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

Viktória Mozgai; Bernadett Bajnóczi; Zoltán May; Zsolt Mráv

doi:10.1007/s12520-021-01321-4

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

Mozgai, Viktória; Bajnóczi, Bernadett; May, Zoltán; Mráv, Zsolt 2021-04-17 00:00:00 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. . . . . . Keywords Late Roman Composite silver objects Handheld XRF Seuso Treasure Chemical composition Gilding Introduction which is written in the metric inscription of one of the platters. The pieces are typical of the period, representing parts of a The Seuso Treasure is one of the most significant treasure dining set used during festive banquets and also including finds from the late Roman Imperial period (Painter 1990; vessels for washing, bathing and beauty treatments. The ob- Mango and Bennett 1994; Mráv and Dági 2014; Dági and jects of the Seuso Treasure are amongst the largest known late Mráv 2019). The Treasure is composed of 14 large, domestic Roman silver vessels, and they are outstanding in both their silver vessels (Fig. 1), as well as the copper cauldron in which artistic and material value. Most of the silver vessels were they were hidden. The name originates from the owner, Seuso, manufactured in the fourth century AD, although some may have also been produced in the early fifth century AD. They were likely hidden in NE Pannonia (present-day Hungary) * Viktória Mozgai when the Romans fled from a “barbarian” attack in the late mozgai.viktoria@csfk.org fourth or early fifth century AD (Mráv and Dági 2014;Dági * Bernadett Bajnóczi and Mráv 2019). bajnoczi.bernadett@csfk.org During the final centuries of the Roman Empire, other sil- ver hoards were similarly hidden underground in various parts Institute for Geological and Geochemical Research, Research Centre of the Empire (e.g. Hoxne (England); Mildenhall (England); for Astronomy and Earth Sciences, Eötvös Loránd Research Kaiseraugst (Switzerland); Vinkovci (Croatia); Esquiline, Network (ELKH), H-1112 Budaörsi út 45, Budapest, Hungary Rome (Italy); Traprain Law (Scotland)). X-ray fluorescence Institute of Materials and Environmental Chemistry, Research Centre (XRF) analysis has been used to examine most of the other for Natural Sciences, Eötvös Loránd Research Network (ELKH), Roman silver treasures (Hughes and Hall 1979;Langetal. H-1117 Magyar tudósok körútja 2, Budapest, Hungary 1984; Feugère 1988;Hughes et al. 1989; Lang 2002;Cowell Hungarian National Museum, H-1088 Múzeum körút 14–16, and Hook 2010; Hook and Callewaert 2013; Minning and Budapest, Hungary 83 Page 2 of 20 Archaeol Anthropol Sci (2021) 13:83 Fig. 1 The Seuso Treasure: 1. Geometric Platter; 2. Meleager Platter; 3. Achilles Platter; 4. Seuso (or Hunting) Platter; 5. Hippolytus Ewer; 6. Hippolytus Situla A; 7. Hippolytus Situla B; 8. Animal Ewer; 9. Dionysiac Ewer; 10. Amphora; 11. Toilet Casket; 12. Geometric Ewer A; 13. Basin; 14. Geometric Ewer B. The red numbers indicate the composite objects discussed in the present paper (photo: A. Dabasi and J. Kardos (HNM)) Ponting 2013; Sánchez and Lansing Maish 2014;Lang and semi-quantitative elemental information can be gained Hughes 2016;Greiff 2017; Angelini et al. 2019; Arias et al. quickly. Moreover, sampling sites for more detailed anal- 2019), although other techniques were also used to determine ysis, e.g. quantitative elemental, lead isotopic and metallo- the elemental composition of the objects, such as emission graphic analysis, can be planned based on the hXRF spectroscopy (Lang et al. 1977;Berthoudetal. 1988; measurements. Mango and Bennett 1994) and particle-induced X-ray emis- However, the hXRF method has some limitations, sion spectroscopy (PIXE) (Tate and Troalen 2009;Doračić which must be taken into consideration during data evalu- et al. 2015;Vulić et al. 2017). ation. Because XRF is a surface analytical method, the Non-destructive handheld X-ray fluorescence spectrom- measured concentrations represent the outer part (usually etry (hXRF) is one of the most popular elemental analytical a few tens of microns) of the analysed objects. The signal methods in the fields of archaeology and cultural heritage comes from different depths, depending on the element and (Shackley 2012; Frahm and Doonan 2013;Zlateva 2017), the matrix (Tate 1986;Massand Matsen 2013). Metal ob- and it is often utilised in the analysis of archaeological and jects can be chemically heterogeneous for several reasons, historical metal objects, particularly in the elemental anal- such as phase segregation in silver-copper alloys during ysis of precious metal objects (e.g. Karydas et al. 2004; manufacture; acid treatments after preparation (etching), Cesareo et al. 2008; Melcher et al. 2009; Parreira et al. which dissolve copper from the surface layers; polishing 2009; Asderaki-Tzoumerkioti and Karydas 2011;Pardini during and after manufacture; corrosion and tarnishing; et al. 2012; Mass and Matsen 2013; Zori and Tropper remnants of gilding, etc. (Mass and Matsen 2013). 2013; Lehmann et al. 2014; Živković et al. 2014; Mozgai Surface enrichment of silver alloys is a well-known phe- et al. 2017;Mozgaietal. 2018; Horváth et al. 2019a; nomenon, during which base metals (e.g. copper and lead) Szenthe et al. 2019;May 2020;Mozgaietal. 2020). XRF are leached out from the surface, while silver and gold are is a simultaneous, multi-element analytical method, where- enriched towards the surface (Hall 1961;Lejček et al. by the concentrations of most elements of the periodic 2010), artificially exaggerating the silver and gold content table (Z = 12–92, from Mg to U) can be determined (major, at the expense of copper. Therefore, non-destructive sur- minor and trace elements). face analytical results, like hXRF data, may not represent The elemental analysis of silver objects is essential to the core metal composition. Surface enrichment can affect understand the contemporaneous raw material use, high-quality (> 90 wt%) silver objects as well, observed on alloying practice and manufacturing and decoration tech- silver coins (e.g. Beck et al. 2003;Becketal. 2004;Caridi niques. The major element content helps us to understand et al. 2013;Hrnjić et al. 2020;Hrnjić et al. in press). In whether any conscious technological choice of alloys was order to reduce the effect of the surface enrichment, applied for the different parts of the composite silver ob- polishing or abrasion of a small area before XRF analysis jects. The minor and trace element content can provide is usually carried out (e.g. Hughes and Hall 1979;Lang information about the used ore sources, raw materials and et al. 1984;Lang 2002; Lang and Hughes 2016;Greiff metallurgical techniques. Non-destructive analytical 2017). methods, such as handheld XRF, are particularly useful Metal samples taken from objects in the Seuso Treasure in the analysis of precious metal objects, where sampling were previously analysed by ICP-OES and scanning electron is not or only limitedly allowed due to the high value of the microscopy (Mango and Bennett 1994). However, no analy- objects. By using hXRF, the objects can be measured sys- ses were performed on the Hippolytus Ewer, and only one tematically at numerous points in situ in the museums, and metal sample was measured from the Toilet Casket, which is Archaeol Anthropol Sci (2021) 13:83 Page 3 of 20 83 comprised of three parts. The ICP-OES results are sometimes Materials and methods inaccurate, as concentrations of gold were noticeably low in most cases. These limitations justify the utilisation of new, Materials: the composite silver objects of the Seuso more detailed elemental analyses on the objects. Treasure The aim of this study is to determine the elemental com- position of the late Roman Seuso Treasure silver vessels Technological observations suggest that composite objects are using handheld XRF to classify the objects, to detect chem- composed of several parts (body, base, handle, lid, upper ical differences between the objects, as well as chemical beaded rim, thumbpiece, feet) and were manufactured from inhomogeneity within the objects, to determine the raw different silver casts (Mango and Bennett 1994; Dági and material (ore) used and to characterise the gilding and join- Mráv 2019). They are classified into groups based on their ing techniques. These results contribute to a more detailed shape and function (for parameters and decoration reconstruction of late Roman craftsmanship, including sil- techniques of the objects, see Table 1). versmithing, manufacturing, alloying, decoration and as- The relief-decorated Amphora is embellished with sembling practices. Dionysiac motifs, animal fighting scenes and xenia images, The Seuso objects were in good condition; thus, no ad- and its shape and decoration suggest that it was used to serve ditional surface cleaning (polishing or abrasion) was per- wine. It was constructed from several parts: a body, a base, formed before this study’s hXRF measurements. In return two panther-shaped handles and a stopper connected with a for the lack of cleaning, we performed measurements at chain. The body was manufactured either with the lost-wax several points on each part of the objects. Our approach casting technique (like the Baratti amphora was, Arias et al. differs from archaeometric studies performed on other 2019) or was hammered out of a single piece of silver, with no Roman silver hoards, because those objects were usually visible joins or seams. The cast base was hammered, and a only measured at a few points (1–20 points) per object centring point for a lathe is visible on it. The handles were (Lang et al. 1977; Hughes and Hall 1979;Langetal. likely cast using the lost-wax technique. 1984;Berthoudetal. 1988;Feugère 1988;Hughesetal. The Animal Ewer is decorated with chased figures and a 1989;Lang 2002; Cowell and Hook 2010; Hook and variety of geometric patterns. It may have belonged to a bath- Callewaert 2013; Minning and Ponting 2013;Doračić ing set, or it may have been used to serve wine, like the et al. 2015;Langand Hughes 2016;Greiff 2017;Vulić Amphora was. The body and base were cast or raised from a et al. 2017;Angelinietal. 2019; Arias et al. 2019), where- single piece of silver by hammering, while the upper beaded as our hXRF analysis eventuated a much larger data set (~ rim was cast separately and soldered to the body. The lid, 1600 points). Due to the high number of measurement made from a piece of silver, shows traces of hammering. points, surface cleaning was even more impossible, as the The handle was cast from a small bar of silver. importance of the treasure meant that it was not appropriate The Dionysiac Ewer is the smallest ewer in the Seuso to abrade the surface in order to expose the underlying Treasure. Based on its decoration with Dionysiac imagery metal over an area of about 3–8mmindiameter(7–50 (depicting the thiasos, the retinue of Dionysus), it was proba- mm ), large enough to match the XRF beam, especially bly used to serve wine. The body, the base and the neck were on the highly decorated, clearly visible sides. cast or hammered from a single piece of silver. The octagonal Two of the platters (Seuso/Hunting Platter and rim was made separately by casting or hammering and was Geometric Platter) manufactured from single casts were then soldered to the body. The handle was cast from a single previously analysed by hXRF alongside two other late bar of silver. Roman platters (Ribbon Platter and Rosette Platter from Geometric Ewers A and B are decorated with identical the Sava River find), which revealed a slight variation in chased geometric motifs. The ewers likely formed a set with the concentration of silver and copper along the radii of the the Basin. The bodies were hammered out of individual pieces plates manufactured from high-quality silver (> 95 wt% of silver, while the bases were made separately by hammering Ag) (Mozgai et al. 2017). The two other large, silver plat- and were then mechanically attached to the bodies. The upper ters (Meleager Platter and Achilles Platter) and the Basin, beaded rims were cast separately and were soldered to the also made from high-quality silver, have a more homoge- bodies, whereas the handles were cast from small bars of neous composition (Mozgai et al. 2020). In this paper, we silver. focus on the composite objects (ewers, situlas, amphora The Hippolytus Ewer depicts scenes from Greek mytholo- and toilet casket), which are assembled from several parts, gy (episodes from the Hippolytus story) and comprises a bath- and examine, in detail, the chemical differences between ing set, along with two situlas. The body was cast or raised by the various parts of the objects. Furthermore, the hXRF hammering from a single silver piece. The base was cast and data are compared with the previously published ICP- hammered from a separate piece of silver, after which it was mechanically attached and soldered to the body. The upper OES data (Mango and Bennett 1994). 83 Page 4 of 20 Archaeol Anthropol Sci (2021) 13:83 Table 1 Parameters and decoration techniques of the analysed relief from the back or the inside of the object by means of hammers and composite silver objects from the Seuso Treasure. *repoussé technique: punches. The name derives from the French word re-+ pousser meaning method of decorating metals in which parts of the design are raised in to push back (Untracht 1968; Maryon 1971; McCreight 1991) Find name Height (cm) Weight (kg) Capacity (litre) Repoussé technique* Dot- Chasing Gilding Niello inlays punching Ewers and amphora Amphora 38.5 2.5 – XX X X Animal Ewer 51.0 3.98 4 X X X X Dionysiac Ewer 43.5 3.0 4 X X X X Geometric Ewer A 52.8 2.65 4 X X X Geometric Ewer B 55.0 2.8 4 X X X Hippolytus Ewer 57.3 4.05 – XX X X Cylindrical objects Hippolytus Situla A 22.7 4.44 – XX X X Hippolytus Situla B 22.9 4.48 – XX X X Toilet Casket 32.0 2.05 – XX X beaded rim was cast separately and was then soldered to the Methods body. The lid, handle and lion-shaped thumbpiece were made using the lost-wax technique. After thorough macroscopic observation, the objects from the The Hippolytus Situla A and B form a bathing set and are Seuso Treasure were systematically analysed by handheld X- decorated with the same Greek mythological scenes as the ray fluorescence spectrometry (hXRF) along a pre-designed Hippolytus Ewer is. The bodies were cast or hammered out grid at several points on each object (see Online Resource 1). of single sheets of silver. The beaded rims were cast separately The number of measurement points ranged from 2 to 70 points and were then soldered to the bodies, while the three feet were per part, depending on the size of the measured part of each cast using the lost-wax technique and were also soldered to the object. bodies. The handles were cast and riveted to the decorative In this study, two hXRF instruments from different manu- busts, which were likewise soldered to the body. facturers were used: (i) a Thermo Scientific Niton Xl3t The Toilet Casket was probably stored smaller ointment con- GOLDD+ (Waltham, Massachusetts, USA) and (ii) a tainers using in daily toiletries. Both the body and the lid were SPECTRO xSORT Combi (Kleve, Germany) (see Table 2 cast or manufactured by hammering from single sheets of silver. for the analytical conditions). During the measurements, the The interior pierced disc was produced from a hammered sheet concentrations of the following major, minor and trace ele- of silver and contains seven pierced holes for flask storage. ments were determined: Ag, Cu, Au, Pb, Bi, Sb, Sn, Zn and The objects of the Seuso Treasure were