Safranin-O dye in the ground state. A study by density functional theory, Raman, SERS and infrared spectroscopy.

The analysis of ground state structural and vibrational properties of Safranin-O is presented. The experimental results, obtained by FTIR, Raman and SERS spectroscopy, are discussed in comparison to the results of DFT calculations carried out at the B3LYP/6-311+G(d,p) level of theory. The calculated spectra reproduce quite satisfactorily the experimental data. The calculated Safranin-O equilibrium structure and the assignment of the vibrational spectra are reported as well. From the changes between Raman and SERS spectra a model is presented for the interaction of Safranin-O with silver nanoparticles.

Metal oxalates in paints: a Raman investigation on the relative reactivities of different pigments to oxalic acid solutions.

One degradation phenomenon that occurs in artworks is the formation of metal oxalates on their surfaces. In order to gain insight into the inclination of pigments to produce oxalates, nine pigments including Na, Ca, Fe, Pb and Cu cations were selected to react with oxalic acid solutions at different concentrations (1 M, 0.1 M, 0.01 M and 0.005 M). Micro-Raman spectroscopy was used to detect the different reaction products. Pigments containing calcium (calcite, gypsum and Volterra gypsum) showed a high tendency to form weddellite as well as whewellite, especially at high acidic concentrations; among copper-based pigments (malachite, azurite, verdigris), the formation of moolooite was observed for high concentrations of acid and down to the lowest concentration (0.005 M) in the case of verdigris. Lead oxalate was detected on lead white. No iron oxalates were observed for hematite; the formation of calcium oxalate crystals was observed instead. Ultramarine blue reacted to produce elemental sulfur. According to the results obtained, calcite and verdigris showed the highest reactivity in oxalic acid environments, resulting in a high tendency to form calcium and copper oxalates, even at very low acidic concentrations; this behavior seems to arise from the high solubilities of these pigments in acidic environments.

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

A small, potentially transportable prototype instrument capable of carrying out Raman, laser-induced breakdown (LIB), and laser-induced fluorescence (LIF) spectroscopy using a single pulsed laser source was developed for the analysis of cultural heritage objects. The purpose of this instrumentation is to perform fast and reliable analysis of surfaces with minimum damage to an object. For this purpose, a compact (51 x 203 x 76 mm) nanosecond Q-switched neodymium doped yttrium aluminum garnet laser (8 ns, 20 Hz, 0.01-115 mJ/pulse) was used as an irradiation source. The use of a nanosecond-gated detector sensitive between 180 and 900 nm allows the acquisition of elemental emissions in LIB spectroscopy and can also be employed for both LIF and time-resolved Raman spectroscopy. In this work, attention is focused on the description of the instrument and its optical components, and two examples of applications for the analysis of pigments and binding media used in works of art are presented.