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Message:: [QUOTE="KurtS, post: 2253329, member: 11786"]The author of this analysis, Rasiel Suarez, has directly given me permission to publish this article on CoinTalk. The author's full title is "A metals analysis of silver Roman imperial coins using X-ray fluorescence spectroscopy." If  you have access to Academia.edu, you can read the entirety <a href="https://www.academia.edu/9159193/A_metals_analysis_of_silver_Roman_imperial_coins_using_X-ray_fluorescence_spectroscopy" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://www.academia.edu/9159193/A_metals_analysis_of_silver_Roman_imperial_coins_using_X-ray_fluorescence_spectroscopy" rel="nofollow">here</a>, including the methodology and calibration--which I'll leave out below in the interest of space. Questions about these analyses should be directed to the author--PM me for his email address. <img src="styles/default/xenforo/clear.png" class="mceSmilieSprite mceSmilie1" alt=":)" unselectable="on" unselectable="on" /> AbstractAn overview of the compositional makeup of silver Roman coins sheds light on a number of poorly understood areas. Contrary to popular belief, the debasement of the Roman denarius was not as linearly progressive as had been initially believed. The testing performed also shows an apparently unrecorded method of counterfeiting late Roman silver coins as well as a blueprint for using this technology as a means to detect forgeries. IntroductionA number of studies have been performed on ancient coins to determine the composition of their alloys using a variety of means. One of the most popular has been X-ray fluorescence spectroscopy (XRF). However, as the process is both expensive and time-consuming the studies have generally been limited in scope. As a result, numismatic researchers have needed to piece together the published data to form a cohesive understanding of the various alloys in use. Gaps in the data have been filled in through extrapolation or speculative hypotheses and where published data conflicts, as is to be expected from disparate methodologies and equipment used, reconciling the differences has resulted in controversy. Equipment and MethodologyFor the purposes of the analyses an Olympus DELTA Professional handheld gun was employed. This late-model unit comes with a 40kV X-ray source and utilizes a silicon drift detector along with multiple ionization beams for its readings. The beam area focus was approximately 10mm. <blockquote>Here I will snip out a lengthy discussion of calibration. If you want to read it, go to the link above or PM me for the complete report in pdf. </blockquote> ResultsA total of 162 Roman and Byzantine coins were analyzed. The amount of information obtained defies any easy way to portray the data holistically and, in fact, lends itself well to having different aspects published separately. The primary focus on the present paper therefore will be to show the purity of the silver and copper coinage in a chronological timeline. <blockquote>Here I snip out a discussion of calibration and detectable silver content as it pertains to the surfaces of worn versus "MS" silver Roman coins, with results displayed in fig. 1. He concludes that: "We should therefore allow a ±5% margin of error when taking into account the of the readings of 84 individual coins dating from approximately 1 CE to 293 CE."</blockquote> In Fig. 2 we can finally appreciate the true extent of the degradation of the denarius and its successor, the antoninianus. The intentional debasement with copper begins in 64 CE at an estimated 1 to 20 ratio and this amount is slowly but steadily increased over the next century. It acquires a critical juncture sometime during the reign of Commodus at which time the amount of silver per coin undergoes a much more rapid decline. However, this debasement is not as linearly progressive as once thought with the fineness frequently bouncing back before a new cycle of debasement would plumb new lows. <img src="https://c1.staticflickr.com/1/666/22206990005_56de63d063_o.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /> If we take a closer look at the above data, in Fig. 3 we find that for the first two centuries of the imperial era, and despite Nero’s deliberate debasement of the denarius, only a very gradual down slope begins to develop. In fact, the silver content remains quite stable and at no point falls below what would be the equivalent today of sterling silver at 92.5%. This, however, is a snapshot of higher grade coins. A look at a worn denarius of provincial mintage dating to 68 CE reveals an interior reading of only 91.46% and several second-century worn denarii, as revealed in Fig. 1, were also found to have a silver content barely reaching the 90% mark. If we make the assumption that when they were in like new condition they should have tested 3% higher in fineness we would still be slightly short of the norm so either these are exceptional or the model needs to be less conservative to maintain the integrity of the findings. As stated before though, the 5% allowance is sufficient to cover these small deviations. <img src="https://c2.staticflickr.com/6/5674/22217311041_d6d58362b8_o.