examined, restored Fe (see Online Resource 1 for the detection limits of each and conserved at the Institute of Archaeology at University hXRF instrument). The built-in calibrations of each instru- College, London between April and December of 1989 ment were used for the measurements (Table 2). The (Bennett in Mango and Bennett 1994). Some of the objects Thermo Scientific Niton Xl3t GOLDD+ instrument measured were covered with calcareous encrustations, silver corrosion Bi and Sb using the ‘General Metals’ calibration, whereas the products and patches of green copper corrosion products. ‘Precious Metals’ calibration was used for the rest of the ele- Furthermore, some parts of the objects were harshly cleaned ments. The quantitative evaluation was performed with the and chemically polished during the period between the exca- built-in fundamental parameters (FP) method, using vation and the restoration in 1989. Unfortunately, no informa- Compton normalization. The results were normalised to tion is known about this period. During the restoration in 100%, and no calibrations in data were applied. The precision 1989, a 15% solution of ammonium thiosulphate and distilled and accuracy of the hXRF instruments were determined by water was used to remove silver corrosion products and cal- separate measurements taken of a Roman silver spoon and on careous encrustations from all visible surfaces. Green copper modern silver-copper alloys (see Online Resource 1 for corrosion products were carefully removed with a 10% solu- details). tion of formic acid and distilled water. After cleaning, each of The XRF spectra were evaluated by using NITON Data the objects were washed several times in distilled water baths Transfer Version NDT_REL_8.0.0 (Thermo Scientific Niton for 2–5 days. A thin layer of Paraloid B-72 was used to con- Xl3t GOLDD+) and XRF Analyzer Pro v.1.9. (SPECTRO serve the objects (Bennett in Mango and Bennett 1994). xSORT Combi) software programs. The data points were Archaeol Anthropol Sci (2021) 13:83 Page 5 of 20 83 Table 2 Comparison of the analytical conditions of the two handheld XRF instruments used for analysing the Seuso Treasure Instrument SPECTRO xSORT Combi Thermo Scientific Niton Xl3t GOLDD+ Detector Energy-dispersive SDD Energy-dispersive LDD X-ray tube 50 kV; Rh-anode 50 kV, Ag-anode Built-in calibrations ‘Light Elements’‘General Metals’ and ‘Precious Metals’ Spot size 3 mm 3 and 8 mm Acquisition time 60 s 50 s and 40 s plotted by using Microsoft Office Excel Professional Plus Cu) (Table 3;Figs. 2, 3 and 4). The gold content is around or 2016 and CorelDraw Graphics Suite 2018 (v.20.1.0.708) soft- below 1 wt% (except the Animal Ewer, discussion below) ware programs. (Table 3;Figs. 2, 3 and 4). The lead content is usually below The relative error of the Thermo Scientific Niton Xl3t 1 wt% (Table 3; Online Resource 2), and the bismuth content GOLDD+ instrument is less than 0.5% for silver, less than of the objects is heterogeneous, even within one object 5% for copper, less than 6% for gold, less than 10% for lead (Table 3;Figs. 2, 3 and 4). The tin, zinc and antimony contents and less than 20% for bismuth. The relative error of the are below the detection limit, with except for some parts of SPECTRO xSORT Combi instrument is better, namely less some of the objects (discussion below). than 0.1% for silver, less than 0.5% for copper, less than 2% The various parts (base, body, handle, stopper) of the for gold, less than 5% for lead and less than 10% for bismuth. Amphora differ chemically from each other. The stopper At some points (less than 7% of the total measurements), contains the least amount of copper (0.8–1.2 wt%), whereas higher relative errors were calculated, but none is above the base contains the most (3.0–3.8 wt%) (Fig. 2). The gold 50%. These points do not show a systematic distribution, and lead contents are not homogeneous between the and not related to an object or to a specific feature of the object Amphora’s parts. The bismuth content of the parts is very (e.g. geometric problems). variable, ranging from 0 to 2600 ppm (Fig. 2; Online For optimal measurements, the handheld XRF instrument Resource 2). requires ideal and reproducible surface geometries, such as The chemical composition of the various parts of the flat surface that are parallel to the spectrometer head. The lack Animal Ewer is also different. The body and the base contain of suitable and reproducible geometries can cause an error of the least amount of copper (0.6–3.3 wt%), whereas the upper 0.5% or more, if the objects have complex geometries (e.g. beaded rim, lid and handle contain the most (1.0–7.3 wt%) ewers, vessels, statues) (Mass and Matsen 2013). Therefore, (Fig. 2). The gold and lead contents are generally below or we aimed to measure surfaces that were as flat as possible, as around 1 wt%. At several points, the gold content of the parts well as to analyse the same locations on each object with each was elevated (> 1 wt%) (discussion below) (Fig. 2). The bis- instrument. muth content of the parts is homogeneous (100–1400 ppm) We compared the performance of the two hXRF instru- (Fig. 2). In the upper beaded rim and the handle, 0.5–0.8 wt% ments based on the analysis of the composite objects of the tin was detected. The chemical composition of the body and Seuso Treasure and concluded that only the data measured the base is identical, but the handle, upper beaded rim and lid by the same XRF instrument, under the same analytical were manufactured from silver alloys of different conditions and using the same built-in calibration can be compositions. reliably compared (see Online Resource 1). As a result, The chemical composition of the various parts of the hereafter we handle the data of the two instruments sepa- Dionysiac Ewer is different. The base and the body have the rately and compare the chemical compositions within these lowest copper content (1.1–1.8 wt%), whereas the handle and separate, independent data sets (according to Brand and the thumbpiece have the highest (2.7–4.3 wt%) (Fig. 2). The Brand 2014). body and the base have the same chemical composition; how- ever, the thumbpiece, handle and upper octagonal rim were made from different silver alloys. The silver and copper con- tents of the upper octagonal rim fall between the composition Results of the thumbpiece and handle and the base and body, respec- tively. The gold and lead contents are below 1 wt% (Fig. 2; Chemical composition of the composite objects of the Online Resource 2). The bismuth content of the Dionysiac Seuso Treasure Ewer is the highest (1200–3200 ppm) of all the Seuso objects (Fig. 2). In the thumbpiece and handle, 0.5–0.6 wt% zinc was In general, the objects were manufactured from high-quality detected. silver alloyed with copper (79.6–99.4 wt% Ag; 0.1–18.6 wt% 83 Page 6 of 20 Archaeol Anthropol Sci (2021) 13:83 Table 3 Chemical composition of the composite objects of the Seuso SPECTRO xSORT Combi hXRF. The minimum–maximum values are Treasure. Ag, Cu, Au, Pb are given in wt%, Bi is given in ppm. N = given. The Au/Ag and Bi/Pb ratios were calculated for each measurement measured using Niton Xl3t GOLDD+ hXRF; S = measured using points and the minimum–maximum values are given as well Instrument No. of analyses Ag Cu Au Pb Bi Au/Ag Bi/Pb Amphora Base N 8 93.7–94.9 3.3–3.8 1.0–1.2 0.6–0.9 1400–1900 0.011–0.013 0.21–0.24 S4 94.0–94.8 3.0–3.6 0.9–1.0 0.6–0.9 1100–1400 0.010–0.011 0.16–0.18 Body N 54 96.1–98.0 0.5–1.9 0.6–1.2 0.4–1.5 0–500 0.006–0.013 0–0.08 S27 96.2–97.7 1.1–1.8 0.5–0.8 0.6–1.0 0–200 0.005–0.008 0–0.03 Handle N 4 95.8–96.2 2.3–2.6 0.4–0.5 1.0–1.1 200–300 0.005 0.01–0.02 S4 95.5–95.9 2.3–2.5 0.4–0.5 1.1 100–200 0.004–0.005 0.01–0.02 Stopper N 2 97.7–98.1 1.1–1.2 0.3–0.5 0.2 2000–2600 0.004–0.006 0.95–1.23 S2 98.2–98.4 0.8 0.3 0.1–0.2 1500–1600 0.003 0.99–1.00 Animal Ewer Body N 64 94.9–97.9 0.8–3.3 0.9–2.4 0.2–0.9 400–1000 0.009–0.025 0.09–0.40 S31 94.2–97.9 0.6–2.2 0.8–1.9 0.1–0.9 100–700 0.008–0.020 0.06–0.25 Base N 11 96.4–98.3 0.5–1.7 0.5–1.6 0.2–0.3 500–900 0.005–0.017 0.26–0.34 S4 95.9–97.0 1.3–1.6 0.9–1.0 0.2–0.3 400–500 0.010 0.16–0.21 Handle N 7 92.9–94.6 3.2–4.7 0.7–1.7 0.4–0.7 900–1100 0.008–0.018 0.15–0.23 S4 94.0–94.5 3.4–4.1 0.8–1.1 0.4–0.5 600–900 0.009–0.011 0.16–0.17 Upper beaded rim N 5 93.7–95.4 2.4–4.0 1.0–1.1 0.3–0.5 700–1400 0.011–0.012 0.21–0.31 S3 94.6–95.0 2.6–3.2 1.2–1.4 0.2–0.4 500–600 0.012–0.015 0.15–0.22 Lid N 10 90.5–96.7 1.0–7.3 0.4–1.4 0.3–0.9 300–1100 0.004–0.015 0.04–0.17 S3 93.2–93.8 3.3–3.7 0.7–0.8 0.7 700–800 0.008–0.009 0.11 Dionysiac Ewer Body N 61 96.6–98.0 1.1–1.8 0.4–1.2 0.1–0.3 1400–2400 0.004–0.013 0.54–1.64 S14 96.4–97.9 1.3–1.6 0.3–0.5 0.1 1200–1700 0.003–0.005 1.13–2.21 Base N 8 97.2–97.8 1.3–1.8 0.4–0.5 0.1–0.2 1600–2000 0.004–0.005 0.86–1.46 S7 97.5–97.9 1.2–1.5 0.3–0.4 0.1 1200–1300 0.004 0.87–2.28 Thumbpiece N 3 94.0–95.0 3.2–4.2 0.5–0.6 0.2–0.3 2800–3200 0.005–0.007 1.05–1.14 Handle N 6 93.2–95.6 2.7–4.3 0.5–0.7 0.2–1.1 2500–3200 0.005–0.007 0.29–1.20 S2 91.2–94.7 3.8–4.1 0.4–0.5 0.2–0.5 2100–2200 0.004–0.006 0.44–1.26 Upper octagonal rim N 6 95.6–96.4 2.3–2.6 0.5–0.6 0.1–0.6 2800–3200 0.005–0.006 0.52–2.31 S5 95.8–96.4 2.3–2.5 0.5–0.6 0.1–0.4 2100–2500 0.005–0.006 0.57–2.62 Geometric Ewer A Body N 70 93.9–97.8 0.9–2.9 0.7–1.1 0.5–1.1 900–1400 0.008–0.012 0.10–0.19 S30 96.3–97.9 0.9–1.6 0.7–0.9 0.4–0.7 500–1000 0.007–0.009 0.09–0.15 Base N 14 94.5–97.1 1.4–4.1 0.7–1.1 0.2–0.5 500–1100 0.008–0.011 0.16–0.25 S9 94.3–96.2 1.1–3.7 0.8–1.1 0.1–0.6 100–700 0.008–0.011 0.04–0.14 Handle N 7 92.3–94.7 3.8–6.1 0.8 0.6–0.8 1000–1200 0.008–0.009 0.13–0.19 S5 93.0–94.8 3.5–5.2 0.7–0.8 0.7–0.8 800–1000 0.007–0.009 0.10–0.14 Upper beaded rim N 4 93.0–95.2 3.7–5.8 0.8–0.9 0.3–0.6 500–900 0.008–0.010 0.17–0.21 S4 91.6–93.0 4.5–6.5 0.7–1.0 0.2–0.6 400–700 0.008–0.010 0.11–0.23 Geometric Ewer B Body N 62 95.2–97.1 1.6–3.2 0.8–1.1 0.2–0.4 600–1000 0.009–0.011 0.17–0.21 S16 95.4–96.4 1.9–2.5 0.7–1.1 0.2–0.3 400–700 0.008–0.011 0.14–0.19 Base N 11 79.6–94.0 4.5–18.6 0.8–1.1 0.4–0.5 700–900 0.009–0.011 0.17–0.31 S7 84.9–93.5 4.5–10.9 0.7–1.0 0.3–0.5 500–800 0.008–0.011 0.15–0.27 Handle N 11 92.4–94.6 3.7–5.9 0.7–0.9 0.6–0.8 800–1100 0.008–0.009 0.11–0.15 S5 93.5–94.2 3.6–4.8 0.7–0.8 0.8 700–900 0.007–0.009 0.09–0.11 Upper beaded rim N 5 90.2–95.6 2.0–7.1 0.7–1.0 0.6–1.3 500–1100 0.008–0.010 0.04–0.17 Archaeol Anthropol Sci (2021) 13:83 Page 7 of 20 83 Table 3 (continued) Instrument No. of analyses Ag Cu Au Pb Bi Au/Ag Bi/Pb S2 89.6–95.5 1.4–4.6 0.8–1.0 0.6–0.9 0–400 0.009–0.011 0.009–0.011 Thumbpiece N 3 93.5–94.8 3.4–4.6 0.8–0.9 0.7–0.8 1000–1200 0.008–0.009 0–0.07 Hippolytus Ewer Body N 32 94.4–96.8 1.8–4.1 0.6–1.0 0.4–0.6 900–1500 0.007–0.011 0.21–0.28 S15 96.2–96.8 1.6–2.1 0.6–0.8 0.4–0.5 700–1000 0.007–0.008 0.16–0.23 Base N 15 95.7–98.4 0.8–2.9 0.5–1.0 0.2–0.4 700–2600 0.005–0.010 0.19–1.09 S8 94.3–97.5 1.3–2.8 0.5–1.0 0.1–0.4 500–1200 0.005–0.010 0.16–0.98 Lid N 8 91.4–95.1 3.6–6.9 0.6–1.0 0.5–0.6 500–900 0.006–0.010 0.09–0.16 S4 92.2–94.2 3.4–6.2 0.5–0.6 0.4–0.6 400–600 0.006–0.007 0.08–0.11 Handle N 9 93.9–97.1 1.6–5.0 0.6–1.1 0.3–1.1 700–2000 0.007–0.011 0.11–0.56 S2 94.8–96.2 2.3–3.4 0.8–0.9 0.3–0.4 400–1300 0.009 0.12–0.40 Upper beaded rim N 8 94.0–97.5 1.5–3.2 0.5–0.9 0.3–1.4 1500–2300 0.005–0.010 0.16–0.62 S4 95.2–97.0 1.7–3.2 0.5 0.2–0.6 1400–1700 0.005–0.006 0.30–0.72 Hippolytus Situla A Handle N 9 95.6–97.2 1.8–2.7 0.6–0.9 0.4–0.7 400–900 0.007–0.009 0.10–0.16 S4 96.6–97.1 1.8–2.0 0.6 0.2–0.5 200–500 0.006–0.007 0.06–0.10 Feet N 8 95.4–97.6 0.8–2.6 0.9–1.1 0.3–0.8 400–1100 0.010–0.011 0.08–0.29 S2 95.2–96.2 2.1–2.6 0.8–0.9 0.4–0.7 600–700 0.008–0.010 0.10–0.14 Body N 32 96.2–98.2 0.6–2.8 0.5–0.9 0.1–0.3 200–900 0.005–0.010 0.07–1.47 S21 95.7–97.2 2.1–2.6 0.4–0.6 0.1–0.2 0–200 0.005–0.006 0–0.12 Upper beaded rim N 5 98.9–99.2 0.4–0.6 0.3–0.4 0–0.1 0–1400 0.003–0.004 0–3.20 S4 95.3–99.0 0.3–0.5 0.3 0–0.04 400–800 0.003 0–6.28 Hippolytus Situla B Handle N 11 96.6–97.7 1.2–2.1 0.6–0.8 0.3–0.5 300–800 0.006–0.008 0.08–0.30 S 4 97.3 1.6–1.7 0.5–0.6 0.3 0–300 0.005–0.006 0–0.10 Feet N 8 94.6–97.3 1.1–2.9 0.7–1.1 0.2–1.3 700–1200 0.008–0.012 0.09–0.33 S2 95.2–95.4 2.5–2.7 0.8 0.4–0.5 700 0.008–0.009 0.14–0.17 Body N 33 95.6–97.5 1.7–3.2 0.5–0.9 0.3–0.5 200–500 0.006–0.010 0.07–0.12 S22 92.5–97.4 1.7–2.7 0.5–1.0 0.2–0.5 100–400 0.005–0.011 0.02–0. 11 Upper beaded rim N 8 98.6–99.3 0.1–0.8 0.3–0.5 0–0.4 500–2000 0.003–0.005 0.18–2.60 S6 98.7–99.4 0.1–0.5 0.2–0.5 0–0.01 0–600 0.002–0.005 0–6.41 Toilet Casket Lid N 55 94.8–96.6 2.0–3.7 0.6–1.2 0.3–0.5 600–1300 0.006–0.013 0.14–0.33 S23 94.8–96.7 1.9–3.5 0.7–1.2 0.3–0.5 500–1000 0.007–0.013 0.13–0.22 Base N 49 94.9–97.5 1.2–3.6 0.8–1.2 0.2–0.5 400–900 0.009–0.013 0.10–0.20 S24 95.0–96.9 1.0–3.4 0.8–1.0 0.2–0.5 100–500 0.009–0.011 0.03–0.11 Pierced disc N 12 93.4–93.8 4.3–4.7 0.8 0.7 1300–1500 0.009 0.19–0.21 S6 91.8–94.1 3.9–4.5 0.7–0.8 0.6–0.8 1000–1200 0.008 0.14–0.16 The two Geometric Ewers (A and B) have a similar chem- (Fig. 3). The chemical composition of the various parts of each ical composition. The bodies contain the least amount of cop- ewer (body, handle, base, thumbpiece, upper beaded rim) in- per (0.9–3.2 wt%), whereas the base of Geometric Ewer B dicates that they were manufactured from silver alloys of dif- shows an elevated amount of copper (4.5–18.6 wt%), with a ferent compositions. very heterogeneous distribution. The base of Geometric Ewer Based on the observed variation in the chemical composi- A exhibits a lower concentration of copper (between the com- tion of the different parts (lid, body, base, handle, upper position of the body and the upper beaded rim and handle) beaded rim) of the Hippolytus Ewer,they weremanufactured (Fig. 3). The gold and lead contents are below 1 wt% (Fig. 3; from different silver alloys. The lid has the highest copper Online Resource 2). The bismuth content is homogeneous content (3.4–6.9 wt%), whereas the base has the lowest 83 Page 8 of 20 Archaeol Anthropol Sci (2021) 13:83 Fig. 2 Silver vs. copper and gold vs. bismuth content of the Amphora, the Niton Xl3t GOLDD+; 2: SPECTRO xSORT Combi; 3: ICP-OES Dionysiac and the Animal Ewers based on the hXRF measurements, (Mango and Bennett 1994) previous ICP-OES data are shown for comparison. Measured with 1: (0.8–2.9 wt%) (Fig. 3). Although the gold and lead contents handle contain a slightly higher percentage of lead (0.2–1.4 are constant and fall below 1 wt%, the upper beaded rim and wt%) (Fig. 3; Online Resource 2). The bismuth content is Archaeol Anthropol Sci (2021) 13:83 Page 9 of 20 83 Fig. 3 Silver vs. copper and gold vs. bismuth content of the Hippolytus GOLDD+; 2: SPECTRO xSORT Combi; 3: ICP-OES (Mango and and the Geometric Ewers based on the hXRF measurements, previous Bennett 1994) ICP-OES data are shown for comparison. Measured with 1: Niton Xl3t much more heterogeneous than the gold and lead content of 400–1500 ppm, and the upper beaded rim and part of the base the parts. The bismuth content of the body, lid and handle is exhibit higher concentrations (500–2600 ppm) (Fig. 3). 