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In this work, warm white (3,000 K) LEDs were used for investigating accelerated ageing of different classes of natural terpenoid compounds. In particular, colophony, sandarac, shellac, and mastic resins were considered. Maximum total irradiance of 80 Mlxh was used, which can be compared to about 130 years of exposure in recommended museum conditions. Moreover, another set of the same resins was kept in darkness conditions in order to assess kinetic differences. Raman spectroscopy was employed to assess molecular changes occurring in resins structures during both dark and light ageing. Spectroscopic information was achieved through a portable Raman scanner provided with a narrow-b and CW diode-pumped Nd:YAG (1,064 nm) laser and an NIR spectrometer equipped with an InGaAs linear array. Vis-LED light appears to be suitable to avoid yellowing in the case of mastic and colophony resins suggesting that it is advisable to use this light with respect to traditional halogen lamps for illuminating museums and art galleries. Conversely, the ageing process of sandarac and shellac appears not to be particularly affected by the UV radiation. Raman spectroscopy in combination with multivariate analysis (principal component analysis) was able to provide information about the ageing process of colophony both in light and dark conditions. [ABSTRACT FROM AUTHOR]

The removal of overpaintings from valuable easel paintings represents a very difficult challenge, which is traditionally approached using solvents and moderate mechanical actions. Here, we explore for the first time the potential of Long Q-Switching Nd:YAG (1,064 nm) laser with a pulse duration of 120 ns for selective ablation of overpainting layers. Mock-ups were prepared in order to approach in a systematic way a concrete uncovering problem concerning a modern painting on canvas. The former were prepared according to the stratigraphy and material compositions of the latter, as measured using optical and ESEM-EDX microscopy along with infrared and portable Raman spectroscopy. The parameterization achieved on the mock-ups allowed interpreting and maximizing the selectivity of the laser conservation treatment carried out on the real case. [ABSTRACT FROM AUTHOR]

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 achieved in 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 along with the portability of the novel device can make in situ Raman characterisation of valuable painted surfaces including photosensitive materials very safe and efficient. [ABSTRACT FROM AUTHOR]

In this work, a portable-Raman device (excitation wavelength 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 wheel moved 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, from those slower due to resins photo-degradation processes. [ABSTRACT FROM AUTHOR]