Magnetic properties of ancient coins

The almost ubiquitous presence of small amounts of iron in ancient coins gives them remanent magnetic properties which can be measured easily on commercial magnetometers. The stability of the remanence suggests that ancient coins might retain information about the geomagnetic field at the time and location of manufacture and so be valuable in setting up archaeomagnetic dating curves. However, measurements show that the remanence directions tend to be too scattered for this purpose, although it is quite possible to distinguish magnetically the obverse and reverse faces of struck coins.Saturation remanence studies of coins and coin analogues indicate that the main carrier of the remanence in struck coins is precipitated fine-grained iron (rather than the oxides of iron) which is produced during the minting process. The intensity of the remanence generated depends upon the thermo-mechanical history of the flan prior to striking, which suggests that the magnetic properties of such coins are not simply related to the provenance of the ores used.     

Plated Iron Age Coins: Official Issues or Contemporary Forgeries

This paper discusses different explanations that have been proposed to account for the existence of plated Iron Age coins, some of which appear to have been struck from the dies used to produce solid metal coins. Evidence occasionally preserved on plated coins proves that at least some of them were struck from dies which had been hubbed from solid metal coins, and it is these solid metal coins that were struck from the dies which the plated coins appear to have been produced from. It is argued that this evidence demonstrates that plated Iron Age coins are merely contemporary forgeries.     

Some medieval Yemenite numismatic problems – observations on some recently sold coins

The article addresses some of the problems arising from the publication of a recent numismatic catalogue including coins from all parts of the Islamic world. The problems concern in particular the coins of the medieval Yemen and the article comprises a critique of those coins listed under the Arabian peninsula and the Yemen.
Catalogue nos. 101 and 104 are dealt with in some detail since they are erroneously ascribed to mints in Mecca and Minā, respectively. The former is struck in the name of a Zaydī imam, the latter is Rasulid and labelled as having been struck "for a special occasion". The intriguing question of the mysterious Ayyubid prince, al-'Ādil Abū Bakr, arises too (nos. 125 etc.), although no definitive answer can yet be suggested. Much more information is now available on the striking of coins in Tha'bāt during Rasulid times. A number of other points bearing on the numismatics, the history, and the geography of the medieval Yemen are discussed in the article.     

THE COMPOSITION OF IRON AGE STRUCK 'BRONZE'COINAGE IN EASTERN ENGLAND

EDXRF was used to analyse the composition of 88 Iron Age copper and copper alloy coins excavated from the site of a pre-Roman shrine and Roman temple at Harlow, Essex. Most of the coins are local to the Essex-Hertfordshire region, with a few of Kentish origin. The earliest struck base metal issues were struck from almost pure copper, but from the late first century BC, their composition shows more variety. Particularly interesting are a group of types belonging to the Romanizing phase of Tasciovanus'coinage, which were struck in brass and possibly represent a distinct denomination. Roman coinage and other metalwork imports from the Roman world presumably provided the initial impetus, and the ultimate source of the brass. However, this experiment was relatively short lived. Cunobelinus, who ruled eastern England during the earlier first century AD, mainly employed bronze to strike his abundant base metal coinage. The products of his Colchester mint reveal a consistently different composition from those struck at his unlocated second mint in the Hertfordshire area, although the precise alloy does vary, sometimes within the same type. This suggests that unlike gold and silver issues, the source and purity of the metal used for minting base metal coinage was not always critical.     

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.     

Yoram Tsafrir,B.A., M.A., PhD (30 January 1938–23 November 2015)

Abstract

The coins attributed to Alexander Jannaeus include a very common type that was apparently struck during the last four years of his 27-year reign, or possibly after his death. The presence or absence of these common coins, at sites where there is a relevant gap in the sequence of the numismatic archaeological finds, can sometimes indicate whether the site was destroyed and abandoned for a period at the end of the second century and/or during the first half of the first century B.C.E. Analysis of this presence or absence can also, in some instances, help to resolve a long-standing question about the attribution of certain other Hasmonean coins to Jannaeus. These contentions are demonstrated through case studies of the numismatic finds at Samaria, Pella, Bethsaida, Khirbet esh-Shuhara, and Gibeon.     

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.     

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.     

Experimental Heating of Moravian Cherts and its Implication for Palaeolithic Chipped Stone Assemblages

The applicability of colour, magnetic susceptibility and remanent magnetization measurements for the identification of heated or accidentally burned Palaeolithic cherts from Moravia (Czech Republic) is tested in this study. We conclude that all these methods are usable. Colour changes are best detectable in materials heated at between 250–350°C, while magnetic susceptibility and remanent magnetization change at higher temperatures, closer to 600°C. This latter temperature, however, is usually destructive for cherts and is probably evidenced by accidentally burned artefacts. With the use of the three methods, we managed to identify three probably heated chert artefacts from two early Upper Palaeolithic assemblages from Moravia.     

The 'folded flan' coinage of eastern Arabia: Some preliminary comments

In recent years a small number of peculiar coins has emerged from the southern shores of the Persian/Arabian Gulf imitating Athenian tetradrachms of the old style and sharing the oddity of being struck on a flan that had been folded before striking. This paper contains an overview of the pieces known so far and attempts to present some preliminary conclusions, while still awaiting a comprehensive study of this and related ancient coinages of the Arabian peninsula.     