83 Page 10 of 20 Archaeol Anthropol Sci (2021) 13:83 Fig. 4 Silver vs. copper and gold vs. bismuth content of the Hippolytus 1: Niton Xl3t GOLDD+; 2: SPECTRO xSORT Combi; 3: ICP-OES Situlas and the Toilet Casket based on the hXRF measurements, (Mango and Bennett 1994) previous ICP-OES data are shown for comparison. Measured with The various parts of the two Hippolytus Situlas (handle, other. The upper beaded rims have the highest silver content feet, body and upper beaded rim) differ chemically from each of all the Seuso objects; in fact, they were manufactured from Archaeol Anthropol Sci (2021) 13:83 Page 11 of 20 83 almost pure silver (> 99 wt%) (Fig. 4). The gold content is volume and a detachment of the soldered parts (handles, heterogeneous. The feet have the highest gold content (0.7– thumbpieces, lids) (Fig. 6a–c). At the joints of the bodies 1.1 wt%), while the upper beaded rim has the lowest (0.2–0.5 and the upper beaded rims of the ewers and the situlas, green wt%). The gold content of the handles and the bodies is sim- copper corrosion products were observed by the naked eye, ilar (0.5–1.0 wt%). The lead content is constant and falls be- which manifested in higher copper concentrations (31.9 wt% low 1 wt%, whereas the bismuth content is heterogeneous, Cu) (Online Resource 3; Fig. 6d). ranging from 0 to 1500 ppm (Fig. 4; Online Resource 2). The parts (lid, base, pierced disc) of the Toilet Casket have different chemical compositions, indicating that they were Discussion manufactured from silver alloys of different compositions. The pierced disc contains the most copper (3.9–4.7 wt%), Major elements: silver and copper and the lid and base contain similar amounts of copper (1.0– 3.7 wt%) (Fig. 4). The gold and lead contents are constant and Each of the objects was manufactured from high-quality fall below or around 1 wt% (Fig. 4; Online Resource 2). silver, which corresponds well with the observation that Bismuth is present in slightly lower concentrations in the base high-purity (80–99 wt% Ag) silver objects were created in (100–900ppm)thaninthelid (500–1300 ppm) and the the late Roman period (Table 4) (Hughes and Hall 1979; pierced disc (1000–1500 ppm) (Fig. 4). Lang et al. 1984;Feugère 1988;Lang 2002;Tateand Troalen 2009; Cowell and Hook 2010;Hook and Callewaert Gilding 2013; Doračić et al. 2015; Lang and Hughes 2016; Greiff 2017;Vulić et al. 2017). Each of the composite objects was selectively gilded, except the Pure silver is too soft to fashion everyday items from, be- Toilet Casket, and the gilding is quite worn in some places (Fig. cause it dents, bends and wears easily. In the late Roman 5). The gilding was analysed at several points, ranging from 2 to period, the most common silver alloying element was copper, 60 points per object, depending on the object and the extent of as it added strength and hardness to the softer silver. The the gilded surfaces. The gold content of the gilded surfaces hardness of an alloy depends not only on its chemical compo- ranges from 1.0 to 76.2 wt% depending on the thickness of the sition but also on the degree of working and heat treatment. gilding (Online Resource 3). The relative thickness of the gilding The hardness increases quickly up to 15% copper content, and was estimated based on the macroscopic observations and on the between 30 and 80% copper it reaches a rather constant value gold content of the gilded areas. In the case of the Amphora, (Hughes and Hall 1979). As the amount of copper that is Animal Ewer, Dionysiac Ewer and the Hippolytus set, mercury added to the molten silver increases, the more yellowish the was detected in the gilded parts (Fig. 5g). Gold spans the edge of alloy will become. During silver extraction, the copper content the gilded area, particularly in the case of the Animal Ewer, may be reduced to 0.2–1%; thus, higher copper concentrations whose flat surfaces were gilded. On the ribs of the Animal indicate intentional alloying (Hughes and Hall 1979). The Ewer, which separate the different sections of the body, gilding copper content of late Roman silver objects ranges from 0.1 was not observed by the naked eye, only at the very edges, in to 15% (Table 4) (Hughes and Hall 1979;Lang etal. 1984; deeper depressions, but the elevated gold content indicates that Feugère 1988; Lang 2002; Tate and Troalen 2009; Cowell and the entirety of the ribs was originally gilded (Online Resource 3; Hook 2010; Hook and Callewaert 2013; Doračić et al. 2015; Fig. 5a, b). In contrast, the gilding of the two Geometric Ewers Lang and Hughes 2016; Greiff 2017;Vulić et al. 2017). The wasanalysedin61and 68 points,respectively, andnomercury copper content of the Seuso objects fits into this range. The was detected in any of analysed points by the handheld XRF differences in the copper contents of the various parts of the (Fig. 5g). The gilding appears to be very thin, is pale yellow composite objects also indicate intentional alloying: and generally follows the decoration lines (Fig. 5e, f). (i) The parts that are more exposed to mechanical effects, Soldering such as handles, bases, rims, lids and feet (e.g. the base and handle of the Amphora, the handles of the Animal, The various parts of the Seuso objects were assembled in Dionysiac, Hippolytus and Geometric Ewers, the bases of different ways. The joints were analysed at several points, the Geometric Ewers, the pierced disc of the Toilet ranging from one to seven points per object. At the joints of Casket), were usually made from alloys with higher cop- handles, feet, lids and thumbpieces, as well as at the ancient per but lower silver contents. repairs, elevated tin and lead contents were measured (1.4– (ii) The parts made with repoussé technique (e.g. the bodies 70.1 wt% Pb; 0.8–43.4 wt% Sn), indicating the use of a soft of the Animal, Dionysiac and Hippolytus Ewers, the lead-tin solder (Online Resource 3;Fig. 6e). The soldering bodies of the Hippolytus Situlas, the lid and the base of material completely recrystallised, resulting in increased the Toilet Casket) were generally made from alloys 83 Page 12 of 20 Archaeol Anthropol Sci (2021) 13:83 Fig. 5 Gilding on the Seuso objects. a, b The Animal Ewer: gilding spreads over the edge of the gilded area and is quite worn, invisible with naked eye at the ribs. c The Hippolytus Situla A. d The Amphora. e, f The Geometric Ewers A and B (photo: A. Dabasi and J. Kardos (HNM)). g hXRF spectra of the gilded areas on the examples of the ewers measured with SPECTRO xSORT Combi instrument containing a higher percentage of silver, which are more point, making it easier to cast the alloy. These parts in- malleable and make it easier to form the small details of clude, e.g. the upper beaded rims of the Animal, the figures and scenes (Greiff 2017). Geometric and Hippolytus Ewers, the octagonal rim of (iii) The parts that were unequivocally manufactured by casting the Dionysiac Ewer, handles of the Amphora, the lid of (handles, thumbpieces, lids, feet, upper beaded and octag- the Animal and Hippolytus Ewers. The upper beaded rims onal rims) usually have higher copper contents, because of the Hippolytus Situlas are exceptions; they were cast alloys with higher copper contents require a lower melting from almost pure silver (> 99 wt% Ag). The use of silver Archaeol Anthropol Sci (2021) 13:83 Page 13 of 20 83 Fig. 6 Solders on the Seuso objects. a Remnants of lead-tin soft solder at the joint of the han- dle to the body of the Dionysiac Ewer. b Remnants of lead-tin soft solder at the joint of lid to the base of the Toilet Casket and at ancient repairs. c Thick, corroded, re- crystallised lead-tin soft solder at the joint of the handle of Geometric Ewer B. d Green cop- per corrosion products along the rim of the Hippolytus Situla A indicating the use of copper- containing hard solder (photo: A. Dabasi and J. Kardos (HNM)). e hXRF spectra of the soft solders on the example of the ewers measured with SPECTRO xSORT Combi instrument. Animal Ewer: at the joint of the lid to the body; Dionysiac Ewer: at the joint of the handle to the body; Geometric Ewer B: at the joint of the handle to the body at the beaded rim; Hippolytus Ewer: at the joint of the lid to the body alloys with higher copper contents can also be economic deriving from the silver ore or from the copper used for (Mango and Bennett 1994). alloying (Hughes and Hall 1979). Their individual content usually does not exceed 1% (except for gold at some points The results of the previous ICP-OES measurements made in the Animal Ewer, discussion below). on bulk metal samples taken from the Seuso objects (Mango In the Roman period, the primary source of silver was and Bennett 1994) show the same trends as our hXRF results silver-bearing lead ores (Tylecote 1962;Forbes 1971). The (Figs. 2, 3 and 4, Online Resource 4). However, as hXRF is a silver ores were roasted, melted and cupelled during silver surface analytical method, the effects of corrosion processes extraction. Cupellation cleansed the silver of impurities are evident: the less noble copper was leached out, and the (e.g. antimony, arsenic, tin, iron and zinc; less well from more noble silver was enriched at the surface. Generally, ICP- copper, gold and bismuth). The volatile elements (antimo- OES measured higher copper concentrations (0.5–5wt% ny, arsenic, mercury, tin and zinc) disappear from the mol- higher) compared to hXRF (Figs. 2, 3 and 4). ten silver during cupellation (Pernicka 2014;L’Héritier et al. 2015); however, they can be present in high concen- Minor and trace elements (impurities) trations (several %) in native silver (Pernicka 2014). The absence of these volatile elements in the analysed objects With the exception of silver and copper, the measured el- indicates that cupelled silver was used for manufacturing. Thepresence of zincand tinin someparts of theobjects ements are naturally occurring and unintentionally added, 83 Page 14 of 20 Archaeol Anthropol Sci (2021) 13:83 Table 4 Chemical composition of contemporaneous silver treasure finds including number of their analysed objects. The results are given in wt% Treasure finds Analytical method No. of analysed objects No. of analyses Ag Cu Au Pb Bi Mildenhall XRF 20 124 93.7–98.0 0.3–4.2 0.4–2.6 0.2–2.2 Hoxne XRF 96 106 85.0–99.0 0.1–4.7 0.1–1.0 0.2–4.4 0–0.3 Kaiseraugst XRF 8 15 95.6–98.6 1.0–3.5 0.3–1.3 0.1–0.9 Vinkovci PIXE 49 56 89.1–99.8 0.2–8.9 0.4–3.4 0.1–1.6 0–0.3 Esquiline XRF 12 32 88.6–98.3 0.4–10.3 0.2–4.7 0.6–1.0 Coleraine XRF 30 30 88.7–97.5 1.2–6.6 0.4–2.2 0.3–2.3 Carthage XRF 20 52 94.3–97.7 1.9–4.5 0.3–1.1 0.1 – 0.9 Caubiac (Thil) XRF 4 4 93.8–98.2 1.1–4.3 0.4–0.8 0.2–0.6 Trier XRF 1 20 81.9–95.1 2.2–14.6 1.1–2.5 0.3–1.9 0–0.2 Water Newton XRF 13 17 88.6–97.9 1.8–9.9 0.2–4.4 0–0.8 11 a Seuso XRF 14 1620 79.6–99.4 0.1–18.6 0.2–2.4 0.1–1.5 0–0.3 The four platters and the Basin of the Seuso Treasure are also included. The minimum–maximum values are given. The number of analyses given for the Seuso Treasure is the sum of the measurements of the two hXRF instruments. Hughes and Hall 1979;Lang etal. 1977; Lang and Hughes 2016; 2 3 4 5 6 7 Cowell and Hook 2010; Lang et al. 1984; Doračić et al. 2015;Vulić et al. 2017; Hughes and Hall 1979; Hook and Callewaert 2013; Lang 2002; 8 9 10 11 Feugère 1988; Greiff 2017; Hughes and Hall 1979; Mozgai et al. 2017; Mozgai et al. 2020; present study (0.5–0.8 wt% Sn in the upper beaded rim and handle of the elevated tin content as well. Therefore, we assume that the Animal Ewer; 0.5–0.6 wt% Zn in the thumbpiece and han- lead content of the Seuso objects derives from the silver ore. dle of the Dionysiac Ewer) indicates that brass and bronze, Bismuth is also helpful in determining the raw material respectively, were used as alloying metals instead of pure provenance of silver objects, as its concentration does not copper. This is supported by the calculated Cu/Sn (~ 83% change significantly during cupellation (Pernicka and Cu;~17% Sn) and Cu/Zn(~87% Cu;~13%Zn)ratios Bachmann 1983; Pernicka 2014;L’Héritier et al. 2015). Dry (Hughes and Hall 1979;Greiff 2017). This alloying prac- ores or native silver have bismuth contents below 0.05% tice was indeed unusual in the Roman times, but later, (Craddock 1995), whereas argentiferous galena contains during the Migration Period, it was commonly practised 0.1–1% bismuth (Gale and Stos-Gale 1981). Based on cupel- (Craddock et al. 2010;Horváth et al. 2019b;Mozgai lation experiments, bismuth is oxidised in the final stages of et al. 2019). Though it is rare in Roman times, but it is cupellation; therefore, bismuth in silver objects is correlated not without example. Elevated Zn content was found in with the degree of cupellation. However, the final Bi/Pb ratio some of the pieces of the Hoxne hoard and concluded as of the cupelled silver depends on the initial Bi content of the the result of alloying with brass typical of Roman period silver-bearing lead ores (L’Héritier et al. 2015). The Bi/Pb (Cowell and Hook 2010). Hughes and Hall (1979) detected ratio indicates that the Seuso objects can be categorised as elevated zinc content in some bowls from the Chaourse having a homogeneous Bi/Pb ratio or a heterogeneous Bi/Pb hoard and in some Sassanian objects, and elevated tin con- ratio in the various parts of the composite objects. The tent in some objects from the Sutton Hoo hoard, indicating Dionysiac Ewer has the highest Bi/Pb ratio (Table 3, Fig. 7). the use of brass or bronze scrap material for alloying. The body, base, handle and thumbpiece have similar compo- Ancient Romans produced high-purity silver with a lead sitions, although the octagonal rim shows the highest Bi/Pb content of 0.5–1% (Hughes and Hall 1979). If silver originates ratio of all the objects. The Animal Ewer and Geometric from silver-bearing lead ores (galena, anglesite or cerussite), Ewers A and B have a very similar and homogeneous Bi/Pb the lead content in the silver alloy ranges from 0.001 to 3% ratio, whereas the Hippolytus Ewer and the Amphora have a (Moorey 1985). The lead content of the analysed Seuso ob- heterogeneous Bi/Pb ratio. The bismuth contents of the body jects falls within this range. The lead contents of the objects and the handles of the Amphora fall below the detection limit differ, because cupellation occurred in multiple steps, which of the XRF (~ 150 and ~ 60 ppm, respectively, Online resulted in the different lead contents, or because silver ores Resource 1). The base and stopper are characterised by a from different sources were used. The low and constant lead low and a high Bi/Pb ratio, respectively. The Bi/Pb ratios of content indicates that lead was not added to the silver ore the body, handle and lid of the Hippolytus Ewer are similar to during smelting. As such, lead isotope analyses may help to the ratios of the Animal and Geometric Ewers, while the upper determine the provenance of the raw material. Lead in the beaded rim and the base have higher Bi/Pb ratios (Table 3, silver objects could derive from the alloying metal, if bronze Fig. 7). The Bi/Pb ratios of the Toilet Casket and Hippolytus or leaded bronze was used, but in this case, we would expect Situla A and B are low and homogeneous, with the exception Archaeol Anthropol Sci (2021) 13:83 Page 15 of 20 83 of the upper beaded rims of the situlas, which exhibit hetero- contents in the bulk metal samples compared to our hXRF geneous Bi/Pb ratios (Fig. 7). The differences in the Bi/Pb values (Figs. 2, 3 and 4), possibly due to digestion problems; ratios indicate that different silver ingots were used to make thus, they are not included in this research. However, the the different parts of the objects. bismuth contents compared well and showed the same trend Gold is completely miscible with silver. During metallur- as the hXRF results (Figs. 2, 3 and 4). Furthermore, our anal- gical processes, the gold content of silver does not change ysis also completes the previous ICP-OES measurements, as drastically (L’Héritier et al. 2015). Consequently, the Au/Ag we determined the chemical composition of each part of the ratio does not alter during cupellation (Pernicka 2014). The Hippolytus Ewer and the Toilet Casket and demonstrated the gold content of argentiferous galena ranges from 0.01 to 1%, use of different silver ingots for their manufacture. whereas the gold content of cerussite and anglesite ranges When our results are compared to other contemporaneous between 0.1 and 0.5% (Karydas et al. 2004 and references silver hoards, it is evident that most of them primarily contain herein). The gold content of late Roman silver objects falls platters, plates and bowls, which were generally manufactured between 0.1 and 4.7% (Table 4) (Hughes and Hall 1979; Lang from a single silver batch. The Seuso Treasure is unique, be- et al. 1984; Feugère 1988; Lang 2002; Tate and Troalen 2009; cause it is mostly composed of large, composite objects Cowell and Hook 2010; Hook and Callewaert 2013;Doračić (ewers, amphora, situlas, casket) that were manufactured from et al. 2015; Lang and Hughes 2016;Greiff 2017;Vulić et al. several parts. Ewers, the casket and the amphora from the 2017). There are several reasons that gold concentrations ex- Trier, Vinkovci and Esquiline hoards were analysed at several ceed 1%, such as the presence of remnants of former gilding, points (Online Resource 5) (Hughes and Hall 1979;Doračić the re-usage of scrap gilded silver or the use of gold-silver et al. 2015;Greiff 2017;Vulić et al. 2017). Of these objects, ores. The gold content of the Seuso objects shows constant the Apostle jug from Trier exhibits a noticeable chemical dif- values and falls within the range typical of late Roman objects. ference between the various parts, indicating that it was not This indicates that primary silver ore was used during manu- manufactured from one, large, uniform batch of silver. The facture, instead of the re-usage of scrap silver, which would body, which is heavily decorated, has the highest silver con- result in a wide range of variation in the gold values. The tent (93.9–95.1 wt% Ag), whereas the handle and the differences in the gold content of the Seuso objects indicate thumbpieces exhibit higher copper concentrations (81.9– the use of different ingots. 