Raman, X-ray fluorescence Spectroscopies and graphene oxide modified screen printed electrodes to identify the pigments and earth present in ancient leather samples

Micro-Raman and X-Ray Fluorescence combined with electrochemical techniques proved to be suitable for the unambiguous identification of the green pigment in a very deteriorated historical leather. The colouring matter resulted in a mixture of blue and yellow. Raman identified the blue indigo, whereas iron and arsenic were identified by XRF. The redox status of these two elements was investigated by Square Wave Cathodic Stripping Voltammetry (SWCSV). Results demonstrated the presence of As(III), probably As2S3 (orpiment), and Fe(III), characterising the red earths. The quantitative results obtained by SWCSV were also confirmed for Fe and As by ICP-MS (Inductively Coupled Plasma Mass spectrometry). Voltammetric techniques, applied here for the identification of the redox status of the elements, contained in pigments, are useful to understand two important aspects: the chemical-physical composition of the colors and the best strategy to be applied for the preservation of the pigments in ancient/deteriorated artwork objects.