Studies of ancient metals generally focus on the chemical nature of the metal or alloy and the production technique, as well as identifying corrosion processes and analysing surface deposits.
The analysis is carried out on metal microsections. Surface replicas are analysed to identify certain characteristics: types of inlay, polychrome decoration, and deposits, as well as typical corrosion products.
Objects made from ancient copper alloys (bronze, brass, etc.) exhibit specific types of deterioration, such as intra- or inter-granular corrosion, differential degradation of a specific phase in the metal, weathering of lead globules, or even the formation of a surface patina consisting of metal salts.
The objective of the analysis is to identify the weathering condition of the metal on the object's surface: presence or absence of natural, long-term corrosion or artificial weathering.
Identification of the process used to make the object and analysis of the composition of the alloy and any non-metallic inclusions (sulphides, oxides, etc.) are compared with archaeometallurgy data to verify that there are no technical anomalies.
Analysis of the deposits and their interaction with corrosion products on the surface of the alloy make it possible to identify the object's preservation environment and any ancient or recent surface treatments.
The methods used to study these materials are similar to those for silver objects, as the only difference consists of specific deterioration in their composition and appearance.
Stereomicroscope examination of the object reveals information about its structure and production technique, as well as its general weathering condition. Surface examination may be complemented by X- or gamma-ray radiography.
Inverted optical microscope examination of a microsection makes it possible to identify any surface weathering of the metal, as well as any non-metallic inclusions in the matrix, prior to SEM-EDX analysis.
"Chemical exposure" of the metal, followed by examination under an optical microscope, is used to determine the stages involved in producing the object (casting, annealing, swaging, etc.).
This is systematically associated with a scanning electron microscope (SEM) examination, coupled with elemental analysis (EDX), to determine the composition of the alloy (semi-quantitative analysis), non-metallic inclusions, corrosion by-products, and any surface deposits.
It may be necessary to determine the precise composition of the alloy, in cases where the detection of trace elements (less than 1% of the overall composition) may be decisive for authentication. In those cases, we offer composition analyses using qualitative and quantitative methods: WDX and/or PIXE.
When the alloy contains lead, it is possible to determine whether it is under or over 100 years old (lead 210 test).
If the clay casting core is still present inside the sculpture, it is possible to date it by thermoluminescence (TL dating).