Magnetic Alteration of Soils by Late Holocene Hunter–Gatherer Groups (Tierra Del Fuego,South America)

The present work aims to analyse the magnetic signature from the Late Holocene open‐air archaeological deposits of hunter–gatherer ephemeral occupations. For this purpose, two profiles were sampled at the Marazzi 2 site in the north‐western Isla Grande de Tierra del Fuego, Chile, in order to carry out studies of magnetic susceptibility, hysteresis cycles, back‐field remanent magnetization, isothermal remanent magnetization and thermal variation of magnetic susceptibility at high and low temperature. Despite short‐term occupations, the P1 profile shows a magnetic peak at a depth of ~30–70 cm due to magnetite, probably formed by anthropogenic activity related to combustion. The P2 profile instead yields an anomalous peak of coercivity (at a depth of 20–40 cm), which could also be anthropogenic, due to the presence of finely dispersed ancient ‘red ochre’. The red ochre is proposed to form anthropogenic thermal alteration of goethite associated with volcanic ash, the remnants of which were found in thin sections from the P2 subsoil.     

PALAEOMAGNETIC STUDY OF HOXNIAN LACUSTRINE SEDIMENTS

The remanent magnetization of samples spanning Zones I to III of the Hoxnian Interglacial at Hoxne has declination values that lie within 30° of the present-day declination, and inclination values that are not more than 10° steeper or 20° shallower than the present-day inclination.     

AN ARCHAEOMAGNETIC STUDY OF POTTERY KILNS FROM BRÜHL-PINGSDORF (GERMANY)*

Four pottery kilns from Brühl-Pingsdorf (Germany) were dated by comparing their characteristic remanent magnetization with a curve of the palaeo-secular variation of the geomagnetic field. Archaeomagnetic results suggest last heating events between AD 775 and 1020. The archaeological evidence generally supports the relative temporal succession and the duration of use, but indicates that the kilns are about 150 years younger on average. Hence, a systematic offset between these independently developed chronologies must be considered. Rock magnetic parameters display radial variations through the kiln walls. These variations are controlled by the maximum temperature the rock was exposed to. These parameters were used to identify specimen which acquired a thermoremanent magnetization.     

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.     

云南香格里拉迪庆藏族自治州博物馆藏币的科学分析

为了解西藏钱币的制作工艺,采用金相显微镜组织观察和扫描电子显微镜分析的方法,对云南香格里拉迪庆藏族自治州博物馆收藏的五枚藏币样品进行分析。分析结果表明,五枚藏币可以分作两类,一类为铜质,一类为银铜合金。铜质钱币为含铜率高达99%,可以判定为纯铜制品;银铜合金币的配比基本符合"银八铜二"的合金化的要求。五枚钱币全部采用机械冲压制作,符合当时社会的生产动力变化。本研究成果对进一步研究西藏地区钱币的工艺技术有一定价值。     

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.     

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.     

Palaeomagnetic dating of fluid-flow events in dolomitized rocks along the Highland Boundary Fault, central Scotland

Palaeomagnetic and geochemical studies of Cambrian–Ordovician serpentinite in the Highland Border Complex (HBC), a tectonic terrane along the Highland Boundary Fault (HBF) in Scotland, indicate that the HBF was a conduit for fluids in the Carboniferous–Permian. The fluids caused dolomitization, silicification, and haematite authigenesis. Both red dolomitized serpentinite and relatively unaltered serpentinite were sampled at multiple localities. The unaltered serpentinite contains a poorly defined magnetization with westerly declinations that resides in magnetite and has a pole which plots well off the apparent polar wander path. Most specimens of the red dolomitized serpentinite contain a magnetization with southerly declinations and negative inclinations that resides in haematite. A regional fold test suggests that this magnetization post‐dates tilting and the pole positions for the different locations fall on the Carboniferous to Permian part of the apparent polar wander path. In some specimens of red dolomitized serpentinite, alternating field (AF) demagnetization prior to thermal treatment removes a component with a similar direction. Dolomitized basement rocks along the fault contain a similar although apparently slightly older magnetization. Fluid inclusion and geochemical studies indicate that the fluids were hydrothermal in origin (110–240°C) and had a range of sources. The Carboniferous–Permian magnetization in haematite is interpreted as a chemical remanent magnetization that formed when warm fluids moved along the fault zone and caused haematite authigenesis. The component removed by AF treatment is interpreted as a thermal resetting of primary magnetite by the fluids. The variability of the palaeomagnetic, fluid inclusion, and stable isotope results suggests that there were probably multiple flow events that caused the alteration. The origin of the fluids could be related to the intrusion of late Carboniferous dikes in central Scotland and/or to reactivation of the HBF in the Carboniferous–Permian.     

A coin in the name of Hawfi'amm Yuhan'im and the sequence of Qatabanian coinages

The author presents the first known coins in the name of Qatabanian kings Hawfi'amm Yuhan'am and his son Shahr Yagul. While the first coin is a transitional issue linking earlier Qatabanian coins to the so-called Royal HRB series, the second coin represents the first issue of the Royal HRB series. The numismatic dating of both coins is in agreement with dates provided by K.A.Kitchen for both kings.