Optimum acquisition of Raman spectra in pigment analysis with IR laser diode and pulsed UV irradiation

Abstract

Fluorescence, due to the binding media, is the main problem that one encounters in the molecular analysis of artistic pigments using Raman spectroscopy. With the object of minimizing this problem, we propose the use of a semiconductor IR laser in Raman spectral acquisition and the application of local irradiation with a pulsed UV laser on the analysis zone. The Raman analysis with an IR source shows advantages compared to that with visible lasers, such as the reduction of fluorescence and its shot noise, although a price has to be paid in the form of the small intensity of the obtained spectra with the same acquisition time. Also, in this paper we demonstrate that controlled levels of pulsed UV radiation over the analyzed painting (pigment + binding media) can improve even more the Raman spectral quality obtained with the IR laser, which leads us to conclude that the local use of a pulsed UV laser, prior to Raman analysis with the IR source, can bring optimum quality results in pigment identification. The spectral quality of these experimental results for different pigments has been measured by calculating in each case the signal-to-noise ratio (SNR) of the corresponding spectra. From a quantitative point of view, in some practical cases (chromium yellow and ultramarine blue) an SNR improvement of 16 dB is achieved when pulsed UV irradiation and IR laser Raman analysis are used instead of a simple Raman analysis with a visible laser.

A Decade of Raman Spectroscopy in Art and Archaeology

“…Most pigment investigations are performed using a red laser. However, especially in pigment analysis, many authors still apply several lasers for their Raman spectroscopic research to remove the likelihood of sample degradation being experienced with some systems 2 Use of different lasers as a function of their field of application and as a function of time. …”

“…However, especially in pigment analysis, many authors still apply several lasers for their Raman spectroscopic research to remove the likelihood of sample degradation being experienced with some systems. 70 When following the evolution of the number of published Raman research papers using a specific laser wavelength (Figure 2b), it is remarkable that the applications of most laser wavelengths are seen to be on the increase since 2004. This can be partially explained by the increase in the total number of research papers (Figure 1), although a problem arises from the adoption of multiple lasers in many studies now appearing.…”

Recent Advances in linear and nonlinear Raman spectroscopy I

“…Further investigations of pigments, dyes, and paints were made by Chaplin et al 106 on nine variants of the greenblue pigment verdigris, and by López-Gil et al 107 on various artists' pigments excited with both IR laser diode and pulsed UV irradiation. SERS was employed for the ultrasensitive identification of natural dyes in works of art 108 and to obtain highly detailed spectra of artists' red lake pigments and colorants by Whitney et al 109 Maya blue, invented by the Maya around the 7th and 8th century and used by many Mesoamerican people in preHispanic time, was studied extensively by Sánchez del Rio et al 110 Other historical materials (printed plates, folios, icons, crucifix, wood, paper, stones) from the early 13th century Islamic 'Book of Curiosities of the Sciences and Marvels for the Eyes'.…”

Composition of Renaissance Paint Layers: Simultaneous Particle Induced X-ray Emission and Backscattering Spectrometry

“…In order to analyze the organic components of the paintings, other independent techniques, such as Fourier transform-infrared spectrometry (FT-IR), gas chromatography (GC) and related methods (mass spectrometry GC/MS, pyrolysis PyGC, and high-performance liquid chromatography HPLC) have to be carried out. Up until now and for specific cases, only infrared and Raman spectroscopies are able to qualitatively analyze organic and mineral matters. , In this article, we propose to associate two ion beam techniques in order to simultaneously collect information on mineral compounds by PIXE and on organic compounds by backscattering spectrometry (BS). , …”