Analysis of silver objects

Metals cannot actually be dated. Analysis of these materials, however, produces a great deal of information, indicating whether the object's composition and weathering are compatible with its assumed origin and age.  

Silver, like gold, is never pure, but is always used in the form of natural or artificial alloys (copper, gold, etc.). 

Silver objects are analysed on the basis of metal microsections and surface replicas, to determine their chemical composition and weathering processes. 


Contributions

Ancient silver alloys exhibit weathering phenomena specific to this material, mainly resulting in the appearance of cracks on the surface of the metal that weaken the material's structure. These cracks are not present when the object is made, but are related to long, natural weathering, intrinsic to the material. Like many other weathering by-products (silver sulphides and chloride, cuprous oxide, tenorite, and copper chloride in the case of copper alloys, etc.), they provide clues that help to determine the probable age of the object.

Identification of the process used to make the object, combined with analysis of the composition of the alloy and inclusions (lead, copper sulphide, etc.) are compared with available archaeometallurgy data for the civilization(s) concerned 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 determine the object's preservation environment, as well as any treatments applied after its discovery. 


Methodology 

The methods used to study these materials are similar to those for copper alloys, as the only differences consist of specific deterioration in their composition and appearance. However, special attention is paid to marks left on the surface during production (swaging, burnishing, or possible rolling of the metal), which may be significant for assessing the object's age. 

Analysis of a silver object starts with a general examination to determine its structure and production technique, as well as assessing its weathering status. It may be complemented by X- or gamma-ray radiography.  

Optical microscope and metallographic examination of a microsection reveals whether or not there is a weathering gradient between the metal matrix and surface corrosion products, as well as the appearance of this corrosion. The shape, size, and colour of any inclusions inside the matrix may also be observed, as well as the proportion present in the alloy.  
"Chemical exposure" of the metal, followed by examination under an optical microscopic, reveals indications of the stages involved in producing the object (casting, annealing, swaging, etc.).

This is systematically associated with scanning electron microscope (SEM) examination coupled with elemental analysis (EDX) to determine the composition of the alloy (semi-quantitative analysis) and any inclusions. 
These analyses also make it possible to determine the composition of the corrosion products, as well as any surface deposits. 


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In some cases, determining the very precise composition of the alloy or detecting trace elements (less than 1% of the overall composition) may be decisive for authentication of the object. In those cases, we offer composition analyses using qualitative and quantitative methods: WDX and/or PIXE.