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X-ray Fluorescence analytical criteria to assess the neness of ancient silver coins:Application on Ptolemaic coinage

Vasiliki Kantarelou a,⁎, Francisco José Ager b,c, Despoina Eugenidou d, Francisca Chaves e,Alexandros Andreou d, Elena Kontou d, Niki Katsikosta d, Miguel Angel Respaldiza b, Patrizia Seran f ,Dimosthenis Sokaras a, Charalambos Zarkadas g, Kyriaki Polikreti h, Andreas Germanos Karydas a, i

a Institute of Nuclear Physics, NCSR “ Demokritos” , Aghia Paraskevi Attikis, 153 10, Greeceb Departamento de Física Aplicada I, Universidad de Sevilla, Sevilla, Spain

c Centro Nacional de Aceleradores, Avda. Thomas A. Edison, 7. E-41092 Sevilla, Spaind Numismatic Museum, Athens (NMA), Athens, Greecee Departamento de Prehistoria y Arqueología, Universidad de Sevilla, Sevilla, Spainf Dipartimento di Beni Culturali, Musica e Spettacolo, Università degli Studi di Roma “ Tor Vergata” , Roma, Italyg PANalytical B.V., 7600 AA Almelo, The Netherlandsh Hellenic Ministry of Culture, Directorate of Conservation of Ancient and Modern Monuments, Dept. of Applied Research, Pireos 81, 105 53, Athens, Greecei Nuclear Spectrometry and Applications Laboratory, IAEA, Seibersdorf, Austria

a b s t r a c ta r t i c l e i n f o

Article history:

Received 25 January 2011

Accepted 3 August 2011

Available online 10 August 2011

Keywords:XRF

Ancient coin

Silver enrichment

Hellenistic coinage

Theapplication of X-ray Fluorescence (XRF) analysis in a non-invasive manner on ancient silver coins maynot

provide reliable bulk compositional data due to possible presence of a surface, silver enriched layer. The

present work proposes a set of three complementary analytical methodologies to assess and improve the

reliability of XRF data in such cases: a) comparison of XRF data on original and cleaned micro-spots on coin

surface, b) Ag K/L ratio test and c) comparison of experimental and theoretically simulated intensities of the

Rayleigh characteristic radiation emitted from the anode.

The proposed methodology was applied on 82 silver coins from the collection of Ioannes Demetriou, donated

to the Numismatic Museum of Athensin the1890s.The coins originate from differentmints andare attributed

to the rst ve Ptolemaic kings' reign (321–180 B.C.). They were analyzed in-situ by using a milli-probe XRF

spectrometer.

The presence of an Ag-enriched layer was excluded for the majority of them. The silver neness was found to

be high, with very low concentrations of copper and lead. The composition data provide important

information about possible sources of silver during the Ptolemaic period and indications of a gradual coinage

debasement after 270 B.C. due to economic or technical reasons.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Surface measurements on ancient silver coins may not result inreliable bulk composition data due to silver enrichment of the near

surface layers [1]. This may be a consequence of the original coin

production process [2], a special post-production treatment used

mainly during the Roman period [3], past conservation treatments [1]

or corrosion [4].

Therefore, traditional surface techniques like XRF, EPMA and PIXE,

where only a surface layer of limited depth (from a few micrometers

up to a few tens of micrometers) is analyzed, have to be used

cautiously in such studies [5,6]. Several methodologies have been

proposed to ensure reliability of surface measurements in silver bulk

composition determination [1,7–10]. Most of them are based in the

idea of drawing an Ag-prole from the surface to the bulkof the object

(LA-ICP-MS [11], PIXE and RBS [1]). Within this study a set of threecomplementary XRF methodologies is proposed to be used as an aid

for the reliable non-destructive evaluation of silver coin neness.

Eighty two Hellenistic silver coins were analyzed by means of a

portable XRF spectrometer. The coins are part of the Ioannes

Demetriou collection that belongs to the Numismatic Museum

(Athens, Greece) which consists of nearly 13,000 coins of the

Ptolemaic kings and coins of Egypt under the Roman administration

[12]. The analyzed coins cover the period between Ptolemy I and

Ptolemy V (323–181 B.C.) (Fig. 1).

Comparison of the compositional data of such a large number of

Ptolemaic coins to those of other silver coins of the same period

[13,14] is expected to shed some light on the silver sources available

in the Hellenistic Mediterranean. Ptolemaic Egypt had a direct access

to gold and coppermines(at Nubia andCyprus, respectively [15]), but

Spectrochimica Acta Part B 66 (2011) 681–690

⁎ Corresponding author.

E-mail addresses: [email protected] (V. Kantarelou), [email protected]

(F.J. Ager), [email protected] (K. Polikreti), [email protected] (A.G. Karydas).

0584-8547/$ – see front matter © 2011 Elsevier B.V. All rights reserved.

doi:10.1016/j.sab.2011.08.001

Contents lists available at ScienceDirect

Spectrochimica Acta Part B

j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s a b


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not to silver mines. The sourceof silver for the immense production of

Ptolemaic tetradrachms was probably the rich mines of the Taurus

Mountains in Cilicia (south coastal region of Asia Minor) [16].

However, during the Syrian Wars, Ptolemy II (285–246 B.C.) lost

Syria and Palestine and consequently lost access to the precious metal

[17]. The only silver source of the period that could export large

quantities of silver was the Iberian Peninsula (especially the mines of

Sierra Morena) and the area of modern Cartagena [18], where

Carthaginians had control over the mine exploitation or at least the

metal trade. However, the defeat of Carthage by Rome in 206 B.C.

could justify the interruption of the Hispanic silver supply to Egypt

and the total collapse of the silver coinage minting at the area [19,20].

Previous analyses of silver coins from different Ptolemaic reigns

and mints have been conducted by using a combination of destructive

(wet chemical analysis) and non-destructive (Neutron and Deuteron

Activation Analyses, NAA-DAA) bulk analyses [13], whereas recently

XRFanalyses of Greek drachmae from the Emporion site in Spain have

been also reported [14]. For the slightly earlier silver tetradrachms of

Philip II and Alexander the Great (minted between 356 and 300 B.C.),

the compositional results showed a very high neness (AgN97.5%), Pb

content less than 1% and Bi content between 20 and 3000 ppm [21].

