Temperature-controlled portable Raman spectroscopy of photothermally sensitive pigments

In this work, an innovative NIR Raman device (excitation wavelength at 1064 nm) was developed in order to avoid thermal stress and consequent chemical alterations of the materials analyzed. In particular, we devised and tested for the first time a sensored Raman probe allowing for temperature-controlled measurements based on a thermoelectric sensor providing the feedback signal for suitably modulating the output power of the laser source and then limiting undesired heating effects within the irradiated volume. The experimentation was carried out on cinnabar, lead white and indigo pigments frequently used during the past centuries, which presents pronounced photothermal instability. The results achievedin a set of instrumental and analytical tests using different measurement control parameters allowed demonstrating the effectiveness and reliability of the present approach for preventing thermal alterations effects during Raman spectroscopy and speeding the measurements, as well as for monitoring spectral variations associated with the crystals anharmonicity over large temperature ranges. These features alongwith the portability of the novel device can make in situ Raman characterisation of valuable paintedsurfaces including photosensitive materials very safe and efficie

Detection of the Glass Transition of Polymers Used in Art and Art-Conservation Using Raman Spectroscopy

In this work, Raman spectroscopy was employed for the detection of the glass transition temperatures (Tg) of some thermoplastic polymers and natural terpenoid resins. In particular, our attention was focused on evaluating the Tg of polystyrene and colophony. The measurements returned Tg values in accordance with those reported in the literature obtained using the DSC technique, thus confirming the reliability of the approach proposed herein. Further studies will be focused on the evaluation of Tg temperature changes depending on materials treatments and ageing

Development of an efficient and thermally controlled Raman system for fast and safe molecular characterization of paint layers

An innovative high-efficiency Raman system (exc. wav. 1064 nm) for safe molecular characterization of paint layers and other photosensitive materials has been developed and successfully tested. It was equipped with a novel optical probe, which has been designed and built in order to perform Raman scattering measurements on a relatively large spot at laser intensities lower than the typical ones of the commercial instruments. Original optical solutions were implemented in order to achieve such improved efficiency. Furthermore, the instrument was also equipped with an active thermal control line allowing to prevent alterations of the material under study and to optimize the measurement cycles by means of suitable modulations of the laser power. Comparative tests using the novel analytical tool and an alternative setup based on a commercial Raman probe were carried out on a set of pure pigments and oil paint layers, which allowed assessing the significantly higher efficiency and reliability of the former with respect to the latter

Exploring the Potential of Portable Spectroscopic Techniques for the Biochemical Characterization of Roots in Shallow Landslides

In the present work, Raman, Fourier Transform Infrared (FTIR) and elemental Laser-Induced Breakdown Spectroscopy (LIBS) spectroscopic techniques were used for the assessment of the influence of plant root composition towards shallow landslide occurrence. For this purpose, analyses were directly carried out on root samples collected from chestnut forests of the Garfagnana basin (northern Apennines, Italy) in different areas devoid and affected by shallow landslides due to frequent heavy rain events. Results have highlighted a correlation between the biochemical constituents of wooden roots and the sampling areas. In particular, different content of lignin/cellulose, as well as minerals nutrients, have been detected in roots collected where shallow landslides occurred, with respect to more stable areas. The results achieved are in line with the scientific literature which has demonstrated the link between the chemical composition of roots with their mechanical properties and, in particular, tensile strength and cohesion. Finally, portable spectroscopic instrumentations were employed without the need for either any sample preparation for Raman and LIBS spectroscopy or minimal preparation for FTIR spectroscopy. This novel and fast approach has allowed achieving information on the content of the major constituents of the root cell, such as cellulose and lignin, as well as their mineral nutrients. This approach could be reasonably included among the vegetation protection actions towards instability, as well as for the evaluation of shallow landslide susceptibility, combining geological, vegetational and biochemical parameters with sustainability

Automated characterization of varnishes photo-degradation using portable T-controlled Raman spectroscopy

In this work, a portable-Raman device (excitationwavelength 1064 nm)was employed for the first time for continuously monitoring the complex molecular dynamics of terpenoid resins (dammar, mastic, colophony, sandarac and shellac), which occur during their ageing under artificial light exposure. The instrumentation was equipped with a pyroelectric sensor allowing for temperature control of the sample's irradiated surface while the acquisition of spectra occurs by setting fixed maximum temperature and total radiant exposure. Resins were dropped into special pits over a dedicated rotating wheelmoved by a USB motor. The rotation allowed samples sliding between the positions designated for the acquisition of the Raman spectra and that for artificial ageing. Samples were exposed to artificial light for 45-days and almost 400 spectra for each resin sample were collected. The exposure to artificial light led to significant changes allowing the characterization of the alteration process. The automated acquisition of a large number of spectra overtime during light-exposure has given the possibility to distinguish fast dynamics,mainly associated to solvent evaporation, fromthose slower due to resins photo-degradation processes

"Argento Deaurato" or "Argento Biancheggiato"? A Rare and Interesting Case of Silver Background in Italian Painting of the XIII Century

The painting depicting the "Virgin with the Child and two angels" by a Tuscan anonymous artist of the XIII century, has raised great interest regarding the execution technique including the use of silver, applied on wood as a background. An in-depth investigation was carried out especially concerning the burnishing process of the silver leaves as well as a detailed inspection of the nature of the organic compounds over the metal leaf and the degradation products of the silver layer. To this aim, a multianalytical approach was used including UV–VIS microscopy along with an Ultra-High-Resolution Scanning Electron Microscopy (UHR-SEM), as well as Fourier Transform Infrared (FTIR), fluorescence and micro-Raman spectroscopies. As a result, the presence of an oil-resin varnish layer in the uppermost layer and a wax-protein layer between the varnish and the metal layer as well as the evidence that the silver leaf was applied with high accuracy directly to the preparation layer, were clearly demonstrated. Furthermore, degradation products of the silver leaf were identified as sulphides, chlorides, and oxides. The holistic approach herein adopted enabled a step forward in the knowledge of the 13th century silver leaf gilding technique, adding value to the originality of this artwork. In this respect, the scientific evidence led to the assumption that likely this painting originally showed a silver-colored background ("argento biancheggiato") as compared to the initial theory of a case of "argento deaurato"

Spot‐on SERS Detection of Biomolecules with Laser‐Patterned Dot Arrays of Assembled Silver Nanowires

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Automatic morphology-based cubic p-spline fitting methodology for smoothing and baseline-removal of Raman spectra

Noise filtering is considered a crucial step for the proper interpretation of Raman spectra. In this work, we present a new denoising procedure which enhances the Raman information whilst reducing unwanted contributions from the most frequent noise sources, i.e. the shot noise and the fluorescence's baseline. The procedure increases the signal-to-noise ratio whilst preserving simultaneously the shapes, positions and intensity ratios of the Raman bands. The method relies on cubic penalized spline fitting and mathematical morphology and requires no user input. We describe the details of this method and include a benchmark to study the performance of the presented approach compared with the most commonly used denoising techniques. The method has been successfully applied to improve the signal quality of Raman spectra from artistic pigments. The reliable results that were obtained make the methodology a useful tool to help the analyst in the interpretation of Raman spectra from pigments in artworks. Copyright © 2017 John Wiley & Sons, Ltd.Peer ReviewedPostprint (author's final draft

A chemometric study of ageing in lead-based paints

Raw data to accompany the results and discussion in the manuscript "A chemometric study of ageing in lead-based paints"