Results of spectroscopic investigation of the historical copper and copper alloy objects covered by patina and surface contamination are reported and discussed in this work. For analysis of the surface layers (bulk material, primer/grounding, patina and atmospheric contamination) the Laser Induced Breakdown (LIBS), Raman and X-ray fluorescence (XRF) spectroscopic techniques are used. Useful data on chemical structure and composition are obtained from stratigraphic analysis performed by a stepwise layer penetration with successive laser pulses. The LIBS, XRF and Raman spectra confirm the presence of patina and contamination layers of the compositions influenced by the atmospheric environment. The elemental composition reveals in the case of the original copper substrate the presence of Cu with traces of Ag and Sb, and of impurities Fe and Pb, while objects made of copper alloys (brass) show different Zn/Cu ratios greater than 20% in all cases and admixtures of Sn and Pb. Consistent results are obtained from the elemental and Raman data indicating presence of the antlerite (Cu3(OH)4SO4), carbon and microcrystalline calcite which are ascribed to patina, surface contamination (atmospheric soot) and primer layers, respectively.
In this work the time-resolved Laser-Induced Plasma Spectroscopy (LIPS) is applied for investigation of samples containing calcium carbonate (CaCO3) which represents a marker in the identification of historical stone and pigment materials. The relatively broad bands in the range of 547-560 nm and between 580 nm and 650 nm ascribed to the CaO molecular emission are clearly observed together with the collection of sharp peaks characteristic for the atomic Ca I and ionic Ca II lines. For suppressed oxide formation processes by means of recording the spectra in the N2 environment a marked change in the time evolution of the CaO bands is observed and reaction kinetics different from that observed in air is concluded. This supports the CaO assignment and is confirmed by values of the decay time constant of 2,49 μs for nitrogen and 0,81μs for air derived from fitting of the experimental decay curves of the molecular emission. The case of CaO confirms that the time-resolved LIPS analysis provide useful supplementary data and contribute to reliability of the material identification.