A new compact instrument for Raman, laser-induced breakdown, and laser-induced fluorescence spectroscopy of works of art and their constituent materials

Fluorescence Lifetime Phasor Analysis and Raman Spectroscopy of Pigmented Organic Binders and Coatings Used in Artworks

Fluorescence analysis of materials used as binders and coatings in artworks is often hampered by numerous factors, leading to uncertainties in data interpretation. Fluorescence lifetime (FL) measurements enable improvement of the specificity with respect to steady-state measurements by resolving the decay dynamics of the fluorophore emissions. In this work, layers of natural resin, oil, and wax—in pure form, pigmented, in mixtures, and spread on different substrates—were analyzed using a compact, portable, fiber-based FL instrument. FL data were processed via the phasor method and integrated with Raman spectroscopy to obtain complementary chemical information on the different substances. It was observed that the τ-phase of the mixtures is affected by both the pigments and the dispersing medium, and that the presence of the metal substrate contributes to changes in the FL of mixtures. The results obtained with our portable FL system combined with Raman spectroscopy pave the way for a systematic study of a larger number of materials for future in situ applications on works of art.

Integrated Laser Sensor (ILS) for Remote Surface Analysis: Application for Detecting Explosives in Fingerprints

Here, we describe an innovative Integrated Laser Sensor (ILS) that combines four spectroscopic techniques and two vision systems into a unique, transportable device. The instrument performs Raman and Laser-Induced Fluorescence (LIF) spectroscopy excited at 355 nm and Laser-Induced Breakdown Spectroscopy (LIBS) excited at 1064 nm, and it also detects Laser Scattering (LS) from the target under illumination at 650 nm. The combination of these techniques supplies information about: material change from one scanning point to another, the presence of surface contaminants, and the molecular and elemental composition of top target layers. Switching between the spectroscopic techniques and the laser wavelengths is fully automatic. The instrument is equipped with an autofocus, and it performs scanning with a chosen grid density over an interactively-selected target area. Alternative to the spectroscopic measurements, it is possible to switch the instrument to a high magnification target viewing. The working distances tested until now are between 8.5 and 30 m. The instrument is self-powered and remotely controlled via wireless communication. The ILS has been fully developed at ENEA for security applications, and it was successfully tested in two outdoor campaigns where an automatic recognition of areas containing explosives in traces had been implemented. The strategies for the identification of nitro-compounds placed on various substrates as fingerprints and the results obtained at a working distance of 10 m are discussed in the following.

Portable Spectroscopy

Until very recently, handheld spectrometers were the domain of major analytical and security instrument companies, with turnkey analyzers using spectroscopic techniques from X-ray fluorescence (XRF) for elemental analysis (metals), to Raman, mid-infrared, and near-infrared (NIR) for molecular analysis (mostly organics). However, the past few years have seen rapid changes in this landscape with the introduction of handheld laser-induced breakdown spectroscopy (LIBS), smartphone spectroscopy focusing on medical diagnostics for low-resource areas, commercial engines that a variety of companies can build up into products, hyphenated or dual technology instruments, low-cost visible-shortwave NIR instruments selling directly to the public, and, most recently, portable hyperspectral imaging instruments. Successful handheld instruments are designed to give answers to non-scientist operators; therefore, their developers have put extensive resources into reliable identification algorithms, spectroscopic libraries or databases, and qualitative and quantitative calibrations. As spectroscopic instruments become smaller and lower cost, "engines" have emerged, leading to the possibility of being incorporated in consumer devices and smart appliances, part of the Internet of Things (IOT). This review outlines the technologies used in portable spectroscopy, discusses their applications, both qualitative and quantitative, and how instrument developers and vendors have approached giving actionable answers to non-scientists. It outlines concerns on crowdsourced data, especially for heterogeneous samples, and finally looks towards the future in areas like IOT, emerging technologies for instruments, and portable hyphenated and hyperspectral instruments.

Mobile Spectroscopic Instrumentation in Archaeometry Research

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.