2. Materials and methods

2.1. Coins preservation state and pre-analysis treatment

The mint, production date and reign attributed to the analyzed

coins are given in Table 1 (classied as in [12]). Apart from the

compositional XRF data for each coin, the table includes a small

description of preservation state and possible past conservation

treatment(s). Various treatments were applied on these coins in the

past, including chemical ones. The coins were grouped in ve

categories, based on treatment type: a) U: untreated, S: supercially

cleaned using solvents and cotton swabs, M: mechanically treated

using a pin pick, HM: mechanically treated (hard treatment),

C: chemically treated, CM: mechanically treated after chemical

cleaning, usually using glassbristle brush. XRF analysis was conductedon both sides of the coins, on at areas of a good preservation state,

supercially cleaned using solvents (alcohol and acetone).

Four coins were selected and tiny areas at the coin edges were

mechanically cleaned with a thin scraper pin to remove surface

corrosion and prepare an area of about 1 mm2 for the application of

the micro-XRF beam. Walker et al. [22] scraped or abraded small areas

of about 1–2 mm2 at the coin periphery, to be analyzed by XRF while

Schmitt et al. [23] and King and Northover [24] abraded and then

polished the coin edges prior to the application of electron-probemicroanalysis in association with wavelength dispersive X-ray

spectrometry (EPMA-EDX).

2.2. Experimental

The portable milli-XRF spectrometer [25] is based on a side-

window low power X-ray tube with a Rh anode (75 μ m Be window).

Analyses were performed at 40 kV, normal incidence. A composite

lter made of Nickel (42.5 mg/cm2) and Vanadium (33.0 mg/cm2)

foils was interposed in the excitation beam's path. This lter

considerably improves “peak to background” ratio in the low energy

region up to about 14 keV, improving the sensitivity and precision

when minor or trace elements such as Au, Pb and Bi in a silver matrix

are analyzed. The beam spot size at the sample position is about2.7 mm and the counting interval was set at 3 min. The characteristic

X-rays emitted from the sample are detected by a Si-PIN diode X-ray

detector (Amptek XR-100CR, with 165 eV FWHM at MnKα, 500 μ m Si

crystal thickness and 12.7 μ m Be window) placed at 45° from sample

normal. Two laser spots coupled on the spectrometers head are

aligned in such a way to ensure the placement of the analyzed area on

the reference plane.

The quantication was based on the Fundamental Parameter (FP)

method by means of in-house (N.C.S.R. “Demokritos”) developed

software. The geometrical (G) factor of the spectrometer was

determined using pure element or compound targets. In principle, G

factor should be element independent. However, the uncertainties of

the various FPs involved in the calculations (e.g. the exciting tube

spectrum distribution, atomic fundamental parameters, etc.), result in

an experimental mean G value with a relative standard deviationof 6%

(sixteen pure element targets were used for the calibration). The

incorporation of the G factor to the quantitative analysis improves

accuracy and compensates for most FP method uncertainties. The

accuracy of quantitative analysis of major and minor elements (Cu,

Pb) in silver alloys was found to be satisfactory. The evaluation was

done by comparing the XRF composition results for reference alloys

(Ag–Au and Ag–Cu–Pb) [26,27] to SEM-EDX data for the same

material.

The micro-probe XRF analysis of four selected coins was carried

out using a customized version of an Artax (Bruker AXS) spectrom-

eter. The spectrometer composes of commercial, state-of-the-art

hardware components: an X-ray microfocus Rh-anode tube (spot size

50×50 μ m, max 50 kV, max 1 mA, 30-W maximum power consump-

tion, Be window 0.2-mmthickness) and a polycapillary X-ray lens as afocusing optical element (IfG) with a focal distance of about 21.2 mm.

The X-ray detection chain consists of a thermoelectrically cooled 10-

mm2 silicon drift detector (X-Flash, 1000B) with 146 eV FWHM at

10 kcps coupled with a digital signal processor. A color CCD camera

(with approximately ×13 times magnication) combined with a

dimmable white LED and a spot laser beam assures reproducible

positioning of the measuring probe, as well as visualization and

documentation of the analyzed area. Three stepping motors coupled

with the spectrometer head allow three-dimensional movement for

elemental mapping and precise setting of the analysis spot at the focal

distance of thepolycapillary lens. Thescansover thecoin surface areas

were performed at the following operational conditions: 50 kV,

600 μ A, 20 s/step, step size of 200 or 300 μ m and total scanned area

of about 0.9× 0.9 mm2. A lter consisting of Ti, Co and Pd was used toimprove the quality (monochromaticity) of the excitation beam and

avoid diffraction patterns in the spectrum [28]. The spatial resolution

Fig. 1. Tetradrachm and decadrachm from the collection of “Ioannes Demetriou”

(Numismatic Museum of Athens). Top: coin #2, Ptolemy I, Svoronos 18α [2], obverse

and reverse. Bottom: coin #25, Ptolemy II, Svoronos 444α [2], obverse and reverse. The

compositional data for the coins are given in Table 1.

682 V. Kantarelou et al. / Spectrochimica Acta Part B 66 (2011) 681–690


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Table 1

Concentrations obtained by XRF of the obverse side of the coins. Abbreviations for cleaning procedures: N: untreated, S: super cial, solvents and cotton swabs, M: mechanical with

pin pick, M*: Mechanical with Au pin pick in the area of analysis, HM: hard mechanical in the past, C: chemical, CM: mechanical-after chemical cleaning, usually with glass bristle

brush, Abbreviations for notes: PL: silver plated coin/Cu bulk, SR: silver reduction.

#

(N=86)

Reign Svoronos

number

Denom.

(drachms)

Mint Date

(B.C.)

