60 years of street art: a comparative study of the artists’ materials through spectroscopic and mass spectrometric approaches

Street art murals are an artistic expression strictly interwoven in the urban landscape, and in recent years have received increasing attention as cultural heritage at risk. Today there is intense debate regarding the value assessment and choices related to the conservation of urban art; however, the evaluation of the stability of modern paint materials in outdoor environment is preliminary to any possible preservation strategy. In particular, the identification of the materials constituting a street artwork is critical for the preservation of these non-permanent heritage elements and to define the best restoration approaches. In this work, we performed a set of analyses of microsamples based on spectroscopy, analytical pyrolysis, gas and liquid chromatography, and mass spectrometry to identify paint materials (binders, pigments, additives, degradation products and conservation/restoration materials) of a selection of mural paintings, covering 60 years of history (1953–2014). The goal of this work was to identify the materials used to produce different mural paintings and to relate and compare their different compositions with previous studies in order to describe the evolution of the materials during the last 60 years. The collected knowledge and the limited data available in literature were exploited to increase the scientific background on the materials used by street artists, and to fill the lack of knowledge on this emerging topic.