95.0 wt%) (Online Resource 5)(Greiff 2017). This chemical The similarities and differences in the chemical composi- difference between the various parts of the Apostle jug is very tions of the various parts of the objects support the technolog- similar to that of the ewers in the Seuso Treasure. ical observations (Mango and Bennett 1994; Dági and Mráv, 2019). The different compositions of the various parts of the Gilding objects indicate the use of different ingots. Based on their manufacturing techniques, the ewers can be classified into The hXRF data show that the Seuso objects were decorated two groups: (i) the body and the base were cast or raised from with two types of gilding: (i) fire gilding, which contained a single silver sheet (e.g. Animal and Dionysiac Ewers) and mercury; and (ii) a different gilding technique that did not (ii) the body and base were made separately and were later contain mercury. Mercury was detected in the gilding of the joined mechanically (e.g. Hippolytus Ewer and Geometric Amphora, Dionysiac Ewer, Animal Ewer and the Hippolytus Ewers A and B). set, indicating the use of fire gilding. In contrast, mercury was The previous ICP-OES analyses (Mango and Bennett absent from the gilding of Geometric Ewers A and B, indicat- 1994, Online Resource 4) systematically measured lower gold ing the possible use of a different gilding technique (Fig. 5). Fig. 7 Au/Ag vs. Bi/Pb ratio of the Seuso objects based on the hXRF measurements. Measured with Niton Xl3t GOLDD+ (ligh- ter colours) and SPECTRO xSORT Combi (darker colours) instruments 83 Page 16 of 20 Archaeol Anthropol Sci (2021) 13:83 Fire gilding was likely invented in China in the fourth century was too worn to determine the method used (Mango and BC (Lechtman 1971; Lins and Oddy 1975;Oddy 1981, 1988, Bennett 1994). Our present data do not support the use of fire 1991, 1993, 2000). In the fire gilding technique, gold was gilding for the Geometric Ewers, as mercury is always detect- dissolved in hot mercury, and the resulting gold amalgam able in fire gilding (Anheuser 1997) but is absent from the was rubbed on to the cleaned metal surface, after which the Geometric Ewers. Further invasive investigations are planned object was heated for a few minutes at 250–300 °C (below the to confirm whether diffusion bonding was used on the boiling point of mercury, 357 °C) until it changed from silver Geometric Ewers. It is possible to bond gold leaf to pure silver to yellow. It is important to avoid overheating the object. If (or to pure copper) without the use of an adhesive, by burnish- silver is overheated, the gold discolours or even disappears ing and minimally heating the object to promote interdiffusion into the substrate. This phenomenon restricts the maximum between the gold and silver. Diffusion bonding (or hot clad- firing temperatures to approximately 350 °C. A firmly bonded ding) was invented as early as 1200 BC, and was commonly but porous, matte gilded layer will form, which must then be used on silver from the late Hellenistic and early Roman pe- burnished. This technique is still used in Nepal (Anheuser riods (Lechtman 1971;Oddyetal. 1981;Oddy 1981, 1988, 1997; Oddy 2000). In the Roman period, fire gilding was 1991, 1993, 2000). This method of gilding is thus far not considered by Pliny the Elder (first century AD) to be a costly found on Roman silver objects from the fourth century AD. and rarely utilised method. However, it became the standard However, microscopic examinations of Roman objects from method of gilding in the third–fourth centuries AD and con- the Chaourse (second–third centuries AD) and Mâcon tinued to be used throughout medieval Europe, until the in- Treasures (third century AD) (Hughes et al. 1989), as well vention of electroplating in the mid-nineteenth century AD as of several earlier objects (e.g. an Elamite dish and a (Lechtman 1971; Lins and Oddy 1975; Oddy 1981, 1988, Parthian bowl) (Oddy 1988), revealed the presence of diffu- 1991, 1993, 2000). As such, the presence of mercury is com- sion bonded gilding on these objects. mon in the gilding of third century AD Roman objects, but The lack of mercury could indicate some sort of restoration, rare in the gilding of earlier Roman objects. This may be during which gilding could be lost due to, e.g. repeated an- because supplies of mercury became more available for com- nealing, and was subsequently replaced. If the lack of mercury mon use in the third century AD. Another method of fire would indicate some restoration, then it is highly unlikely that gilding is to apply a layer of mercury to the metal surface to the complete gilding of the Geometric Ewers was restored and be gilded and then lay pieces of gold leaf on top. The gold leaf no sign of restoration was found on the other Seuso objects. dissolves in the mercury, creating a gold amalgam in situ, after Moreover, based on the description of the restoration process which the object is heated and burnished. This method is still performed in 1989 (Mango and Bennett 1994), no such resto- used in Japan (Anheuser 1997;Oddy 2000). Anheuser’s ration, which would provide enough heat to drive off the mer- (1997) experiments showed that 8–25% of mercury is retained cury, was performed on the Seuso objects. during fire gilding and can be detected later on. The typical Higher gold concentrations were measured at several macroscopic features of fire gilding, such as gold spreading points on the Animal Ewer, in places where gilding could over the edge of the gilded area, splashes of gold on ungilded not be seen by the naked eye (Fig. 5a, b). Mercury was also areas and thicker gold deposits in engraved lines, were ob- detected at these points. These are residues of former gilding, served on the Seuso objects (Fig. 5a–d). Fire gilding was the in which the gold diffused into the silver, but the gilding typical gilding method used on other contemporaneous late became worn over time. Roman silver hoards (Lang et al. 1984;Feugère 1988; Hughes et al. 1989; Cowell and Hook 2010; Hook and Assembling of the objects—joining techniques Callewaert 2013;Doračić et al. 2015; Lang and Hughes 2016;Greiff 2017;Vulić et al. 2017). There are several ways to join the different parts of a compos- The two types of gilding on the Seuso objects were also ite silver object: (i) make simple linkages by folding the edges supported by Mango and Bennett (1994), using mercury in of the metal; (ii) use pins, rivets or twisted components; or (iii) both cases: (i) a gold amalgam was prepared and rubbed onto create a joint by applying heat to metal (e.g. welding, casting the surface of the object, after which the object was heated and on, sintering, brazing and soldering). Both brazing (or hard the mercury evaporated; (ii) the surface of the object was soldering) and soft soldering require the use of filler metal, amalgamated by rubbing mercury on to it or by dipping it into such as low-temperature lead-tin soft solders, high- a solution of soluble mercury salt, and then gold leaf (some- temperature silver-copper hard solders and intermediate tem- times several layers) was laid on top, after which the object perature alloys of silver and mercury or of silver and tin (Lang was heated as before. It was thought that the Geometric Ewers and Hughes 1977, 1984, 1988). were gilded by the first method, whereas the Dionysiac Ewer, The various parts of the composite Seuso objects were Animal Ewer and the vessels of the Hippolytus set were dec- assembled in three different ways. The bases of the orated with the second method. The gilding of the Amphora Hippolytus and Geometric Ewers were mechanically attached Archaeol Anthropol Sci (2021) 13:83 Page 17 of 20 83 to the body by inserting the bases of the ewers into a hole in objects can be categorised, which suggests that different silver the foot and hammering the metal (Mango and Bennett 1994). ingots were utilised. The ewers were constructed in two ways: The handles, lids, feet and thumbpieces were attached with (i) the base and the body were made separately, or (ii) the base using lead-tin soft solders (Fig. 6). Lead-tin soft solders were and the body were raised or cast from a single silver sheet. The also used for ancient repairs (e.g. on the body of the composite objects were assembled following three methods: Amphora). The upper beaded and octagonal rims were at- (i) mechanical attachment, (ii) lead-tin soft solders or (iii) tached to the body with silver-copper hard solders, indicated copper-silver hard solders. Two types of gilding were used by the presence of green copper corrosion products (Fig. 6). for decoration, one with remnants of mercury (fire-gilding) The use of these soldering materials was common in the late and another without mercury (presumably diffusion bonding). Roman period (Lang and Hughes 1988). Hard soldering oc- The results of previous studies performed on the Seuso curs at a higher temperature, which may be near to the melting objects were interpreted and new observations were made, point of the body metal. In contrast, soft soldering requires a specifically, that the chemical composition of every part of lower melting point alloy and occurs at a much lower temper- every object (including the Toilet Casket and Hippolytus ature than the melting point of the body metal (Lang and Ewer) was determined, that the gilding and soldering of each Hughes 1977). The temperature range of the solders available object were identified. Regarding the Geometric Ewers, diffu- to ancient Roman craftsmen varied from the melting point of sion bonding was likely used instead of fire gilding, as previ- silver (960 °C) to Tinman’s solder containing 66% tin and ously hypothesised. The hXRF data serve as a guide with 34% lead, which is very close to the eutectic point of the which to select sites to sample (with minimal invasiveness) system (183 °C) (Lang and Hughes 1984). The differences for further lead isotope and bulk elemental composition anal- in the chemical compositions of the soft solders potentially yses, the results of which will be published in a subsequent indicate the use of different soldering alloys and different paper. working temperatures. The behaviour of a solder primarily depends on its composition, as well as on the conditions under which the soldering is performed (e.g. temperature, surface Supplementary Information The online version contains supplementary material available at https://doi.org/10.1007/s12520-021-01321-4. finish, flux, reducing or oxidising atmosphere). If several op- erations must be executed, the highest melting point solders Acknowledgements The hXRF measurements were performed within must be used first (Lang and Hughes 1988). the framework of the Seuso Research Project supported by the State of Hungary from 2014 to 2019. The authors are grateful to Balázs Lencz, Tamás Szabadváry and András Szabó at the Hungarian National Museum for their help during hXRF analysis. Ariana Gugora is thanked for proof- Conclusions reading the manuscript. Furthermore, the authors are thankful to Mária Tóth, Norbert Németh and Balázs Lencz for providing the silver reference Non-destructive handheld X-ray fluorescence spectrometry is materials. a useful tool in the determination of the chemical composition Funding Open access funding provided by ELKH Research Centre for of composite silver objects, if a significant number of analyses Astronomy and Earth Sciences. are performed and the same instrument is used for the mea- surements. With enough analyses, the inhomogeneity Open Access This article is licensed under a Creative Commons amongst the various parts of the objects and the similarities Attribution 4.0 International License, which permits use, sharing, adap- tation, distribution and reproduction in any medium or format, as long as and differences between the objects can be revealed, and the you give appropriate credit to the original author(s) and the source, pro- objects can be classified. Moreover, raw materials, vide a link to the Creative Commons licence, and indicate if changes were manufacturing and decoration techniques used can be made. The images or other third party material in this article are included characterised, which help to better reconstruct past technolog- in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's ical practices and craftsmanship. Creative Commons licence and your intended use is not permitted by The chemical composition of the objects of the Seuso statutory regulation or exceeds the permitted use, you will need to obtain Treasure shares similarities with other late Roman period sil- permission directly from the copyright holder. To view a copy of this ver finds. The differences in the chemical composition of the licence, visit http://creativecommons.org/licenses/by/4.0/. various parts of the composite objects are clear evidence that different ingots of silver were used for each part, which sup- ports the earlier technological observations (Mango and References Bennett 1994). The different copper contents explain the use of intentional alloying. The constant gold content implies that Angelini I, Canovaro C, Venturino M, Artioli G (2019) The silver trea- the objects were not manufactured from reused or remelted sure of Marengo: silver provenancing and insights into late antiquity scrap silver. The likewise constant and low lead content indi- Roman and Gallo-Roman hoards. Archaeol Anthropol Sci 11:4959– cates the use of cupelled silver. 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Publisher: Springer Journals
Copyright: Copyright © The Author(s) 2021
ISSN: 1866-9557
eISSN: 1866-9565
DOI: 10.1007/s12520-021-01321-4