Concentrations (%) Past

cleaning

procedure

Notes

Ag Cu Au Pb Bi Fe Zn Hg

1 Ptolemy I 18α 4 Egypt 317–311 99.0 0.095 0.46 0.20 b0.02 0 .29 b0.02 b0.02 S

2 Ptolemy I 24α 4 Egypt 317–311 96.1 0.250 0.51 0.09 b0.02 3 .00 b0.02 b0.02 S

3 Ptolemy I 42ε 4 Egypt 311–305 99.4 0.042 0.18 0.26 b0.02 b0.07 0.03 b0.02 CM

4 Ptolemy I 35β 1/2 Egypt 311–305 97.3 b0 .0 25 0 .3 7 0 .3 7 b0.02 b0.07 b0.02 2.00 S

5 Ptolemy I 146ζ 4 Egypt 305–285 99.2 b0 .0 25 0 .5 4 0 .2 3 b0.02 b0.07 b0.02 b0.02 S SR

6 Ptolemy I 146θ 4 Egypt 305–285 99.2 0.130 0.64 0.041 b0.02 b0.07 0.04 b0 .0 2 C + H M

7 Ptolemy I 168δ 4 Egypt 305–285 99.3 0.039 0.41 0.29 b0.02 b0.07 b0.02 b0.02 CM

8 Ptolemy I 168στ 4 Egypt 305–285 95.3 0.091 1.00 0.37 b0.02 0 .25 b0.02 3.00 N Reverse

10 Ptolemy I 117α 4 Egypt 305–285 99.3 0.099 0.42 0.17 b0.02 b0.07 b0.02 b0.02 C

11 Ptolemy I 183α 4 Egypt 305–285 99.1 0.100 0.46 0.31 b0.02 b0.07 b0.02 b0.02 CM

12 Ptolemy I 205δ 4 Egypt 305–285 98.9 0.110 0.48 0.48 b0.02 b0.07 b0.02 b0.02 C

13 Ptolemy I 245β 4 Egypt 305–285 98.2 0.097 0.69 0.15 b0.02 b0.07 0.86 b0.02 CM

14 Ptolemy I 254α 4 Egypt 305–285 98.9 0.160 0.45 0.53 b0.02 b0.07 b0.02 b0.02 C

15 Ptolemy I 263α 4 Egypt 305–285 99.1 0.120 0.43 0.33 b0.02 b0.07 b0.02 b0.02 N

16 Ptolemy II 364α 1 Egypt 285–246 96.8 0.23 0.73 0.19 b0.02 2 .0 0 b0.02 b0.02 S?

17 Ptolemy II 366α 4 Egypt 285–246 98.7 0.066 0.58 0.68 b0.02 b0.07 b0.02 b0.02 C

18 Ptolemy II 373β 4 Egypt 285–246 98.6 0.320 0.70 0.33 b0.02 b0.07 b0.02 b0.02 CM

20 Ptolemy II 395β 4 Egypt 285–272 98.8 0.100 0.67 0.12 b0.02 0 .27 b0.02 b0.02 C?

22 Ptolemy II 420α 10 Egypt 270 97.7 0.490 0.71 0.32 b0.02 0 .78 b0.02 b0.02 CM

23 Ptolemy II 421α 4 Egypt 270 99.1 b0 .0 25 0.63 0 .2 8 b0.02 b0.07 b0.02 b0.02 CM

24 Ptolemy II 435α 4 Egypt 267 98.9 0.084 0.66 0.39 b0.02 b0.07 b0.02 b0.02 C

25 Ptolemy II 444α 10 Egypt 266 98.9 0.065 0.58 0.25 b0.02 0 .2 1 b0.02 b0.02 CM

26 Ptolemy II 488α 10 Egypt 258 98.9 0.091 0.53 0.14 b0.02 0 .3 1 b0.02 b0.02 C

27 Ptolemy II 496α 10 Egypt 254 98.2 0.090 0.56 0.36 b0.02 0.34 0.46 b0.02 CM

28 Ptolemy II 420α 10 Egypt 270 92.5 0.460 1.00 3.00 b0.02 0.24 3.00 b0.02 CM

29 Ptolemy II 567β 4 Egypt 281 99.1 0.140 0.54 0.24 b0.02 b0.07 b0.02 b0.02 CM

30 Ptolemy II 596α 4 Egypt 266 98.8 0.120 0.50 0.36 b0.02 0 .18 b0.02 b0.02 C

31 Ptolemy II 596β 4 Egypt 266 99.4 b0 .0 25 0 .5 8 0 .0 5 b0.02 b0.07 b0.02 b0.02 CM

32 Ptolemy II 602β 1 Egypt 285–246 98.8 0.180 0.50 0.55 b0.02 b0.07 b0.02 b0.02 C

33 Ptolemy II 626α 4 Tyre 285/4 99.2 0.180 0.43 0.076 b0.02 0 .07 2 b0.02 b0.02 C

34 Ptolemy II 626β 4 Tyre 285/4 99.0 0.096 0.46 0.20 b0.02 0 .2 8 b0.02 b0.02 C

35 Ptolemy II 637ιζ 4 Tyre 279 98.7 0.430 0.76 0.08 b0.02 b0.07 b0.02 b0.02 C PL

36 Ptolemy II 713β 4 Sidon 285/4 99.1 b0 .0 25 0.71 0 .1 6 b0.02 b0.07 b0.02 b0.02 CM

37 Ptolemy II 734α 4 Sidon 255 99.1 b0 .0 25 0.68 0 .1 8 b0.02 b0.07 b0.02 b0.02 CM

38 Ptolemy II 775α 4 Ptolemais 254 98.6 0.110 0.68 0.57 b0.02 b0.07 b0.02 b0.02 CM39 Ptolemy II 828α 4 Gaza 255 98.5 b0 .0 25 0 .5 1 0 .7 2 b0.02 0 .22 b0.02 b0.02 C

