A new method to remove copper corrosion stains from stone surfaces

This paper reports on a methodological study carried out in order to propose a cleaning procedure to remove stains produced by bronze corrosion products on surface of limestone (namely travertine); the procedure is effective and more environmentally friendly than the methods commonly used today. Several copper complexing or chelating agents were considered, including three amino acids and compared with some ion exchange resins. After a first laboratory phase on pure copper products and on artificially stained quarry samples, the optimized procedure was tested on the pedestal of a bronze statue in the Sapienza campus, in Rome. Colorimetry and ICP/OES were used to evaluate the efficiency of the cleaning procedure.

► This research presents a methodological study that led to a innovative cleaning procedure for limestone (namely travertine) surfaces, stained by copper compounds coming from the corrosion of bronze part of artworks.
► The obtained goal is an alternative to the currently used cleaning products, based on ammonia or ammonium salts. Really the last gives not completely satisfactory results. Moreover, it is well known that ammonia is eco toxic and its dispersion in the environment is almost unavoidable during the cleaning procedure; due to its toxicity, restorers need a protection during the cleaning as ammonia is an irritant for skin, eyes, throat and lungs.
► On these bases we can state that our amino acid based solution is not only more effective but also more environmental friendly and safe for the operator than now are used as cleaning solutions.