Atomic oxygen cold plasma for oil paint surface cleaning – comparing the impact of treatment on fresh and aged paint

Surface cleaning presents one of the most important and frequently carried out procedures in cultural heritage conservation. To tackle challenging cases, such as cleaning delicate or water sensitive surfaces, where typical contact methods might not be applicable, a novel approach is being investigated by the ongoing European project MOXY. It aims to develop an instrument for conservators based on the application of atomic oxygen (AO) for the non-contact surface cleaning of cultural heritage objects. This paper presents results of an investigation conducted as part of the MOXY project into the impact of AO on oil paint. The experiments were based on treatment of simplified handmade oil paint models with atomic oxygen and their subsequent comparison with the normal untreated paint samples to relate observed changes to the effect of AO. Specific focus was placed on the comparison of the effect between freshly prepared and naturally aged (1- and 2-year-old) mock-up models. Samples were prepared using ultramarine blue pigment, selected for its known promotion of oxidative degradation in oil paints, and binder (linseed or safflower oil). Oil paints were selected as object of this investigation based on their potential sensitivity to the oxidizing action of AO For the analysis of chemical alterations in the binder ATR-FTIR, DSC, EGA-MS and SPME GC-MS were utilized. The methodological approach implemented proved efficient in detecting the expected impact of AO treatment of freshly prepared oil paint layers. A partial degradation of cross-linked lipid structure and the production of species associated with oxidative degradation were observed. The treatment of aged model paint layers leads to significantly less changes, and data seems to indicate a promotion of cross-linking over oxidative degradation. Further investigations are in course in order to enable a systematic comparison of the extent of change upon AO treatment with other non-contact cleaning methods.