Biodegradation effects of three Aspergillus species on iron-based oxides (Hematite − Goethite) in paint layer in oil paintings

The inorganic colour layer based on iron oxide is affected by microorganisms (fungi) and leads to its deterioration due to feeding on the mineral elements through the chemical composition of the colour in the presence of a suitable environment (medium). Damage occurs as a result of heavy metal elements being removed from the colour, leading to a defect in the chemical composition and the fading of the colours. The current study showed the effect of the different types of the most common fungi on oil paintings (Aspergillus flavius, Aspergillus fumigatus and Aspergillus niger) after cultivating the different types of fungi and obtaining pure colonies for each fungus separately and conducting a fungal infection on experimental samples with preparing the old techniques, coloured with hematite red and goethite yellow. Each colour is mixed with different proportions of linseed oil (1, 2, 3). They were aged artificially and incubated at a temperature of 26^2+- degrees and examined periodically until the fungi appeared on the surface in the form of colour spots ranging from very dark (severe infestation) to light (low infestation). The change in chemical composition was measured by Raman and EDX analyses of the samples before and after infection. Fungi showed the appearance of spoilage products from metal sulfides and metal carboxylates. The iron oxide ion decreased in both the red and the yellow colours, leading to a change after the fungal infection. Examination of the morphological surface using SEM, USB and measurement of colour change showed the change in the red colour more than the yellow and scattering of green and black colour dots on the surface of the sample. Correlation and Simple Linear Regression were applied for each colour before and after besides both colours together. It was found that these colours appeared around some of the fungal colonies as a result of the activities. Fungal species of some strains reduced Fe⁺³ to Fe⁺² . This provides new insights into the role of microorganisms in the deterioration of painted surfaces.