Non-destructive handheld XRF study of archaeological composite silver objects\u2014the case study of the late Roman Seuso Treasure

Viktória Mozgai,Zoltán May,Bernadett Bajnóczi,Zsolt Mráv

doi:10.1007/s12520-021-01321-4

Abstract

This study details the non-destructive chemical analysis of composite silver objects (ewers, situlas, amphora and casket) from one of the most significant late Roman finds, the Seuso Treasure. The Seuso Treasure consists of fourteen large silver vessels that were made in the fourth–early fifth centuries AD and used for dining during festive banquets and for washing and beautification. The measurements were systematically performed along a pre-designed grid at several points using handheld X-ray fluorescence analysis. The results demonstrate that all the objects were made from high-quality silver (above 90 wt% Ag), with the exception of the base of the Geometric Ewer B. Copper was added intentionally to improve the mechanical properties of soft silver. The gold and lead content of the objects shows constant values (less than 1 wt% Au and Pb). The chemical composition as well as the Bi/Pb ratio suggests that the parts of the composite objects were manufactured from different silver ingots. The ewers were constructed in two ways: (i) the base and the body were made separately, or (ii) the ewer was raised from a single silver sheet. The composite objects were assembled using three methods: (i) mechanical attachment; (ii) low-temperature, lead-tin soft solders; or (iii) high-temperature, copper-silver hard solders. Additionally, two types of gilding were revealed by the XRF analysis, one with remnants of mercury, i.e. fire-gilding, and another type without remnants of mercury, presumably diffusion bonding.

Highlights

The Seuso Treasure is one of the most significant treasure finds from the late Roman Imperial period (Painter 1990; Mango and Bennett 1994; Mráv and Dági 2014; Dági and Mráv 2019)
Non-destructive handheld X-ray fluorescence spectrometry is one of the most popular elemental analytical methods in the fields of archaeology and cultural heritage (Shackley 2012; Frahm and Doonan 2013; Zlateva 2017), and it is often utilised in the analysis of archaeological and historical metal objects, in the elemental analysis of precious metal objects (e.g. Karydas et al 2004; Cesareo et al 2008; Melcher et al 2009; Parreira et al 2009; Asderaki-Tzoumerkioti and Karydas 2011; Pardini et al 2012; Mass and Matsen 2013; Zori and Tropper 2013; Lehmann et al 2014; Živković et al 2014; Mozgai et al 2017; Mozgai et al 2018; Horváth et al 2019a; Szenthe et al 2019; May 2020; Mozgai et al 2020)
The aim of this study is to determine the elemental composition of the late Roman Seuso Treasure silver vessels using handheld X-ray fluorescence (XRF) to classify the objects, to detect chemical differences between the objects, as well as chemical inhomogeneity within the objects, to determine the raw material used and to characterise the gilding and joining techniques

Summary

Introduction

The Seuso Treasure is one of the most significant treasure finds from the late Roman Imperial period (Painter 1990; Mango and Bennett 1994; Mráv and Dági 2014; Dági and Mráv 2019). X-ray fluorescence (XRF) analysis has been used to examine most of the other Roman silver treasures

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Conclusion