Chemical Composition of Song Dynasty, Chinese ... - ACS Publications

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Chapter 12

Chemical Composition of Song Dynasty, Chinese, Copper-Based Coins via Energy Dispersive X-ray Fluorescence 1

2

1

Jessica Misner , 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

Two hundred twenty four Chinese coins (Song Dynasty, ca. 990-1080 A.D.) were analyzed via energy dispersive X-ray fluorescence spectrometry for the following elements: copper (Cu), zinc (Zn), tin (Sn), lead (Pb), iron (Fe), nickel (Ni), manganese (Mn), antimony (Sb), gold (Au), platinum (Pt), palladium (Pd), and silver (Ag). The coins routinely appear to be leaded bronze. However, the amount of lead present in these coins was in many cases significantly higher than expected.

Introduction The Sung Dynasty (960 - 1280 A.D.) was one link in a chain of imperial dynasties throughout the history of China. At the time of the manufacture of the coins used in this study, established practice dictated that the coins be cast in clay molds, in a traditional manner that was already nearly one thousand years old. Thus, the coins analyzed in this study are all round, with a square hole in the center, have four characters on one side and none on the other, and are said to be of copper, bronze, or brass (7, 2). The characters on such coins are read from top

© 2007 American Chemical Society

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

231


232 to bottom and right to left. The top and bottom characters are the emperor's title, and those on the right and left proclaim the minting authority. A single emperor often had more than one title in the course of his reign. The changes are chronological, and have been summarized in Table I. Schjoth numbers in this table refer to one of the standard reference books for identifying and cataloguing Chinese coins of the various dynasties (/). The study numbers that make up the final column of Table I are assigned by the authors as a shorter identifier than imperial titles by which to designate the coins. The coins of three emperors have been examined.

Table I. Imperial Names, Titles, and Identification Numbers Emperor

Title

Dates (A.D.)

Schjoth #(2)

Study #

Chen Tsung

Hsien-p'ing

998-1004

469

SA

Hsian-fu

1008-1016

473-478

SB, SBB, SC

T'ien-his

1017-1021

479-482

SD

T'ien-sheng

1023-1031

484-486

SE, SF

Ching-yu

1034-1037

492-494

SG

Pao-yuan

1038-1039

496-500

SH

Shao-sheng

1094-1097

582-591

SI, SJ

Yuan-fii

1098-1100

599-603

SK

Jen Tsung

Che Tsung

Our interest in this series of coins stems from earlier research in which coinage of emperors of the Ch'ing Dynasty (also transliterated "Qing") were examined and found to be impure brass (5). We are interested in determining how far back such minting, and the required metallurgical knowledge, went.

Experimental Conditions A Spectrace QuanX energy dispersive X-ray fluorescence spectrometer was used, with a rhodium target X-ray tube, running on fundamental parameters



233 software, which normalizes the elements examined to 100%, and running on pure element standards. Sample excitation conditions were as follows: 22 k V , 0.10 mA, 100 sec count, Κ α β for Fe, Co, N i , Cu, Zn, As, Pt, A u , B i , Pb, followed by: 45 k V , 0.72 mA, 60 sec count, for Pd, A g , Sn, Sb. Certified brass samples ranging from 36% to 94% copper were run daily prior to each run to ensure instrument accuracy and precision. A l l samples underwent sonication in hot, soapy water for 15 min, to ensure surfaces were clean and free of dirt or other surface contamination. After sonication, samples were examined visually and via 7-30X microscope to ensure each sample had metal exposed to the X ray beam, and not surface patination or metal oxides.

Discussion Modern brass and bronze alloys come in many different compositions, but 2:1 ratios of copper and zinc or tin respectively are used in a number of applications. Ancient and medieval alloys that are called brass and bronze are often mixtures of all three elements, with several other elements present as well. Observing a clean composition of copper and zinc or of copper and tin in any of the samples in this study would be a good indicator of a modern, counterfeit coin. None with such a composition were found. Previous studies (3, 4) and older literature (5-7) indicate small amounts of lead are sometimes present and were allowed in Oriental coins, perhaps to lower working temperatures of batches of molten metal. Studies of artifacts of other cultures also indicate that metals such as lead might be present, but such can not be used as a direct indicator for these samples (8-20). Beyond this, when initiating this study, we had no specific expectations of the compositions being more than copper, zinc, tin, and lead. The elemental compositions of the first emperor in the study, Chen Tsung, are represented graphically in Figures 1-3, with each graph representing the coins from one imperial title. A total of 14 coins composed the sample for Figure 1, 36 for Figure 2, and 28 for Figure 3. Figures 4-6 represent the compositions of the coin samples of Emperor Jen Tsung, with 45 coins composing the sample set for Figure 4, 28 for Figure 5, and 13 for Figure 6. The final two, Figures 7 and 8, display the compositions of those coins of Emperor Che Tsung, with 45 coins making up the sample set for Figure 7, and 15 for Figure 8. Each figure thus represents only those coins of a specific imperial title. The multiple Schjoth numbers, listed in Table I, simply delineate the coins of a specific title based on minor stroke differences in the characters on each coin.(7). In each graph and illustrated in Figure 1 is an example, which also serves the following Figures 2 - 8 , the diamond icons represent the copper percentage of a specimen, the triangles represent the lead percentages, the circles the tin,



SA Coin Sample Number

Figure 1. Compositions of Coins of the Emperor Chen Tsung, Imperial Title Hsien-p 'ing.

