Raman and infrared spectroscopic study of the basic copper chloride minerals - implications for the study of the copper and brass corrosion and "bronze disease"

Abstract

The vibrational spectra of both synthetic and natural atacamite and clinoatacamite are compared with natural paratacamite, have been obtained at 298 using a combination of FTIR and Raman microscopy. The vibrational spectra of the minerals are different, in line with differences in crystal structure and composition. The vibrational spectra of paratacamite are different from that of both atacamite and clinoatacamite. Paratacamite is not polymorphic with atacamite but rather is a separate phase. Some similarity in the Raman spectra of the polymorphs exists, particularly in the OH stretching region, but characteristic differences in the OH deformation regions are observed. These differences may be used to characterize the minerals. Differences are also observed in the chloride stretching and deformation regions. The implication from the study of these minerals is that copper, brass and bronze objects of archaeological, antiquarian and medieval significance can be studied by the use of Raman spectroscopy. Indeed the restoration of these types of articles can be aided by the application of Raman spectroscopy to the study of the degradation products from paintings of antiquity.