Abstract
Our research was conducted on a copper disc-butted axe, with a surface decoration made of a tin-based alloy, which was found east of the Carpathian Mountains in the Moldavian Plateau. This unique piece is thought to belong to the Middle Bronze Age in the Western Carpathians—Wietenberg, Suciu de Sus and Otomani–Füzesabony cultures. In order to evaluate the application process and the origin of the ores used, the surface and volume phase variation of the concentration of the metal components of the basic alloy (copper) and of the ornament was analysed using optical microscopy (OM), stereomicroscopy (SM) and SEM-EDX. The archaeometric features, formed both during its use and during its lying in the archaeological site, were identified and later used in archaeometallurgical evaluations and in determining the preservation condition of the two components (axe and ornament) on the surface, interface and in stratigraphic section. Experimental data revealed that, after its casting in porous silicon stone moulds, the object was coated with a thin film by immersion in an easily fusible tin alloy, which included copper as the major alloying component and arsenic and iron as minor components. After finishing the shiny white coat, a beautiful decoration was applied by incision and engraving. Used as a battle axe, it also had a rank function, as it belonged to the community leaders. The data prove the ability of ancient craftsmen to design and process copper alloys to obtain authentic extremely beautiful artefacts, which provide new possibilities to reveal the social and symbolic function of certain ancient bronze objects.
Highlights
Copper derived from nuggets, with traces of microelements of the same base ore; semi-bronzes, with alloying elements derived from two or more copper ores, different in terms of chemical composition; bronzes made of base metal and alloying elements in the form of ingots, obtained separately from copper ores and from ores rich in tin, zinc, lead etc
In relation to previous studies [3,6], which analysed the layout of chemical compounds formed in the three stages, this paper discusses the profile of variation in the concentrations of metal elements of the two structural components—the base alloy and the ornament, in representative areas, both on the surface and in cross-section
Since its commissioning, starting with the stage of ornamentation by soldering and inlay, a galvanic system with many electrode reactions was created at the interface of the hammer with the gilding layer, which is due to the different concentrations of metals more active than Sn, such as: As, Zn and Fe
Summary
Compared to gold and silver, bronzes are harder, but they are less eye catching. Ancient bronze artefacts (tools, weapons, vessels, mirrors, etc.) were either polished/gilded or ornamented on the surface. Ornamentation was performed by several ancient handicraft processes: chiselling and encrustation of the surface of the object [3,6]; tinning (initially by rubbing with tin ores reduced with charcoal at temperatures much lower than the bronze melting temperatures, as later by immersion in molten tin) [3,7,8,9,10]; silvering and gilding by polishing [11,12,13,14]. In the case of the last two surface filming processes, ornamentation was performed either before or after polishing or tinning
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