40 Ptolemy II/III 902β 4 Ephesus 285–246 or

247/6–221/20

98.7 0.170 0.79 0.31 b0.02 b0.07 b0.02 b0.02 C SR

41 Ptolemy II/III 903α 4 Ephesus 285–246 or

247/6–221/20

98.9 0.110 0.74 0.21 b0.02 b0.07 b0.02 b0.02 CM

42 Ptolemy II/III 905γ 4 Ephesus 285–246 or

247/6–221/20

97.7 0.039 1.1 0.32 b0.02 0.47 0.39 b0.02 CM

43 Ptolemy II/III 907α 4 Uncertaina 285–246 or

247/6–221/20

98.5 0.240 1.00 0.26 b0.02 b0.07 b0.02 b0.02 CM

44 Ptolemy III 938β 10 Egypt 245 99.2 0.047 0.65 0.13 b0.02 b0.07 b0.02 b0.02 CM

45 Ptolemy III 940δ 10 Egypt 242 94.8 0.210 0.74 0.66 b0.02 0.62 3.00 b0.02 C + (M) SR

46 Ptolemy III 961α 10 Egypt 221 96.6 0.100 0.81 2.00 b0.02 0 .63 b0.02 b0.02 N

48 Ptolemy III 988α 12 Egypt 247/6–221/20 99.1 b0 .0 25 0.77 0 .1 6 b0.02 b0.07 b0.02 b0.02 C

49 Ptolemy III 989α 5 Egypt 247/6–221/20 99 b0.025 1.00 b0.02 b0.02 b0.07 b0.02 b0.02 CM

50 Ptolemy III 1013α 4 Tyre 245 98.4 0.065 0.53 0.79 b0.02 0 .2 1 b0.02 b0.02 NO

51 Ptolemy III 1014α 4 Tyre 245 98.0 0.290 0.68 0.41 b0.02 b0.07 0.66 b0.02 CM PL

52 Ptolemy III 1015α 4 Tyre 244 98.4 0.100 0.61 0.50 b0.02 0 .4 2 b0.02 b0.02 S53 Ptolemy III 1019α 4 Tyre 243 95.7 0.033 0.82 1.10 b0.02 0 .18 b0.02 b0.02 CM

54 Ptolemy III 1025α 4 Sidon 245 98.9 0.054 0.67 0.40 b0.02 b0.07 b0.02 b0.02 CM

55 Ptolemy III 1027α 4 Sidon 244 98.1 0.140 0.60 0.77 0.21 0.16 b0.02 b0.02 CM

56 Ptolemy III 1031α 4 Sidon 242 95.1 0.120 0.74 2.00 b0.02 2 .00 b0.02 b0.02 CM

57 Ptolemy III 1033α 4 Sidon 241 97.2 0.140 0.65 1.00 b0.02 1 .00 b0.02 b0.02 CM

58 Ptolemy III 1035α 4 Ptolemais 245 98.2 0.100 0.75 0.73 b0.02 b0.07 0.24 b0.02 CM

59 Ptolemy III 1036α 4 Ptolemais 244 98.1 0.031 0.59 0.88 b0.02 0.29 0.09 b0.02 C

60 Ptolemy III 1090α 4 Marathus 240 98.2 0.410 0.67 0.67 b0.02 b0.07 0.04 b0.02 S Cu products

61 Ptolemy III 1091α 4 Marathus 239 87.6 11.0 0.45 0.47 b0.02 b0.07 0.08 0.35 C +HM

62 Ptolemy III 1102α 4 Marathus 230 97.1 0.790 0.50 0.97 b0.02 0.55 0.04 b0.02 CM

63 Ptolemy III 1103α 4 Marathus 229 97.9 0.640 0.71 0.55 b0.02 0 .2 2 b0.02 b0.02 C

64 Ptolemy III 1105α 4 Marathus 228 98.5 0.120 0.57 0.84 b0.02 b0.07 b0.02 b0.02 S

65 Ptolemy III 1108α 4 Marathus 225 98.3 0.440 0.76 0.51 b0.02 b0.07 b0.02 b0.02 S

66 Ptolemy III 1109α 4 Marathus 224 92.9 3.0 1.00 1.00 b0.02 0.10 2.00 b0.02 CM

67 Ptolemy IV 1115α 4 Egypt 221/20–204/3 99.3 b0 .0 25 0 .6 1 0 .1 0 b0.02 b0.07 b0.02 b0.02 N

68 Ptolemy IV 1122β 4 Egypt 221/20–204/3 96.2 0.210 2.00 0.85 b0.02 b0.07 0.69 b0.02 CM

69 Ptolemy IV 1124α 4 Egypt 221/20–204/3 98.5 0.032 1.4 0.05 b0.02 b0.07 b0.02 b0.02 C+ HM SR

70 Ptolemy IV 1135α 4 Egypt 221/20–204/3 97.6 1.0 0.85 0.17 b0.02 0.24 0.12 b0.02 CM M* (obverse)

(continued on next page)

683V. Kantarelou et al. / Spectrochimica Acta Part B 66 (2011) 681–690


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of the micro-XRF spectrometer was determined to be 76–31 μ m for

characteristic X-rays of energies between 22 and 4.5 keV, respectively

[29].

At the edges of the selected four coins, scanning micro-XRF

analysis [30,31] was applied on areas that unavoidably include

untreated sub-areas, to identify semi-quantitative differences in the

elemental composition. The results were compared to those obtained

by milli-probe and scanning micro-XRF analyses of at areas located

on both sides of the coins. The scanning micro-probe XRF analysis

results on both coin sides and at the cleaned edges offer a rough

estimation of the minor elements (Fe, Cu, Au, Pb) spatial distribution

and concentration. These results may also give useful information on

possible association of the minor elements to surface contamination

or corrosion. The XRF spectra for coin #2 are shown in Fig. 2.

3. Results and discussion

The element concentrations determined from the milli-probe XRF

data are presented in Table 1. Table 2 shows mean values and

standard deviations for different reigns and mints. Normalization

factor values were found to be 1.02±0.02 and 1.02±0.014 for the

obverse and reverse of the coins, respectively. Fig. 3 shows the

absolute differences in Ag andCu concentrationsmeasuredon thetwo

coin sides. Large differences in Ag concentrations are associated with

considerable increase of other minor elements (Zn, Fe or Pb).

3.1. Silver and copper

Ag and Cu concentrations are given in Table 1. Two of the coins

from the mint of Tyre (coins #35 and #51) were plated with a rather

thick silver foil. However, the Ag and Cu concentrations of the foil are

not different than those of the bulk silver. Two of the coins,

tetradrachms from the mint of Marathus (Ptolemy III) show high

concentration of Cu on both sides (coin #61(10%) and #66 (2.6–

3.8%)). Such high values could be a result of deliberate addition of

copper or use of recycled silver [32]. Since the rest of the analyzed

coins of Ptolemy III from the mint of Marathus do not show high

concentrations of Cu, further general comments would not be safe.

Comparison of Ag-Kα and Cu-Kα micro-XRF intensities from the

clean coin areas to those from the original coin surface (obverse/

reverse) are shown in Table 3. The Ag-Kα intensities calculated from

the area scans show a relative standard deviation of 3% (except for

coin #4 which shows a standard deviation of 19% possibly due to the

presence of Hg), whereas the Cu-Kα intensities show much a broader

spread mainly due to larger statistical uncertainties in individual

measurements. In conclusion, no statistically signicant difference

was observed for theAg andCu intensities between thetwo examined

areas.

