Contribution of surface analytical techniques for the microchemical study of archaeological artefacts

Synergistic Inhibition Effect of Chitosan and L-Cysteine for the Protection of Copper-Based Alloys against Atmospheric Chloride-Induced Indoor Corrosion

The protection of metals from atmospheric corrosion is a task of primary importance for many applications and many different products have been used, sometimes being toxic and harmful for health and the environment. In order to overcome drawbacks due to toxicity of the corrosion inhibitors and harmful organic solvents and to ensure long-lasting protection, new organic compounds have been proposed and their corrosion inhibition properties have been investigated. In this work, we describe the use of a new environment-friendly anticorrosive coating that takes advantage of the synergism between an eco-friendly bio-polymer matrix and an amino acid. The corrosion inhibition of a largely used Copper-based (Cu-based) alloy against the chloride-induced indoor atmospheric attack was studied using chitosan (CH) as a biopolymer and l-Cysteine (Cy) as an amino acid. To evaluate the protective efficacy of the coatings, tailored accelerated corrosion tests were carried out on bare and coated Cu-based alloys, further, the nature of the protective film formed on the Cu-based alloy surface was analyzed by Fourier-transformed infrared spectroscopy (FTIR) while the surface modifications due to the corrosion treatments were investigated by optical microscopy (OM). The evaluation tests reveal that the Chitosan/l-Cysteine (CH/Cy) coatings exhibit good anti-corrosion properties against chloride attack whose efficiency increases with a minimum amount of Cy of 0.25 mg/mL.

Microchemical, structural and mineralogical study of ancient Moroccan pyrometallurgical remains and data sharing through the support of a QGIS software

The mining areas of the Middle Atlas, already inhabited in the Neolithic period, have been under the influences of different cultures, firstly Phoenician, then Punic or Ibero-Punic, Berber, Roman and finally Islamic. The impact of external cultures on the evolution and development of ancient metallurgy in the north-central Atlas region and the Southern Rift occurred since prehistoric times to Arab domination in the Middle Ages. This study proposes the development of an up-to-date protocol for archaeometallurgical investigation, based on the correlation between the chemical-physical analysis of the pyrometallurgical materials and the contextual systematic geoarchaeological excavations. The microchemical analysis has been carried out on opportunely selected pyrometallurgical materials, coming from different mining areas of the Middle Atlas regions in Morocco (Tabarouch for Cu and Aouam for Pb/Ag) in order to understand the evolution of the technological knowledge in archaeometallurgical work of local people. After that, the analytical results have been included in a Geographic Information System (GIS) software with the aim of creating an easily usable database that will support multidisciplinary research on the ancient metallurgical activities also with its future development and implementation. The GIS application could indeed correlate all the data coming from different extraction/work sites, present in the exploited mining veins. Furthermore, the GIS application is a starting point for an integrated study of the different mining archaeological sites in the Mediterranean basin proposing an innovative method of data exchange of archaeological, physical and geological chemical results.

Rebuilding of the Burial Environment from the Chemical Biography of Archeological Copper-Based Artifacts

The long-term interaction between Cu-based alloys and environmental species gives rise to the formation of different and sometimes unusual compounds (i.e., the patina) with distinctive chemical and structural features as a function of the peculiar characteristics of the context. In this paper, we describe some representative case studies concerning degraded bronze Roman valuable or common use objects, and we show that an attentive study at a microscale level, as for forensic analysis, allows one to understand the chemical processes that underlie the formation of the surface alteration products. The achieved information describe fragments of chemical life and disclose the complex chemical changes suffered by the artifacts, allowing one to write their chemical biography. This challenging approach expands the panorama of available information and demonstrates that it is possible to reconstruct the different modes through which the bronze surfaces and interfaces have interacted with environmental species, organic matter, and microorganisms, opening up a new possibility to describe complex environmental chemical stories, in certain cases interrelated.

Ancient mercury-based plating methods: combined use of surface analytical techniques for the study of manufacturing process and degradation phenomena

Fire gilding and silvering are age-old mercury-based processes used to coat thesurface of less precious substrates with thin layers of gold or silver. In ancient times, these methods were used to produce and decorate different types of artefacts, such as jewels, statues, amulets, and commonly-used objects. Gilders performed these processes not only to decorate objects but also to simulate the appearance of gold or silver, sometimes fraudulently. From a technological point of view, the aim of these workmen over 2000 years ago was to make the precious metal coatings as thin and adherent as possible. This was in order to save expensive metals and to improve the resistance to the wear caused by continued use and circulation. Without knowledge about the chemical-physical processes, the ancient crafts-men systematically manipulated these metals to create functional and decorative artistic objects. The mercury-based methods were also fraudulently used in ancient times to produce objects such as jewels and coins that looked like they were made of silver or gold but actually had a less precious core. These coins were minted by counterfeiters but also by the official issuing authorities. The latter was probably because of a lack of precious metals, reflecting periods of severe economic conditions. In this Account, we discuss some representative cases of gold- and silver-coatedobjects, focusing on unique and valuable Roman and Dark Ages period works of art, such as the St. Ambrogio's altar (825 AD), and commonly used objects. We carried out the investigations using surface analytical methods, such as selected area X-ray photoelectron spectroscopy and scanning electron microscopy combined with energy-dispersive spectroscopy. We used these methods to investigate the surface and subsurface chemical features of these important examples of art and technology, interpreting some aspects of the manufacturing methods and of disclosing degradation agents and mechanisms. These findings may contribute to cultural heritage preservation, thus extending the applicability of the surface analytical techniques.