The miniaturisation of laser sources, charge-coupled device electronic control boxes and increasing Lap-top computer capacity led to a revolution in Raman spectrometry: Measurements can be made outside the laboratory with transportable, mobile and ultramobile instruments, even in severe conditions (e.g. rock shelter in mountains). However, many specific difficulties must be previously solved: The variety of mobile laser sources remains limited to red and green excitations, the positioning/focusing and protection against solar/bulb lighting are difficult and, more importantly, the spectral resolution and spectral window are limited. Nevertheless, the definition of good procedures and the use of advanced optics allow the on-site analysis of various cultural heritage materials: pigments of pastels, miniatures, drawings, glasses, enamels and glazes, rock art, crystalline and amorphous phases of pottery, enamelled glass artefacts or stained glasses, bronze and brass patinas, etc. Simultaneously, mobile instruments equipped with a telescope and pulsed Yttrium Aluminum Garnet laser are being implemented for planetary mission (Mars). The present state of the art and future development are discussed. Copyright © 2012 John Wiley & Sons, Ltd.

The on-site/remote Raman analysis with mobile instruments: a review of drawbacks and success in cultural heritage studies and other associated fields

Minerals, as raw structural materials or pigments, play a fundamental role in archaeometry, for the understanding of nature, structure and status of an artefact or object of interest for cultural heritage. A detailed knowledge of the mineral phases is crucial to solve archaeological problems: Raman spectroscopy is a powerful investigation technique and has been applied extensively in the last 30 years on mineral identification and on pigment degradation. Here we report an updated review, covering the last decade, of the applications of Raman techniques to issues in which raw minerals, including mineral pigments, are involved. Particular attention is devoted to cases where the Raman analysis of minerals is deeper than a simple identification of the phases present in an archaeological or artistic object. Copyright © 2016 John Wiley & Sons, Ltd.

Raman spectroscopy of minerals and mineral pigments in archaeometry

Mobile instrumentation is of growing importance to archaeometry research. Equipment is utilized in the field or at museums, thus avoiding transportation or risk of damage to valuable artifacts. Many spectroscopic techniques are nondestructive and micro-destructive in nature, which preserves the cultural heritage objects themselves. This review includes over 160 references pertaining to the use of mobile spectroscopy for archaeometry. Following a discussion of terminology related to mobile instrumental methods, results of a literature survey on their applications for cultural heritage objects is presented. Sections devoted to specific techniques are then provided: Raman spectroscopy, X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy, laser-induced breakdown spectroscopy, and less frequently used techniques. The review closes with a discussion of combined instrumental approaches.

https://journals.sagepub.com/doi/pdf/10.1177/0003702815611063

Mobile Spectroscopic Instrumentation in Archaeometry Research.

Raman spectroscopy is widely applied in the cultural heritage field to perform non-destructive measurements in situ, in order to identify materials, specifically pigments. The spectra collected can be challenging to interpret because certain source laser wavelengths may be absorbed by specific pigments, leading to large fluorescence backgrounds which obscure the weak Raman signals, or worse cause photodegradation of the sample. Furthermore, the reference spectra for a specific pigment obtained from a particular laser wavelength is not always available and is a crucial step in the detective work of pigment identification, especially when the resonance Raman effect can enhance some signals. As the range of lasers available increases, spectral libraries do not always record spectra acquired with the same wavelength used to carry out the measurements in field. In this work, reference spectra of 32 different compounds, mostly used in mediaeval manuscripts as pigments and inks, are recorded. Five different wavelengths were used as excitation sources. The aim is to provide a useful and more complete reference source to enable better planning of which laser wavelength is the most appropriate to study a specific set of pigments, and to allow comparisons between spectra acquired with the same wavelength, leading to the unequivocal pigment identification in a step by step manner.

/pdf/raman-spectroscopic-library-of-medieval-pigments-collected-13ryh7n0tt.pdf

Raman spectroscopic library of medieval pigments collected with five different wavelengths for investigation of illuminated manuscripts

Multi-technique investigation of Roman decorated plasters from Villa dei Quintili (Rome, Italy)

A portable X-ray fluorescence (XRF) spectrometer and portable Raman spectrophotometer were utilized at the Coriglia, Castel Viscardo excavation site near Orvieto, Italy to study pigments found on fresco. Over eighty fresco samples were analyzed. Identified pigments included vermillion, red ochre, yellow ochre, terre verte, Egyptian blue, and hematite. XRF spectroscopic data were collected utilizing three separate sets of instrument conditions. Various data processing and analysis approaches were evaluated for the XRF and Raman spectroscopic data including scatterplots and analysis of variance on integrated peak areas, live time correction of the XRF spectral intensities, principle components analysis on both the integrated peak areas and spectra, and data fusion of the spectra. Fusion of the high voltage and low voltage under vacuum XRF spectroscopic data provided improved data clustering results over single technique data. Fusion of high voltage XRF spectroscopic data with Raman data also was demonstrated to provide improved differentiation results for certain pigments. Data from individual pigments were then evaluated using these demonstrated best approaches for possible source variations with encouraging results.

Evaluation of data processing and analysis approaches for fresco pigment studies by portable X-ray fluorescence spectrometry and portable Raman spectroscopy

A. M. Daigle

Papers

Evaluation of data processing and analysis approaches for fresco pigment studies by portable X-ray fluorescence spectrometry and portable Raman spectroscopy