Chemical analysis and computed tomography of metallic inclusions in Roman glass to unveil ancient coloring methods

Abstract

This paper describes the analysis of two near-spherical metallic inclusions partially incorporated within two Roman raw glass slags in order to elucidate the process that induced their formation and to determine whether their presence was related to ancient glass colouring processes. The theory of metallic scraps or powder being used in Roman times for glass-making and colouring purposes is widely accepted by the archaeological scientific community, although the assumption has been mainly based on oral traditions and documented medieval practices of glass processing. The analysis of the two inclusions, carried out by X-ray computed tomography, electrochemical analyses, and scanning electron microscopy, revealed their material composition, corrosion and internal structure. Results indicate that the two metallic bodies originated when, during the melting phase of glass, metal scraps were added to colour the material: the colloidal metal–glass system reached then a supersaturation condition and the latter ultimately induced metal expulsion and agglomeration. According to the authors’ knowledge, these two inclusions represent the first documented and studied finds directly associated with the ancient practise of adding metallic agents to colour glass, and their analysis provides clear insights into the use of metallic waste in the glass colouring process.

X-ray Tomography Unveils the Construction Technique of Un-Montu’s Egyptian Coffin (Early 26th Dynasty)

“…X-ray computed tomography is a non-invasive and non-destructive 3D imaging technique capable of revealing crucial information about the manufacturing and assembly techniques of complex objects, such as the Un-Montu coffin. The CT technique investigates the entire volume of an artefact, providing scholars and restorers with knowledge of inner hidden details such as joints and dowels [20,21,29], the presence of different materials [10,30], the construction technique [22,31,32], or the casting process [33,34], and helps to elucidate possible restoration treatments and preservation conditions [10,35,36].…”