Publisher site: See Article on Publisher Site

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. . . . . . Keywords Late Roman Composite silver objects Handheld XRF Seuso Treasure Chemical composition Gilding Introduction which is written in the metric inscription of one of the platters. The pieces are typical of the period, representing parts of a The Seuso Treasure is one of the most significant treasure dining set used during festive banquets and also including finds from the late Roman Imperial period (Painter 1990; vessels for washing, bathing and beauty treatments. The ob- Mango and Bennett 1994; Mráv and Dági 2014; Dági and jects of the Seuso Treasure are amongst the largest known late Mráv 2019). The Treasure is composed of 14 large, domestic Roman silver vessels, and they are outstanding in both their silver vessels (Fig. 1), as well as the copper cauldron in which artistic and material value. Most of the silver vessels were they were hidden. The name originates from the owner, Seuso, manufactured in the fourth century AD, although some may have also been produced in the early fifth century AD. They were likely hidden in NE Pannonia (present-day Hungary) * Viktória Mozgai when the Romans fled from a “barbarian” attack in the late mozgai.viktoria@csfk.org fourth or early fifth century AD (Mráv and Dági 2014;Dági * Bernadett Bajnóczi and Mráv 2019). bajnoczi.bernadett@csfk.org During the final centuries of the Roman Empire, other sil- ver hoards were similarly hidden underground in various parts Institute for Geological and Geochemical Research, Research Centre of the Empire (e.g. Hoxne (England); Mildenhall (England); for Astronomy and Earth Sciences, Eötvös Loránd Research Kaiseraugst (Switzerland); Vinkovci (Croatia); Esquiline, Network (ELKH), H-1112 Budaörsi út 45, Budapest, Hungary Rome (Italy); Traprain Law (Scotland)). X-ray fluorescence Institute of Materials and Environmental Chemistry, Research Centre (XRF) analysis has been used to examine most of the other for Natural Sciences, Eötvös Loránd Research Network (ELKH), Roman silver treasures (Hughes and Hall 1979;Langetal. H-1117 Magyar tudósok körútja 2, Budapest, Hungary 1984; Feugère 1988;Hughes et al. 1989; Lang 2002;Cowell Hungarian National Museum, H-1088 Múzeum körút 14–16, and Hook 2010; Hook and Callewaert 2013; Minning and Budapest, Hungary 83 Page 2 of 20 Archaeol Anthropol Sci (2021) 13:83 Fig. 1 The Seuso Treasure: 1. Geometric Platter; 2. Meleager Platter; 3. Achilles Platter; 4. Seuso (or Hunting) Platter; 5. Hippolytus Ewer; 6. Hippolytus Situla A; 7. Hippolytus Situla B; 8. Animal Ewer; 9. Dionysiac Ewer; 10. Amphora; 11. Toilet Casket; 12. Geometric Ewer A; 13. Basin; 14. Geometric Ewer B. The red numbers indicate the composite objects discussed in the present paper (photo: A. Dabasi and J. Kardos (HNM)) Ponting 2013; Sánchez and Lansing Maish 2014;Lang and semi-quantitative elemental information can be gained Hughes 2016;Greiff 2017; Angelini et al. 2019; Arias et al. quickly. Moreover, sampling sites for more detailed anal- 2019), although other techniques were also used to determine ysis, e.g. quantitative elemental, lead isotopic and metallo- the elemental composition of the objects, such as emission graphic analysis, can be planned based on the hXRF spectroscopy (Lang et al. 1977;Berthoudetal. 1988; measurements. Mango and Bennett 1994) and particle-induced X-ray emis- However, the hXRF method has some limitations, sion spectroscopy (PIXE) (Tate and Troalen 2009;Doračić which must be taken into consideration during data evalu- et al. 2015;Vulić et al. 2017). ation. Because XRF is a surface analytical method, the Non-destructive handheld X-ray fluorescence spectrom- measured concentrations represent the outer part (usually etry (hXRF) is one of the most popular elemental analytical a few tens of microns) of the analysed objects. The signal methods in the fields of archaeology and cultural heritage comes from different depths, depending on the element and (Shackley 2012; Frahm and Doonan 2013;Zlateva 2017), the matrix (Tate 1986;Massand Matsen 2013). Metal ob- and it is often utilised in the analysis of archaeological and jects can be chemically heterogeneous for several reasons, historical metal objects, particularly in the elemental anal- such as phase segregation in silver-copper alloys during ysis of precious metal objects (e.g. Karydas et al. 2004; manufacture; acid treatments after preparation (etching), Cesareo et al. 2008; Melcher et al. 2009; Parreira et al. which dissolve copper from the surface layers; polishing 2009; Asderaki-Tzoumerkioti and Karydas 2011;Pardini during and after manufacture; corrosion and tarnishing; et al. 2012; Mass and Matsen 2013; Zori and Tropper remnants of gilding, etc. (Mass and Matsen 2013). 2013; Lehmann et al. 2014; Živković et al. 2014; Mozgai Surface enrichment of silver alloys is a well-known phe- et al. 2017;Mozgaietal. 2018; Horváth et al. 2019a; nomenon, during which base metals (e.g. copper and lead) Szenthe et al. 2019;May 2020;Mozgaietal. 2020). XRF are leached out from the surface, while silver and gold are is a simultaneous, multi-element analytical method, where- enriched towards the surface (Hall 1961;Lejček et al. by the concentrations of most elements of the periodic 2010), artificially exaggerating the silver and gold content table (Z = 12–92, from Mg to U) can be determined (major, at the expense of copper. Therefore, non-destructive sur- minor and trace elements). face analytical results, like hXRF data, may not represent The elemental analysis of silver objects is essential to the core metal composition. Surface enrichment can affect understand the contemporaneous raw material use, high-quality (> 90 wt%) silver objects as well, observed on alloying practice and manufacturing and decoration tech- silver coins (e.g. Beck et al. 2003;Becketal. 2004;Caridi niques. The major element content helps us to understand et al. 2013;Hrnjić et al. 2020;Hrnjić et al. in press). In whether any conscious technological choice of alloys was order to reduce the effect of the surface enrichment, applied for the different parts of the composite silver ob- polishing or abrasion of a small area before XRF analysis jects. The minor and trace element content can provide is usually carried out (e.g. Hughes and Hall 1979;Lang information about the used ore sources, raw materials and et al. 1984;Lang 2002; Lang and Hughes 2016;Greiff metallurgical techniques. Non-destructive analytical 2017). methods, such as handheld XRF, are particularly useful Metal samples taken from objects in the Seuso Treasure in the analysis of precious metal objects, where sampling were previously analysed by ICP-OES and scanning electron is not or only limitedly allowed due to the high value of the microscopy (Mango and Bennett 1994). However, no analy- objects. By using hXRF, the objects can be measured sys- ses were performed on the Hippolytus Ewer, and only one tematically at numerous points in situ in the museums, and metal sample was measured from the Toilet Casket, which is Archaeol Anthropol Sci (2021) 13:83 Page 3 of 20 83 comprised of three parts. The ICP-OES results are sometimes Materials and methods inaccurate, as concentrations of gold were noticeably low in most cases. These limitations justify the utilisation of new, Materials: the composite silver objects of the Seuso more detailed elemental analyses on the objects. Treasure The aim of this study is to determine the elemental com- position of the late Roman Seuso Treasure silver vessels Technological observations suggest that composite objects are using handheld XRF to classify the objects, to detect chem- composed of several parts (body, base, handle, lid, upper ical differences between the objects, as well as chemical beaded rim, thumbpiece, feet) and were manufactured from inhomogeneity within the objects, to determine the raw different silver casts (Mango and Bennett 1994; Dági and material (ore) used and to characterise the gilding and join- Mráv 2019). They are classified into groups based on their ing techniques. These results contribute to a more detailed shape and function (for parameters and decoration reconstruction of late Roman craftsmanship, including sil- techniques of the objects, see Table 1). versmithing, manufacturing, alloying, decoration and as- The relief-decorated Amphora is embellished with sembling practices. Dionysiac motifs, animal fighting scenes and xenia images, The Seuso objects were in good condition; thus, no ad- and its shape and decoration suggest that it was used to serve ditional surface cleaning (polishing or abrasion) was per- wine. It was constructed from several parts: a body, a base, formed before this study’s hXRF measurements. In return two panther-shaped handles and a stopper connected with a for the lack of cleaning, we performed measurements at chain. The body was manufactured either with the lost-wax several points on each part of the objects. Our approach casting technique (like the Baratti amphora was, Arias et al. differs from archaeometric studies performed on other 2019) or was hammered out of a single piece of silver, with no Roman silver hoards, because those objects were usually visible joins or seams. The cast base was hammered, and a only measured at a few points (1–20 points) per object centring point for a lathe is visible on it. The handles were (Lang et al. 1977; Hughes and Hall 1979;Langetal. likely cast using the lost-wax technique. 1984;Berthoudetal. 1988;Feugère 1988;Hughesetal. The Animal Ewer is decorated with chased figures and a 1989;Lang 2002; Cowell and Hook 2010; Hook and variety of geometric patterns. It may have belonged to a bath- Callewaert 2013; Minning and Ponting 2013;Doračić ing set, or it may have been used to serve wine, like the et al. 2015;Langand Hughes 2016;Greiff 2017;Vulić Amphora was. The body and base were cast or raised from a et al. 2017;Angelinietal. 2019; Arias et al. 2019), where- single piece of silver by hammering, while the upper beaded as our hXRF analysis eventuated a much larger data set (~ rim was cast separately and soldered to the body. The lid, 1600 points). Due to the high number of measurement made from a piece of silver, shows traces of hammering. points, surface cleaning was even more impossible, as the The handle was cast from a small bar of silver. importance of the treasure meant that it was not appropriate The Dionysiac Ewer is the smallest ewer in the Seuso to abrade the surface in order to expose the underlying Treasure. Based on its decoration with Dionysiac imagery metal over an area of about 3–8mmindiameter(7–50 (depicting the thiasos, the retinue of Dionysus), it was proba- mm ), large enough to match the XRF beam, especially bly used to serve wine. The body, the base and the neck were on the highly decorated, clearly visible sides. cast or hammered from a single piece of silver. The octagonal Two of the platters (Seuso/Hunting Platter and rim was made separately by casting or hammering and was Geometric Platter) manufactured from single casts were then soldered to the body. The handle was cast from a single previously analysed by hXRF alongside two other late bar of silver. Roman platters (Ribbon Platter and Rosette Platter from Geometric Ewers A and B are decorated with identical the Sava River find), which revealed a slight variation in chased geometric motifs. The ewers likely formed a set with the concentration of silver and copper along the radii of the the Basin. The bodies were hammered out of individual pieces plates manufactured from high-quality silver (> 95 wt% of silver, while the bases were made separately by hammering Ag) (Mozgai et al. 2017). The two other large, silver plat- and were then mechanically attached to the bodies. The upper ters (Meleager Platter and Achilles Platter) and the Basin, beaded rims were cast separately and were soldered to the also made from high-quality silver, have a more homoge- bodies, whereas the handles were cast from small bars of neous composition (Mozgai et al. 2020). In this paper, we silver. focus on the composite objects (ewers, situlas, amphora The Hippolytus Ewer depicts scenes from Greek mytholo- and toilet casket), which are assembled from several parts, gy (episodes from the Hippolytus story) and comprises a bath- and examine, in detail, the chemical differences between ing set, along with two situlas. The body was cast or raised by the various parts of the objects. Furthermore, the hXRF hammering from a single silver piece. The base was cast and data are compared with the previously published ICP- hammered from a separate piece of silver, after which it was mechanically attached and soldered to the body. The upper OES data (Mango and Bennett 1994). 83 Page 4 of 20 Archaeol Anthropol Sci (2021) 13:83 Table 1 Parameters and decoration techniques of the analysed relief from the back or the inside of the object by means of hammers and composite silver objects from the Seuso Treasure. *repoussé technique: punches. The name derives from the French word re-+ pousser meaning method of decorating metals in which parts of the design are raised in to push back (Untracht 1968; Maryon 1971; McCreight 1991) Find name Height (cm) Weight (kg) Capacity (litre) Repoussé technique* Dot- Chasing Gilding Niello inlays punching Ewers and amphora Amphora 38.5 2.5 – XX X X Animal Ewer 51.0 3.98 4 X X X X Dionysiac Ewer 43.5 3.0 4 X X X X Geometric Ewer A 52.8 2.65 4 X X X Geometric Ewer B 55.0 2.8 4 X X X Hippolytus Ewer 57.3 4.05 – XX X X Cylindrical objects Hippolytus Situla A 22.7 4.44 – XX X X Hippolytus Situla B 22.9 4.48 – XX X X Toilet Casket 32.0 2.05 – XX X beaded rim was cast separately and was then soldered to the Methods body. The lid, handle and lion-shaped thumbpiece were made using the lost-wax technique. After thorough macroscopic observation, the objects from the The Hippolytus Situla A and B form a bathing set and are Seuso Treasure were systematically analysed by handheld X- decorated with the same Greek mythological scenes as the ray fluorescence spectrometry (hXRF) along a pre-designed Hippolytus Ewer is. The bodies were cast or hammered out grid at several points on each object (see Online Resource 1). of single sheets of silver. The beaded rims were cast separately The number of measurement points ranged from 2 to 70 points and were then soldered to the bodies, while the three feet were per part, depending on the size of the measured part of each cast using the lost-wax technique and were also soldered to the object. bodies. The handles were cast and riveted to the decorative In this study, two hXRF instruments from different manu- busts, which were likewise soldered to the body. facturers were used: (i) a Thermo Scientific Niton Xl3t The Toilet Casket was probably stored smaller ointment con- GOLDD+ (Waltham, Massachusetts, USA) and (ii) a tainers using in daily toiletries. Both the body and the lid were SPECTRO xSORT Combi (Kleve, Germany) (see Table 2 cast or manufactured by hammering from single sheets of silver. for the analytical conditions). During the measurements, the The interior pierced disc was produced from a hammered sheet concentrations of the following major, minor and trace ele- of silver and contains seven pierced holes for flask storage. ments were determined: Ag, Cu, Au, Pb, Bi, Sb, Sn, Zn and The objects of the Seuso Treasure were examined, restored Fe (see Online Resource 1 for the detection limits of each and conserved at the Institute of Archaeology at University hXRF instrument). The built-in calibrations of each instru- College, London between April and