Multi-component archaeological adhesives: an innovative analytical approach to study chemical interactions and natural aging degradation

The core of archaeology is the reconstruction of past through the study of material remains, and, in such way, to understand the customs and traditions of our ancestors. This focus on material evidence has created, during times, the need to study things more and more thoroughly, which leads to the requirement of scientific approaches to the study of the past, and for this reason, archaeology has increasingly interacted with physics, chemistry, biology, and the earth sciences, paving the way for a new interdisciplinary scientific branch: archaeometry [1], [2]. Within this framework, this thesis serves as a bridge between analytical chemistry and archaeology, promoting the use of chemistry not merely as a supplementary technique, but as a fundamental tool to maximize the information obtained from artifacts. The work focuses on the analysis of archaeological adhesives: complex organic substances that require hard chemical characterization for accurate identification. The first chapter provides a comprehensive literature review. After outlining the evolution of the relationship between chemistry and archaeology, it defines archaeological adhesives and examines how these materials fit into the liaison between the two sciences. The second part of the chapter focuses on the materials commonly found as adhesives in archaeological contexts and describes the analytical tools used for their characterization, supported by relevant application examples. Chapters 2 and 3 constitute the analytical core of this PhD project, developing along two interconnected paths. Chapter 2 presents a series of case studies in which mass spectrometry was applied to characterize adhesive materials found on several archaeological artifacts. Beyond material identification, this study allowed for the gathering of additional data, such as the distribution of different bonding technologies in Italy from the Neolithic to the Iron Age. Furthermore, it highlighted a frequently underestimated issue: the contamination of artifacts during preliminary archaeological study. This emphasizes the need for handling protocols suitable for subsequent chemical analysis. This chapter also underscores the limitations of analytical chemistry when used only for identification purposes, which often results in a superficial understanding of ancient technologies and lacks information regarding the aging processes of these materials. To address these limitations, Chapter 3 demonstrates how the study of reference materials, produced through experimental archaeology, can provide crucial insights. To this aim, pitch from several tree species and beeswax, two of the most common adhesive categories in archaeological contexts, were initially studied individually. The focus then shifted to complex mixtures, based on experimental information obtained after the analyses of the samples set recovered from the site of Antinoe. This approach enabled the clarification of aging mechanisms and the technical motivations behind the selection of specific materials and preparation procedures.