GOLD AND COPPER TRACES IN LATE ATHENIAN SILVER BY MARGARET THOMPSON

American Numismatic Society

ARLY in 1Y5Y eighty-six Athenian silver coins of the late Hellenistic p a i d were analyzed by the neutron activation method to determine the amounts E of gold and copper present. These spread-flan tetradrachms. designated by

numismatists as “ N m Style” to distinguish them from the earlier “owls” of Athens with their thicker, smaller flans and somewhat different reverse type, constitute a long series of annual issues struck between 196/5 and 88/7 B.C. Intensive study of the coinage has resulted in a year-by-year sequence of strikings of individual

Of the specimens tested. the vast majority was supplied by the Hebcrden Coin Room of the Ashmolean Museum through the courtesy of Dr. Colin M. Kraay. In addition to the Oxford coins a relatively small group of tctradrachms from the collections of the American Numismatic Society, of E.S.G. Robinson and of Burton Y. Berry was examined. As was the case with earlier coin analyses (reported in Archacometry I and 2) the specimens were irradiated with neutrons in an atomic pile at Harwell and the ensuing radioactivity was examined with a gamma-ray spectrometer by Miss Vera M. Emeleus of the Oxford Research Laboratory for Archaeology and the History of Art. To all those who co-operated in makhg material available and in conducting the scientific tests the writer is deeply grateful.

The purpose of the tests was fourfold: ( I ) to see if variations in gold and copper content had any chronological signifi-

cance. Earlier chemical analysis of a limited number of New Style bronze coins. had revealed a striking correlation between metallic composition and the date of the specimens tested and it was thought that some similar pattern might a n a g e with respect to the composition of the silver coins.

(2) to determine whether or not the readings of thirteen coins considaed “suspect” because of their abnormal style were notably different from other readings.

(3) to explore the possibility of a relationship between metallic composition and a series of control combinations which appear on the reverses of the coins. I t seems likely that the latter are associated in s m e way with the source of the bullion. hence coins marked with a particular control combination might show a distinctive pattern of gold and copper content.

(4) to provide data from a late period of Athenian coinage for comparison with the analyses of sixth and fifth century coins from the same mint already published by Dr. Kraay (Archacometry 1. pp. 1-5; 2. pp. 1-16).

Omitting the “suspect” pieces. the tctradrachms of certain Athenian origin numbered seventy-three. Sixteen of these belong to the Early Period of the coinage (196169 B.C.). thirty-nine to the Middle Period (168-132 B.C.) and eighteen to the Late Period (131-87 B.C.). Figures 14 illustrate the results of the analysbs of the coins of thcse three pcnds,t

Brother Roman Leonard Wianrki. S.M., a graduate student at the mmc inrtitution.

0.00bS gold, haw been omitted from Figurea 2 and 4.

analYSeS.

Tlmc analyses were made by Profasor Earlc R. Caley of Ohio State University and by

t Two coin8 of the MiddlePeriod. one with 0.008 copper and the other with less than

A I C H A E O Y E T ~ Y 11

As a prdiminary step in the intcrprctation of the readings. information was sought 011 the extent of ancient mining operations in the Laurium area. which was Athens’ chief source of silver. and also on the amount of variation that one might apst in ore from the same mine or from mines in the same general region. Miss Margarrt Crosby’s p u b t i o n of mining leases (Hespmiu. 1950. pp. 189-312) gives & names of over forty mines which wcrc being worked in the fourth century. The distance betwecn the northernmost and southernmost of thesc mines was fifteen kilometers. according to Professor John H. Young of The Johns Hopkins University who has made a long and careful study of the Laurium district. Ancient workings have been found on the surface and ancient galleries about 200 metres below ground. We d o not know how many of these mines wcrc in operation a t the same time or how many continued to be worked in the second cmtury but the statistics of the earlier period do provide an indication of the extent of activity in the Laurium region.

Data on the ancient mines and the modern analyses were then submitted to a mining engineer. Mr. Sandford R. Knapp. Mr. Knapp and several of his associates in the mining firm of Taylor-Knapp Company most kindly ptepared a helpful memorandum giving their considered judgment on specific points at issue. In sscnce. assuming a generally high grade silver ore. a wide variation in copper and gold is to be expected from “pocket to pocket. betwcen different veins or seams in the same mine, from the surface to a 200-metre depth. and certainly from different mines in a fifteen kilometer area.” An additional factor to be considered in relation to the coppcr content is variability in temperature control during the smelting and refining processes. Certain pockets of ore might well have contained as much. or more, copper as the amount found in some coins and if the smelting pot were heat@ above the melting point of copper. which is higher than silver, some portion of the copper would mix and probably alloy with the silver.