December of 1989 ment were used for the measurements (Table 2). The (Bennett in Mango and Bennett 1994). Some of the objects Thermo Scientific Niton Xl3t GOLDD+ instrument measured were covered with calcareous encrustations, silver corrosion Bi and Sb using the ‘General Metals’ calibration, whereas the products and patches of green copper corrosion products. ‘Precious Metals’ calibration was used for the rest of the ele- Furthermore, some parts of the objects were harshly cleaned ments. The quantitative evaluation was performed with the and chemically polished during the period between the exca- built-in fundamental parameters (FP) method, using vation and the restoration in 1989. Unfortunately, no informa- Compton normalization. The results were normalised to tion is known about this period. During the restoration in 100%, and no calibrations in data were applied. The precision 1989, a 15% solution of ammonium thiosulphate and distilled and accuracy of the hXRF instruments were determined by water was used to remove silver corrosion products and cal- separate measurements taken of a Roman silver spoon and on careous encrustations from all visible surfaces. Green copper modern silver-copper alloys (see Online Resource 1 for corrosion products were carefully removed with a 10% solu- details). tion of formic acid and distilled water. After cleaning, each of The XRF spectra were evaluated by using NITON Data the objects were washed several times in distilled water baths Transfer Version NDT_REL_8.0.0 (Thermo Scientific Niton for 2–5 days. A thin layer of Paraloid B-72 was used to con- Xl3t GOLDD+) and XRF Analyzer Pro v.1.9. (SPECTRO serve the objects (Bennett in Mango and Bennett 1994). xSORT Combi) software programs. The data points were Archaeol Anthropol Sci (2021) 13:83 Page 5 of 20 83 Table 2 Comparison of the analytical conditions of the two handheld XRF instruments used for analysing the Seuso Treasure Instrument SPECTRO xSORT Combi Thermo Scientific Niton Xl3t GOLDD+ Detector Energy-dispersive SDD Energy-dispersive LDD X-ray tube 50 kV; Rh-anode 50 kV, Ag-anode Built-in calibrations ‘Light Elements’‘General Metals’ and ‘Precious Metals’ Spot size 3 mm 3 and 8 mm Acquisition time 60 s 50 s and 40 s plotted by using Microsoft Office Excel Professional Plus Cu) (Table 3;Figs. 2, 3 and 4). The gold content is around or 2016 and CorelDraw Graphics Suite 2018 (v.20.1.0.708) soft- below 1 wt% (except the Animal Ewer, discussion below) ware programs. (Table 3;Figs. 2, 3 and 4). The lead content is usually below The relative error of the Thermo Scientific Niton Xl3t 1 wt% (Table 3; Online Resource 2), and the bismuth content GOLDD+ instrument is less than 0.5% for silver, less than of the objects is heterogeneous, even within one object 5% for copper, less than 6% for gold, less than 10% for lead (Table 3;Figs. 2, 3 and 4). The tin, zinc and antimony contents and less than 20% for bismuth. The relative error of the are below the detection limit, with except for some parts of SPECTRO xSORT Combi instrument is better, namely less some of the objects (discussion below). than 0.1% for silver, less than 0.5% for copper, less than 2% The various parts (base, body, handle, stopper) of the for gold, less than 5% for lead and less than 10% for bismuth. Amphora differ chemically from each other. The stopper At some points (less than 7% of the total measurements), contains the least amount of copper (0.8–1.2 wt%), whereas higher relative errors were calculated, but none is above the base contains the most (3.0–3.8 wt%) (Fig. 2). The gold 50%. These points do not show a systematic distribution, and lead contents are not homogeneous between the and not related to an object or to a specific feature of the object Amphora’s parts. The bismuth content of the parts is very (e.g. geometric problems). variable, ranging from 0 to 2600 ppm (Fig. 2; Online For optimal measurements, the handheld XRF instrument Resource 2). requires ideal and reproducible surface geometries, such as The chemical composition of the various parts of the flat surface that are parallel to the spectrometer head. The lack Animal Ewer is also different. The body and the base contain of suitable and reproducible geometries can cause an error of the least amount of copper (0.6–3.3 wt%), whereas the upper 0.5% or more, if the objects have complex geometries (e.g. beaded rim, lid and handle contain the most (1.0–7.3 wt%) ewers, vessels, statues) (Mass and Matsen 2013). Therefore, (Fig. 2). The gold and lead contents are generally below or we aimed to measure surfaces that were as flat as possible, as around 1 wt%. At several points, the gold content of the parts well as to analyse the same locations on each object with each was elevated (> 1 wt%) (discussion below) (Fig. 2). The bis- instrument. muth content of the parts is homogeneous (100–1400 ppm) We compared the performance of the two hXRF instru- (Fig. 2). In the upper beaded rim and the handle, 0.5–0.8 wt% ments based on the analysis of the composite objects of the tin was detected. The chemical composition of the body and Seuso Treasure and concluded that only the data measured the base is identical, but the handle, upper beaded rim and lid by the same XRF instrument, under the same analytical were manufactured from silver alloys of different conditions and using the same built-in calibration can be compositions. reliably compared (see Online Resource 1). As a result, The chemical composition of the various parts of the hereafter we handle the data of the two instruments sepa- Dionysiac Ewer is different. The base and the body have the rately and compare the chemical compositions within these lowest copper content (1.1–1.8 wt%), whereas the handle and separate, independent data sets (according to Brand and the thumbpiece have the highest (2.7–4.3 wt%) (Fig. 2). The Brand 2014). body and the base have the same chemical composition; how- ever, the thumbpiece, handle and upper octagonal rim were made from different silver alloys. The silver and copper con- tents of the upper octagonal rim fall between the composition Results of the thumbpiece and handle and the base and body, respec- tively. The gold and lead contents are below 1 wt% (Fig. 2; Chemical composition of the composite objects of the Online Resource 2). The bismuth content of the Dionysiac Seuso Treasure Ewer is the highest (1200–3200 ppm) of all the Seuso objects (Fig. 2). In the thumbpiece and handle, 0.5–0.6 wt% zinc was In general, the objects were manufactured from high-quality detected. silver alloyed with copper (79.6–99.4 wt% Ag; 0.1–18.6 wt% 83 Page 6 of 20 Archaeol Anthropol Sci (2021) 13:83 Table 3 Chemical composition of the composite objects of the Seuso SPECTRO xSORT Combi hXRF. The minimum–maximum values are Treasure. Ag, Cu, Au, Pb are given in wt%, Bi is given in ppm. N = given. The Au/Ag and Bi/Pb ratios were calculated for each measurement measured using Niton Xl3t GOLDD+ hXRF; S = measured using points and the minimum–maximum values are given as well Instrument No. of analyses Ag Cu Au Pb Bi Au/Ag Bi/Pb Amphora Base N 8 93.7–94.9 3.3–3.8 1.0–1.2 0.6–0.9 1400–1900 0.011–0.013 0.21–0.24 S4 94.0–94.8 3.0–3.6 0.9–1.0 0.6–0.9 1100–1400 0.010–0.011 0.16–0.18 Body N 54 96.1–98.0 0.5–1.9 0.6–1.2 0.4–1.5 0–500 0.006–0.013 0–0.08 S27 96.2–97.7 1.1–1.8 0.5–0.8 0.6–1.0 0–200 0.005–0.008 0–0.03 Handle N 4 95.8–96.2 2.3–2.6 0.4–0.5 1.0–1.1 200–300 0.005 0.01–0.02 S4 95.5–95.9 2.3–2.5 0.4–0.5 1.1 100–200 0.004–0.005 0.01–0.02 Stopper N 2 97.7–98.1 1.1–1.2 0.3–0.5 0.2 2000–2600 0.004–0.006 0.95–1.23 S2 98.2–98.4 0.8 0.3 0.1–0.2 1500–1600 0.003 0.99–1.00 Animal Ewer Body N 64 94.9–97.9 0.8–3.3 0.9–2.4 0.2–0.9 400–1000 0.009–0.025 0.09–0.40 S31 94.2–97.9 0.6–2.2 0.8–1.9 0.1–0.9 100–700 0.008–0.020 0.06–0.25 Base N 11 96.4–98.3 0.5–1.7 0.5–1.6 0.2–0.3 500–900 0.005–0.017 0.26–0.34 S4 95.9–97.0 1.3–1.6 0.9–1.0 0.2–0.3 400–500 0.010 0.16–0.21 Handle N 7 92.9–94.6 3.2–4.7 0.7–1.7 0.4–0.7 900–1100 0.008–0.018 0.15–0.23 S4 94.0–94.5 3.4–4.1 0.8–1.1 0.4–0.5 600–900 0.009–0.011 0.16–0.17 Upper beaded rim N 5 93.7–95.4 2.4–4.0 1.0–1.1 0.3–0.5 700–1400 0.011–0.012 0.21–0.31 S3 94.6–95.0 2.6–3.2 1.2–1.4 0.2–0.4 500–600 0.012–0.015 0.15–0.22 Lid N 10 90.5–96.7 1.0–7.3 0.4–1.4 0.3–0.9 300–1100 0.004–0.015 0.04–0.17 S3 93.2–93.8 3.3–3.7 0.7–0.8 0.7 700–800 0.008–0.009 0.11 Dionysiac Ewer Body N 61 96.6–98.0 1.1–1.8 0.4–1.2 0.1–0.3 1400–2400 0.004–0.013 0.54–1.64 S14 96.4–97.9 1.3–1.6 0.3–0.5 0.1 1200–1700 0.003–0.005 1.13–2.21 Base N 8 97.2–97.8 1.3–1.8 0.4–0.5 0.1–0.2 1600–2000 0.004–0.005 0.86–1.46 S7 97.5–97.9 1.2–1.5 0.3–0.4 0.1 1200–1300 0.004 0.87–2.28 Thumbpiece N 3 94.0–95.0 3.2–4.2 0.5–0.6 0.2–0.3 2800–3200 0.005–0.007 1.05–1.14 Handle N 6 93.2–95.6 2.7–4.3 0.5–0.7 0.2–1.1 2500–3200 0.005–0.007 0.29–1.20 S2 91.2–94.7 3.8–4.1 0.4–0.5 0.2–0.5 2100–2200 0.004–0.006 0.44–1.26 Upper octagonal rim N 6 95.6–96.4 2.3–2.6 0.5–0.6 0.1–0.6 2800–3200 0.005–0.006 0.52–2.31 S5 95.8–96.4 2.3–2.5 0.5–0.6 0.1–0.4 2100–2500 0.005–0.006 0.57–2.62 Geometric Ewer A Body N 70 93.9–97.8 0.9–2.9 0.7–1.1 0.5–1.1 900–1400 0.008–0.012 0.10–0.19 S30 96.3–97.9 0.9–1.6 0.7–0.9 0.4–0.7 500–1000 0.007–0.009 0.09–0.15 Base N 14 94.5–97.1 1.4–4.1 0.7–1.1 0.2–0.5 500–1100 0.008–0.011 0.16–0.25 S9 94.3–96.2 1.1–3.7 0.8–1.1 0.1–0.6 100–700 0.008–0.011 0.04–0.14 Handle N 7 92.3–94.7 3.8–6.1 0.8 0.6–0.8 1000–1200 0.008–0.009 0.13–0.19 S5 93.0–94.8 3.5–5.2 0.7–0.8 0.7–0.8 800–1000 0.007–0.009 0.10–0.14 Upper beaded rim N 4 93.0–95.2 3.7–5.8 0.8–0.9 0.3–0.6 500–900 0.008–0.010 0.17–0.21 S4 91.6–93.0 4.5–6.5 0.7–1.0 0.2–0.6 400–700 0.008–0.010 0.11–0.23 Geometric Ewer B Body N 62 95.2–97.1 1.6–3.2 0.8–1.1 0.2–0.4 600–1000 0.009–0.011 0.17–0.21 S16 95.4–96.4 1.9–2.5 0.7–1.1 0.2–0.3 400–700 0.008–0.011 0.14–0.19 Base N 11 79.6–94.0 4.5–18.6 0.8–1.1 0.4–0.5 700–900 0.009–0.011 0.17–0.31 S7 84.9–93.5 4.5–10.9 0.7–1.0 0.3–0.5 500–800 0.008–0.011 0.15–0.27 Handle N 11 92.4–94.6 3.7–5.9 0.7–0.9 0.6–0.8 800–1100 0.008–0.009 0.11–0.15 S5 93.5–94.2 3.6–4.8 0.7–0.8 0.8 700–900 0.007–0.009 0.09–0.11 Upper beaded rim N 5 90.2–95.6 2.0–7.1 0.7–1.0 0.6–1.3 500–1100 0.008–0.010 0.04–0.17 Archaeol Anthropol Sci (2021) 13:83 Page 7 of 20 83 Table 3 (continued) Instrument No. of analyses Ag Cu Au Pb Bi Au/Ag Bi/Pb S2 89.6–95.5 1.4–4.6 0.8–1.0 0.6–0.9 0–400 0.009–0.011 0.009–0.011 Thumbpiece N 3 93.5–94.8 3.4–4.6 0.8–0.9 0.7–0.8 1000–1200 0.008–0.009 0–0.07 Hippolytus Ewer Body N 32 94.4–96.8 1.8–4.1 0.6–1.0 0.4–0.6 900–1500 0.007–0.011 0.21–0.28 S15 96.2–96.8 1.6–2.1 0.6–0.8 0.4–0.5 700–1000 0.007–0.008 0.16–0.23 Base N 15 95.7–98.4 0.8–2.9 0.5–1.0 0.2–0.4 700–2600 0.005–0.010 0.19–1.09 S8 94.3–97.5 1.3–2.8 0.5–1.0 0.1–0.4 500–1200 0.005–0.010 0.16–0.98 Lid N 8 91.4–95.1 3.6–6.9 0.6–1.0 0.5–0.6 500–900 0.006–0.010 0.09–0.16 S4 92.2–94.2 3.4–6.2 0.5–0.6 0.4–0.6 400–600 0.006–0.007 0.08–0.11 Handle N 9 93.9–97.1 1.6–5.0 0.6–1.1 0.3–1.1 700–2000 0.007–0.011 0.11–0.56 S2 94.8–96.2 2.3–3.4 0.8–0.9 0.3–0.4 400–1300 0.009 0.12–0.40 Upper beaded rim N 8 94.0–97.5 1.5–3.2 0.5–0.9 0.3–1.4 1500–2300 0.005–0.010 0.16–0.62 S4 95.2–97.0 1.7–3.2 0.5 0.2–0.6 1400–1700 0.005–0.006 0.30–0.72 Hippolytus Situla A Handle N 9 95.6–97.2 1.8–2.7 0.6–0.9 0.4–0.7 400–900 0.007–0.009 0.10–0.16 S4 96.6–97.1 1.8–2.0 0.6 0.2–0.5 200–500 0.006–0.007 0.06–0.10 Feet N 8 95.4–97.6 0.8–2.6 0.9–1.1 0.3–0.8 400–1100 0.010–0.011 0.08–0.29 S2 95.2–96.2 2.1–2.6 0.8–0.9 0.4–0.7 600–700 0.008–0.010 0.10–0.14 Body N 32 96.2–98.2 0.6–2.8 0.5–0.9 0.1–0.3 200–900 0.005–0.010 0.07–1.47 S21 95.7–97.2 2.1–2.6 0.4–0.6 0.1–0.2 0–200 0.005–0.006 0–0.12 Upper beaded rim N 5 98.9–99.2 0.4–0.6 0.3–0.4 0–0.1 0–1400 0.003–0.004 0–3.20 S4 95.3–99.0 0.3–0.5 0.3 0–0.04 400–800 0.003 0–6.28 Hippolytus Situla B Handle N 11 96.6–97.7 1.2–2.1 0.6–0.8 0.3–0.5 300–800 0.006–0.008 0.08–0.30 S 4 97.3 1.6–1.7 0.5–0.6 0.3 0–300 0.005–0.006 0–0.10 Feet N 8 94.6–97.3 1.1–2.9 0.7–1.1 0.2–1.3 700–1200 0.008–0.012 0.09–0.33 S2 95.2–95.4 2.5–2.7 0.8 0.4–0.5 700 0.008–0.009 0.14–0.17 Body N 33 95.6–97.5 1.7–3.2 0.5–0.9 0.3–0.5 200–500 0.006–0.010 0.07–0.12 S22 92.5–97.4 1.7–2.7 0.5–1.0 0.2–0.5 100–400 0.005–0.011 0.02–0. 11 Upper beaded rim N 8 98.6–99.3 0.1–0.8 0.3–0.5 0–0.4 500–2000 0.003–0.005 0.18–2.60 S6 98.7–99.4 0.1–0.5 0.2–0.5 0–0.01 0–600 0.002–0.005 0–6.41 Toilet Casket Lid N 55 94.8–96.6 2.0–3.7 0.6–1.2 0.3–0.5 600–1300 0.006–0.013 0.14–0.33 S23 94.8–96.7 1.9–3.5 0.7–1.2 0.3–0.5 500–1000 0.007–0.013 0.13–0.22 Base N 49 94.9–97.5 1.2–3.6 0.8–1.2 0.2–0.5 400–900 0.009–0.013 0.10–0.20 S24 95.0–96.9 1.0–3.4 0.8–1.0 0.2–0.5 100–500 0.009–0.011 0.03–0.11 Pierced disc N 12 93.4–93.8 4.3–4.7 0.8 0.7 1300–1500 0.009 0.19–0.21 S6 91.8–94.1 3.9–4.5 0.7–0.8 0.6–0.8 1000–1200 0.008 0.14–0.16 The two Geometric Ewers (A and B) have a similar chem- (Fig. 3). The chemical composition of the various parts of each ical composition. The bodies contain the least amount of cop- ewer (body, handle, base, thumbpiece, upper beaded rim) in- per (0.9–3.2 wt%), whereas the base of Geometric Ewer B dicates that they were manufactured from silver alloys of dif- shows an elevated amount of copper (4.5–18.6 wt%), with a ferent compositions. very heterogeneous distribution. The base of Geometric Ewer Based on the observed variation in the chemical composi- A exhibits a lower concentration of copper (between the com- tion of the different parts (lid, body, base, handle, upper position of the body and the upper beaded rim and handle) beaded rim) of the Hippolytus Ewer,they weremanufactured (Fig. 3). The gold and lead contents are below 1 wt% (Fig. 3; from different silver alloys. The lid has the highest copper Online Resource 2). The bismuth content is homogeneous content (3.4–6.9 wt%), whereas the base has the lowest 83 Page 8 of 20 Archaeol Anthropol Sci (2021) 13:83 Fig. 2 Silver vs. copper and gold vs. bismuth content of the Amphora, the Niton Xl3t GOLDD+; 2: SPECTRO xSORT Combi; 3: ICP-OES Dionysiac and the Animal Ewers based on the hXRF measurements, (Mango and Bennett 1994) previous ICP-OES data are shown for comparison. Measured with 1: (0.8–2.9 wt%) (Fig. 3). Although the gold and lead contents handle contain a slightly higher percentage of lead (0.2–1.4 are constant and fall below 1 wt%, the upper beaded rim and wt%) (Fig. 3; Online Resource 2). The bismuth content is Archaeol Anthropol Sci (2021) 13:83 Page 9 of 20 83 Fig. 3 Silver vs. copper and gold vs. bismuth content of the Hippolytus GOLDD+; 2: SPECTRO xSORT Combi; 3: ICP-OES (Mango and and the Geometric Ewers based on the hXRF measurements, previous Bennett 1994) ICP-OES data are shown for comparison. Measured with 1: Niton Xl3t much more heterogeneous than the gold and lead content of 400–1500 ppm, and the upper beaded rim and part of the base the parts. The bismuth content of the body, lid and handle is exhibit higher concentrations (500–2600 ppm) (Fig. 3). 