Identification of parameters useful for the identification of fakes of metal artefacts of archaeological interest - Identificazione di osservabili utili all'individuazione di falsi nell'ambito del reperti metallic di interesse archeologico

The problem of the identification of counterfeited artefacts of artistic and archaeological interest is of outstanding importance in the management and safeguard of Cultural Heritage, because of the implications, also of juridical nature, deriving from the circulation and trade on the world market of these artifacts, in high percentage coins and jewels. With this consideration in mind, the ultimate goal of this study, the design of an analytical-informatic movable apparatus for the identification of the authenticity of metal artifacts, may be proposed to the justice system, to police forces, to auction houses and antiquaries, due to the high amount of the international trade of metal artifacts. The trade of artifacts, in particular coins and jewels, involves a tremendous amount of money with a relatively high probability of buying a fake or a counterfeited object; moreoever the production of copies of luxurious, rare and expensive artefacts has been recently increased and more and more sophisticated technologies have been employed thus increasing the difficulty of identifying the fakes. Up to now this validation is carried out by rare and scarcely available experts that use a simple visual observation. The design of a movable apparatus, that includes different analytical techniques to be used for acquiring microchemical, micromorphological and microstructural data and handling the scientific and historical information, may improve the authentication capability. The various steps of this interdisciplinary study may be divided into partial objectives: 1. identification of chemical-physical parameters, typical of ancient and modern original artifacts and of fakes, to be employed in the determination of the authenticity of artefacts 2. selection of historic-artistic information useful for the identification of original and counterfeited artifacts 3. design of the software for the acquisition and treatment of data organized in a data base 4. design of the hardware components also for optimizing the geometry of the various analytical techniques Some preliminary results obtained on a series of coins are shown. The study has been carried out on coins of the Museo Nazionale Romano, where are collected more than 500.000 coins from ancient to modern ages and also copies af different ages together with a collection of minting dies produced by coiners between XVIII and XIX centuy. Different kinds of fakes have been considered for the characterization. There are interesting examples of fakes produced by the official mints sometimes contemporaneously to the originals, as suberatii, Roman coins with the core of copper covered by a thin silver layer. There are modern fakes produced in order to cheat the purchasers, some of them are coarse counterfeits addressed to incompetent tourists, others are produced by skilled artists able to produce and to age artifacts, difficult to recognize by a visual examination. By means of different analytical non-destructive techniques, some microchemical and microstructural parameters have been identified. If the counterfeits are more accurate, more sophisticated analytical techniques have to be utilized, in order to evidence the microchemical and microstructural features of the production processes and of the interaction with the environment. For example the presence in the corrosion products layers of silicates, phosphates, carbonates, etc., could be indicative of slow interaction processes between the metallic artefacts and the soil, while the presence of selenium compounds, unknown element in antiquity, the presence of sulphates on artifacts coming from archaeological excavations are oftern indicative of fakes. The presence of stratified corrosion layers, as shown in the cross-section of the bronze coins, is indicative of its authenticity; as shown by XRD analysis in contact with the core metal there is cuprite (Cu2O), on top of it, tenorite CuO, malachite Cu2(OH)2CO3 and azzurrite Cu3(OH)2CO3. Other corrosion products may be present: calcocite Cu2S, bornite Cu5FeS4, covellite CuS, athacamite Cu2(OH)3Cl, nantokite CuCl, brochantite Cu4(OH)6(SO)4, calcantite CuSO4.5 H2O, smithsonite ZnCO3, romarkite SnO, cassiterite SnO2.

Lo studio verte sull'identificazione di possibili osservabili chimico-fisici quali dati microchimici, elettrochimici, microstrutturali e micromorfologici di superficie, specifici e di riscontro esclusivo o in manufatti metallici originali o in manufatti falsi e/o contraffatti. La presenza di tali osservabili viene identificata e discussa anche in base a considerazioni sulle antiche metodologie di produzione e lavorazione dei metalli oltre che in base a considerazioni storico-archeologiche. La ricerca è finalizzata alla progettazione di un apparato analitico-informatico che permetta l'acquisizione e l'elaborazione di dati utili alla determinazione dell'originalità dei manufatti metallici mediante la scelta delle caratteristiche analitiche e strumentali. Vengono qui di seguito presentati i risultati ottenuti su monete conservate al Museo Nazionale Romano, dove sono presenti oltre alle monete autentiche di età antica, medioevale e moderna, anche riproduzioni di monete di epoca antica e di età moderna.