THE ANALYSIS OF GOLD COINS—A COMPARISON OF RESULTS OBTAINED BY NON-DESTRUCTIVE METHODS

This paper discusses a systematic difference between the results found when one series of Dark-Age gold coins were analysed both by neutron activation and by specific gravity analysis and when a second series of similar coins was analysed by the Oxford Milliprobe and by specific gravity. No reason is given for this systematic difference, although there is evidence that all three methods are slightly in error, two of them giving results for gold which are too high and the specific gravity method giving results which are too low.     

NEUTRON ACTIVATION ANALYSIS OF ANCIENT BURMESE SILVER COINS WITH A LOW FLUX AMERICIUM/BERYLLIUM NEUTRON SOURCE

Nondestructive neutron activation analysis is by now a well-established technique for the analysis of ancient silver coins. The high activation cross-section of silver for thermal neutrons makes it possible to also use this method with the low neutron fluxes available from an isotopic neutron source. In this case due consideration must be given to minimize the self-shielding effect which is encountered with coins above a few tenths of a millimetre thickness. A simple method for the determination of the silver, copper and gold content in silver coins based on the self-shielding properties of silver alloys of different fineness is described. The method has been found to be useful for the quick routine assay of silver coins for the purpose of their classification. Seventeen ancient Burmese silver coins from three different cultural periods of Burma, and two British coins for comparison have been analyzed by this method.     

AN ANALYSIS OF SOME THIRD-CENTURY ROMAN COINS FOR SURFACE SILVERING AND SILVER PERCENTAGE OF THEIR ALLOY CONTENT

The silver content within the body and at the surface of 22 Roman ‘bronze’coins dating to a.d. 274–305 was determined by X-ray fluorescence to discover whether these coins were silver dipped and/or issued with a deliberately added amount of silver in their alloy. Results of this analysis indicate that antoniniani and fractional coins of the period 274–294 were probably both silver dipped and minted in an argentiferous alloy. Radiate and laureate fractions issued after 295 do not seem to have had an argentiferous alloy, nor does this analysis provide any evidence that they were silverdipped.     

NON-DESTRUCTIVE RADIOISOTOPE X-RAY FLUORESCENCE ANALYSIS OF OLD SILVER COINS

The paper presents the results of a feasibility study of the application of X-ray fluorescence analysis to nondestructive analysis of coins. Radioisotope sources ⁵⁵Fe, ²⁴¹Am, ¹⁰⁹Cd and ²³⁸Pu were used for excitation and a Si/Li detector with a multichannel analyser for the measurement of characteristic X-ray lines. Silver and copper in Polish renaissance coins have been analysed. Analysis using Ag K and Ag L lines allows one to distinguish between blanched and unblanched coins. The accuracy of the silver determination using Ag K X-rays is claimed to be ± 0.5% Ag for homogenous coins and ± 1.0% Ag for blanched but well-preserved uncorroded coins.     

A STUDY OF THE SILVERING PROCESS OF THE GALLO‐ROMAN COINS FORGED DURING THE THIRD CENTURY AD*

We have observed by fast neutron activation analysis (FNAA) that the global composition of the official silver coins of the Gallic emperor Postumus is not the same as those from the contemporary unofficial mints. In order to explain this phenomenon, we have carried out a metallographic study of the artefacts. Then, we have re‐created the silvering process of unofficial coins in order to better understand the manufacturing process of silvering. The different steps of the replication process are explained in this paper.     

STUDY OF ANCIENT GREEK COPPER COINS FROM NIKOPOLIS (EPIRUS) AND THESSALONIKI (MACEDONIA)

Ancient copper coins from the Greek cities Nikopolis in Epirus and Thessaloniki in Macedonia, minted during Roman imperial times (31 BC to AD 268), were analysed non-destructively by proton induced X-ray emission, after removal of the patina. An intercompar-ison study using different analytical methods was also performed on five coins. Eleven elements were analysed quantitatively on all coins. Statistical analysis of the results was performed for their presentation in the form of dendrograms. Finally, the variations in the concentrations of some individual elements from emperor to emperor were examined.     

COMPARISON OF METHODS OF ANALYSIS OF SILVER AND GOLD IN SILVER COINS

A series of silver coins was analysed for silver and gold contents by three methods—chemical wet analysis, activation analysis and X-ray fluorescence using a point source linear spectrometer (milliprobe). The results indicate that while the X-ray fluorescence technique gives better agreement with chemical analysis for major components the use of activation analysis with automated equipment results in a considerable saving of time and has a high sensitivity for some minor components.     

DETECTION OF NEAR-SURFACE SILVER ENRICHMENT ON ROMAN IMPERIAL SILVER COINS BY X-RAY SPECTRAL ANALYSIS*

A collection of 218 Roman imperial silver coins, covering three centuries, was analysed non-destructively by two variants of X-ray spectral analysis. Electron beam excitation and energy-dispersive spectrometry was used for the analysis of the uppermost thin layer (3 μm) of each coin, while X-ray tube excitation and wavelength-dispersive spectrometry was applied for the analysis of thicker layers (30 μm), Ag and Cu as major constituents and 18 minor elements were determined quantitatively. Comparing the silver content of the obverse and the reverse of a coin, inhomogeneities could be identified. By comparison of the silver content of the upper thin and the thick surface layers, near-surface silver enrichment could be detected. Inhomogeneities and enrichments increase in the second and more so in the third century. A large scatter of the silver content and silver enrichment for coins of the same emperor was attributed to varying abrasion of Ag-enriched layers of the individual coins during decades of circulation.     