Having in mind the imponderables involved, k t us turn to the analyses them- selves. It is immediately apparent from the graphs that the three chronoloqical divisions of the coinagt reveal markedly different patterns of gold and copper percentages. For the Early Period there is a great diversity of metallic commsition. gold ranging from 0.0076 to 0.33 and copper from 0.035 to 5.3. and a notable lack of concentration points. It is interesting that this diversity of composition is in keeping with the character of the early coinage. The issues are uneven in size. some very small and others extensive: the quality of the workmanship varies from excellent to mediocre or worse; the bullion supply seems to have been drawn from a large number of relatively unproductive sources. It seems safe t o assume that the wide range of copper and gold shown in the analyses of the early coins is due in part at least to ore coming from numerous small workings rather than from a few rich lodes. Furthermore, it seems likely that the variation in copper content also reflects a carelessness in temperature control during the rehning process. which would be in accord with 0th- indications of a generally unstable situation with regard to minting activity during the period in question. It is perhaps significant that the earliest coins of Athens, the “wappenmunzen” of the sixth century. show a lack of uniformity in composition very similar to that of the coins of the early New Style period and it may well be that the determining factors in both cases were roughly the same.+

Dr. Kraay suggesta that the diversity of the sixth century coins may be due either to silver from less homogeneous surface deposits at Laurium or to bullioi. recured elrewhere.

12 A R C H A E O M E T R Y

A T H E N S N E W S T Y L E EARLY PERIOD (196-169 B.C.)

16 GOLD PERCENTAGE

Athenian Coins . Fig. 1

A T H E N S N E W S T Y L E MIDDLE PERIOD (168-132 B.C.)

37 GOLD PERCENTAGE

Athenian Coins . 4 Imitations Fig. 2

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14 A R C H A E O M E T R Y

By contrast the Middle Period shows a marked degree of consistency in metallic composition. with gold concentrating at 0.09 - 0.25 and copper at 0.05 - 0.4. The coinage of this period is also far more homogeneous than that of the Early Period. Its style is good, its dies are carefully cut, and its production is relatively $table from year to year with bullion seemingly supplied from the yield o f a few highly productive sources. Careful supervision of the refining process and a uniform overall supply of metal from a limited number of homogeneous deposits would seem to be the explanation of the consistent pattern of gold and copper content in the Middle Period. Again one finds a parallel situation prevailing in early Athens. The “owls” of the tifth century B.C., minted from rich. deep veins of Laurium silver. show substantially less gold and somewhat less copper than the New Style coins of the Middle Period but they do resemble the latter in their uniformity of composition.

For the Late Period the relationship between metallic composition and other aspects of the coinage breaks down. Percentages are uniformly high, concentrated between 0.25 - 0.5 gold and 1.5 - 5.5 copper, but there is n o corresponding stability in mint operations. Style deteriorates gradually, emissions decrease from very large to very small, sources of silver are apparently both diversified and scanty. The high copper content in all coins may well be the result of deliberate adulteration for the purpose of strengthening the alloy or stretching the silver. Certainly carelessness in temperature control, the explanation which best tits the fluctuating percentages of the Early Period, is less likely to be the reason for the consistently high readings of the Late Period. The increased gold content, however, is another matter since this is something which could not have been alter@ in the refining process. It seems very possible that the answer lies in the importation of silver from abroad. The size of the annual issues. reduced after 120 B.C. and little more than tokcri strikings from 112-87 B.C.. suggests that the supply of silver was growing scarce. From the new evidence of metallic composition it would appear that at an even earlier date, c. 130 B.C.. the Laurium mines were being worked out and supplementary sources were being tapped throughout the Late Period.

As mentioned earlier, thirteen “suspect” coins. were examined. Of these, five proved to be plated. Six qthers showed a metallic composition so different from that of regular Athenian coins of the period as to confirm decisively the stylistic argument for their rejection as products of the Athenian mint. Five are plotted on the graphs of the Middle and Late Periods and it will be clearly seen how far they lie outside the concentration points of the other coins. A sixth piece could not be plotted since the phenomenally high gold reading of 2.73 made it impossible to determine its copper content. The two remaining coins of the “suspect” group have readings not unlike those of genuine Athenian coins of the Late Period. They are still “suspect” on the basis of style but the case for separating them from the out- put of the Athenian mint is in no way strengthened by the evidence of metallic composition.

In summary, it may be said that the results of the tests have proved informative to a degree exceeding all expectation. They provide no clear pattern of consistent upward or downward changes in gold or copper content in line with the chrono- logical evolution of the .‘coinage. and they produce no evidence for a correlation between metallic composition and control combinations. It was probably too much to suppose that they would, given the degree of variation that seems to be normal for the ore of a single mine or group OT mines. They do, however, reveal a most interesting parallelism between composition and the general character of the coinage in its Early and Middlt Periods. and in this connection they suggest a further

A R C H A E O M E T R Y 1s

parallelism with two earlier groups of Athenian coins. An unexpected and highly important development relates to the probability that from about 130 B.C. Athens’ silver supply was being supplemented from sources beyond Laurium. Finally, in the case of eleven “suspect” coins the evidence of metallic composition supports in gratifying fashion the evidence of style for a non-Athenian provenance.

It is greatly to be hoped that the Oxford Laboratory will be able t o continue its work in the field of neutron activation analysis of ancient coinages. If a substantial amount of material from many mints can be tested, we shall in time have a fund of incalculable value to both the numismatist and the economic historian.