The application of fibre optic spectroradiometry for pigment analysis is bringing the art and science worlds together
The Fitzwilliam Museum has recently launched a new interdisciplinary research project, MINIARE (www.miniare.org), in collaboration with the Hamilton Kerr Institute and the Department of Chemistry, University of Cambridge. The project uses advanced scientific analyses in combination with arts and humanities methodology to study the painting materials and techniques used in illuminated manuscripts. MINIARE stands for Manuscript Illumination: Non-Invasive Analysis, Research & Expertise. It will undertake non-invasive analysis of Western, Egyptian, Byzantine, Slavonic, Armenian, Persian, Mughal, Ottoman, Sanskrit and Tibetan illuminated manuscripts, as well as a selection of early printed material. The scientific results will inform studies of the artistic, cultural, political, social and economic environments in which the manuscripts were created, taking into account trade routes, social and international mobility, intellectual and technological developments. MINIARE will therefore bring together Cambridge’s rich manuscript collections and world-class expertise in the sciences, arts, humanities and social sciences. Combining advanced, non-invasive scientific analyses with interpretation in a broad historical and cultural framework, it will develop new, cross-disciplinary methods for the study of illuminated manuscripts.
[caption id="attachment_30865" align="alignright" width="200" caption="Figure 2: Pigment analysis with the FieldSpec 4 of an illuminated manuscript cutting: (Left) Fitzwilliam Museum, Marlay cutting It. 13ii. Italy, Florence, ca. 1409. (Right) Reflectance spectra obtained at selected sites on the manuscript cutting, marked on the image on the left in colours corresponding to the spectra. The spectral characteristics allow identification of most of the pigments used, and in some cases also of the paint binder (egg yolk). Areas in which egg yolk cannot be identified were likely painted using gum or egg white as binders."][/caption]
Our long-term vision is to establish a new, interdisciplinary research and teaching centre dedicated to the art historical and non-invasive scientific analysis of works of art in different media, combined with a comprehensive contextual interpretation of visual and material culture. The centre will foster collaboration with research institution worldwide and will offer postgraduate degrees (Master and Doctoral) and postdoctoral specialisation in conservation science and technical art history, using direct research on original art works to train a new generation of scholars that will bridge the divide between the arts and the sciences.
Few places in the world are as well suited as Cambridge to host such an ambitious interdisciplinary project. The Fitzwilliam Museum, Cambridge University Library and the Colleges preserve one of the largest and finest collections of European medieval and Renaissance manuscripts as well as important African and Asian material, representing the history of manuscript production across three continents over four millennia (1350 BC-19th c. AD). Additionally, Cambridge has an extraordinary concentration of leading scholars working in the arts, social sciences and humanities, as well as some of the world's finest conservators and scientists. The research expertise of the Departments of Chemistry and Physics ranks them among the foremost in the world. Existing collaborations between scholars in these diverse fields have laid the foundation of the sciences-humanities-arts synergy indispensible for MINIARE.
Our research team is currently based at the Department of Manuscripts and Printed Books at the Fitzwilliam Museum. The main immediate objective of our work is the non-invasive identification of artists’ materials used by illuminators across Europe and beyond. The materials in question are natural and synthetic, organic and inorganic pigments that were in circulation before the 17th century, as well as organic binding media based on proteins, lipids, and polysaccharides. The project is interdisciplinary by nature, at the frontier between science and art, bringing together a team of investigators with different backgrounds and aiming to have an impact on both fields.
The project is initially focusing on the holdings of the Fitzwilliam Museum, which include some of the finest manuscripts produced between the 9th and the 16th centuries in major centres across Europe or by leading illuminators, some of which also practiced as panel/fresco painters, stained glass designers, jewelers or print makers. Subsequent phases of the project will expand the range of manuscripts to include Egyptian (ancient, Coptic, Mamluk, Ethiopian), Byzantine, Slavonic, Armenian, Persian, Mughal, Ottoman, Sanskrit and Tibetan examples, in addition to early printed material, thus tracing the history of manuscript and book production and representing cultural and religious traditions from across the world.