3.2. Minor elements

Au was detected in all the analyzed coins. Bi was present only inve coins (b0.2%), Hg was detected in two coins in concentrations

larger than 1% and in minor amounts in a third coin (0.2%–0.4%),

whereas Zn and Fe were measured in percentages larger than 0.5%

only in nine and eleven coins respectively. Four coins of Ptolemy IV

and seven coins of Ptolemy V were found with Αu concentrations up

to 1% which are higher than the rest of the coins of Ptolemy I, II and III.

In order to investigate the minor element spatial distribution, area

micro-XRF scans were performed and intensity maps for the Au-L α,

Fe-Kα and Pb-L α characteristic X-ray intensities were generated for

coin #2 (Fig. 4) and Hg-L α and Zn-Kα for coins #4 and #28 (Fig. 5).

The area scans were performed on either the obverse or reverse of the

coins and at the cleaned edges. The measurement details can be found

in the respective gure captions. It is evident in Fig. 4 that Au intensity

does not show large variations, therefore it most probably associateswith the silver alloy matrix. The intensity maps of Pb-L α and Fe-Kα X-

rays indicate that these elements are distributed non-homogeneously

Table 1 (continued)

#

(N=86)

Reign Svoronos

number

Denom.

(drachms)

Mint Date

(B.C.)

Concentrations (%) Past

cleaning

procedure

Notes

Ag Cu Au Pb Bi Fe Zn Hg

71 Ptolemy IV 1181α Tyre 221/20–204/3 96.4 0.280 1.4 0.99 b0.02 b0.07 0.96 b0.02 CM

72 Ptolemy IV 1188α 4 Ascalon 221/20–204/3 98.5 0.190 1.00 0.21 b0.02 0.11 b0.02 b0.02 N M*

73 Ptolemy IV 1209α 2 Egypt 210 98.3 0.068 0.50 1.10 0.03 b0.07 b0.02 b0.02 C74 Ptolemy IV 1212β 2 Egypt 206 96.4 0.072 0.28 3.00 0.04 0.20 b0.02 b0.02 CM

75 Ptolemy V 1216α 2 Egypt 202 98.5 0.160 0.51 0.75 0.05 b0.07 b0.02 b0.02 S

76 Ptolemy V 1226α 2 Egypt 195 98.4 0.140 0.25 1.20 0.04 b0.07 b0.02 b0.02 C

77 Ptolemy V 1231ε 4 Egypt 205/4–180 98.9 b0.02 5 0.96 0 .0 9 b0.02 b0.07 b0.02 b0.02 CM SR

78 Ptolemy V 1262γ 4 Cyrene? 205/4–180 97.2 1.0 0.59 0.60 b0.02 0.58 b0.02 b0.02 S

79 Ptolemy V 1263α 4 Cyrene? 205/4–180 97.6 0.720 0.78 0.94 b0.02 b0.07 b0.02 b0 .02 NO or S

80 Ptolemy V 1264α 4 Cyrene? 205/4–180 98.3 0.280 1.00 0.37 b0.02 b0.07 b0.02 b0.02 C

81 Ptolemy V 1267α 4 Cyrene? 205/4–180 98.5 0.190 1.00 0.19 b0.02 b0.07 0.13 b0.02 CM

82 Ptolemy V 1271α 4 Unknown 204/3 98.1 0.400 0.98 0.48 b0.02 b0.07 b0.02 b0.02 N

83 Ptolemy V 1283α or

1283β

4 Unknown 196 98 0.520 1.00 0.48 b0.02 b0.07 b0.02 b0.02 CM

84 Ptolemy V 1289α 4 Damascus? 205/4–180 98.5 0.180 1.00 0.45 b0.02 b0.07 b0.02 b0.02 CM SR

85 Ptolemy V 1292α 4 Sidon 205/4–180 97.6 0.510 0.94 0.10 b0.02 0.62 0.18 b0.02 CM

86 Ptolemy V 1293α 4 Sidon 205/4–180 98.8 0.400 0.69 0.15 b0.02 b0.07 b0.02 b0.02 S

a Uncertain mint in Asia Minor or Thrace.

Fig. 2. XRF spectra acquired from the surface of a tetradrachm of Ptolemy I (coin #2,Svoronos 24α 21 [2]) with a milli- and a micro-spectrometer. The micro-XRF spectrum

is thetotal spectrumof 16measurements (20 s perstep). Theasterisks denotethe X-ray

tube anode scattered characteristic X-ray lines.



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on the surface (Fig. 4). The behavior of Pb may be explained by its

reduced solubility in silver alloy matrices [33]. On the other hand,

variations in Fe are obviously associated to surface contamination

from the burial environment.

Mercury was detected in three coins only (coins #4, #8 and #61).

In literature, Hg is attributed either to contamination from the burial

environment [34] or to its presence in the raw silver mineral as an

impurity [35]. Amalgam gilding is not considered possible in such an

early period, as it was introduced and extensively used later on,

during the Roman period [22]. The relative larger uncertainty of AgKα

intensity on coin #4 is a strong indication that Hg is a surface

contaminant. It is also obvious in Fig. 5 that Hg is signicantly more

abundant on the coin surface than in the edge. This observation

indicates that Hg is related to surface contamination.

TheZn-Kα distributionmap shows that Zn is much more abundant

on the clean area at the coin edge than on the reverse of the coin. In

very few cases large differences were observed between the milli-

probe XRF measurements on the two coin sides. Nevertheless, it can

be suggested that Zn is associated with the matrix of the silver alloy,

whereas its rather occasional presence in some of the coins may

indicate that the silver metal has not been puried. According to

Craddock [36], Zn is usually lost during cupellation, although not

completely [37].

3.3. Surface enrichment in silver

According to Beck et al. [2], for Ag–Cu alloys with more than 72%

Ag, theactual surface composition is the composition of thesilver-rich

primary phase (Ag =92%). For silver of higher neness (higher than

92%) there is no data published to assess possible Ag surface

enrichment. According to [2], in such cases there is no difference

between surface and bulk silver compositions. Nevertheless, three

complementary methodologies were explored in this study to

validate the compatibility of XRF data with the hypothesis adopted

for the quantication process, that the coins are made of a

homogeneous silver alloy: a) comparison of XRF data on original

and cleaned micro-spots on coin surface, b) Ag K/L ratio test and

c) comparison of experimental and theoretically simulated intensities

of the Rayleigh characteristic radiation emitted from the anode.

