engleski

Studying uv ageing effects in modern artists´ paints with MeV-SIMS

MeV-SIMS is a highly surface-sensitive technique that can provide information of the chemical composition in the uppermost layers of materials under investigation. By irradiating the sample with an ion beam in the MeV energy range, intact molecules are desorbed from the surface through electronic sputtering which leads to less fragmentation and a more straightforward interpretation of the mass spectra compared to keV-SIMS. For this reason, MeV-SIMS has emerged as a powerful tool with application to many fields, one of which is cultural heritage studies where it has been successfully applied in identification of synthetic organic pigments (SOPs) in paint materials [1] and for molecular imaging of modern paints [2]. In this work artificially aged alkyd and acrylic self-made paints, containing SOPs from different chemical classes (phthalocyanine, quinacridone and diketopyrrolo-pyrrole) were studied using MeV- SIMS with the aim to investigate chemical changes that are taking place in the surface layer due to paint ageing. Two-component mock- up samples were prepared and exposed to accelerated artificial UV ageing conditions for two and four months. The obtained results show that the investigated SOPs are stable under accelerated ageing conditions and can be easily identified in aged paints. New chemical species were detected in the aged paints compared to the unaged samples which were identified as the degradation products of the binder portions of the paints, both alkyd and acrylic. Enrichment of the pigment relative to the binder on the sample surface was also observed. Acrylic binder exhibited slightly higher stability to photo-degradation compared to the alkyd medium, while the kinetics of the degradation processes were roughly found to be dependent on the pigment present in the paint, with phthalocyanines having the highest photo- stabilizing effect among the studied pigments. This study will significantly facilitate identification of modern paint materials in real artworks that have been exposed to environmental conditions, having undergone chemical transformation in the surface layer.

MeV-SIMS ; UV ageing ; artists' paints ; synthetic organic pigments ; alkyd ; acryl

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