83 Page 10 of 20 Archaeol Anthropol Sci (2021) 13:83 Fig. 4 Silver vs. copper and gold vs. bismuth content of the Hippolytus 1: Niton Xl3t GOLDD+; 2: SPECTRO xSORT Combi; 3: ICP-OES Situlas and the Toilet Casket based on the hXRF measurements, (Mango and Bennett 1994) previous ICP-OES data are shown for comparison. Measured with The various parts of the two Hippolytus Situlas (handle, other. The upper beaded rims have the highest silver content feet, body and upper beaded rim) differ chemically from each of all the Seuso objects; in fact, they were manufactured from Archaeol Anthropol Sci (2021) 13:83 Page 11 of 20 83 almost pure silver (> 99 wt%) (Fig. 4). The gold content is volume and a detachment of the soldered parts (handles, heterogeneous. The feet have the highest gold content (0.7– thumbpieces, lids) (Fig. 6a–c). At the joints of the bodies 1.1 wt%), while the upper beaded rim has the lowest (0.2–0.5 and the upper beaded rims of the ewers and the situlas, green wt%). The gold content of the handles and the bodies is sim- copper corrosion products were observed by the naked eye, ilar (0.5–1.0 wt%). The lead content is constant and falls be- which manifested in higher copper concentrations (31.9 wt% low 1 wt%, whereas the bismuth content is heterogeneous, Cu) (Online Resource 3; Fig. 6d). ranging from 0 to 1500 ppm (Fig. 4; Online Resource 2). The parts (lid, base, pierced disc) of the Toilet Casket have different chemical compositions, indicating that they were Discussion manufactured from silver alloys of different compositions. The pierced disc contains the most copper (3.9–4.7 wt%), Major elements: silver and copper and the lid and base contain similar amounts of copper (1.0– 3.7 wt%) (Fig. 4). The gold and lead contents are constant and Each of the objects was manufactured from high-quality fall below or around 1 wt% (Fig. 4; Online Resource 2). silver, which corresponds well with the observation that Bismuth is present in slightly lower concentrations in the base high-purity (80–99 wt% Ag) silver objects were created in (100–900ppm)thaninthelid (500–1300 ppm) and the the late Roman period (Table 4) (Hughes and Hall 1979; pierced disc (1000–1500 ppm) (Fig. 4). Lang et al. 1984;Feugère 1988;Lang 2002;Tateand Troalen 2009; Cowell and Hook 2010;Hook and Callewaert Gilding 2013; Doračić et al. 2015; Lang and Hughes 2016; Greiff 2017;Vulić et al. 2017). Each of the composite objects was selectively gilded, except the Pure silver is too soft to fashion everyday items from, be- Toilet Casket, and the gilding is quite worn in some places (Fig. cause it dents, bends and wears easily. In the late Roman 5). The gilding was analysed at several points, ranging from 2 to period, the most common silver alloying element was copper, 60 points per object, depending on the object and the extent of as it added strength and hardness to the softer silver. The the gilded surfaces. The gold content of the gilded surfaces hardness of an alloy depends not only on its chemical compo- ranges from 1.0 to 76.2 wt% depending on the thickness of the sition but also on the degree of working and heat treatment. gilding (Online Resource 3). The relative thickness of the gilding The hardness increases quickly up to 15% copper content, and was estimated based on the macroscopic observations and on the between 30 and 80% copper it reaches a rather constant value gold content of the gilded areas. In the case of the Amphora, (Hughes and Hall 1979). As the amount of copper that is Animal Ewer, Dionysiac Ewer and the Hippolytus set, mercury added to the molten silver increases, the more yellowish the was detected in the gilded parts (Fig. 5g). Gold spans the edge of alloy will become. During silver extraction, the copper content the gilded area, particularly in the case of the Animal Ewer, may be reduced to 0.2–1%; thus, higher copper concentrations whose flat surfaces were gilded. On the ribs of the Animal indicate intentional alloying (Hughes and Hall 1979). The Ewer, which separate the different sections of the body, gilding copper content of late Roman silver objects ranges from 0.1 was not observed by the naked eye, only at the very edges, in to 15% (Table 4) (Hughes and Hall 1979;Lang etal. 1984; deeper depressions, but the elevated gold content indicates that Feugère 1988; Lang 2002; Tate and Troalen 2009; Cowell and the entirety of the ribs was originally gilded (Online Resource 3; Hook 2010; Hook and Callewaert 2013; Doračić et al. 2015; Fig. 5a, b). In contrast, the gilding of the two Geometric Ewers Lang and Hughes 2016; Greiff 2017;Vulić et al. 2017). The wasanalysedin61and 68 points,respectively, andnomercury copper content of the Seuso objects fits into this range. The was detected in any of analysed points by the handheld XRF differences in the copper contents of the various parts of the (Fig. 5g). The gilding appears to be very thin, is pale yellow composite objects also indicate intentional alloying: and generally follows the decoration lines (Fig. 5e, f). (i) The parts that are more exposed to mechanical effects, Soldering such as handles, bases, rims, lids and feet (e.g. the base and handle of the Amphora, the handles of the Animal, The various parts of the Seuso objects were assembled in Dionysiac, Hippolytus and Geometric Ewers, the bases of different ways. The joints were analysed at several points, the Geometric Ewers, the pierced disc of the Toilet ranging from one to seven points per object. At the joints of Casket), were usually made from alloys with higher cop- handles, feet, lids and thumbpieces, as well as at the ancient per but lower silver contents. repairs, elevated tin and lead contents were measured (1.4– (ii) The parts made with repoussé technique (e.g. the bodies 70.1 wt% Pb; 0.8–43.4 wt% Sn), indicating the use of a soft of the Animal, Dionysiac and Hippolytus Ewers, the lead-tin solder (Online Resource 3;Fig. 6e). The soldering bodies of the Hippolytus Situlas, the lid and the base of material completely recrystallised, resulting in increased the Toilet Casket) were generally made from alloys 83 Page 12 of 20 Archaeol Anthropol Sci (2021) 13:83 Fig. 5 Gilding on the Seuso objects. a, b The Animal Ewer: gilding spreads over the edge of the gilded area and is quite worn, invisible with naked eye at the ribs. c The Hippolytus Situla A. d The Amphora. e, f The Geometric Ewers A and B (photo: A. Dabasi and J. Kardos (HNM)). g hXRF spectra of the gilded areas on the examples of the ewers measured with SPECTRO xSORT Combi instrument containing a higher percentage of silver, which are more point, making it easier to cast the alloy. These parts in- malleable and make it easier to form the small details of clude, e.g. the upper beaded rims of the Animal, the figures and scenes (Greiff 2017). Geometric and Hippolytus Ewers, the octagonal rim of (iii) The parts that were unequivocally manufactured by casting the Dionysiac Ewer, handles of the Amphora, the lid of (handles, thumbpieces, lids, feet, upper beaded and octag- the Animal and Hippolytus Ewers. The upper beaded rims onal rims) usually have higher copper contents, because of the Hippolytus Situlas are exceptions; they were cast alloys with higher copper contents require a lower melting from almost pure silver (> 99 wt% Ag). The use of silver Archaeol Anthropol Sci (2021) 13:83 Page 13 of 20 83 Fig. 6 Solders on the Seuso objects. a Remnants of lead-tin soft solder at the joint of the han- dle to the body of the Dionysiac Ewer. b Remnants of lead-tin soft solder at the joint of lid to the base of the Toilet Casket and at ancient repairs. c Thick, corroded, re- crystallised lead-tin soft solder at the joint of the handle of Geometric Ewer B. d Green cop- per corrosion products along the rim of the Hippolytus Situla A indicating the use of copper- containing hard solder (photo: A. Dabasi and J. Kardos (HNM)). e hXRF spectra of the soft solders on the example of the ewers measured with SPECTRO xSORT Combi instrument. Animal Ewer: at the joint of the lid to the body; Dionysiac Ewer: at the joint of the handle to the body; Geometric Ewer B: at the joint of the handle to the body at the beaded rim; Hippolytus Ewer: at the joint of the lid to the body alloys with higher copper contents can also be economic deriving from the silver ore or from the copper used for (Mango and Bennett 1994). alloying (Hughes and Hall 1979). Their individual content usually does not exceed 1% (except for gold at some points The results of the previous ICP-OES measurements made in the Animal Ewer, discussion below). on bulk metal samples taken from the Seuso objects (Mango In the Roman period, the primary source of silver was and Bennett 1994) show the same trends as our hXRF results silver-bearing lead ores (Tylecote 1962;Forbes 1971). The (Figs. 2, 3 and 4, Online Resource 4). However, as hXRF is a silver ores were roasted, melted and cupelled during silver surface analytical method, the effects of corrosion processes extraction. Cupellation cleansed the silver of impurities are evident: the less noble copper was leached out, and the (e.g. antimony, arsenic, tin, iron and zinc; less well from more noble silver was enriched at the surface. Generally, ICP- copper, gold and bismuth). The volatile elements (antimo- OES measured higher copper concentrations (0.5–5wt% ny, arsenic, mercury, tin and zinc) disappear from the mol- higher) compared to hXRF (Figs. 2, 3 and 4). ten silver during cupellation (Pernicka 2014;L’Héritier et al. 2015); however, they can be present in high concen- Minor and trace elements (impurities) trations (several %) in native silver (Pernicka 2014). The absence of these volatile elements in the analysed objects With the exception of silver and copper, the measured el- indicates that cupelled silver was used for manufacturing. Thepresence of zincand tinin someparts of theobjects ements are naturally occurring and unintentionally added, 83 Page 14 of 20 Archaeol Anthropol Sci (2021) 13:83 Table 4 Chemical composition of contemporaneous silver treasure finds including number of their analysed objects. The results are given in wt% Treasure finds Analytical method No. of analysed objects No. of analyses Ag Cu Au Pb Bi Mildenhall XRF 20 124 93.7–98.0 0.3–4.2 0.4–2.6 0.2–2.2 Hoxne XRF 96 106 85.0–99.0 0.1–4.7 0.1–1.0 0.2–4.4 0–0.3 Kaiseraugst XRF 8 15 95.6–98.6 1.0–3.5 0.3–1.3 0.1–0.9 Vinkovci PIXE 49 56 89.1–99.8 0.2–8.9 0.4–3.4 0.1–1.6 0–0.3 Esquiline XRF 12 32 88.6–98.3 0.4–10.3 0.2–4.7 0.6–1.0 Coleraine XRF 30 30 88.7–97.5 1.2–6.6 0.4–2.2 0.3–2.3 Carthage XRF 20 52 94.3–97.7 1.9–4.5 0.3–1.1 0.1 – 0.9 Caubiac (Thil) XRF 4 4 93.8–98.2 1.1–4.3 0.4–0.8 0.2–0.6 Trier XRF 1 20 81.9–95.1 2.2–14.6 1.1–2.5 0.3–1.9 0–0.2 Water Newton XRF 13 17 88.6–97.9 1.8–9.9 0.2–4.4 0–0.8 11 a Seuso XRF 14 1620 79.6–99.4 0.1–18.6 0.2–2.4 0.1–1.5 0–0.3 The four platters and the Basin of the Seuso Treasure are also included. The minimum–maximum values are given. The number of analyses given for the Seuso Treasure is the sum of the measurements of the two hXRF instruments. Hughes and Hall 1979;Lang etal. 1977; Lang and Hughes 2016; 2 3 4 5 6 7 Cowell and Hook 2010; Lang et al. 1984; Doračić et al. 2015;Vulić et al. 2017; Hughes and Hall 1979; Hook and Callewaert 2013; Lang 2002; 8 9 10 11 Feugère 1988; Greiff 2017; Hughes and Hall 1979; Mozgai et al. 2017; Mozgai et al. 2020; present study (0.5–0.8 wt% Sn in the upper beaded rim and handle of the elevated tin content as well. Therefore, we assume that the Animal Ewer; 0.5–0.6 wt% Zn in the thumbpiece and han- lead content of the Seuso objects derives from the silver ore. dle of the Dionysiac Ewer) indicates that brass and bronze, Bismuth is also helpful in determining the raw material respectively, were used as alloying metals instead of pure provenance of silver objects, as its concentration does not copper. This is supported by the calculated Cu/Sn (~ 83% change significantly during cupellation (Pernicka and Cu;~17% Sn) and Cu/Zn(~87% Cu;~13%Zn)ratios Bachmann 1983; Pernicka 2014;L’Héritier et al. 2015). Dry (Hughes and Hall 1979;Greiff 2017). This alloying prac- ores or native silver have bismuth contents below 0.05% tice was indeed unusual in the Roman times, but later, (Craddock 1995), whereas argentiferous galena contains during the Migration Period, it was commonly practised 0.1–1% bismuth (Gale and Stos-Gale 1981). Based on cupel- (Craddock et al. 2010;Horváth et al. 2019b;Mozgai lation experiments, bismuth is oxidised in the final stages of et al. 2019). Though it is rare in Roman times, but it is cupellation; therefore, bismuth in silver objects is correlated not without example. Elevated Zn content was found in with the degree of cupellation. However, the final Bi/Pb ratio some of the pieces of the Hoxne hoard and concluded as of the cupelled silver depends on the initial Bi content of the the result of alloying with brass typical of Roman period silver-bearing lead ores (L’Héritier et al. 2015). The Bi/Pb (Cowell and Hook 2010). Hughes and Hall (1979) detected ratio indicates that the Seuso objects can be categorised as elevated zinc content in some bowls from the Chaourse having a homogeneous Bi/Pb ratio or a heterogeneous Bi/Pb hoard and in some Sassanian objects, and elevated tin con- ratio in the various parts of the composite objects. The tent in some objects from the Sutton Hoo hoard, indicating Dionysiac Ewer has the highest Bi/Pb ratio (Table 3, Fig. 7). the use of brass or bronze scrap material for alloying. The body, base, handle and thumbpiece have similar compo- Ancient Romans produced high-purity silver with a lead sitions, although the octagonal rim shows the highest Bi/Pb content of 0.5–1% (Hughes and Hall 1979). If silver originates ratio of all the objects. The Animal Ewer and Geometric from silver-bearing lead ores (galena, anglesite or cerussite), Ewers A and B have a very similar and homogeneous Bi/Pb the lead content in the silver alloy ranges from 0.001 to 3% ratio, whereas the Hippolytus Ewer and the Amphora have a (Moorey 1985). The lead content of the analysed Seuso ob- heterogeneous Bi/Pb ratio. The bismuth contents of the body jects falls within this range. The lead contents of the objects and the handles of the Amphora fall below the detection limit differ, because cupellation occurred in multiple steps, which of the XRF (~ 150 and ~ 60 ppm, respectively, Online resulted in the different lead contents, or because silver ores Resource 1). The base and stopper are characterised by a from different sources were used. The low and constant lead low and a high Bi/Pb ratio, respectively. The Bi/Pb ratios of content indicates that lead was not added to the silver ore the body, handle and lid of the Hippolytus Ewer are similar to during smelting. As such, lead isotope analyses may help to the ratios of the Animal and Geometric Ewers, while the upper determine the provenance of the raw material. Lead in the beaded rim and the base have higher Bi/Pb ratios (Table 3, silver objects could derive from the alloying metal, if bronze Fig. 7). The Bi/Pb ratios of the Toilet Casket and Hippolytus or leaded bronze was used, but in this case, we would expect Situla A and B are low and homogeneous, with the exception Archaeol Anthropol Sci (2021) 13:83 Page 15 of 20 83 of the upper beaded rims of the situlas, which exhibit hetero- contents in the bulk metal samples compared to our hXRF geneous Bi/Pb ratios (Fig. 7). The differences in the Bi/Pb values (Figs. 2, 3 and 4), possibly due to digestion problems; ratios indicate that different silver ingots were used to make thus, they are not included in this research. However, the the different parts of the objects. bismuth contents compared well and showed the same trend Gold is completely miscible with silver. During metallur- as the hXRF results (Figs. 2, 3 and 4). Furthermore, our anal- gical processes, the gold content of silver does not change ysis also completes the previous ICP-OES measurements, as drastically (L’Héritier et al. 2015). Consequently, the Au/Ag we determined the chemical composition of each part of the ratio does not alter during cupellation (Pernicka 2014). The Hippolytus Ewer and the Toilet Casket and demonstrated the gold content of argentiferous galena ranges from 0.01 to 1%, use of different silver ingots for their manufacture. whereas the gold content of cerussite and anglesite ranges When our results are compared to other contemporaneous between 0.1 and 0.5% (Karydas et al. 2004 and references silver hoards, it is evident that most of them primarily contain herein). The gold content of late Roman silver objects falls platters, plates and bowls, which were generally manufactured between 0.1 and 4.7% (Table 4) (Hughes and Hall 1979; Lang from a single silver batch. The Seuso Treasure is unique, be- et al. 1984; Feugère 1988; Lang 2002; Tate and Troalen 2009; cause it is mostly composed of large, composite objects Cowell and Hook 2010; Hook and Callewaert 2013;Doračić (ewers, amphora, situlas, casket) that were manufactured from et al. 2015; Lang and Hughes 2016;Greiff 2017;Vulić et al. several parts. Ewers, the casket and the amphora from the 2017). There are several reasons that gold concentrations ex- Trier, Vinkovci and Esquiline hoards were analysed at several ceed 1%, such as the presence of remnants of former gilding, points (Online Resource 5) (Hughes and Hall 1979;Doračić the re-usage of scrap gilded silver or the use of gold-silver et al. 2015;Greiff 2017;Vulić et al. 2017). Of these objects, ores. The gold content of the Seuso objects shows constant the Apostle jug from Trier exhibits a noticeable chemical dif- values and falls within the range typical of late Roman objects. ference between the various parts, indicating that it was not This indicates that primary silver ore was used during manu- manufactured from one, large, uniform batch of silver. The facture, instead of the re-usage of scrap silver, which would body, which is heavily decorated, has the highest silver con- result in a wide range of variation in the gold values. The tent (93.9–95.1 wt% Ag), whereas the handle and the differences in the gold content of the Seuso objects indicate thumbpieces exhibit higher copper concentrations (81.9– the use of different ingots. 