Methodology

 

The main aim of art analysis is to try to obtain the maximum amount of informations on an object while keeping the risk of damage as low as possible. In this regards, non-destructive techniques, such as photoluminescence and Raman spectroscopy, are of great importance. The instruments will be a homemade instrumentation that can give the luminescence properties as well as the Raman spectra from the same spatial region of the samples. For this purposes the instrumentation will possess three different diode lasers with emission at 405, 532 and 1064 nm, respectively. The light will be focalized through an objective of microscope (10x NA 0.25). The laser power will be kept low in order to avoid any heating effects on the samples by using appropriate OD filters (the laser power at the sample surface should not exceed 10 mw). The emitted light will be gathered through an optical fiber bundle and then dispersed in the relative spectrograph (each excitation light has a own spectrometer, plus a wide range spectrometer for the luminescence spectra).

The Raman and micro-Raman analysis allows to identify the main elements but also their crystallographic phase. The paints used to decorate a surface are materials with their own vibrational spectrum, and then with a Raman spectrum which uniquely identifies them. In the case in which, instead, the colour is due to the presence of dopants whose concentration is the minimum percentage with respect to the main phase (doping of less than 1%) the combined analysis of Raman + luminescence may provide a final picture on the nature of the pigment.