While analytical techniques using micro-samples taken from art objects can provide the most accurate identification of artist’s materials, there is a preference for non-invasive methods, especially in the case of small and fragile objects such as manuscript illuminations1. These have become more and more established over the past ten years, and numerous studies have been published regarding the use of analytical techniques such as Raman spectroscopy and XRF for in situ analysis of manuscripts2. It is clear from the published studies that best results are obtained when using a combination of analytical methods, which usually allows researchers to obtain a relatively comprehensive characterisation of the painting materials3.
[caption id="attachment_30866" align="alignleft" width="200" caption="Figure 3: Analysis of green pigments with the FieldSpec 4 of a 15th century Book of Hours: (Left) Fitzwilliam Museum MS 60, fol. 89r (detail). Brittany, before 1418. (Right) The reflectance spectra acquired on green areas show evidence for the use of blue glazing (probably organic) on some green areas painted with a copper-based pigment, likely to be malachite. This causes a blue shift in the visible peak and the appearance of a ‘shoulder’ in the reflectance spectrum."][/caption]
Fiber optics reflectance spectroscopy (FORS) has been used occasionally during the past ten years to partially identify the pigments used by illuminators, but until very recently its application has been limited mostly to the visible range or just beyond (400-1000 nm), thus exploiting only the electronic transitions of pigments, and mostly to identify inorganic materials4. More recently, we have used a FieldSpec 4 spectroradiometer5 allowing us to use FORS in an extended range (350-2500 nm) which has enabled us to obtain an almost complete characterisation of both inorganic and organic materials (pigments and binders) on a few illuminated manuscripts6. Key to the success of this approach is the inclusion of the NIR region (1000-2500 nm) for the analysis of some of the vibrational overtones and band combinations due to functional groups such as hydroxyls, carbonates, and potentially methylenic and amide groups associated with paint binders. For example, one can easily separate green malachite from mixtures of organic yellows and blue azurite. Both being copper carbonates, malachite and azurite are completely indistinguishable by X-ray fluorescence but the latter shows characteristic absorption bands at 1495, 2285, and 2350 nm.
Recent studies have also shown that fat-containing paint binders such as egg yolk can be identified by the presence of specific absorption bands in the NIR range7. The identification of these vibrational features is particularly challenging because the paint layers are only tens of µm thick and these vibrations are weaker in strength than those in the mid-IR and require a spectral sampling of a few nm. The non-invasive identification of organics is of particular interest, as it is arguably amongst the single greatest challenges that scientists face when analysing works of art.
The technical specifications of the FieldSpec 4, including its high sensitivity and high spectral resolution, make it the optimal tool to investigate thin and often complex paint layers. The rapidity of acquisition in addition to the instrument’s compactness and portability allow surveying a large number of objects directly in exhibition Galleries or storage rooms if necessary, with the possibility to yield a substantial comprehensive data set in a short period of time. This allows carrying out large-scale surveys, acquiring spectra on both test panels and works of art, which then can be interpreted and used to both answer some of the questions raised in the initial phase of the research and to inform subsequent phases of the project, during which the characterisation of the materials can be completed, when needed, using supplementary analytical methods such as Raman spectroscopy, XRF, and others.
During the period of the Goetz Instrument Support Program Award (16 April – 15 May 2012)8, reflectance spectra were acquired at the Fitzwilliam Museum on selected folios within 23 bound manuscripts, as well as on 22 manuscript cuttings, a 17th century colour chart (Trinity College 310.b.6A.8) and a number of reference pigments bound in different media and painted out on glass (67 samples) and parchment (151 samples). Data processing is still ongoing, but preliminary results have already been presented at several international conferences, in Italy, Belgium and the UK.
Two examples of such manuscripts and the associated analyses are shown in Figures 2 and 3.
