Fluorescence and Raman spectra on painting materials: reconstruction of spectra with mathematical methods

Abstract

SERDS (shift excitation difference spectroscopy) and SSRS (subtracted shifted Raman spectroscopy) methods were applied for fluorescence-background rejection in the Raman spectra of colored materials. These techniques are based on the assumption that the fluorescence contribution can be completely eliminated by subtracting two Raman spectra acquired at two shifted laser excitation frequencies. For the SERDS method a micro-Raman experimental apparatus coupled with a tunable diode laser (central emission at 684 nm) was set up. SSRS measurements were made on a commercial micro-Raman instrument; in this case the shifted spectrum was obtained by moving the spectrometer grating. Raman spectra were then reconstructed by applying the difference deconvolution method that automatically converts the difference signals in Raman peaks through a deconvolution operation. These techniques were tested on two reference colors (ultramarine and 6,6 -dibromoindigotine) and two colored samples of unknown composition (a Pompeian pink powder and a blue paint from a XVII century painting). Fluorescencebackground subtraction and the following operation of spectra reconstruction took place successfully with no errors in Raman peaks, width and wavenumber position. In addition, even weak spectral details were revealed favoring the comparison with reference data for a molecular identification.

Raman spectroscopy in art and archaeology

“…Hence, different approaches are explored, such as the search for the optimal excitation wavelength 37 or more non-classical approaches with some mathematical treatments of the spectra. 38 An alternative way would be the increase of the Raman signal through surface-enhanced Raman scattering (SERS). Actually, widely used for weak Raman signal or low-concentration samples (especially in biology), 39 the developments of various SERS substrates and the experimentalist's skill offer the opportunity to obtain Raman spectra from highly fluorescent materials and also from micro-samples, allowing their application to work on art dyes or lakes.…”

Micro‐Raman and fluorescence spectroscopy for the assessment of the effects of the exposure to light on films of egg white and egg yolk

“…In contrast, surface-enhanced Raman spectroscopy (SERS) 1 and resonance Raman spectroscopy 2,3 of protein solutions have found wide-ranging applications. However, recent instrumental and theoretical advances may assist in the elimination of fluorescence 4,5 and constitute a significant improvement in the potential of Raman spectroscopy for the identification of proteins. Raman spectroscopy has been used for the analysis of proteins found in the complex mixtures within eggs 6 , for the analysis of food which include lysozyme (egg white), 7 lactalbumin (milk), 8 casein, 9 cheese 10,11 and animal-based gels 12 and has also been used for the determination of egg-based binding media found in works of art.…”

Low-Content Quantification in Powders Using Raman Spectroscopy: A Facile Chemometric Approach to Sub 0.1% Limits of Detection

“…Experimental approaches to background/baseline correction are not suitable here. [29][30][31][32][33][34] A chemometric approach (of which there are many) was preferred because this could be more easily implemented on conventional Raman systems. [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] Morphological weighted penalized least squares (MPLS) 49 was used for baseline correction of Raman spectra because of its inherent simplicity, combined with its flexibility, suitability for automation, and effectiveness at mitigating baseline artefacts.…”