Although 75% of the analyzed coins were treated by chemical

means in the past, no difference was observed between Ag

concentrations of chemically treated and untreated ones. This is a

strong indication against the presence of an Ag-enriched layer.

Further on, it seems that chemical treatment did not affect the

concentration of minor elements. Forexample,coin #72, shows minor

element concentrations similar to those observed on the chemically

treated coins. The coin was originally covered by a thick layer of silver

corrosion products and treated mechanically with a pin pick for

analysis purposes.

The K/L ratio test was introduced by Linke et al. [7] in order toassessthe presence of a surface Ag rich layer in 15th century medieval

coins [8,9]. The K/L test is similar to the analytical methodology

followed by Klockenkamper et al. [10] in the analysis of 218 Roman

imperial silver coins. More specically, two variants of X-ray spectral

analysis were applied in this case; EPMA-EDS provided the elemental

Table 2

Mean concentrations obtained by XRF of the coins sorted by periods and mints.

Concentrations (wt.%)

Reign Mint (# coins) Ag Cu Au Pb Bi Fe Zn Hg

Ptolemy I (14 coins) E gypt (14) 98.4 ±1.3 0.11 ±0.05 0.52 ±0.23 0.27 ±0.14 1.2 ±1.6 0.31 ±0.48 2.6 ±0.5

Ptolemy II (26 coins) Egypt (15) 98.2 ±1.8 0.19 ±0.15 0.66 ±0.23 0.5 ± 0.6 0.6 ± 0.7 1.8 ±1.9

Tyre (3) 99.0 ±0.3 0.24 ±0.17 0.55 ± 0.18 0.12 ±0.07 0.2 ± 0.1Sidon (2) 99.1 ±0.1 0.7 ±0.02 0.17 ±0.01

Ptolemais (1) 98.6 0.11 0.68 0.57

Gaza (1) 98.5 0.51 0.72 0.22

Ephesus (3) 98.4 ±0.6 0.11 ±0.07 0.88 ± 0.2 0.28 ±0.06 0.5 0.4

Uncertain mint in Asia Minor or Thrace (1) 98.1 0.243 1.4 0.26

Ptolemy III (22 coins) Egypt (5) 97.6 ±2.0 0.12 ±0.08 0.86 ±0.27 0.71 ±0.83 0.63 ±0.01 3.3

Tyre (4) 97.6 ±1.3 0.12 ±0.12 0.66 ± 0.12 0.70 ±0.31 0.27 ±0.13 0.7

Sidon (4) 97.1 ±1.8 0.11 ±0.04 0.67 ± 0.06 1.12 ±0.78 0.21 1.2 ± 1.0

Ptolemais (2) 98.2 ±0.1 0.07 ±0.05 0.67 ± 0.11 0.81 ±0.11 0.29 0.16 ±0.11

Marathus (7) 95.8 ±4.1 2.3 ±3.8 0.68 ± 0.22 0.74 ±0.27 0.29 ±0.23 0.6 ±1.2 0.4

Ptolemy IV (8 coins) Egypt (6) 97.8 ±1.1 0.28 ±0.41 0.87 ±0.52 0.83 ±1.02 0.04 ±0.01 0.2 0.4 ±0.4

Tyre (1) 96.4 0.28 1.4 0.99 0.96

Ascalon (1) 98.1 0.19 1.4 0.21 0.11

Ptolemy V (12 coins) Egypt (3) 98.6 ±0.3 0.15 ±0.01 0.57 ±0.36 0.68 ±0.56 0.04 ±0.01

Cyrene ? (4) 97.9 ±0.6 0.58 ±0.44 0.84 ± 0.20 0.53 ±0.32 0.6 0.1

Unknown (2) 98.0 ±0.2 0.46 ±0.08 1.09 ±0.16 0.48 ±0.01

Damascus? (1) 98.3 0.18 1.2 0.45Sidon (2) 98.2 ±0.8 0.46 ±0.08 0.82 ± 0.18 0.13 ±0.04 0.6 0.2

Fig. 3. Absolute difference of concentrations measured on the obverse and reverse of

the coins for Ag and Cu.

Table 3

The ratio of the Ag-Kα and Cu-Kα micro-XRF intensities among the scraped periphery

and the obverse or reverse of the surface, respectively.

Coin Relative X-ray yield treated periphery/surface

# Ag-Kα Cu-Kα

2 0.93 ±0.04 0.75 ± 0.25

4 0.86 ±0.14 0.92 ± 0.4528 0.99 ±0.04 1.29 ± 0.52

76 1.03 ±0.04 0.75 ± 0.26



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composition of the rst 3 μ m of the coin surface layers, whereas the

wavelength dispersive mode of XRF analysis determined the

elemental compositions in deeper layers. Comparison between the

two Ag compositions is expected to reveal the possible presence of an

Ag-enriched surface layer. TheAg K/Lratios measured using the AgKα

and AgL α intensities of our reference silver alloys and from both sides

of the coins are presented in Table 3. Although a much higher meanK/L value was calculated for the silver coins (88±11), the large error

value does not allow a clear differentiation from the respective mean

K/L value for the reference alloys (79±2). In Table 4 the experimental

and the theoretically calculated Ag Kα/L α ratio one is presented

exhibiting an excellent agreement. For the complete FP calculation, all

the possible secondary interactions that enhance the Ag L α intensity

were taken into account, such as the secondary Ag K to AgL α

uorescence intensityand thecascade K to L α contribution, whereas a

semi-empirically described exciting tube spectrum distribution wasalso considered. In the case of the coins, the Ag K/L ratio should be

even smaller if the enrichment scenario was valid. Simulations

Fig. 4. Spatial distribution of Au,Fe andPb characteristic X-rays from thesurface (a,c, e) andthe edge (b, d, f) of thecoin #2.Left— surface: analyzed area 0.9× 0.9 mm2, 0.3 mm step

size, 16 measurements(n =16),Right— edge: analyzed area 0.8×0.8 mm2, 0.2 mm step size, 25measurements (n=25). Approximately, thehalf rightpart ofthe edge area hasbeen

treated mechanically.



