'Save Art' Treatment: new Improvements in Removable-Protective Coatings for Metallic Archaeological Finds

摘要

The problem, never completely solved, of protecting metallic handworks from the corrosion, the so called bronze cancer, is complicated by the justified reluctance of the museum responsible to authorize the treatment of antique artwork, frequently very precious, without the certitude of its possible removal in safe manner. The authors have proposed a process, patent pending, based on the deposition over the metallic substrate of a first soluble organic coating, transparent and achromatic, relatively thick (30-60 micron), and of a second thin multilayer structure, also transparent and achromatic, acting as barrier for oxygen water vapour, composed by ceramic layers (SiO_2, Al_2O_3 or ZnS) vacuum deposited by Ion Plating and organic (resin) or semi-organic layers (SiO_xC_y) deposited by Plasma Enhanced Chemical Vapour Deposition. Pre-feasibility tests, presented in the SVC Technical Conference 2011, have shown good compatibility of oxides, deposited by Ion Plating Plasma Assisted (IPPA), with an organic acrylic polymer, spray deposited, showing good adherence, good transparency and achromaticity and easy to be removed by a simple Lift-off method. This paper presents a further phase of the research aimed at exploring some specific aspects on Transparency, Achromaticity, Removability and Compatibility of treatment, before optimizing the performances barrier to oxygen and water vapour.