Advancing approaches in glass conservation: characterisation of altered archaeological glass and artificially aged glass replicas to shed light into the mechanisms of glass corrosion.

Glass finds application in multiple domains, from the technological to the artistic and archaeological one, and the study of its durability is crucial to determine its potential to replace several dangerous and polluting materials such as plastics, particularly now in the era of the circular economy. Because of the thermodynamic properties of glass and its high variety of compositions, the evaluation of glass durability and alteration mechanisms remains a challenge. For this reason, the study of glass corrosion is considered a complex research topic that requires the ability to take into consideration a big number of factors, some of which are hardly represented in laboratory experiments. The most influential of these is with no doubt the time given to the transformation, which is directly responsible of both the kinetics and the dynamics of the processes involved. The present PhD project aims to study the complex phenomenon of glass corrosion from the perspective of ancient glass samples, which represent unique evidence of the effect of long-lasting environmental ageing on such material. The goal is to highlight how the study of ancient and archaeological glass offers an outstanding opportunity to fill the gaps in the various theories about glass corrosion, which, in fact, have been formulated on the basis of research carried out under laboratory conditions and only partially reproducing the circumstances of environmental degradation. The ultimate purpose is twofold. On one hand, this work wants to highlight how far research on glass corrosion has come by studying model systems created in laboratory to simulate different alteration conditions and glass compositions. On the other, it wants to point out what the critical aspects that still need to be investigated are and how the study of archaeological glass may complement the results obtained over the years in research carried out on laboratory models. Archaeological glass gives indeed the unique opportunity to observe the effect of long-term natural ageing on a real material, and the results obtained from its study are key to fill the gaps that are still present in the theory of glass corrosion. This PhD thesis starts with the gathering of the results obtained about glass corrosion and its interaction with the environment, considering studies performed both on experimental and archaeological samples. The aim is to understand where the scientific today, what are the critical points that still need to be investigated and what may be the future perspective for glass preservation and applications (for instance for the development of sustainable protective treatments), to help the scientific community in the design of future, more complete, research. An innovative strategy to approach the problem of glass corrosion and its stabilisation is proposed in this work: the development of an ideal conservation treatment able to slow down the alteration process of ancient glass requires the in-depth investigation of ancient glass and of the artificially aged glass mock-ups in order to obtain a comprehensive evaluation of the modification of glass structure, its kinetic over time, and its final visible results. The information obtained from this course of the research of glass corrosion represent the basis and inspiration for a modern way of thinking about glass conservation that overcomes the limits imposed by traditional principles, such as reversibility, by exploiting the properties of cutting-edge technology such as nanotechnology.