In order to restore the original aesthetic aspect, to improve the state of the age patina and of the gold halo, similar processes are required. The cleaning process is one of the most important aspects for an artwork and is considering a series of deteriorations and degradations, like dirt deposits (clogged or unclogged) opalescent varnish, colors blackening, burns, blisters, gaps (missing ground, painting layer or varnish). This step in the restoration process includes physical and mechanical proceedings like dusting (with a vacuum), brushing (with a brush), scraping (with a scalpel), removal or polishing etc. The scalpel and the milling process are rough unconventional means that are used only in exceptional cases. The wet cleaning of dirt includes classic washing processes, with water or other complex systems of organic solvents (emollients, surface additives or surfactants, mixtures of solvents). Cleaning the clogged dirt deposits with unconventional methods can be done by means of electronic laser, ion and thermal exchange or ultrasounds. Laser cleaning is often used in removing unwanted dirt deposits from different layers of the art piece. A lot of attention goes towards the controlled elimination of the exterior protection layer (varnish), which can be photo- degraded and oxidized by atmospheric exposure. Visual analysis, with enlargers (OM, SEM, AFM etc.) combined with transmission or penetration techniques (radiography, endoscopy, X-ray diffraction etc.) provides information on the superficial structures of the art work. In order to determine the modifications of the desiccant oils, SEM was used to observed the changes in the morphology of the oil painting layers. Gas chromatography/mass spectrometry (GC/MS) can be used to detrmine detergent residues on the painting layer.
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