The Non-Invasive Analysis of Painted Surfaces A two-day international symposium Washington DC, February 2014 By Paola Ricciardi

The conference programme included fourteen plenary lectures, two short talks and a panel discussion. Talks on day 1 focused largely on analytical imaging methods, while day 2 included presentations of multi-technique case studies followed by an afternoon focused on X-ray fluorescence (XRF) analyses. About 150 people were in attendance, including a large number of students and young graduates.
The audience was welcomed by Tiarna Doherty, Chief of Conservation at the Lunder Conservation Centre. She introduced the first speaker for the day, David Saunders, Keeper of Conservation and Scientific Research at the British Museum. David’s inspiring keynote address challenged the audience with a thorough discussion of the benefits and drawbacks of non-invasive analyses compared to analyses which do require sampling artworks. Starting with a comparison between two analytical studies of the sarcophagus of Seti I carried out in the early 19th and the early 21st century, David introduced the two main types of motivation behind technical analyses: to understand the histories of production, use and meaning of objects, and to understand the material nature of objects in view of their future preservation. Case studies highlighted the variety of analytical methods nowadays available for analysis of art objects: from simple visual examination to a range of complex imaging methods, from various types of spectroscopic point analysis to the detailed examination of samples. Finally, David outlined the main points one should keep in mind when faced with the ever-challenging conundrum ‘to sample or not to sample’: employ collaborative decision-making, carry out a risks vs benefits analysis, ensure rigorous documentation of each process and retain samples and all technical information for the future.
Philip Klausmeyer from the Worcester Art Museum discussed the use of laser shearography to quantify and map induced strain in canvas paintings. This imaging method, relatively new to the field of cultural heritage science, was used to monitor the mechanical response of oil paintings on canvas to thermal gradients and to assess the suitability of different backing materials for a stretched canvas. Most recently, shearography data have been tentatively correlated with topography information such as the presence of cracks on a painting’s surface.
Haida Liang from Nottingham Trent University presented a state-of-the-art instrument used to analyse painted surfaces by optical coherence tomography. This imaging technique yields ‘virtual cross sections’ of easel and wall paintings, thereby allowing the study of the stratigraphy of painted layers, otherwise unobtainable by non-invasive methods. It can also be used for real-time monitoring of the drying process of varnishes and of the effectiveness of conservation treatments.
Opening the afternoon session, Gwendoline Fife and Tyler Meldrum discussed the results of a project involving institutions in the Netherlands, Germany and the United States, focused on the use of nuclear magnetic resonance (NMR) spectroscopy to monitor the effects of organic solvent treatments on paintings. They showed the importance of understanding the effect of different cleaning techniques for an improved risk assessment and proved the usefulness of NMR for an effective comparison of such techniques.
Austin Nevin from the Politecnico di Milano discussed the use of fluorescence lifetime imaging (FLIM) to map and identify pigments in 19th century paintings including a painting on paper by Vincent Van Gogh. FLIM revealed the presence of a highly luminescent white pigment with a lifetime of about 1.2 microseconds, which the team were able to identify as a zinc-based material with small amounts of copper impurities giving rise to the unusually strong and long-lived luminescence emission.
Lori Wong from the Getty Conservation Institute showed the results of comprehensive study of the wall paintings in the tomb of Tutankhamen by means of portable instrumentation. The paintings’ layer stratigraphy and the presence of past conservation treatments carried out on the four walls of the pharaoh’s burial chamber were successfully investigated despite harsh environmental conditions which put the analytical equipment to the test.
Bruno Brunetti from the University of Perugia summarised the activity of the European mobile laboratory called ‘MOLAB’, part of the EU-funded project CHARISMA. He compared the analytical performance of different kind of portable spectroscopic equipment and showed the results obtained in a few of the 60 projects that the MOLAB team has been involved with in 19 European countries, travelling over 176,000 km in 10 years. Day 1 ended with a reception at Cuba Libre restaurant which I was not, alas, able to attend…
I had the pleasure of delivering the first talk of the second day of the conference, presenting the cross-disciplinary approach taken by the MINIARE project at the Fitzwilliam Museum in Cambridge for the study of illuminated manuscripts. My talk focused on the need to employ multiple methodologies, including visual observation, analysis of the quire structure, infrared imaging, photomicroscopy, reflectance spectroscopy and XRF to shed light on the authorship of the complex and extensive decorative programme of a 13th century Psalter.
Kate Seymour, Marya Albrecht and Melissa Daugherty from the Stichting Restauratie Atelier Limburg discussed their technical analysis of two 15th century Spanish panel paintings as if they were investigating a crime scene, using multiple methodologies. The iconography, the construction methods and apparent modifications of the panels as well as the information gained about the painting materials and techniques all contributed to the conclusion that the panels were painted in Barcelona or Catalunya by either Jaume Huguet or Joan Reixach.
Jennifer Mass from the University of Delaware described the combined use of XRF and UV-induced visible and infrared fluorescence imaging to study the alteration of cadmium sulphide pigments in paintings by Edvard Munch and Henri Matisse. The combination of multiple imaging techniques proved invaluable in detecting both incipient and advanced alteration of these pigments on monumental paintings which could not be comprehensively studied by site-specific methods.
Maria Kokkori from the Art Institute of Chicago shared her insights into ‘Painterly realism of a football player – colour masses in the 4th dimension’, a 1915 painting from Kazimir Malevich’s ‘suprematist’ period. Most intriguingly, Maria discussed the identification of cobalt violet, very unusual for Russian standards at the time because of its high price and its social and political connotation as a ‘bourgeois material’.
The afternoon session focused on the use of XRF, certainly one of the methods most widely used by conservation science professionals to analyse works of art. The session was opened by Nicholas Barbi from PulseTor LLC, one of the industrial sponsors of the conference. He introduced ELIO, a new portable XRF spectrometer developed in collaboration with XGLab srl, specifically designed for cultural heritage applications.
Brian Baade presented a comparative discussion of portable vs laboratory-based XRF instruments, based on the analysis of historically representative paint samples carried out with his co-authors at the University of Delaware. He focused particularly on the effectiveness of XRF at identifying traditional paint driers and siccatives as well as the mordants associated with red lake pigments.
In two short talks, Aniko Bezur from the Centre for Conservation and Preservation at Yale University and Erich Uffelman from Washington and Lee University gave examples of ways in which portable XRF equipment can be used to train both conservators and chemistry students.
John Delaney from the National Gallery of Art in Washington delivered the final talk presenting a novel macro-scanning system which combines XRF with visible to near-infrared reflectance hyperspectral data. In one of his case studies, he presented material maps of a multi-panel painting by Cosimo Tura, in which the combination of the two imaging modalities was key to identifying the presence of a copper green pigment (possibly a copper resinate) in landscape areas which now appear brown. He also discussed a promising new application of pump-probe two-photon microscopy to distinguish pigment mixtures from layering effects without the need for sampling. This talk was followed by a panel discussion chaired by Chris McGlinchey from the Museum of Modern Art in New York City about present and future trends in the use of XRF to analyse cultural heritage objects.
Proceedings of conference papers will be published in 2015 by the Smithsonian Institute Press following peer-review. This will be a full colour publication, available both in print and online in open access, entitled ‘Advances in the Non-Invasive Analysis of Painted Surfaces: Applications to Conservation’.
Videos of all the plenary lectures as well as the panel discussion are freely available at:
https://www.youtube.com/playlist?list=PL7gn_68Hr4h_qnMshu8PN6wZdPrKoa6sL