Mahgoub, Hend; (2020) Quantitative Chemical Hyperspectral Near Infrared Imaging of Historical Cellulosic Materials. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Hyperspectral imaging in the visible and near infrared (VNIR) regions is slowly becoming routine process in the documentation and characterization of historic surfaces. The VNIR spectral region contains colour information and limited chemical information. Conversely, the spectral region further in the NIR (short-wavelength IR, SWIR) is much less explored although suitable hyperspectral cameras exist. The first quantitative application in heritage science was published in 2011. Due to the complexity of NIR data hypercubes where the spectra holds thousands of C-H, O-H and N-H molecular bonds representing the chemical and physical features of the investigated object in addition to their spatial distribution, multivariate data analysis methods are required to extract qualitative and quantitative information such as acidity and molecular weight from a historical object e.g. document or canvas, which are important indicators of its state (condition). Using imaging to document the spatial distribution of an object’s chemical composition and condition is therefore possible, however, significant research work is still necessary to understand how the measurement conditions (lighting spectral distribution and intensity, concentrations of the imaged component, calibration) as well as the stability of calibrations over time, affect the analytical outcome. This project will explore analytical robustness of quantitative chemical imaging as well as studying two specific areas of application from the historical cellulosic materials: Islamic paper (distribution of sizing and polishing components, acidity, and cellulose degree of polymerization - DP) and painting canvases (distribution of acidity and cellulose DP). This aims to provide a better understanding of degradation processes and provide a measure of change in collections through imaging which will reflect on the management and preservation plans of collections. Another area of application from the historical cellulosic materials: Papyri will also be explored by investigating the effect of imaging through glass on the accuracy of the acquired data from the spatial and spectral perspectives in addition to the extraction of chemical information that could be used to enrich our scientific knowledge about papyri. Moreover, the degradation behaviour of the historical materials under investigation, exploring their degradation rate and study their stability is investigated with the aid of accelerated degradation in controlled conditions allowing for the study of different scenarios of storage environment conditions leading to better preservation decisions. The PhD project is a collaboration between researchers with a strong experience in collections research; University College London, Rijksmuseum, University of Barcelona, ZFB GmbH, and Gilden Photonics Ltd, in addition to being a part of the H2020 Nanorestart project.

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