Non-Invasive Techniques applied to Cultural Heritage: Raman Spectroscopy and X-Ray Fluorescence for the Study of Medieval Manuscripts

Abstract

Nowadays, in the cultural heritage field, non-invasive analysis are more and more widespread, in order to interact as less as possible with the art objects. In fact, the growing demand of the use of instruments directly transportable in loco, is accompanied with the increasing demand of their minimum impact on the constituent materials. First, to better understand the importance in the choice of the most appropriate analysis for a particular art object is useful to distinguish between two categories of analyses: destructive/non-destructive and invasive/non-invasive. Destructive analysis are diagnostic methods that do not preserve the structural integrity and functionality of the art material, and generally, they require sampling. Non-invasive analysis, instead, do not alter the physical and the chemical conditions of the manufacture, allowing to not interfere with the changing processes between the manufacture and the environmental. Thus, the non-invasively of a technique corresponds to the capacity to not alter the system from the thermodynamic point of view. For this reason, in this work, non-invasive and non-destructive and techniques were chosen. In particular, X-Ray Fluorescence and Raman Spectroscopy were applied, as complementary techniques, in the investigations of medieval fragments made up of parchment. These fragments were discovered in 2007, by the Merowe Dam Archaeological Salvage Campaign, on the island of Sur in Northern Sudan. This finding probably comes from a library collection of a church of the Classic Christian Period (XI century). All the fragments are characterised by black and red writings. In particular, this work aims to study ancient manuscripts to answer questions regarding the inks composition and if possible discover its provenience as well as for curatorial and conservation purposes. X-Ray Fluorescence Spectrometry and Raman Spectroscopy, in fact, have become one of the most optimum tools for the analyses of inks on documents. Especially, XRF is very useful to identify inorganic metal-based inks, such us iron-gall, cinnabar and red lead. Raman spectroscopy, instead, is employed for the investigation of both inorganic and organic inks. The first part of this work focuses on parchment as writing support with the description of the most inks used. In particular are described the development of the parchment among the century, its chemical composition, its physical and mechanical properties and the manufacturing steps. Moreover, the most applied black and red inks are presented, from both the historical and the chemical point of view. This theoretical part can help to understand the degradation of both parchment and inks during the century and it is fundamental for the interpretation of the analyses performed on the fragments. The second part of the work, instead, focuses on the medieval fragments. First, a description of their state of conservation is presented followed by XRF and Raman experimental analyses performed.