An analytical Raman spectroscopic study of an important english oil painting of the 18th Century

An opportunity was afforded to analyse pigment specimens from an unrestored oil painting in the style of the English School of the mid-18th Century prior to conservation being undertaken. Raman spectroscopy was adopted to characterise the pigments and indicated the presence of a novel red pigment which was assigned to the complex chromium mineral, hemihedrite, in addition to other interesting materials found in combination. This is the first recorded identification of hemihedrite spectral signals in an art context in a range of mineral pigments that are otherwise typical of this period and some hypotheses are presented to explain its presence based on its occurrence with associated mineral pigments. It is suggested that the presence of powdered glass identified in certain areas of the painting enhanced the reflectivity of the pigment matrix.

The role of mobile instrumentation in novel applications of Raman spectroscopy: archaeometry, geosciences, and forensics

The applications of analytical Raman spectroscopy in the characterisation of materials associated with archaeologically excavated artefacts, forensic investigations of drugs of abuse, security and crime scenes, minerals and rocks and future astrobiological space missions are now well established; however, these applications have emphasised the need for new developments in the area of miniaturised instrumentation which extends the concept and breadth of the analytical requirement to facilitate the provision of data from 'in field' studies. In this respect, the apparently unrelated themes of art and archaeology, forensic science, geological science and astrobiology as covered by this review are unified broadly by the ability to record data nondestructively and without resorting to sampling and the subsequent transfer of samples to the analytical laboratory. In studies of works of art there has long been a requirement for on-site analysis, especially for valuable paintings held under strict museum security and for wall paintings which cannot physically be removed from their setting; similarly, the use of portable Raman spectroscopy in archaeological and geological field work as a first-pass screening device which obviates the necessity of multiple and wasteful specimen collection is high on the wish-list of practicing spectroscopists. As a first-pass screening probe for forensic crime scenes, Raman spectroscopy has proved to be of inestimable value for the early detection of dangerous and prohibited materials such as drugs of abuse, explosives and their chemical precursors, and banned contraband biomaterials such as ivories and animal products; in these applications the advantage of the Raman spectroscopic technique for the recognition of spectral signatures from mixtures of inorganic and organic compounds is paramount and not afforded by other less portable instrumental techniques. Finally, in astrobiological work, these requirements also apply but with the additional prerequisite for system operation remotely - often over distances of several hundred million kilometres - as part of instrumental suites on robotic spacecraft and planetary landers; this necessitates robust and reliable instrumentation for the observation of unique and characteristic spectral features from the planetary geological surface and subsurface which are dependent on the assignment of both biological and geological band signatures.

Planetary geochemical investigations using Raman and laser-induced breakdown spectroscopy

An integrated Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS) instrument is a valuable geoanalytical tool for future planetary missions to Mars, Venus, and elsewhere. The ChemCam instrument operating on the Mars Curiosity rover includes a remote LIBS instrument. An integrated Raman-LIBS spectrometer (RLS) based on the ChemCam architecture could be used as a reconnaissance tool for other contact instruments as well as a primary science instrument capable of quantitative mineralogical and geochemical analyses. Replacing one of the ChemCam spectrometers with a miniature transmission spectrometer enables a Raman spectroscopy mineralogical analysis to be performed, complementing the LIBS chemical analysis while retaining an overall architecture resembling ChemCam. A prototype transmission spectrometer was used to record Raman spectra under both Martian and Venus conditions. Two different high-pressure and high-temperature cells were used to collect the Raman and LIBS spectra to simulate surface conditions on Venus. The resulting LIBS spectra were used to generate a limited partial least squares Venus calibration model for the major elements. These experiments demonstrate the utility and feasibility of a combined RLS instrument.

Note: Light ageing with simultaneous colorimetry via fibre optics reflection spectrometry

In this article, the design and characteristics of a micro-fadeometer is presented. The technique allows for a non-(micro-) destructive evaluation of the light fastness of colorants on various materials and can be used to directly assess valuable materials, such as heritage objects, and develop safer display strategies to promote their preservation. The presented instrument has several benefits over standard light ageing methods--low operating cost, non-damaging, real time measurement of induced changes for kinetics studies, and automated high throughput screening of materials. A selection of data is presented to demonstrate the flexibility of the presented instrument and illustrate how it can be used to evaluate museum lighting and oxygen-free display of heritage objects.