Analysis, testing and development of safe cleaning methods of rusted stone material

Rust stains are a widespread problem for natural stones of both civil buildings and cultural heritage, particularly for white marbles. For this reason, the aim of this work was to develop new methods of treatment/application, in order to identify a safe protocol for cleaning rusted marbles. Three different treatments were applied on several specimens of both dolomitic and calcitic marble, properly stained with rust to mimic real situations (the stone specimens were exposed to the natural environment for about six months in contact with rusted iron). Marble specimens were characterized before and after treatment and monitored during the cleaning tests. The specimens were characterized by SEM-EDS (Scanning Electron Microscopy coupled with Energy Dispersive System), XRD (X-Ray Diffraction), XRF (X-Ray Fluorescence), FTIR (Fourier Transform Infrared Spectroscopy) and color measurements. In addition, microscopic and macroscopic analyses of the stone surface along with tests of short and long term capillary absorption were carried out. A series of test trials were conducted in order to identify the best conditions in terms of concentrations and contact time, starting from the data reported in literature. New methods of treatment application were verified, substituting the usual Cellulose Poultice with Agar. The latter is a gel already used in many other contexts, being something new in this field, which possesses great applicability in the field of conservation of stone materials. After the application of the cleaning method, the specimens were characterised again in order to understand which treatment was more effective and less harmful. The study indicates that for a very intense and deep penetration into the stone, a solution of 3.5% (w/v) of Sodium Dithionite buffered with Ammonium Carbonate to pH 7 applied with Agar support would be appropriate.