Some samples of oil paintings (5 × 5 cm) were prepared on wooden panel with four types of fungi commonly encountered on oil paintings were selected for this study. Each of the fungi is associated with different colored stains. Fungus Alternaria tenuis is associated by a dense black stain, Chetomium globosum by a brownish gray stain, Aspergillus flavus by a yellowish stain, and Fusaruim oxysporum by a pinkish stain. Fungi growing on oil paintings affect the surface characteristics by forming a variety of colored patches typically composed of many complex chemical substances that are produced during metabolic processes. These colored stains may be encrusted in spores, present in mycelium or secreted to a substance such as oil paintings surfaces. While the fungal stains can sometimes be extracted with appropriate solvents, there are some stains that resist solvent extraction entirely. Developing new solvent system that might attack the paint structure, and is time consuming and requires a great deal of trial and error. Mechanical stain removal is also problematic in that it often produces abrasion of the surface, markedly deteriorating the artwork, and is extra ordinarily fine and tedious. For these reasons, we decided to examine an alternative physical technique as a new approach to deal with stain removal. Since the stains are due to the existence of fungi, we thought it a good idea to remove them by singlet oxygen. We applied the photo dynamic process through which the fungi stains were covered with organic dye derivatives in solution under controlled illumination in the lab. The samples were then irradiated by low power Laser light from a He-Ne laser, the dye will be photodecomposed and produce singlet oxygen. We report in this work the results obtained as a function of: - The concentration and types of the organic dye in solution, - The presence of certain amounts of liquids added to the solution, - The scanning speed of the laser beam on the sample surface, - The irradiation time. For each case fresh samples were used and photographed before and after the treatment. The results obtained will be speculated and discussed. This procedure was applied to the cleaning of archaeological oil paintings for the first time to our knowledge. The method could well be considered as a new field of combined science and technology applied to laser stain removal and represents a significant addition to the techniques available to art conservation.
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