8/11


presented in Fig. 6 show that the information depth for the Ag-L α

intensity does not exceed a thickness of 2 μ m for a typical Ag–Cu alloy

with a composition of Ag, 80% or 92%. On the contrary, 90% of the Ag-

Kα intensity is produced from a layer thickness of 40 μ m. Therefore, if

an Ag enriched surface layer exists (of a thickness of 0–10 μ m for

example), the Ag-L α intensity is expected to reach its saturation level

originating from the top Ag rich layer mainly, whereas the Ag-Kα

intensity would be less due to the signicant contribution of deeper

layers being less abundant in Ag. The nal K/L value would then be

thus smaller than the one expected if the bulk Ag concentration was

similar to the surface one. In order to evaluate in a quantitative

manner this argument, complete FP based calculations were

performed for the Ag Kα to AgL α intensity ratio assuming a double

layered alloy system composed by a pure Ag top layer of variable

thickness and a bulk binary Ag/Cu alloy of variable composition. The

K/L ratios were normalized with respect to the respective pure silver

alloy value (Fig. 7). In the FP calculations, the inter- and intra layer

secondaryuorescence Ag-K/Cu-K to Ag-L α, the ternary Ag–K–Cu–K–

AgL α and the Ag K to L cascade contribution were taken into account.

If the presence of such an internal structure can be conrmed by anindependent method and the K/L ratio is decreased less than about

50% of its thick pure Ag target value, then useful information for the

range of the Ag concentration in the bulk alloy and for the thickness of

the top Ag layer can be extracted. The XRF compositional analysis

through the Ag-L α intensity has similarities to the Ag detection by

EPMA-EDS. Further on, it should be noted as it is also deduced from

Fig. 7, that the K/L ratio for homogenous silver alloys changes about

10% if the Ag content varies in the range 80–100%. The results do not

support the existence of an Ag-enriched, surface layer, but certainly

denite conclusions cannot be extracted. The K/L ratios for example

determined by Linke et al. [7], change only up to 20% even when the

differences between the core and surface Ag concentration are almost

100%.

Fig. 6 shows that the most penetrating radiation for a typical Ag–Cu alloy is the Rh-Kα Rayleigh scattered radiation; 90% of Rayleigh

innite thickness intensity emanate from a depth of about 50 μ m.

Fig. 5. Spatial distribution ofHg andZn characteristic X-raysfromthe surface (a,c) andthe edge (b,d) of coins #4 and#28,respectively.Approximatelythe half right part of theedge

area has been treated mechanically.

Table 4

The ratio between Ag-Kα and Ag-L α intensities, as measured form from a pure silver

alloy, the reference silver alloys and the obverse or reverse of the coins. Composition of

the silver reference alloys: CNR — 91: Ag 97.0%, Cu 1.5%, Pb 1.5%, CNR — 152: Ag 96.5%,

Cu 3.5%, CNR — 141: Ag 92.5%, Cu 7.5%. A theoretical estimation of thepuresilverAg-Kα

and Ag-L α intensity ratio is also presented based on fundamental parameter approach

accounting properly for all secondary contributions to the Ag-L α intensity.

Type of sample Number of measurements

or samples

AgKα/AgL α

Pure Ag 5 78.3 ± 1.8 — Theory-FP: 79.5

CNR-141 2 81.1 ± 1.1

CNR-152 4 78.3 ± 3.7

CNR-91 8 78.2 ± 2.2Silver coins (obverse) 82 87.8 ± 10

Silver coins (reverse) 81 88 ± 11



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Since theelastic scattering cross section scales as a power of the target

atomic number, if the Ag concentration of the coin bulk was lowerthan in the surface enriched layer, we would expect lower Rayleigh

intensities than those emanated from a homogenous silver alloy. The

intensity of the Rh-Kα Rayleigh scattered radiation was measured for

the reference silver alloys and the coins (Fig. 8). The data were

normalized with respect to theRh-Kα Rayleigh scatteredintensity of a

pure silver, thick target. The statistical uncertainty, associated with

each measurement (180 s counting time) was about 3.5%. A

theoretical estimation was also performed for the normalized

Rayleigh scattered yield based on the differential scattering cross

sections (scattering angle =135°) of Rh-Kα radiation on Ag and Cu

elements. The mean normalized Rayleigh intensity was measured to

be 0.936±0.053 and 0.945±0.057 for the obverse and reverse of the

coins, respectively (four coins with Ag b95% were excluded from

mean value calculations). The experimental Rh-Kα data was found to

be compatible with that from the Ag reference alloys, although a

systematic underestimation was observed in comparison with the

theoretical estimations, most probably due to possible inaccuracies of

theoretical cross sections of Rh-Kα Rayleigh scattering on Cu and Ag

atoms.

For the third test, a surface Ag-enrichment hypothesis was

adopted (Ag= 98% in a surface layer of 0–40 μ m thickness and

Ag=75% in the bulk). Then the Ag-Kα and Rh-Kα intensities were

calculated, using theFP method(including an analytical description of

the X-ray tube energy distribution, uorescence cross sections,

secondary uorescence enhancement etc.). Both intensities were

normalized to the respective pure silver, thick target intensity and are

presented in Fig.9 together with the experimental data from thesilver

coins analyzed here. It is evident from Fig. 9 that the initial hypothesis

of an Ag-enriched, surface layer on a bulk alloy of 75% Ag would be

compatible with the experimental data only if the enrichment layer

was thicker than about 26 μ m. Lower thicknesses are expected if the

Ag bulk concentration is higher than 75%. The data certainly exclude

the scenario that assumes Ag surface enrichment in a surface layer of

about 10–15 μ m and a silver bulk with Ag concentration from about

75% to 92%.

3.4. Coin alloy composition

The major reason for the dif culties in the interpretation of coin-

alloy analyses is the fact that the present elemental composition is

considerably different from that of the silver raw material. Smelting,

purication, alloying and corrosion have produced an almost entirely

different material. However, several safely deduced conclusions can

be extracted by the XRF data. All coins are made of silver, with minor

amounts of Cu, Au and Pb, Fe and Zn, in agreement with other results

for contemporary silver [22–24]. The mean Ag value concentration

Fig. 6. Information depth for Ag-Κα, Ag-L α and Rh-Kα characteristic X-rays in binary

Ag/Cu alloys.

Fig. 7. The normalized Ag Kα to AgL α intensity ratio calculated for a double layeredalloy system composed by a pure Ag top layer of variable thickness and a bulk binary

Ag/Cu alloy of variable composition. The Kα/L α ratios were normalized with respect to

the respective pure silver alloy value.

