desorption ionization mass spectrometry (LDI–MS). Often, a combination of techniques has been used to examine these pigments. This paper describes use of Raman spectroscopy to create a database of colorants including two pigments not previously reported, PO1 and PO2. Then, using Raman spectroscopy in combination with LDI–MS, samples from modern works of art by artists including Mark Rothko, Barnett Newman, and José de Rivera were examined in order to identify the pigments present. One finding was that Rothko used a variety of red pigments over the course of his career including PR11 which has not been previously reported in artwork, and PO2 found with its positional isomer PR1. Knowledge of the colorants serves to inform conservators about display and treatment decisions. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

SERS spectrum of red dyes in the Mapuche belts from the beginning of the XXth century

“…. The following spectral assignment based on published data and those reported by Colombini et al in PO36 and by Suwaiyan et al in benzimidazole and Krishnakumar et al in the fragment 2‐hydroxybenzimidazole, supports the present proposition. The most intense SERS bands of the sample 3357 at 1605 and 1144 cm −1 are attributed to νCO/νCC arom.…”

“…The spectral analysis of the SERS spectra was performed on the basis of Raman data on related molecular systems, [48][49][50][51] and on previous [46] and our own theoretical Raman data for PR57. The present Raman spectrum of PR57 is shown in Fig.…”

Identification of artistic materials in paintings and drawings by Raman spectroscopy: some challenges and future outlook

“…To date, numerous libraries containing reference spectra of synthetic organic pigments have been reported. [30,32,36,37,40] When inks are colored by red organic natural pigments, such as cochineal, SERS is necessary to overcome the fluorescent background and enhance the signals of the colorants. [92] Particularly complex binding media were mixed with colorants in early lithographic inks that generally consist of a 'varnish' or carrying vehicle, containing processed linseed oil, rosin, and soap, and several additives or modifying agents, such as iron sulfate, lead acetate, litharge, Ceara rubber seed, sodium amyl sulfate, wax, mastic, copal, gum lac, shellac, tallow, soda ash, and turpentine.…”

Automatic classification system of Raman spectra applied to pigments analysis

“…It is well known that Raman spectroscopy is able to distinguish different molecular species based on the acquired Raman spectra. The discrimination between the pigments found in natural and synthetic forms [6][7][8] or in different crystalline structures [9][10][11][12][13][14][15] is an important topic in conservation science because the pigments may differ not only in their chemical and physical characteristics (such as stability, solubility and hue) but also appeared at different times on the paint market, and thus they may be used as chronological markers. In art analysis, daily tasks concerning pigment identification are not automatized unlike in other scientific fields.…”