Atomic oxygen technology for the surface cleaning of art objects. Investigation into the effect on oil paint

Surface cleaning is among the most important and frequently performed procedures in art conservation. Historically it was carried out either by “dry” methods, which include mechanical removal of dirt, or by “wet” methods, which utilize water and solvents for the removal of contaminants. In the last 50 years, alternative methods began to be developed – laser ablation and the use of gels to control the depth of solvent penetration. However, in some cases, solvents may be toxic, while in others, control of the process may be difficult. When surfaces are sensitive to solvents and/or mechanical action, non-contact cleaning approaches may be required. To tackle these problems and advance the use of green approaches, MOXY project was developed. It aims to create a non-contact technique based on atomic oxygen (AO) for the cleaning of the cultural heritage objects. It involves the use of cold plasma and allows for non-liquid, non-thermal treatment. Atomic oxygen is a highly reactive agent with short lifetime of few milliseconds, so the expected effect on the organic contaminants is their oxidation with the production of volatile products. However, before applying it to actual historical objects, we must understand how the oxidation from AO treatment can affect the underlying substrate material and compare it to other more established cleaning methods. Application of this technology to oil paints can help overcome a number of conservation issues – difficulties with detailed impasto areas or delicate flaking areas, issues with water sensitivity of many modern paintings and others. The topic of oxidation of oil has been well studied- at its core they are radical chain reactions, which include the formation of peroxides and hydroperoxides, many internal recombinations and a termination step with the occurrence of secondary oxidation products – aldehydes, ketones, alcohols etc. Understanding the possible outcome of such chemical interaction, and implementing analytical methodologies, we can shape our approach towards the qualitative and quantitative assessment of the effect from the AO treatment on the substrate. To this effect, a number of simplified mock-up models consisting of handmade oil paint were prepared and subjected to the atomic oxygen treatment. These samples include oil paint with ultramarine blue pigment and varied binders – linseed oil traditionally used in oil paints, safflower oil more frequently encountered in modern paints and methyl linoleate which provides a simplified chemical model of oil paint. Treatment with atomic oxygen was performed on fresh and naturally aged (1 and 2-year-old) samples of the identical composition. Following that, analysis on treated and untreated areas was performed in order to detect changes in the chemical composition of binder both in bulk and on the surface, as well as investigation of the volatile organic compounds, released from the sample. The following techniques were utilized. LC-ESI-MS was used to compare the glyceride profile of the paint layers, EGA-MS to characterize polymeric structure of the binder and its thermal stability, SPME GC-MS to investigate the difference in the volatile organic compounds released, ATR-FTIR to analyze changes induced on the surface and DSC to evaluate the presence of hydroperoxides and active radicals. Obtained results are presented in this poster and display a first set of analytical data which serves as a stepping stone in the further research into the applicability of the technology for actual objects of art.