Fig. 8. Experimental mean Rayleigh (Rh-Kα) intensities measured on obverse and

reverse of the coins, respectively (for Ag N95%). The dotted line represents a theoretical

estimation on the basis of a binary Ag/Au alloy. Experimental and theoretical data have

been normalized with respect to the respective pure Ag Rayleigh (Rh-Kα) intensity.

Experimental data corresponding to Ag concentration less than 95% is also given.

Fig. 9. Theoretically estimated Ag-Kα and Rh-Kα intensities (normalized to the

respective pure silver intensities) for a double layered silver alloy structure (Ag/Cu

binary alloy, top layer, Ag=75% and variable thickness, bulk composition withAg= 75%) in comparison with the experimental data (within one sigma) deduced by

the silver coin measurements (shadowed blocks). Four coins with Ag b95% have been

excluded from the statistics presented.



10/11


(98%) of the coins shows the high purity of early Ptolemaic silver. At

the end of the Ptolemaic dynasty silver coinage suffered from severedebasement, with Cleopatra VII to issue staters composed of 2/3

copper and 1/3 silver [13]. The coins analyzed in this work however

cover the period from to 320 to 180 B.C., which is considered to be a

period of high purity silver [13]. In Fig. 10, the amount of Cu in the

coins is plotted against date of issue since Cu-content is a good

measure of debasement [13]. A slight debasement trend is obvious,

even in this period of Ptolemaic peak power.

In most of the coins the concentration of Cu was found below 1%.

By excluding any surface enrichment scenario, Cu content reects, the

raw silver mineral provenance, being either argentiferous lead ores or

silver bearing minerals such as jarosite [38,39]. However, copper

could also be present as a result of deliberate addition, either in small

quantities for hardening purposes after cupellation, or in larger

quantities due to monetary policy or economic necessity. Mc Kerrel

and Stevenson [40] argue that the presence of Cu in concentrations

higher than 2–3% in a silver object would be evidence of its deliberate

addition. Such high concentrationsare observed in two of the Ptolemy

III tetradrachms from the mint of Marathus (#61 and #66) and a

deliberate addition of copper can be thus concluded.

Lead concentrations were also found below 1% in most of the cases.

Lead is probably the best indicator of the technological level of

purifying processes and such low concentrations indicate effective

rening. The lead cupellation process was used in the nal stages of

silver purication [41] and could reduce copper and lead to less than

1% [40].

The mean concentration of Au in the coins is 0.7%. Gold in such

low concentrations is generally considered as an indicator of the

parent ore composition since it is not expected to be affected by

smelting and cupellation [21,40,42]. A plot of Au versus Pb is given

in Fig. 11 and shows small scale composition differences between

alloys of different time periods. The coins are grouped in four

groups, which are actually chronological: Group 1 includes coins of the reign of Ptolemy I, Group II those of Ptolemy II, Group III of

Ptolemy III and Group IV includes coins of Ptolemies IV and V. If we

accept that Au is an indicator of the silver source and Pb a

technological indicator, we can follow a gradual increase in Au

concentration over time. During the reigns of Ptolemies I, II and III,

Au concentrations never exceed 0.8–1% while for the coins issued

during the reigns of Ptolemies IV and V, Au concentrations are

systematically higher than this value. This change may reect a

change of the silver source during the reign of Ptolemy IV but such

hypothesis needs more evidence, both historical and analytical to

be conrmed. Additionally, during the reigns of Ptolemies I and II,

Pb concentrations are limited to 0.7% indicating good rening

processes. From Ptolemy III to Ptolemy V, Pb concentrations

increase up to 2%.Regarding other elements, trace amounts of Bi were detected in

just ve of the coins, mainly in coins of Ptolemy IV and Ptolemy V. Its

absence from the majority of the coins can be explained by its

reduction during the purication process or/and the use of a raw

material with low Bi content [38,43].

The concentration of iron shows high inhomogeneity as can be

seen on the micro-XRF map of coin #2. This heterogeneity may be

related to surface contamination from the burial environment.

However, the relatively high iron content of many coins, with similar

compositions on both coin sides, may be connected to the use of silver

bearing jarosite for melting [39]. It has to be noted that jarosite is

related to the primary source of silver in the silver ore deposits in

Spain, from the Late Bronze Age [39,44] although the Pb minerals for

jarosite smelting were usually imported.

4. Conclusions

The full exploitation of the analytical information recorded in

an XRF spectrum and the application of appropriate experimental

and theoretical FP based methodologies can provide a set of semi-

quantitative criteria to assess the presence or not of enriched Ag-

layers on silver coin surfaces. The present work proposes a set of

three complementary analytical methodologies as a tool to assess

the reliability of XRF data in such cases: a) comparison of XRF data

on original and cleaned micro-spots on coin surface, b) Ag K/L

ratio test and c) anode characteristic radiation Rayleigh scattered

test.

Additionally, the XRF technique has proved of great usefulness in

the analysis of silver coins, mainly due to its analytical capacity toeasily detect the presence of certain minor elements, which are

critical in understanding surface nishing techniques, production

processes and nally provenance of the raw materials used.

Non-destructive XRF analysis was applied on 82 Hellenistic silver

coins, from different mints, produced during the reigns of Ptolemies

I to V. The results show that the coins were made by high purity

silver whereas a good rening process was applied in general. The

elevated amounts of Pb measured in many coins indicate that the

rening process was not too detailed. The relatively high Au

concentration is similar to the corresponding one of silver coins of

the same period. In addition, coins of Ptolemy IV and Ptolemy V

show higher concentration of Au, whereas Bi was detected in the

didrachms. This difference may reect a change of silver source. In

the case of Marathus mint, a deliberate addition of Cu was found fortwo of the coins, probably dictated by monetary policy or economic

necessity.

Fig. 10. Change of copper content versus date of issue for the analyzed coins (Coins #61

and #66 with Cu concentrations of 3 and 11% correspondingly are not plotted).

Fig. 11. Pb versus Au for the analyzed coins. Ellipses have no statistical signicance;

they are drawn to include most of the data for each group. (Coins #28 and #74 with Pb

concentrations of 3% are not plotted).



11/11


Acknowledgments

A.G. Karydas would like to thank Despoina Kotzamani and Ignaci

Queralt for their useful comments and suggestions.

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