Combined photoluminescence and Raman microscopy for the identification of modern pigments: explanatory examples on cross-sections from Russian avant-garde paintings

Sara Mosca,Marta Ghirardello,Alessia Artesani,Daniela Comelli,Gianluca Valentini,Austin Nevin

doi:10.1186/s40494-019-0258-x

Abstract

In conservation science, the identification of painting materials is fundamental for the study of artists’ palettes, for dating and for understanding on-going degradation phenomena. For these purposes, the study of stratigraphic micro-samples provides unique information on the complex heterogeneity of the pictorial artworks. In this context, we propose a combined-microscopy approach based on the application of time-resolved photoluminescence (TRPL) micro-imaging and micro-Raman spectroscopy. The TRPL device is based on pulsed laser excitation (excitation wavelength = 355 nm, 1 ns pulse width) and time-gated detection, and it is suitable for the detection of photoluminescent emissions with lifetime from few nanoseconds to hundreds of microseconds. In this work, the technique is beneficially applied for identifying different luminescent semiconductor and mineral pigments, on the basis of their spectral and decay kinetic emission properties. The spatial heterogeneities, detected in the micro-sample, are investigated with Raman spectroscopy (785-nm in CW mode) for a further identification of the paint composition on basis of the molecular vibrations associated with the crystal structure. The effectiveness and limits of the proposed combined method is discussed through analysis of a corpus of stratigraphic micro-samples from Russian Avant-garde modern paintings. In the selected samples, the method allows the identification of modern inorganic pigments such as cadmium-based pigments, zinc white, titanium white, chrome yellow, ultramarine and cinnabar.

Highlights

In conservation science, the identification of painting materials is fundamental for the study of artists’ palettes, for dating and for understanding on-going degradation phenomena
One effective way to improve the efficiency of Raman spectroscopy is to combine several excitation wavelengths as reported in [6] in order to optimized the tradeoff between the signal to noise ratio and the competitive fluorescence baseline arising from different materials
We investigate the combination of timeresolved photoluminescence (TRPL) microscopy and micro-Raman spectroscopy for pigment identification, taking the advantages of the different sensitivity of the two methods to the phenomena described before and of the elevated flexibility of both systems that are custombuilt

Summary

Introduction

The identification of painting materials is fundamental for the study of artists’ palettes, for dating and for understanding on-going degradation phenomena. One effective way to improve the efficiency of Raman spectroscopy is to combine several excitation wavelengths as reported in [6] in order to optimized the tradeoff between the signal to noise ratio and the competitive fluorescence baseline arising from different materials. Another possibility is the use of a single near-infrared laser, for reducing the fluorescent contribution, and applying specific acquisition protocols, such as the Subtracted Shifted Raman spectroscopy (SSRS) or the Shifted Excitation Raman Difference Spectroscopy (SERDS) [9,10,11]. All these strategies aim at diminishing the limitations imposed by fluorescent samples

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Discussion

Conclusion