Molecular spectroscopy for the in-situ investigation of cultural heritage materials

In 1815, the British scientist Sir Humphry Davy , discoverer of chemical elements such as sodium, potassium and calcium, published in the Philosophical Transactions of the Royal Society of London an essay “on the colours used in painting by the ancients”, after analyzing by wet chemistry methods pigments drawn from wall paintings of imperial Rome. Since then, the need to identify cultural heritage materials was maintained and even increased, not only for sake of knowledge but also as a basis for conservation, possibly restoration and even authentication of works of art. At the same time, the range of objects to be analyzed has enlarged to include, besides paintings, many other expressions of art and craftsmanship of the past. Moreover, in some cases not only original materials but also their possible alteration products need to be recognized. In the meanwhile, the development of a wide range of synthetic materials used in contemporary art has made the task of their identification even more challenging. On the side of analytical techniques, the evolution towards instrumental methods, especially spectroscopic ones, opened the possibility of increasing information while reducing the amount of sample required, till the development of completely non-invasive techniques. In this context, given the complexity of the analytical problem, the use of molecular spectroscopy has a meaningful role, especially if the highly compound-specific vibrational spectroscopies are considered. The potentiality of in-situ non-destructive infrared and micro-Raman analyses by means of compact, movable equipment will be described for different kinds of artefacts, together with the combined use of Raman instrumentation for micro-fluorimetric measurements.