Chemical characterisation of spray paints by a multi-analytical (Py/GC-MS, FTIR, μ-Raman) approach

This study outlines the chemical characterisation of a large number of commercial spray paints as used in street art, graffiti vandalism and for decoration purposes. The analyses were focused on the identification of the synthetic binding media, pigments and additives such as plasticisers and fillers, providing a database as well as a methodology which could remarkably help investigations in a broad panorama of case studies, ranging from forensic science to cultural heritage. A protocol has been developed based on a multi-technique approach. In particular, Fourier Transform Infrared (FTIR) spectroscopy, Pyrolysis/Gas Chromatography-Mass Spectrometry (Py/GC-MS) and μ- Raman spectroscopy were applied and their strength and weakness points as to the identification of all spray paints components are outlined. Each sample was first examined with FTIR spectroscopy as a preliminary screening step to obtain indications on the main binder, which could then be confirmed and detailed using Py/GC-MS. Some pigments and extenders could be efficiently identified by examination of the FTIR spectra and pyrolysis products. However, for most samples a μ-Raman spectroscopy investigation was required in addition to the mentioned techniques in order to achieve the complete chemical characterisation of organic and inorganic pigments, extenders and fillers. Differences and common features among brands/colours are highlighted and discussed.