An insight into spray paints for street art: Chemical characterization of two yellow varnishes by spectroscopic and MS-based spectrometric techniques

In recent decades, modern murals and graffiti have become valuable artistic expressions that deserve attention for their dissemination and conservation. The chemical composition of spray paints with improved technical performance reflects the assortment of materials used in these artworks. Understanding the spray formulations is important in preventing deterioration of street art. In this study, two yellow varnishes were investigated by attenuated total reflectance Fourier-transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopies (XPS), laser desorption ionization (LDI) and matrix-assisted (MA) LDI mass spectrometry (MS). ATR-FTIR allowed us to distinguish the occurrence of acrylic and styrene-acrylic resins as the main binders with some additional components, while XPS shed light on the recognition of some silicone-based additives, which aggregate at the most superficial varnish layers. Several established experimental conditions of MALDI-MS including matrix, salt dopant and extraction solvent, revealed the use of polyethylene glycol as an additive, while direct LDI-MS/MS analysis proved to be very useful in characterizing the yellow (PY74) and orange (PO36) pigments. Some insight into the minor components of the spray paints, such as surfactant, humectant and silicone-based levelling or anti-cratering agents, which were not easily obtained through conventional ap-proaches, was also gained.