A Trial PIXE/PIGME analysis of Pre-Islamic Arabian Coinage

Eight previously published (1) pre-Islamic coins minted in Arabia were subjected to non-destructive ion beam analysis by Proton Induced X-Ray (PIXE) and Gamma-Ray Emission (PIGME) at Lucas Heights. The results (2) were interpreted using Principal Components Analysis (PCA). The relative X-ray intensities of fifteen elements, supplemented with additional L alpha lines for two of the elements, were extracted for this analysis. PCA (results appended) was first carried out on the whole dataset where the distinctive high iron and nickel composition of two coins (331 and 335) resulted in their position as outliers. A second analysis of the subset of silver coins showed the compositional similarity between four coins (44, 222, 226, 359) and distinguished two separate outliers. One of these (369) has a high lead and tin content while the other (354) has a greater proportion of elements present as impurities (?) including iron and nickel. The two outliers and the relatively homogenous compositions of the group of four coins suggest that three compositional types of silver coinage are represented in the dataset: 1. a relatively silver-rich group of four coins; 2. silver coins debased with lead; and 3. silver coins debased with iron and nickel.     

THE ACCURACY OF THE SPECIFIC GRAVITY METHOD FOR THE ANALYSIS OF GOLD ALLOYS

Two possible sources of error in the measurement and interpretation of the specific gravities of gold coins are investigated. First, the effect of the presence of copper was measured and found to be more significant than previously thought. It is shown that the presence of 5% of copper in a gold-silver alloy results in a measured gold content which is 3.3% too low when the coin is analysed by the specific gravity method. Secondly, the importance of cleaning the coins before measuring the specific gravity is also demonstrated.     

北宋和南宋青铜钱币对比分析研究

宋代是我国钱币的一个大发展时期,宋代钱币在我国钱币史上占有极其重要的地位.为了解南、北宋钱币的成分、显微结构的差异对铸币保存状况的影响,通过显微镜观察、合金成分分析、显微结构分析,对南宋和北宋各21枚钱币的保存状况进行了对比分析研究,以了解这42枚钱币的锈蚀状况、锈蚀原因,以及成分、显微结构的差异对铸币保存状况的影响.同时在分析研究的过程中,对北宋、南宋钱币的合金成分、铸造工艺进行了对比研究.研究结果表明,南宋钱币的保存状况比北宋的差一些,合金成分及显微结构的差异,是导致保存状况不同的重要原因.这些钱币主要是由铜、锡、铅铸造而成,分析结果进一步证实北宋钱币合金成分比较稳定,成分配比比较科学.而南宋成分数据比较分散,早期铜、锡含量较高,铅含量较低,晚期铜、锡含量较低,铅含量明显增高,合金品质大大降低.本研究可为了解当时的科学技术、社会经济形态进一步提供基本信息.     

THE USE OF SPECIFIC HEAT IN THE NON-DESTRUCTIVE ANALYSIS OF SILVER/COPPER ALLOY COINS

Using partly plastic apparatus, specific heats of coins have been found calorimetricly to an accuracy of ± 3% for most coins. For silver/copper alloys the specific heat varies approximately linearly with the weight percentage composition, so the latter can be calculated for coins of unknown composition.     

THE CHRONOLOGY OF GROUPS OF DIES FOR LARGE ISSUES OF ANCIENT COINS USING MAHALANOBIS DISTANCES*

Discriminant analyses of distances and angles obtained from 25 coins struck by P. Crepusius in 82 BC permitted the correct chronology for five groups of closely-related dies to be obtained by the method of Carter and Frurip. Twenty distances and 15 angles were measured on 10 x projections of the coins which represented five groups of dies separated in time from each other. The use of all or many variables gave poorer results than the use of five to ten variables having a high ‘figure of merit’, defined as the maximum range of mean values for a given variable in the five groups of dies divided by the mean standard deviation of the variable in the five groups. It is recommended that chronologies of ancient coins be determined from Mahalanobis distances by using only variables of relatively high figure of merit.     

X-RAY FLUORESCENT ANALYSIS OF ANGLO SAXON JEWELLERY

X-ray fluorescence analysis of 30 pieces of Anglo Saxon jewellery, from the Ashmolean Museum, Oxford, is followed by a comparison with similar results obtained from contemporary coinage. The standards of fineness for the coinage are applied to the jewellery and used to date its manufacture. An appendix describes repeatanalyses of some coins which, at first, had widely differing results from XRF and specific gravity methods.     

