Elemental Compositions of Herodian Prutah, Copper Coinsâof the

Chapter 13

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Elemental Compositions of Herodian Prutah, Copper Coins—of the Biblical "Widow's Mites" Series—via Energy Dispersive X-ray Fluorescence 1

2

1

Meghann Mouyianis , Jeffe Boats , and Mark A. Benvenuto 1

2

Departments of Chemistry and Biochemistry and Mathematics and Computer Science, University of Detroit Mercy, Detroit, MI 48221

Thirty six small copper coins issued under the authority of Herod Agrippa I were analyzed using energy dispersive X-ray fluorescence spectrometry for copper, zinc, tin, lead, antimony, iron, gold, silver, and several other elements. This series of coins show significant amounts of lead in the coins, but an otherwise unadulterated bronze composition, with very little in the way of trace elements. The metallurgical make up of the samples and implications of the findings are presented here.

Introduction The coins of the Herodian Kings, as well as coinage of other subordinate kings and rulers of the Roman Empire, were tolerated in the early imperium, producing an overall coinage system that was Roman throughout the Empire, but that had areas of local production and influence as well. The coins analyzed in this study, prutahs, each display what appears to be three wheat ears on one side,

246

© 2007 American Chemical Society

Glascock et al.; Archaeological Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 2007.

247


and an umbrella on the other and were minted under the authority of King Herod Agrippa I (ca. 40 A.D.) (7). These or their smaller siblings are often referred to as "widow's mites" because of the Biblical reference to them. According to the King James Bible, M k 12: 41-44: "And Jesus sat over against the treasury, and beheld how the people cast money into the treasury; and many that were rich cast in much. And there came a certain poor widow, and she threw in two mites, which make a farthing. And he called unto him his disciples, and saith unto them, Verily I say unto you, That this poor widow hath cast more in, than all they which have cast into the treasury; For all they did cast in of their abundance; but she of her want did cast in all that she had, even all her living." It is difficult today to determine what value such coins had in ancient times, but it is certainly apparent that these were the small change of their era and locale. Roman coins were available and used throughout the Roman Empire, but these coins were used within the smaller, localized area of influence of the Herodian kings (2). Whether Herodian coins were used in other transactions besides those involving the Temple treasury is also difficult to determine exactly. But it seems logical to conclude that there was most likely other local, commercial uses for such coinage as well (7, 2). Older references to these coins simply indicate them to be copper, brass, or bronze (7, 2). The experience from our research and that of others indicates that ancient alloys are usually more complex than either a single element, or a simple alloyed mixture (3-18).

Experimental Conditions The sample set consisted of 36 coins, all being of a design representing three wheat ears on one side, and what is generally considered an umbrella on the other. The coins are round, though not perfectly so, with minimum diameters from 14.1 - 18.2 mm (standard deviation 0.890), and maximum diameters of 15.9 - 19.3 mm (standard deviation 0.848), as seen in Table I. Their thicknesses range from 1.6 - 2.5 mm (standard deviation 0.212). While this sample set is not excessively large, it is larger than most previous studies of coins of the Roman Republic or Empire (13, 16), and encompasses a sampling of an overall mintage that is most likely much less than that of the Roman Empire at a comparable time (since the Herodian kings were subordinate to the Empire and had authority over


Table I. Physical Measurements and Chemical Compositions of the Coins


Sample MinD U (mm)

Max D (mm)

Thick (mm)

