Emilio Catelli¹, Kidane Fanta Gebremariam¹, Lise Lyngsnes Randeberg², Bjørn Kåre Alsberg¹, Victoria Juhlin³, Stein Olle Johansen³ and Florinel-Gabriel Banica¹

1. Department of Chemistry, Norwegian University of Science and Technology (NTNU), N-7491, Trondheim, Norway
2. Department of Electronics and Telecommunications, Norwegian University of Science and Technology (NTNU), N-7491, Trondheim, Norway
3. Norwegian University of Science and Technology (NTNU) University Library, Department of Special Collections, N-7012, Trondheim, Norway

A non-invasive analytical approach for investigation of illuminated manuscripts and fragments from the collections of the NTNU (Norwegian University of Science and Technology) Library

Illuminated manuscripts are made up of multiple layers of highly heterogeneous materials, comprised of organic and inorganic in nature, with some of them transformed through time since their production. Considering their relatively small size, fragility and the necessity to maintain the integrity of the manuscripts, sampling for analysis is impractical. Non-invasive analytical methods are the customary choices. The availability of analytical instruments in portable version allowed in-situ analysis of these precious artworks, usually kept in controlled environmental conditions. Miniature illuminations, initials, other texts and decorations were investigated by applying multiple analytical approaches on two illuminated manuscripts, a Franciscan antiphonary (MS Fol 724), and a breviary (MS Oct 922), and two fragments: fragment 006, dated from the middle ages with an antiphon and psalm from Virginibus officium and fragment 14, part of a Missale, concerning the Commune unius confessoris et pontificis de virginibus. The illuminated manuscripts and the fragments belong to the collections of the Norwegian University of Science and Technology (NTNU) University Library, Trondheim, Norway.

Light microscopy, digital portable fluorescence and infrared microscopes, portable X-ray fluorescence (pXRF), Raman spectroscopy, visible (VIS) near infrared (NIR) and short wavelength infrared (SWIR) hyperspectral imagings were used in the investigation. Hyperspectral imaging serves as a versatile tool for archival imaging with capability to reveal obscured and faded information. When radiometric calibration to reflectance is applied, it can also be used to identify pigments and mapping their spatial distribution. The method is based on the distinctive spectral features of the radiations absorbed by the different constituent materials in the visible, near infrared and short wavelength infrared region. With its ability to cover the entire area of the illumination or folio under investigation, it is versatile to complement the results obtained with X-ray fluorescence and Raman spectroscopy, which are site specific techniques. Statistical approaches were employed in the course of processing and interpreting the data in the case of hyperspectral imaging and pXRF analyses. The intention in investigation was primarily to identify the different materials and techniques used in the preparation of the parchment, the text inks and the manuscript illuminations.

Systematic documentation of the pigments, inks, and components of the parchment with insight into their state of deterioration could serve as a basis for well-informed conservation intervention and reconstruction of original appearance. It can also provide useful information to complement art historical studies geared towards addressing the issues of dating, provenance, attribution and identifying previous conservation\restoration\retouching attempts, among others. Here we describe the in-situ investigations carried out on the illuminated manuscripts and fragments through the application of the multiple analytical techniques and the results obtained, highlighting their implications. Drawn on the experience gained from the investigations, future works that can be conducted are indicated.