90 A

100



2

4

5

6

7

8

SB, SBB, SC Coin Sample Number

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Figure 2. Compositions of Coins of the Emperor Chen Tsung, Imperial Title Hsian fu.

3



1

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

SD Coin Sample Number

18

19 20

21

22

23

24

25

Figure 3. Compositions of Coins of the Emperor Chen Tsung, Imperial Title T'ien-hsi.

2


26

27

28


90

Figure 4: Compositions of Coins of the Emperor Jen Tsung, imperial Title T'ien-sheng.

SE, SF Coin Sample Number



1

3

4

5

6

7

8

9 10

11

13

14

15

16

17

SG Coin Sample Number

12

18

19 20

21

22

23

24

25

Figure 5. Compositions of Coins of the Emperor Jen Tsung, Imperial Title Ching-yu.

2


26

27

28


90

1

3

4

5

6

7

8

SH Coin Sample Number

9

10

11

12

Figure 6. Compositions of Coins of the Emperor Jen Tsung, Imperial Title Pao-yuan.

2


13


100

Figure 7. Compositions of Coins of the Emperor Che Tsung, Imperial Title Shao-sheng.

SI, SJ Coin Sample Number



Figure 8. Compositions of Coins of the Emperor Che Tsung, Imperial Title Yuan-fu.



242 and the square boxes all the remaining elements. Each vertical series of four points thus represents the composition of a single coin. It is evident that copper appears to be the major component in most of the coins of all emperors and titles. What becomes interesting is that lead is almost always the major component in the percent fraction of elements other than copper, even more so than tin. In Figures 1 - 3, for instance, it appears most prominently that even with the outliers removed, lead is present in greater amounts than tin. Focusing on the outliers themselves, one realizes that enough lead was occasionally added to the alloy such that the coin could be considered a primarily lead piece. For the most pronounced example, Figure 4, the T'ienSheng title of Emperor Jen Tsung, sample number 23 has lead greater than 50%, with copper very close to 25%. This is not a surface enrichment phenomenon, as the density of this sample, and that of other outliers, is significantly greater than the other coins within their respective sets. The most uniform series in terms of standard deviation of lead content percentage is that of Figure 6, although the lot size was small enough - 13 coins - that a larger sample may have revealed similar anomalies. Zinc is virtually non-existent in the samples, and thus is included with the trace elements, represented as square boxes. In very few instances do we have a trace element combined percentage that rises towards 5% (such as coins SC30, SF23, SH8, SI2, and SK14). Thus, it appears that a change in composition occurs between these coins of the Song Dynasty and later coins of the Qing Dynasty (3, 5). Since certain Qing Dynasty coins have already been found to be leaded brass, it may be worth studying several sets of coins at points between that of the date of manufacture of these coins (ca. 1000 A.D.) and those already examined of the Qing Dynasty time frame (ca. 1750 A.D.) (3, 5), to determine i f only one change in composition occurred, if several occurred, or i f one occurred slowly over the course of many years. A n interesting trend is seen when the coins are grouped by emperor-title and we consider the total content percentage of additives, that is, the non-copper and non-tin impurities, as shown in Table II. While the mean percentage for additives hovers around 22% in all samples, the standard deviation is seen to decrease approximately linearly with time through the Chen Tsung rule and into the Jen Tsung, before sharply reversing. The decreasing trend may indicate a steadier, more consistent smelting technique being passed down over time. The reversal could represent some disruption in the normal allocation of mineral resources. It is known, for example, that northern border skirmishes early in Jen Tsung's reign led to mounting military expenditures later on (21). Further study with a larger sample of coins might prove insightful.



13.19 10.72

70.41 66.64

1001

1012

1019

SB,SBB,SC

SD

SE,SF

10.65 10.82 11.51 8.71

66.10 68.64 67.68 71.90

1027

1035.5

1038.5

SG

SH

Stdev

SA

Mean

Midyear (A.D.)

Coin Studies

% Copper

8.57

10.04

11.60

9.84

9.38

7.78

Mean

22.43

5.34

18.71

6.95

10.74

21.64 4.24 4.26

8.80

19.07

3.80

10.34

10.25

22.44

4.43

Stdev 14.23

Mean

%Lead

21.29

4.31

Stdev

%Tin

19.54

22.28

19.76

24.07

23.98

21.82

11.03

10.90

9.25

9.99

10.78

11.70

Stdev

% Additives Mean

Table II. Means and Standard Deviations of Content Percentages


244


Conclusions The coins appear in almost all cases to be leaded bronze. In a number of samples, the outliers contained as much or more lead than copper, and in many instances, the lead content was significantly higher than that of tin. None of the coins can be considered to be brass. While a few of the many samples did have a small amount of zinc, most had such low concentrations that they were close to the lower detection limit of the instrument. The bronze compositions are decidedly different from the elemental make up of later series of Qing Dynasty cash from the 18 century, which are brass (5). Perhaps obviously, a significant change in coin metallurgy occurred between these two eras. It may be worth investigating when this change occurred, and determining what the reasons were for such. Finally, paying attention to the outliers of these series, the element lead seems to be added almost at random to all the series of coins, though over time the use of additives seems to have become more consistent, for the most part. There is certainly more lead present than is required to effect lower working temperatures for molten alloys. Other than this variance in lead however, these coins have a notably consistent composition. It appears that the mintmasters and workmen of the foundries had a good understanding and control of copper, lead, and tin in the production of alloys. th

References 1. 2. 3.

4. 5. 6. 7. 8.

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Chemical Composition of Song Dynasty, Chinese ... - ACS Publications

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