The application of an innovative green material "sapoline" for the cleaning of historical metal objects

In this study, a novel green cleaning medium ‘sapoline’ was designed by dissolving saponin powder in aquoline, a natural deep eutectic solvent made from choline chloride and water. The cleaning efficacy of sapoline and its low aquoline content version (low-aquo sapoline) was evaluated on artificially aged brass and steel samples, with the support of multi-analytical techniques. While sapoline showed a relatively slow cleaning rate and required longer application times, the cleaning with low-aquo sapoline occurred faster on both brass and steel, for which the saponin concentration played a more critical role than the application time. The cleaning efficiency of different loading matrices was also compared. It was observed that agar gels showed a higher cleaning efficiency than Evolon microfilament tissues.