Advanced Analytical Methods and Technologies for the Conservation, Diagnostics and Archaeometry of Copper-based heritage items

The study of ancient metals is of great importance, given the interest they present from many point of view, from production technology and corrosion science, to the history of society and economy. In particular, archaeological copper-based alloys have so far attracted only little attention from the Cultural Heritage science community, despite being extremely abundant in our historical heritage and presenting major scientific challenges to be addressed. Their strong opacity of copper-based materials towards optical probes, the extreme complexity risen by metallic bulk and corrosion features make their investigation extremely challenging by non-invasive means. The missing knowledge about their corrosion mechanisms and the inability to define the conservation status of each single item in a time-efficient and non-invasive way makes even the formulation and implementation of tailored protective treatments tricky and inconsistent. On top of this, there is the fact that copper-based items are found in enormous amounts during archaeological excavations, also determining concern on the management and handling of such number of artifacts. This research successfully responds to these challenges starting from the observation of real current practise and of the current limitations in protection and investigation of archaeological metals, and then pushing the technological limit towards new standards. More in detail, this has been achieved by exploiting advanced analytical techniques for the study and long-term preservation of archaeological copper-based objects, defining new protocols, designing new experimental procedures and hardware components, and proposing a different approach for their conservation. In particular, a new XCT-based protocol for the rapid investigation of archaeological copper-based coinage is tested. A new form of silver corrosion, never identified before on ancient metals, is observed and deeply investigated by making use of X-ray Photoelectron Spectroscopy (XPS) and Scanning Photoelectron Microscopy (SPEM). Focused Ion Beam coupled with SEM (FIB-SEM) is here used for the first time to produce deep trenches, in order to attain subsurface and near-bulk information in a micro-invasive way. Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS) is also applied to the same goal, and its potential and limitations are highlighted. Towards conservation purposes, both the preparation of mock-up samples mimicking burial conservation conditions, and the testing phase through Electrochemical Impedance Spectroscopy (EIS) are addressed. In particular, a new EIS setup specifically devoted to archaeological copper-based items is designed and tested, allowing for the totally non-invasive investigation of the residual corrosion activity on highly corroded artifacts. Finally, the design of an oxalic acid-based protective treatment, inspired by the diagnostic information collected throughout the PhD project, is proposed, showing promising preliminary results. The focus of the methodologies and procedures developed in this work is on small items completely covered by thick corrosion patinas, and their further application to other kind of samples is not straightforward. Nonetheless, this research have implications that from the specific research topic, affecting many other fields of Heritage Science and, in particular, the real practise of archaeologists, conservators and conservation scientists. In detail, the FIB and LA-ICP-MS protocols investigated here have the potential evolve the way archaeometric and diagnostic study of archaeological copper-based objects is conceived today. At the same time, ...