Study of behaviour on simulated daylight ageing of artists¿ acrylic and poly(vinyl acetate) paint films

[EN] This work proposes a multi-method approach that combines advanced microscopy (SEM/EDX, AFM) and spectroscopy (UV-vis and FTIR) techniques. This approach not only characterises the behaviour of the additives of two commercial poly(vinyl acetate) (PVAc) and acrylic emulsion paints but also simultaneously characterises the changes in chemical composition and morphology observed in the paint films as a result of ageing due to the paints being exposed to an intense source of simulated daylight. In parallel, a series of mechanical tests were performed that correlate the chemical changes in composition and the changes observed in the films' mechanical properties. This work was a comparative study between both types of acrylic and PVAc paints. The results obtained are of great interest for the modern paint conservation field as they provide valuable information on the mid- and long-term behaviours of these synthetic paints.Financial support is gratefully acknowledged from the Spanish "I+D+I MICINN" project CTQ2008-06727-C03-01/BQU supported by ERDEF funds and from the "Generalitat Valenciana" I+D project ACOMP/2009/171 and the AP2006-3223 project ascribed to the Predoctoral Stages Programme of Universitary Researchers in Spanish Universities and Research Centres from the Spanish Ministry of Science and Innovation (MICINN). The authors wish to thank Mr. Manuel Planes i Insausti and Dr. Jose Luis Moya Lopez, the technical supervisors responsible for the Electron Microscopy Service at the Polytechnic University of Valencia.Domenech Carbo, MT.; Silva, MF.; Aura Castro, E.; Fuster López, L.; Kröner ., SU.; Martínez Bazán, ML.; Mas Barberà, X.... (2011). Study of behaviour on simulated daylight ageing of artists¿ acrylic and poly(vinyl acetate) paint films. Analytical and Bioanalytical Chemistry. 399:2921-2937. https://doi.org/10.1007/s00216-010-4294-3S2921293739

An initial assessment of thermally assisted hydrolysis and methylation-gas chromatography/mass spectrometry for the identification of oils from dried paint films

Conservation scientists are frequently asked to identify the materials that are contained in microscopic fragments from works of art. For decades, the only technique successfully used for characterising the type of oil binder used from dried oil paints has been gas chromatography/ mass spectrometry (GCMS). Unfortunately, the process requires a lengthy sample preparation and some of the derivatisation processes used present serious health and safety implications. Although thermally assisted hydrolysis and methylation-GCMS (THM-GCMS) has been used more recently for the analysis of traditional paint binders, its ability to distinguish between different oil types has yet to be ascertained. This paper describes the use of THM-GCMS to examine differences in the fatty acid composition of dried pigmented films of linseed, linseed stand, poppy, safflower and walnut oil. The results were compared for pyrolysis at 610 and 770 \ub0C, two of the most commonly used temperatures in Curie point pyrolysis, in order to verify reproducibility of the results. Based on three runs for each sample, the fatty acid composition (measured as methyl esters) was found to be temperaturedependent, as previously suggested in literature. At the lower pyrolysis temperature (610 \ub0C), a higher degree of reproducibility was seen and the ability to differentiate between each of the dried oil types using palmitate/stearate (P/S) ratios was improved. Interestingly, the P/S observed for each oil at this pyrolysis temperature were found to be close to those obtained by published GCMS procedures. In addition, samples of dried pigmented films of egg yolk were investigated and it was confirmed that this medium could be differentiated from each of the drying oils at this pyrolysis temperature from their azelate/palmitate ratios. These preliminary findings are encouraging for the use of THM-GCMS as an alternative method to GCMS for the identification of oils used as binders in paints