Mahir Hrnjić

Laser cleaning, as a conservation technique, is a selective, precise and minimal intrusive method of removing corrosion product layers. Nevertheless, in order to optimise this method as a standard conservation technique, it is still necessary to define different laser cleaning methodologies. In this study, laser cleaning was performed with near-IR lasers on artificially aged copper specimens and on two copper coins coming from Bubastis (Egypt) in order to remove the patinas in a totally non invasive way. Different irradiance and different number of passes were utilised and compared. Treated surface is characterised by optical and scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Results show that near-IR laser has successfully removed corrosion products from the surface. An alteration of the metallic surface is observed only after treatments performed with higher irradiance values or with numerous passes.

In the Viking Age, silver coins, ornaments and jewellery found their way to Europe and Scandinavia in such vast quantities that some researchers refer to the period as the ‘Age of Silver’. Countless archaeological finds of Viking hoards provide some answers about how silver was used and how it forged and formed the Vikings’ world, and where this precious metal initially came from.

A common issue in non-destructive surface analysis of historical silver coins is depletion of Cu from the near-surface areas, which in turn results in higher Ag content at a coin’s surface. This paper reports a non-destructive analytical strategy using µXRF for identification of Ag and Cu surface enrichments and depletions by comparing peak intensity ratios of Ag Kα/Ag Lα, Cu Kα/Ag Kα and Cu Lα/Ag Lα for coins and Ag-Cu standards of similar composition. Our characterization of coins from different contexts and chronologies shows that a multi-standard approach provides the most reliable identification of surface enrichment of Ag and depletion of Cu. Coins possessing Ag surface enrichment were further analysed with LA-ICP-MS to determine any differences in trace element composition between the cores and surface of the coins. We show that the near-surface regions of these coins are enriched in Au and depleted in Co, Ni, As, and Pt relative to their cores. These systematics allow for a more robust assessment of the degree of silver coin surface alteration critically important in measuring the original composition of historical silver coins.

The Viking Age concurrently begins with the deposition of silver hoards throughout Scandinavia. Vikings engaged in long-distance trading networks with the communities and political entities in the East, resulting in vast amounts of silver pouring into Northern Europe. Through such trade, a supra-regional communication network was established that supported social-ties and strong economic interactions between actors involved. Objects found in hoards, provide a valuable foundation for studying communication and trade networks in the Early Middle Ages. One of the most intriguing group of silver objects are Perm'/Glazov and Duesminde neck- and arm-rings. They are evidence of strong socioeconomic ties between communities in Scandinavia and Eastern Europe. Alongside rings, an important indicator of dynamic long-distance relationship are the vast number of silver coins (dirhams) found in hoards. Most of dirhams can be put in direct relation with the historical regions in which they were minted; however, they lack information about where was the silver mined. The origin and the form of silver that reached Northern Europe varied depending on political, economic and other changes that occurred during the Viking Age. Through application of techniques used for geochemical and archaeometallurgical study, it is possible to develop an insight in the origins of silver used for producing rings and coins, as well as changes through time. The analytical methods, such as the lead isotope analysis done by MC-ICP-MS and trace elements identification obtained by μXRF, have been applied with a high degree of success in determining the origin of different silvers. The aim of the research is to understand the development of long-distance communication and networks between Northern Europe and Eurasia, by understanding the provenance of 8th and 9th century silver found in Scandinavia.