Comparative Laser Spectroscopy Diagnostics for Ancient Metallic Artefacts Exposed to Environmental Pollution

Metal artworks are subjected to corrosion and oxidation processes due to reactive agents present in the air, water and in the ground that these objects have been in contact with for hundreds of years. This is the case for archaeological metals that are recovered from excavation sites, as well as artefacts exposed to polluted air. Stabilization of the conservation state of these objects needs precise diagnostics of the accrued surface layers and identification of original, historical materials before further protective treatments, including safe laser cleaning of unwanted layers. This paper presents analyses of the chemical composition and stratigraphy of corrosion products with the use of laser induced breakdown spectroscopy (LIBS) and Raman spectroscopy. The discussion of the results is supported by material studies (SEM-EDS, XRF, ion-analyses). The tests were performed on several samples taken from original objects, including copper roofing from Wilanów Palace in Warsaw and Karol Poznański Palace in ŁódŸ, bronze decorative figures from the Wilanów Palace gardens, and four archaeological examples of old jewellery (different copper alloys). Work has been performed as a part of the MATLAS project in the frames of EEA and Norway Grants (www.matlas.eu) and the results enable the comparison of the methodology and to elaborate the joint diagnostic procedures of the three project partner independent laboratories

Copper sulphosalts in early metallurgy (2600-1900 BC) - chemical-mineralogical investigation of artefacts from southern Poland

We describe a methodology of investigation of both Cu metal matrix and its mineral inclusions that aims at increasing the effectiveness of identifying the type of ore used in metal production. We point to sulphosalt ores as the main source of metal for the Final Neolithic/Early Bronze Age copper artefacts from southern Poland. The inclusions, rich in Ag, As, Sb and Sn, document the type of ore, regardless of the metallurgical process leading to depletion of As and Sb. The copper metal should contain neither Sb nor As, hence both of these elements, if originally present in ore, can be preserved only in inclusions. The concentrations of Ag, Sb, As and Sn in the artefacts investigated, the presence of inclusions, and their chemical composition, are the key indicators for the determination of the mineralogical composition of the original ores. Given the high concentrations of Sb, As and Ag in the Cu metal and mineralogy of the inclusions, the ore must have contained varying proportions of Ag-bearing tetrahedrite (Cu,Fe)12Sb4S13 and tennantite (Cu,Fe)12As4S13. Mineralogical compositions of the copper ores indicate the deposits in Slovakia (Spania Dolina) as the source of metal for the artefacts investigated. The results of Pb and Cu isotopic analyses carried out for this study support those conclusions