Effect of iron rust on color layer and structural integrity of historical oil paintings

In recent years, the study of the deterioration phenomena and factors of oil paintings has attracted great attention from the scientific community. However, the number of articles that contain a study of the phenomenon of rust damage on paintings and an explanation of the mechanism of damage on canvas is small, so this article focused on studying the effect of rust resulting from the use of iron nails in fixing the canvas holder and due to aging and exposure to damaging conditions on colors containing metals (red-yellow-blue) in oil paintings, which results in damage products from rust, and different on the surface appearance of the colors and change the chemical composition of the color. This article aims to discuss (1) the phenomenon of rust that affects paintings (2) the problems associated with the effect of rust that migrates through the layers on the rest of the parts of the painting other than the colors, such as the canvas layer and the preparation layer (3) describing the mechanism of atmospheric corrosion of iron by interacting with ground colors (red ochre-yellow ochre-blue) using experimental models covered with rust and exposed to thermal and light aging to evaluate damage before and after accelerated aging and the most important damage products (4) and the evaluation of damage was done by using color change measurement For the samples, the front and back morphological surfaces of the fabrics were monitored before and after aging through the average color measurements of the three colors. It became clear that the blue color shows the greatest change after complete aging in color ∆E = *42.7 Followed by red, which shows a complete change in color ∆E* = 23.6, followed by yellow, which shows a complete change in color, ∆E* = 21.7. Microscopic examination showed that the rust was distributed in an uneven manner on the back surface of the fabric, and the front surface with the colors, and the appearance of large orange spots on the surface randomly, and the appearance of fine cracks penetrating the layers in the areas mixed with iron rust products, and their mixing with the color grains. The change in the chemical composition of the colors was monitored before and after aging by FTIR, EDS, which showed changes in terms of the appearance of the iron element (Fe) and an increase in its concentration after aging, which confirms that the color was affected by iron rust resulting from the rust of the iron nails fixed to the fabric layer stained with rust that migrates through the layers that are damaged due to the migration of Fe²⁺ ions to the surface of the colors in the presence of alkaline metal cations in the chemical composition of the three earth colors. In the presence of moisture, the damage increases because the ionic diffusion across the thickness of the formed film leads to the disintegration of the paint because the polarization of the cathodic substrate encourages the migration of cations through the color layer, and the color change in the yellow and red colors resulted from the presence of the iron ion that reacts with Fatty acids in oil.