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /> A glance at Fig. 4 below however shows us a chaotic third act for the denarius and the antoninianus clearly showing a jumble of peaks and valleys within short spans of time. The critical point is reached during the decade of the 260s at which point the level of silver has reached such a low amount that what little remains is reserved for an aesthetic coating with a nearly fully debased core composed primarily of copper, though here with a rising trend in the content of lead, tin and other metals Fig. 5. <img src="https://c1.staticflickr.com/1/595/22019211438_83239224cd_o.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /> <img src="https://c2.staticflickr.com/6/5723/21585969273_ed7a5d35e4_o.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /> After the collapse of the silver coinage a new high-purity coin is introduced in 294 CE but it too rapidly succumbs to the ravages of inflation until, as before, it remains only at trace levels. While high quality silver coins will be sporadically minted from this point forward most will be issued in extremely limited circumstances as ceremonial distributions. Silver coinage will not circulate to any great extent until a new denomination, the siliqua, is mass-produced towards the middle of the fourth century. Unfortunately, an insufficient number of these coins were available for this study. All the same, a look at the few tested hints at significant debasement as Rome’s economy continued to falter (Fig. 6) but the most surprising revelation is the previously unknown use of a tin-copper-antimony alloy as a faux stand-in for silver (Fig. 7). <img src="https://c2.staticflickr.com/6/5777/21585969153_440ca04d9b_o.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /> <img src="https://c2.staticflickr.com/6/5642/22018909040_0554ca1fca_b.jpg" class="bbCodeImage wysiwygImage" alt="" unselectable="on" /> Addressing the issue of counterfeiting, XRF is quickly gaining ground in archaeometry as an important tool in revealing ancient and modern deception schemes alike. The opportunity to study samples of these was limited in this case to just three coins. A Caligula denarius of good imperial style and showing considerable circulation wear, which was already suspected of being a silver-plated contemporary copy due to a small but telltale surface break, was confirmed as such when the XRF reading showed an anomalously low silver content of 89.55%. Two denarii, a Marciana and a Pertinax, both particularly desirable by collectors for their rarity, of reasonably good design and carefully weathered to conceal their inauthentic nature, were quickly unmasked by the analyzer which reported unacceptably low readings of 82.00% and 80.09%, respectively. ConclusionThe steady decline in the fineness of the silver used in the denarius had been known well before the advent of analytical equipment able to confirm this. However, where the decline had been suspected of occurring at a measured pace this study shows only modest drops in the fineness during the first and second centuries. This much more closely correlates to the historical period when the Roman economy was at its strongest. The integrity of the coin then begins to quickly fall apart over the course of half a century until the nominally silver coinage had but traces of this metal left. While the trend is inexorably towards decreasing silver content many individual issues prove to have anachronistically high levels of silver; perhaps due to abortive policy attempts at stalling inflation but possibly simply explained as inconsistencies in the available supply and shoddy quality control.While admittedly not a conclusive standalone tool, the use of XRF analysis proves its worth in telling apart counterfeit coins from genuine ones whether ancient or modern in origin.AcknowledgementsThe author would like to show his deep appreciation to Olympus for providing the generous loan of the analytical equipment used in this test. ReferencesA. Italiano, L. T. (n.d.). A comparative analysis of old and recent Ag coins by XRF methodology. ESE - Salento University Publishing.Carter G. F., K. M.-B. (1978). Chemical Compositions of Copper-Based Roman Coins. V. Imitations of Caligula, Claudius and Nero. Revue numismatique, 6e série - Tome 20, 69-88.L. Beck, S. B. (2004). Silver surface enrichment of silver–copper alloys: a limitation for the analysis of ancient silver coins by surface techniques. Elsevier B.V.Wanhill, R. J. (2001). Microstructurally-induced embrittlement of archaeological silver. Amsterdam, Netherlands: National Aerospace Laboratory NLR. The coins used in testing are available for further study online (contact me for the link)[/QUOTE]

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