QUANTITATIVE ANALYSIS OF COPPER-TIN BRONZES BY MEANS OF GLOW DISCHARGE OPTICAL EMISSION SPECTROMETRY

Glow discharge optical emission spectrometry (GDOES) has been used for obtaining calibration curves for copper, tin, lead, silver, antimony, arsenic, zinc and iron from standards including copper-base alloys (Cu 61.33-99.95%) and from bronze Punic coins. The GDOES results were calibrated using atomic absorption spectroscopy with inductively coupled plasma atomization (ICPAAS) to analyse the standards and coins. For all these materials, the results show that via GDOES it is possible to obtain reliable and reproducible calibration curves for copper, tin, lead, zinc and iron with a linear behaviour as a function of the content. The quantitative GDOES and ICPAAS data for the coins have been also compared with those obtained via X-ray fluorescence (XRF) and it is shown that GDOES, ICPAAS and XRF agree well with one another considering that the bronze coins are inhomogeneous to some degree. As an example of GDOES analytical features, a depth concentration profile through a thin bronze patina is shown and briefly discussed.     

ROME AND THE EAST. PRODUCTION OF ROMAN PROVINCIAL SILVER COINAGE FOR CAESAREA IN CAPPADOCIA UNDER VESPASIAN, AD 69–79

During the first three centuries AD several eastern provinces of the Roman empire produced silver coinages of specifically local denominations and types. It has been claimed that at certain periods the mint of Rome was employed to strike some of these coinages, rather than the provincial mints to which the coins are traditionally attributed. This claim is based mainly on stylistic observations, but because style is regarded as subjective, some other form of evidence to support these observations is desirable. In this paper three types of coin are submitted to metallurgical analysis: silver denarii struck at Rome; Roman-style provincial silver coinage; and 'local'style provincial silver coinage. The aim is to discover whether the Rome-style and 'local'style coins have different trace element profiles, and whether these might indicate different ore sources or refining techniques. The results are then compared with Roman denarii to see whether there are any similarities between the denarii and the Rome-style provincial silver coins.     

AN ANALYSIS OF THIRTY-ONE COINS FROM THE HELLENISTIC PERIOD

Thirty-one silver coins of the Hellenistic period were examined by the particle induced X-ray emission (PIXE) method, and the results incorporated into a wider study of the coins. Some tentative conclusions reached in the study are mentioned, together with an outline of the PIXE method. A number of patterns emerged in the results, the most important being an apparent deterioration in silver content among the later Seleucid and Ptolemaic issues; some high concentrations of particular elements were also noted.     

ION BEAM ANALYSIS OF COPPER AND COPPER ALLOY COINS

In recent years ion beam techniques have become more and more important since in most cases the analysis of copper and copper alloy coins has to be non-destructive. It is therefore of interest to study the relative advantages of several nuclear methods for a certain type of metal. The results are presented here of a comparison between three non-destructive ion beam techniques: particle induced X-ray emission, proton activation analysis and fast neutron activation analysis.     

Chronological discrimination of silver coins based on inter‐elemental ratios using laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS)

This paper details the application of a statistical method for the chronological discrimination of silver coins using counts per second trace elemental, inter‐elemental ratios. The statistical method described is based on a method that has been applied to similar archaeological materials to determine their provenance. The method makes use of the inter‐element association patterns of multi‐element analytical data determined using laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS). The majority of the 266 coins analysed for this study have already been successfully identified by their mint markings. The data from LA‐ICP‐MS analyses, together with what is known about the coins through visual identification, were used to discriminate the reigning sovereign, and in the case of Mexico, the year of minting, of individual coins within the elemental fingerprint of different mints. Subsequently, unidentified coins can be placed in the confusion matrix, and their trace element information used to identify their year of minting when compared with other, identified coins from the same mint. The interpretational statistical technique linear discriminant analysis (LDA) was used to explore an identification of year of minting of coins that have previously not been identified by other means based on a statistical comparison against a database of compositional analysis of silver coins of known year of minting.     

NON‐DESTRUCTIVE CHEMICAL ANALYSIS OF OLD SOUTH ARABIAN COINS,FOURTH CENTURY BCE TO THIRD CENTURY CE

Studies on Old South Arabian (OSA) coinage are rare and state‐of‐the‐art materials analysis for them lags far behind that of ancient Greece and Rome. Understandably, numismatists responsible for preserving their collections discourage destructive analyses. We have selected coins of the aesthetically and technically developed Himyarite Royal Raydan series (early first to late second century ce ), so‐called Old and New Style Athenian Imitations, among others to provide a wide spectrum of information on OSA coinage. We used non‐destructive neutron diffraction to ascertain the metal compositions and corrosion products. Density determinations using gas‐pycnometry support these experiments. The results provide detailed information with regard to a small, apparently homogeneous, selection of 10 Himyarite period specimens and first insights into the actual and the original metal compositions of about 90 coins of the three main OSA numismatic groups. The analytical results make clear which OSA coins originally were struck and which ones were cast. The analyses provide not only detailed information concerning the manufacture of the selected representative coins, but also suffice to cast a shadow on the reliability of commonplace macro‐optical classification, which proves often to be inaccurate.