Cu%

Pb%

Sn%

Ag%

Fe%

Sb%

WM1

16.1

17.2

1.8

88.3

2.58

8.57

0.06

0.38

0.07

WM2

17.0

18.5

2.0

87.6

8.86

2.72

0.03

0.62

0.10

WM3

16.1

18.8

1.9

81.8

11.01

6.51

0.05

0.43

0.11

WM4

16.4

17.3

2.0

68.7

24.85

5.73

0.02

0.49

0.08

WM5

17.0

17.8

2.5

90.3

4.46

4.06

0.03

0.70

0.09

WM6

15.8

17.9

2.4

90.2

2.80

6.49

0.02

0.30

0.06

WM7

16.6

17.9

1.9

74.2

12.30

12.53

0.06

0.43

0.44

WM8

16.5

17.4

1.9

80.8

7.91

10.48

0.04

0.58

0.11

WM9

14,6

16.3

2.4

91.1

1.30

7.02

0.03

0.41

0.11

WM10

16.0

16.2

2.3

92.7

3.28

3.65

0.01

0.34

0.07

WM11

15.9

17.4

1.8

84.5

10.71

3.94

0.02

0.73

0.10

WM12

15.5

16.2

2.2

80.6

10.31

8.33

0.04

0.61

0.11

WM13

17.0

18.5

1.8

76.5

5.55

16.96

0.05

0.79

0.07

WM14

16.9

17.9

1.8

92.6

1.39

5.64

0.03

0.31

0.05

WM15

16.4

16.8

2.0

77.5

12.20

9.69

0.06

0.33

0.17

WM16

16.3

16.4

2.1

80.1

11.74

7.53

0.01

0.43

0.19

WM17

18.0

18.4

1.9

87.7

2.23

9.70

0.04

0.24

0.09

WM18

17.1

17.2

2.0

68.3

24.03

6.89

0.04

0.66

0.09

WM19

15.1

17.2

2.4

86.2

5.33

7.69

0.04

0.69

0.09

WM20

17.1

17.2

2.0

88.8

8.48

2.09

0.02

0.50

0.04

WM21

15.9

16.3

2.0

93.0

0.61

5.98

0.02

0.29

0.03

WM22

18.2

18.4

2.4

80.2

9.09

9.75

0.03

0.80

0.12

WM23

16.4

17.2

2.2

69.1

19.02

10.72

0.06

0.87

0.15

WM24

16.3

17.3

1.9

82.6

7.40

9.16

0.05

0.58

0.13

WM25

16.8

18.2

2.1

80.5

8.64

10.08

0.04

0.50

0.17

WM26

16.8

18.3

2.0

77.9

14.39

7.10

0.05

0.30

0.19

WM27

14.1

15.9

1.9

71.4

12.87

15.26

0.05

0.23

0.12

WM28

17.0

17.2

2.2

78.6

15.12

5.31

0.04

0.80

0.09

WM29

17.7

18.1

2.4

90.1

7.30

1.87

0.01

0.56

0.13


249 Table I. Continued.


Sample MinD (mm)

MaxD (mm)

Thick (mm)

Cu%

Pb%

Sn%

Ag%

Fe%

Sb%

WM30

15.8

17.0

2.1

71.8

24.58

2.72

0.03

0.73

0.09

WM31

15.1

16.3

2.2

90.9

5.69

2.79

0.01

0.57

0.06

WM32

17.0

17.1

2.1

74.1

19.61

5.45

0.05

0.66

0.10

WM33

15.6

16.5

2.0

68.1

18.04

13.38

0.04

0.31

• 0.09

WM34

17.2

19.3

2.1

91.9

3.00

4.57

0.02

0.42

0.08

WM35

17.3

18.1

2.0

91.4

4.97

2.98

0.02

0.53

0.09

WM36

17.1

18.1

1.6

73.3

15.55

10.39

0.05

0.53

0.12

Std Dev

0.89

0.85

0.21

8.1

6.78

3.70

0.02

0.18

0.07

only a small area of the modern day Middle East, whereas the Roman Empire stretched roughly from modern Britain to modern Iraq). A Spectrace QuanX energy dispersive X-ray fluorescence spectrometer was used, which employed a rhodium target X-ray tube, fundamental parameters software, and pure element standards. Sample excitation conditions were: 30kV, 0.10mA, 100 sec count, Κ α β for Fe, Co, N i , Cu, Zn, As, Pt, A u , B i , and Pb, followed by: 50 k V , 0.72 mA, 60 sec count, for Pd, A g , Sn, and Sb. Certified brass samples were run each day prior to sample runs to ensure instrument accuracy and precision. Samples underwent sonication in hot, soapy water for 15 minutes, to ensure surfaces were clean and free of any surface contamination. The more elaborate preparation method of Carter (70, 73) was not utilized because visual and 7-30X microscopic examination of each coin revealed no remaining encrustation or patination. The entire set of coins was analyzed twice on each side as a minimum, and the results averaged to ensure reproducibility of the data.

Discussion Coins and artifacts of the Roman Empire have been studied extensively (4, 5, 19-39), but a thorough search of the literature indicates these small, copper coins of the Herodian King Agrippa have been omitted from all previous examinations. The iconography of the coins in this sample set is crude, but all have at least a recognizable wheat ear side or an umbrella side. A worn state or



