Ancient coin

A specific feature of the CEMS technique is the possibility for nondestructive testing of the surface composition of paintings, ancient coins, and pottery or other valuable objects. Wagner et al. [445] have investigated Celtic gold coins (from the time period 480-15 b.c.) and have shown that the surface of the coins consist of two phases, one of which is strongly eiuiched in gold compared to the bulk composition. 

The reluctance of museum curators and collectors to allow permanent damage to antiquities was, until not long ago, the main reason for the small amount of analytical work done on ancient coins. This was understandable since performing chemical analysis required removing a sample from the coin or damaging its surface, which meant either the destruction or defacement of, at least, a portion of a coin. More recently, however, a number of nondestructive methods of analysis such as neutron activation, X-ray fluorescence, and some techniques of surface analysis have been successfully applied to obtain information about ancient coins and the people and societies involved in their production (Carter 1993 Barrandon et al. 1977). 

Proton activation analysis (PAA) provides chemical composition of the materials at a depth of 300-500 pm under the irradiated surface. This technique has been used in the study of metallic objects such as ancient coins [27]. 

Beck L, Alloin E, Berthier C, Reveillon S, Costa V (2008) Silver surface enrichment controlled by simultaneous RBS for rehable PIXE analysis of ancient coins. Nucl Instmm Methods Phys Res B 266 2320-2324. 

Brill, R. H., Shields, W. R., Lead Isotopes in Ancient Coins, in Methods... 

Sayles, W. G. Ancient Coin Collecting Vl Krause Publications Iola, WI, 1999 pp 111-112. 

Chinese and Japanese bronze mirrors dating from the first, fifth, seventh, eleventh, and twelfth centuries have been found to contain between 62 and 74 per cent, of copper associated with other metals. A Corean mirror of the tenth century contains 73 per cent, of copper, and considerable proportions have been found in ancient coins, arrow-heads, and water-pots from these lands.5... 

Carter, G. F., Preparation of Ancient Coins for Accurate X-Ray Fluores-... 

Ancient coinage may be considered a special class of archaeological metal but it has been so extensively investigated that it deserves separate consideration. Here again we must pay tribute to Klaproth as a pioneer in that not only was he the first to analyze ancient coins, but in fact invented the method of quantitative metal analysis to do so, and this in the 18th century ... 

The work of Ambrosino and colleagues has already been mentioned. The early volumes of the journal Archaeometry (first published in 1958) also contain some exploratory research on the application of NAA to the problem of coin analysis. Kraay and Emeleus at Oxford realized that NAA was a very practical solution to one of the requirements of ancient coin analysis, and that was, for the rare and most valuable specimens at least, that it be totally non-destructive. They also quickly discovered another benefit because neutrons activated the whole coin, they provided a bulk analysis as opposed to x-ray fluorescence, which gave only the surface composition. They found that a Corinthian coin, thought to be silver, was in fact silver-plated over a copper core. For precise NAA studies, the self absorption of neutrons in solid gold coins requires a substantial correction to the flux. Self absorption in silver, less serious has also been investigated (see below). 

The Unisantis XMF-104 X-ray microanalyzer (Unisantis S.A., www.unisantis.com) was used by researchers at the Institute for Roentgen Optics, Moscow, Russian Federation, to examine nonde-structively the composition of ancient coins from the fourth century BC through the second century AD. The fourth century BC coins were found to be an alloy of 82% Ag/18% Cu, but areas of pure Ag showed the inhomogeneity of the alloy. A drachma coin depicting Alexander was composed of 99% Ag/1% Cu. The XMF-104 system had a 50 W Mo tube, a 2-stage Peltier-cooled compact Si-PIN detector and polycapillary focused X-ray beam with a 50-250 pm focal spot. Spectra, images of the coins, and details are available at www.unisantis.com, application note 605. 

In some cases, activation analysis may be regarded as a nondestructive method, i.e., the sample is not significantly altered, neither visually nor chemically. This attribute is obviously exploited in the aforementioned sequential multielement determinations. It is a valuable characteristic for situations where the sample needs to be preserved, such as forensic objects or irreplaceable historical samples, such as ancient coins or paintings. For general analytical practice, this valuable feature can allow reactivation for the determination of additional elements or for full reanalysis, as well as the use, with appropriate precautions, of another analytical method. 

Talib, D., Ma, R., McLeod, C.W., Green, D. (2004) Multielement analysis of modern and ancient coins using diamond lapping film and laser ablation ICP mass spectrometry. Canadian Journal of Analytical Sciences and Spectroscopy, 49(3), 156-165. 

Analysis of modern and ancient coins using diamond lapping film Nd YAG 266 nm ICP-Q-MS Quantitative analysis of bronze coins using diamond lapping film for in situ microsampling Talib et al. [49]... 

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