Our work continues with the goal to develop a truly comprehensive protocol for the non-invasive analysis of artists’ materials and techniques used for manuscript illumination. The possibility to study large and representative groups of illuminated manuscripts will enable us to better understand them from a scientific, cultural and historical perspective. MINIARE aims to employ a holistic approach to the study of artworks, combining scientific innovation, excellence in conservation and cutting-edge research in the arts and humanities. We hope to create a ‘core’ research community in the UK, able to engage in truly interdisciplinary research, to offer doctoral and post-doctoral training, and to advance both in-depth knowledge of and broad appreciation for works of art of all ages, media and traditions. Ultimately, the results of the MINIARE project will be shared with a broad audience in 2016, when the Fitzwilliam Museum will mark its bicentenary with a major exhibition of illuminated manuscripts, focusing on the evolution of artists’ materials and techniques, and offering a multi-layered gallery interpretation, an accessible and richly illustrated catalogue, and educational programmes presenting the results of MINIARE’s research.
M. Clarke (2001) ‘The analysis of medieval European manuscripts’ Reviews in Conservation 2: 3-17
2 They are too numerous to be listed here. Most of those published up to 2001 can be found in the references section of Clarke (2001)
3 M. Aceto, A. Agostino, G. Fenoglio, M. Gulmini, V. Bianco, E. Pellizzi (2012) ‘Non-invasive analysis of miniature paintings: proposal for an analytical protocol’ Spectrochimica Acta A 91: 352-359; S. Pessanha, M. Manso, M. L. Carvalho (2012) ‘Application of spectroscopic techniques to the study of illuminated manuscripts: a survey’ Spectrochimica Acta B 71-72: 54-61; P. Ricciardi and J. K. Delaney (2011) ‘New trends in the study of medieval illuminated manuscripts: combining visible and infrared imaging spectroscopy with site specific, in-situ techniques for material identification and mapping’ Revista de Historia da Arte n° especial: 254-263 (available online: http://revistadehistoriadaarte.wordpress.com/)
4 M. Aceto, A. Agostino, V. Bianco, F. Crivello, A. Giaccaria, F. Porticelli (2008) ‘An interdisciplinary, non-invasive study of ten manuscripts coming from the San Colombano abbey in Bobbio’. In Proceedings of the 9th International Conference on NDT of Art (available online: http://www.ndt.net/article/art2008/papers/142Aceto.pdf); M. Bacci, M. Picollo, B. Radicati, A. Aldrovandi, A. Migliori (2007) ‘Studio dei materiali pittorici del Graduale 558’. In Fra Giovanni Angelico: pittore miniatore o miniatore pittore?, eds. M. Scudieri and S. Giacomelli, Giunti Ed., Florence: 101-111
5 ASD FieldSpec 4 – see www.analytik.co.uk/portable-remote-sensing-spectroradiometry.htm.
6 P. Ricciardi, J. K. Delaney, L. Glinsman, M. Thoury, M. Facini, E. R. de la Rie (2009) ‘Use of visible and infrared reflectance and luminescence imaging spectroscopy to study illuminated manuscripts: pigment identification and visualization of underdrawings’. In Proceedings of SPIE Vol. 7391: 739106, doi:10.1117/12.827415; P. Ricciardi, J. K. Delaney, M. Facini, L. Glinsman (forthcoming) ‘Use of imaging spectroscopy and in situ analytical methods for the characterization of the materials and techniques of 15th century illuminated manuscripts’ Journal of the American Institute for Conservation 51
7 P. Ricciardi, J. K. Delaney, M. Facini, J. G. Zeibel, M. Picollo, S. Lomax, M. Loew (2012) ‘Near infrared reflectance imaging spectroscopy to map paint binders in situ on illuminated manuscripts’ Angewandte Chemie Int. Ed. 51: 5607-5610
8 The Goetz Instrument Support Program Award is co-sponsored by ASD Inc. and the Geoscience & Remote Sensing Society. More information may be found at www.asdi.com/service-and-support/goetz-instrument-support-program
Dr Paola Ricciardi, Research Associate, Department of Manuscripts and Printed Books, Fitzwilliam Museum, Cambridge