250 weak design elements are actually not detractors in this case. Rather, one can argue that because of the wear the surfaces being analyzed do not suffer from any elemental enrichment process at a surface that might have resulted from the original method of manufacture. The coins appear to be essentially a ternary alloy: copper, tin, and lead. Figure 1 displays the copper percentages of the samples in comparison to each other, and Table I shows all copper and other elemental compositions. While the samples with the lowest percentages are near 70%, nearly half of the sample set shows 90% or higher copper. Samples of ancient coinage with this level of purity are rare, but not unheard of (4). Figure 2 illustrates the lead percentage of each coin in the study, again, in comparison to each other. Note that the y-axis peaks at 30%, thus emphasizing the lead differences somewhat in relation to the copper. Coins W M 4 , W M 1 8 , and WM30 are all high in lead, and predictably, are also low in copper. It is noteworthy however, that over half of the samples contain less than 10% lead. This is much lower than in other studies of ancient or medieval coinage (5, 17, 40, 45). Figure 3 shows the percentages of tin in each sample, compared against each other, in similar format to Figures 1 and 2. In this case, the y-axis peaks at 20%, because the samples contain a relatively small amount of tin in relation to copper. Because it may be difficult to compare the percentages of the three components using only the data as presented in Figures 1-3, Figure 4 shows copper, lead, and tin plotted on the same scale, and Table I reiterates this with the averaged percentage for each coin for each element. While the nuances of the differences in lead and tin compositions may be lessened through the comparison in Figure 4, their relation to copper, the major element, is heightened. It is immediately evident that there is less tin and more lead on average for the coins - the mean lead percentage is 9.9%, compared with only 7.3% tin. Also noteworthy is the relatively large sample standard deviation of 6.78 in lead percentages, as opposed to 3.70 in tin percentages. The standard deviation can also be compared with the lead mean of 9.9%, indicating a wider variation in lead content. While this large standard deviation does not prove unequivocably that lead was added as an alloying element, it does seem to suggest this to be true. Since these coins were produced for local use, and use of a much more limited extent than the coins of the Roman Empire, it can be deduced that ore sources were most likely local or in the near proximity to the minting site. The standard deviation of tin content, when compared with the data, suggests that the tin percentages are normally distributed, the expected result for coins made by the same mint or by the same methods. Twenty-four of the thirtysix coins (approximately 67%) had tin percentages within one standard deviation of the mean, and thirty-four of the coins (approximately 95%) fell within two



10

20

30

40

50

60

70

80

90

100

w

u% ω

^

>j

vo

^

Sample Number

ul•

u!

Figure L Copper Percentages of Widow's Mites Coins

^


252

WM35 WM33


WM31 WM29 WM27

§ ···*

a WM25

g

WM23 WM21 WM19

I

WM17

g

g-

£ ^ "g

g WM15

£

WM13

^

WM11 WM9

S .1

WM7 WM5 WM3 WM1

(%) P™1


253

WM35 WM33


WM31 WM29 WM27 WM25

Cj

WM23 WM21

.

WM19

J

WM17

I

&

WM15

8

WM13

s:

WMll WM9 WM7 WM5 WM3 WM1

(%)

I

"!1 jusarad



Figure 4. Relative Percentages of Copper, Lead, and Tin in Widow's Mites Coins



255 standard deviations. The analysis of lead and copper content offer no evidence contrary to this assertion. Beyond this, iron is present in the range of only 0.2% - 0.9%, which is both quite low and rather uniform. Other studies of coins from different cultures and times show similar, low iron percentages (4, 5, 17, 40). In previous studies on Roman coinage of roughly similar dates, Carter found iron concentrations in the range of 0.05 - 0.4% (10, 13). There appears to be continued disagreement among scholars as to whether iron in the alloys was present in original ores, is a purposeful addition to the alloy, or is a by-product of the alloy being molten in some iron container (42) during the production process. In the case of these 36 coins it remains noteworthy that so little iron was found in any of the samples. Other elements for which this sample set was analyzed were present in statistically insignificant amounts with the exceptions of silver and antimony. Gold, which is present in numerous copper ores even today (and the recovery of which sometimes pays for the electrical requirements of copper refining), is notably absent from these coins. The small amount of silver present is most likely a natural trace in the copper ores. As just mentioned concerning gold, trace amounts of silver are also recovered from copper ores during refining today, and used to help pay for the copper refining operation. In addition, only trace amounts of zinc appear, approximately at the detection limit of the instrument, and in fewer than one quarter of the coins.

Conclusions The coins are leaded bronze. The almost complete absence of zinc indicates they are definitely not brass. The elemental composition shows surprisingly clean make ups overall, considering the technological abilities of the age and culture. This could be an indication that the ancient Judaean foundry workers and miniers had access to remarkably pure ore sources, or could be evidence of their ability to refine those less pure ores which were available to them. The presence of varying amounts of lead in this series of coins appears to be an indicator that the mint workers had some knowledge of leaded alloys and their metallurgy, specifically the knowledge that an alloy was easier to work upon the addition of lead (because the resultant alloy had a lower melting point). Another possibility, that the differing amounts of lead are present in original copper or tin ores in roughly these percentages or ratios simply by chance, seems less likely, because of the variation in lead content from coin to coin.


256

References 1. 2.


3. 4. 5. 6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

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