95.0 wt%) (Online Resource 5)(Greiff 2017). This chemical The similarities and differences in the chemical composi- difference between the various parts of the Apostle jug is very tions of the various parts of the objects support the technolog- similar to that of the ewers in the Seuso Treasure. ical observations (Mango and Bennett 1994; Dági and Mráv, 2019). The different compositions of the various parts of the Gilding objects indicate the use of different ingots. Based on their manufacturing techniques, the ewers can be classified into The hXRF data show that the Seuso objects were decorated two groups: (i) the body and the base were cast or raised from with two types of gilding: (i) fire gilding, which contained a single silver sheet (e.g. Animal and Dionysiac Ewers) and mercury; and (ii) a different gilding technique that did not (ii) the body and base were made separately and were later contain mercury. Mercury was detected in the gilding of the joined mechanically (e.g. Hippolytus Ewer and Geometric Amphora, Dionysiac Ewer, Animal Ewer and the Hippolytus Ewers A and B). set, indicating the use of fire gilding. In contrast, mercury was The previous ICP-OES analyses (Mango and Bennett absent from the gilding of Geometric Ewers A and B, indicat- 1994, Online Resource 4) systematically measured lower gold ing the possible use of a different gilding technique (Fig. 5). Fig. 7 Au/Ag vs. Bi/Pb ratio of the Seuso objects based on the hXRF measurements. Measured with Niton Xl3t GOLDD+ (ligh- ter colours) and SPECTRO xSORT Combi (darker colours) instruments 83 Page 16 of 20 Archaeol Anthropol Sci (2021) 13:83 Fire gilding was likely invented in China in the fourth century was too worn to determine the method used (Mango and BC (Lechtman 1971; Lins and Oddy 1975;Oddy 1981, 1988, Bennett 1994). Our present data do not support the use of fire 1991, 1993, 2000). In the fire gilding technique, gold was gilding for the Geometric Ewers, as mercury is always detect- dissolved in hot mercury, and the resulting gold amalgam able in fire gilding (Anheuser 1997) but is absent from the was rubbed on to the cleaned metal surface, after which the Geometric Ewers. Further invasive investigations are planned object was heated for a few minutes at 250–300 °C (below the to confirm whether diffusion bonding was used on the boiling point of mercury, 357 °C) until it changed from silver Geometric Ewers. It is possible to bond gold leaf to pure silver to yellow. It is important to avoid overheating the object. If (or to pure copper) without the use of an adhesive, by burnish- silver is overheated, the gold discolours or even disappears ing and minimally heating the object to promote interdiffusion into the substrate. This phenomenon restricts the maximum between the gold and silver. Diffusion bonding (or hot clad- firing temperatures to approximately 350 °C. A firmly bonded ding) was invented as early as 1200 BC, and was commonly but porous, matte gilded layer will form, which must then be used on silver from the late Hellenistic and early Roman pe- burnished. This technique is still used in Nepal (Anheuser riods (Lechtman 1971;Oddyetal. 1981;Oddy 1981, 1988, 1997; Oddy 2000). In the Roman period, fire gilding was 1991, 1993, 2000). This method of gilding is thus far not considered by Pliny the Elder (first century AD) to be a costly found on Roman silver objects from the fourth century AD. and rarely utilised method. However, it became the standard However, microscopic examinations of Roman objects from method of gilding in the third–fourth centuries AD and con- the Chaourse (second–third centuries AD) and Mâcon tinued to be used throughout medieval Europe, until the in- Treasures (third century AD) (Hughes et al. 1989), as well vention of electroplating in the mid-nineteenth century AD as of several earlier objects (e.g. an Elamite dish and a (Lechtman 1971; Lins and Oddy 1975; Oddy 1981, 1988, Parthian bowl) (Oddy 1988), revealed the presence of diffu- 1991, 1993, 2000). As such, the presence of mercury is com- sion bonded gilding on these objects. mon in the gilding of third century AD Roman objects, but The lack of mercury could indicate some sort of restoration, rare in the gilding of earlier Roman objects. This may be during which gilding could be lost due to, e.g. repeated an- because supplies of mercury became more available for com- nealing, and was subsequently replaced. If the lack of mercury mon use in the third century AD. Another method of fire would indicate some restoration, then it is highly unlikely that gilding is to apply a layer of mercury to the metal surface to the complete gilding of the Geometric Ewers was restored and be gilded and then lay pieces of gold leaf on top. The gold leaf no sign of restoration was found on the other Seuso objects. dissolves in the mercury, creating a gold amalgam in situ, after Moreover, based on the description of the restoration process which the object is heated and burnished. This method is still performed in 1989 (Mango and Bennett 1994), no such resto- used in Japan (Anheuser 1997;Oddy 2000). Anheuser’s ration, which would provide enough heat to drive off the mer- (1997) experiments showed that 8–25% of mercury is retained cury, was performed on the Seuso objects. during fire gilding and can be detected later on. The typical Higher gold concentrations were measured at several macroscopic features of fire gilding, such as gold spreading points on the Animal Ewer, in places where gilding could over the edge of the gilded area, splashes of gold on ungilded not be seen by the naked eye (Fig. 5a, b). Mercury was also areas and thicker gold deposits in engraved lines, were ob- detected at these points. These are residues of former gilding, served on the Seuso objects (Fig. 5a–d). Fire gilding was the in which the gold diffused into the silver, but the gilding typical gilding method used on other contemporaneous late became worn over time. Roman silver hoards (Lang et al. 1984;Feugère 1988; Hughes et al. 1989; Cowell and Hook 2010; Hook and Assembling of the objects—joining techniques Callewaert 2013;Doračić et al. 2015; Lang and Hughes 2016;Greiff 2017;Vulić et al. 2017). There are several ways to join the different parts of a compos- The two types of gilding on the Seuso objects were also ite silver object: (i) make simple linkages by folding the edges supported by Mango and Bennett (1994), using mercury in of the metal; (ii) use pins, rivets or twisted components; or (iii) both cases: (i) a gold amalgam was prepared and rubbed onto create a joint by applying heat to metal (e.g. welding, casting the surface of the object, after which the object was heated and on, sintering, brazing and soldering). Both brazing (or hard the mercury evaporated; (ii) the surface of the object was soldering) and soft soldering require the use of filler metal, amalgamated by rubbing mercury on to it or by dipping it into such as low-temperature lead-tin soft solders, high- a solution of soluble mercury salt, and then gold leaf (some- temperature silver-copper hard solders and intermediate tem- times several layers) was laid on top, after which the object perature alloys of silver and mercury or of silver and tin (Lang was heated as before. It was thought that the Geometric Ewers and Hughes 1977, 1984, 1988). were gilded by the first method, whereas the Dionysiac Ewer, The various parts of the composite Seuso objects were Animal Ewer and the vessels of the Hippolytus set were dec- assembled in three different ways. The bases of the orated with the second method. The gilding of the Amphora Hippolytus and Geometric Ewers were mechanically attached Archaeol Anthropol Sci (2021) 13:83 Page 17 of 20 83 to the body by inserting the bases of the ewers into a hole in objects can be categorised, which suggests that different silver the foot and hammering the metal (Mango and Bennett 1994). ingots were utilised. The ewers were constructed in two ways: The handles, lids, feet and thumbpieces were attached with (i) the base and the body were made separately, or (ii) the base using lead-tin soft solders (Fig. 6). Lead-tin soft solders were and the body were raised or cast from a single silver sheet. The also used for ancient repairs (e.g. on the body of the composite objects were assembled following three methods: Amphora). The upper beaded and octagonal rims were at- (i) mechanical attachment, (ii) lead-tin soft solders or (iii) tached to the body with silver-copper hard solders, indicated copper-silver hard solders. Two types of gilding were used by the presence of green copper corrosion products (Fig. 6). for decoration, one with remnants of mercury (fire-gilding) The use of these soldering materials was common in the late and another without mercury (presumably diffusion bonding). Roman period (Lang and Hughes 1988). Hard soldering oc- The results of previous studies performed on the Seuso curs at a higher temperature, which may be near to the melting objects were interpreted and new observations were made, point of the body metal. In contrast, soft soldering requires a specifically, that the chemical composition of every part of lower melting point alloy and occurs at a much lower temper- every object (including the Toilet Casket and Hippolytus ature than the melting point of the body metal (Lang and Ewer) was determined, that the gilding and soldering of each Hughes 1977). The temperature range of the solders available object were identified. Regarding the Geometric Ewers, diffu- to ancient Roman craftsmen varied from the melting point of sion bonding was likely used instead of fire gilding, as previ- silver (960 °C) to Tinman’s solder containing 66% tin and ously hypothesised. The hXRF data serve as a guide with 34% lead, which is very close to the eutectic point of the which to select sites to sample (with minimal invasiveness) system (183 °C) (Lang and Hughes 1984). The differences for further lead isotope and bulk elemental composition anal- in the chemical compositions of the soft solders potentially yses, the results of which will be published in a subsequent indicate the use of different soldering alloys and different paper. working temperatures. The behaviour of a solder primarily depends on its composition, as well as on the conditions under which the soldering is performed (e.g. temperature, surface Supplementary Information The online version contains supplementary material available at https://doi.org/10.1007/s12520-021-01321-4. finish, flux, reducing or oxidising atmosphere). If several op- erations must be executed, the highest melting point solders Acknowledgements The hXRF measurements were performed within must be used first (Lang and Hughes 1988). the framework of the Seuso Research Project supported by the State of Hungary from 2014 to 2019. The authors are grateful to Balázs Lencz, Tamás Szabadváry and András Szabó at the Hungarian National Museum for their help during hXRF analysis. Ariana Gugora is thanked for proof- Conclusions reading the manuscript. Furthermore, the authors are thankful to Mária Tóth, Norbert Németh and Balázs Lencz for providing the silver reference Non-destructive handheld X-ray fluorescence spectrometry is materials. a useful tool in the determination of the chemical composition Funding Open access funding provided by ELKH Research Centre for of composite silver objects, if a significant number of analyses Astronomy and Earth Sciences. are performed and the same instrument is used for the mea- surements. With enough analyses, the inhomogeneity Open Access This article is licensed under a Creative Commons amongst the various parts of the objects and the similarities Attribution 4.0 International License, which permits use, sharing, adap- tation, distribution and reproduction in any medium or format, as long as and differences between the objects can be revealed, and the you give appropriate credit to the original author(s) and the source, pro- objects can be classified. Moreover, raw materials, vide a link to the Creative Commons licence, and indicate if changes were manufacturing and decoration techniques used can be made. The images or other third party material in this article are included characterised, which help to better reconstruct past technolog- in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's ical practices and craftsmanship. Creative Commons licence and your intended use is not permitted by The chemical composition of the objects of the Seuso statutory regulation or exceeds the permitted use, you will need to obtain Treasure shares similarities with other late Roman period sil- permission directly from the copyright holder. To view a copy of this ver finds. The differences in the chemical composition of the licence, visit http://creativecommons.org/licenses/by/4.0/. various parts of the composite objects are clear evidence that different ingots of silver were used for each part, which sup- ports the earlier technological observations (Mango and References Bennett 1994). The different copper contents explain the use of intentional alloying. The constant gold content implies that Angelini I, Canovaro C, Venturino M, Artioli G (2019) The silver trea- the objects were not manufactured from reused or remelted sure of Marengo: silver provenancing and insights into late antiquity scrap silver. The likewise constant and low lead content indi- Roman and Gallo-Roman hoards. Archaeol Anthropol Sci 11:4959– cates the use of cupelled silver. 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Non-destructive handheld XRF study of archaeological composite silver objects—the case study of the late Roman Seuso Treasure

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

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

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

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