Preservation of copper against atmospheric corrosion with a film obtained by plasma polymerization of methane

Ancient calcographic plates made of copper metal were restored by cleaning the residual dry ink by means of a surface plasma etching. The clean copper plates require some additional surface preservation in order to protect th em against further atmospheric oxidation and corrosion. We studied the prop erties of polymer film coatings on the copper plates. The films were obtain ed by plasma polymerization of methane gas in a low pressure R.F. reactor. We then studied the surface free energy of the films and their resistance t o ketone solvent. We evaluated thermal stability by thermogravimetric analy sis and their aging behavior by accelerated climatic tests. The electrochem ical behavior of the films was characterized by impedance spectroscopy and polarization curves.