Analytical characterization of artist's paint systems based on emulsion polymers and synthetic organic pigments

The identification of artworks' constituent materials is a prerequisite for the development of appropriate art conservation methodologies, as well as for addressing authenticity issues. The present study focuses on the characterization of acrylic emulsion paints, with the use of Pyrolysis coupled with Gas Chromatography / Mass Spectrometry (Py-GC/MS), in combination with Fourier Transform Infrared in ATR mode (FTIR-ATR) and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDX). Commercial paints manufactured by Liquitex (USA) and Rembrandt series of Royal Talens (NL) were chosen for the study; the four paints selected contained the synthetic organic pigments, Hansa yellow (PY3), diketopyrrolopyrrole (PR264), phthalocyanine blue (PB15) or phthalocyanine green (PG7). The results provide clear evidence of recent changes in the paint formulations regarding the polymeric binder, with the addition of styrene to the copolymer nBA/MMA. Furthermore, different dispersants/surfactants were detected within the paints from the two different brands. Additional information was acquired on the additives incorporated in the paint, such as UV absorbers, optical brighteners, antioxidants and biocides. With regards to the identification of the synthetic organic pigments, several new molecular fragments were recorded using the applied experimental set-up at 600 degrees C, as compared to previous works. The products formed by the pyrolysis of the pigments are presented and discussed, showing evidence of different thermal fragmentation pathways as regards the synthetic organic pigments, when mixed in the emulsion paints.