Portable Spectroscopic Techniques for the Non-invasive Identification of two historical yellow pigments: Applications and Practical Challenges

Decades of technological advances in instrumental analysis have transformed many techniques from laboratory in portable analytical tools with increasing their applicability in situ to the study of cultural heritage. It is known that the painting realisation varies from artist to artist, and the identification of the pigments provides a decisive contribution to trace their authenticity and to support an appropriate restoration work. However, in some cases, due to the complexity of painting composition, it is difficult to distinguish between pigments having a similar chemical composition and colour. Here, a systematic study through combined use of portable non-invasive spectroscopic techniques such as Raman, Total Reflectance FT-IR spectroscopy, Fiber Optical Reflectance spectroscopy and X-Ray Fluorescence was carried out on two yellow pigments, the Naples Yellow (Pb2Sb2O7) and the Giallorino (Pb2SnO4 or PbSnO3 or PbSn1-xSixO3), which sometimes are difficult to distinguish. The results emphasize the techniques' main advantages and drawbacks as well as their limits and the importance of their combination for the discrimination of such pigments