Metallographic Approach to the Investigation of Metallic Archaeological Objects

Abstract

Metallic objects are considered among the most significant findings in Cultural Heritage and represent the 'culture of Materials' and the habits of an historical period and of a population. They also preserve traces of time: from the transformation of the ores in metal (by smelting) to the degradation from metal to oxidised compounds (by corrosion processes). Metallography, historically devoted to connect the microstructural features to production processes and to chemical-physical-mechanical properties is a powerful and relatively easy approach to characterise metallic findings. All analytical tools and methods in the hands of a metallographer are improved through experience and practice and provide a large number of information (elemental composition, primary and secondary microstructures, surface treatments, corrosion rate, original ores traces) by the preparation of a fairly small microdestructive sample. A wise and careful use of the metallography allows the balance "object sacrifice/knowledge improvement" to lean on the right side contributing to the hard work of rebuilding humankind history. Beside a description of a research protocol some practical examples concerning archaeological findings are presented in this paper.

Identification of ancient gilding technology and Late Bronze Age metallurgy by EDXRF, Micro-EDXRF, SEM-EDS and metallographic techniques

“…in the sense that sampling or cleaning of a small surface is frequently required), multielemental, relatively fast and versatile, allowing average compositional information but also local information of small areas [15]. The electronic and optical microscopies are able to provide a wide range of information on metallurgical features and conservation state of the objects, and the metallographic approach can be considered easy to apply, not expensive, a flexible and adaptable research tool [16].…”

Microstructural and Analytical Study of Uncommon Corrosion Features on Archaeological Cu-As Alloys from Tappeh Graziani in Southeastern Iran

“…The preservation of the original microstructure of the objects within the corrosion products may attribute to an epitactic transformation as noted by Scott (2002) in which cuprite preserves pseudomorphic microstructures of the copper alloy as the corrosion progresses inward. Pinasco et al (2007) suggest that retaining the pseudomorphic microstructure in copper alloys when corrosion processes lead to the formation of oxides is more probable than carbonates and chlorides.…”

Metallographic investigation of Early Bronze Age armbands from Western Switzerland (ca. 2200–1500 BC): new highlights about early manufacturing processes

“…To fully address this lack of data, high-quality information can be obtained through metallurgical investigations by exploiting the ability of metallic materials to record its own thermomechanical history (Piccardo et al 2017a(Piccardo et al , 2017b. This way, nondestructive (i.e., which do not alter the sample during analysis) and micro-invasive (i.e., which only require micrometric samples) procedures result in a good compromise between the quality of information and the object alteration (Pinasco et al 2007;Piccardo et al 1997). However, the use of nondestructive and noninvasive methods (e.g., p-XRF) is sometimes not enough to get sufficient information about the metallic core and the presence and distribution of phases and inclusions, when a patina of corrosion product covers the surface of the artifact (Fernandes et al 2013;Nørgaard 2017).…”