Abstract

Leather artifacts from excavation sites, museums, storehouses, and libraries suffer from the impact of inappropriate preservation or storage conditions, leading to various forms of damage. Stains are among the common aspects of deterioration to vegetable-tanned leather in these places. Iron rust stains are particularly damaging and can lead to complete deterioration of the leather artifact, especially in the presence of air pollutants, particularly sulfur dioxide, along with fluctuations in relative humidity in the environment as both of these factors accelerate chemical reactions. There is limited research on removing iron rust stains from vegetable-tanned leather artifacts. This study seeks to explore the effects of iron rust stains on vegetable-tanned leather and assess the effectiveness of using acids either alone or in combination with ultrasonic waves for cleaning these stains, presenting a novel approach. In order to conduct the study, vegetable-tanned leather samples were prepared, and iron-rust stains were applied to them. The samples were then subjected to accelerated thermal ageing to set the iron-rust stains. Cleaning treatments were carried out using orthophosphoric and citric acids at different concentrations, either individually or in combination with ultrasonic waves. The results proved that citric acid effectively removed iron stains without affecting surface morphology. Orthophosphoric acid had some impact but worked well with ultrasonic waves. Iron-stained samples had lower pH values, especially in aged samples. Acid cleaning slightly lowered the pH. Cleaning with citric and orthophosphoric acids at different concentrations maintained the mechanical properties better than those of aged uncleaned samples. Contact angle measurement proved the efficacy of acid cleaning, significantly reducing the contact angle. Acid cleaning methods also minimized colour changes, with citric acid resulting in less colour difference compared to orthophosphoric acid.