Changes in the surface characteristics of artificially aged mastic varnishes after cleaning using alkaline reagents

AbstractThis study investigates the effects of a selection of alkaline reagents, including solutions, pastes and soap gels, used to remove an artificially aged mastic film applied over a primed canvas. Surface changes were examined using visible light and scanning electron microscopy (SEM). Ammonia, whether in solution or gelled with hydroxypropylmethylcellulose (HPMC), required a pH of 10 or higher to remove varnish at an appreciable rate, whereas ammonia in wax paste worked at pH 9. Soap gels based on deoxycholic acid (DCA) were effective at pH 9·5. The rate of removal increases significantly with the addition of benzyl alcohol, while anthracene-9-carboxylic acid (A9C) and 9-fluorenone-4-carboxylic acid (9FOC) soap gels of pH 7·9 worked quickly without the addition of alcohol. Where reagents with a pH of more than 9 were used, some erosion of the priming was observed under SEM. Examination of the topography of residual varnish after treatment and Fourier transform infrared spectroscopy (FTIR) measuremen...