Focus restoration of the Polyptych of the Mystic Lamb. Second installment: investigations into the work

We continue on our four-part “journey” inside the restoration of the Polyptych of the Mystic Lamb, a masterpiece by Jan van Eyck (Maaseik, c. 1390 - Bruges, 1441) and Hubert van Eyck (? - Ghent, 1426): after dealing with the history of the previous restorations and discussing the materials in the first installment, in this second installment we delve into the investigations conducted on the work by technicians from the KIK-IRPA (Royal Institute of Fine Arts) in Brussels, who are working on the laborious intervention whose conclusion is scheduled for this year and which is, however, a major protagonist of the major exhibition on Jan van Eyck, running in Ghent until April 30, 2020, housed in the halls of the Flemish city’s Museum voor Schone Kunsten.

There is a premise to start with: a polyptych such as that of Jan and Hubert van Eyck is a very complex structure. Meanwhile, there is the support material, which in this case are planks of oak wood (of very good quality), imported from the Baltic countries, and worked in such a way that they could be joined together to create a composite structure and to receive theimprimitura, that is, the preparation on which the van Eyck brothers would paint (in this case composed of plaster and animal glue). On the imprimitura was traced a preparatory drawing (what in English is called by perhaps a more eloquent term, underdrawing, literally “underdrawing,” indicating that it would be covered over at a later time), which served to indicate the areas on which the color would be applied: we can imagine it as a kind of “idea” of the final result, made up only of outlines drawn with a pencil or chalk or charcoal (to which some shading, conducted by hatching, could be added for the study of darker areas). A first layer of color, that of the background, was then applied, to which one or more layers were then added for the figures, landscape elements, and details. The elaboration of the painting ended with the application of a special varnish that was used to give the painting the glazed appearance with which it shows itself to the viewer. After drying was finished, another varnish was applied in order to protect the work from dirt and the action of external agents. Each of these elements of the painting can be analyzed with a different technique. In the case of the Polyptych of the Mystic Lamb, technicians have used radiography to study the support so as to assess its state and condition (and additional data may also come from chemical analysis of the material and the use of dendrochronology techniques to learn about the age of the tree from which the panels were taken), infrared photography and infrared reflectography to learn about the preparatory drawing, andultraviolet illumination to study the colors and varnishes.

The campaign to investigate the Polyptych of the Mystic Lamb, which served to study the work “from the inside” and to learn about its state of preservation (both in terms of structure and at the level of painting), was initiated in 2010 (under the coordination of Ron Spronk, professor at Queen’s University in Kingston, Ontario, and at the University Radboud of Nijmegen in the Netherlands) after concerns had emerged in 2007 about the condition of the work, which was kept in an unsuitable case to preserve the appropriate climatic conditions, and preliminary examinations had found the need for for urgent intervention, led by Anne van Grevenstein, on this occasion assisted by Hélène Dubois and Marie Postec of KIK-IRPA, Griet Steyaert of the Royal Institute of Fine Arts of Belgium, and Gwen Fife of the SRAL conservation institute in Maastricht. The urgent intervention consisted of a consolidation of the parts of paint that were flaking off and a cleaning with microfiber fabrics (a choice dictated by the need to avoid intervening with wet products on painted surfaces). At the same time, an air quality analysis was carried out in St. Bavon Cathedral, the place where the polyptych is kept (coordination by Jørgen Wadum of the National Gallery of Denmark, in collaboration with Birkbeck College in London), and then proceeded with continuous monitoring of the climatic conditions of the context. The urgent intervention was completed in October 2010: Anne van Grevenstein and her team, in the final report, emphasized the need for a new and complete restoration, especially due to the fact that, as it was found at the time, the varnishes that had accumulated on the surface of the polyptych over time (and discussed in the first installment of the focus on the work) were experiencing a process of continuous degradation that could have affected the underlying painting, including the original one. Not only that: for the occasion, restorer Jean-Albert Glatigny had also studied the support, coming to the conclusion that, despite the many events that the Polyptych of the Mystic Lamb had experienced in the past, the panels were all in all healthy, but still in need of intervention to consolidate the structure of the work.

Thus, the investigation campaign could begin, conducted individually on all eighteen compartments that make up the polyptych, in this order: dendrochronology, high-resolution visible light macrophotography, high-resolution infrared macrophotography, high-resolution grazing light macrophotography, infrared reflectography, and radiography. In addition, the four central panels were probed with multispectral infrared reflectron scanning and examined with infrared spectroscopy, ultraviolet fluorescence, X-ray fluorescence, and combined XRF/XRD (X-ray fluorescence and X-ray diffraction) analysis. Dendrochronological analysis (conducted by Pascale Fraiture of KIK-IRPA and Peter Klein of the University of Hamburg) allowed us to date the panels on which the Polyptych of the Mystic Lamb was painted (bearing the date of May 6, 1432) to a period between 1415 and 1432 for the lower section and between 1417 and 1434 for the upper section. This was then followed by macrophotography, curated by photographer Luc van Muylem. The entire polyptych was filmed with a SINAR technical camera: 32-megapixel resolution photographs were taken for areas of 16 by 22 centimeters resulting in 1,000 files of about 200 megabytes each (in TIFF format), which made it possible to document the polyptych as never before. Thanks to the high resolution (the same was also used for infrared macrophotography) it was possible to obtain important enlargements of the entire pictorial surface. Already from the infrared macrophotography it was possible to learn about important drawings on the preparatory drawing, especially underneath the embodiments (for example, some corrections in the course of the work, when the drawing was already traced, emerged), and in addition, photographs were also taken at an almost microscopic level, on areas of 6 centimeters by 8 (also with infrared photography) to get more complete details. The KIK-IRPA technicians also performed a digital macrophotographic survey (with a Hasselblad H4D-200MS camera set to 50-megapixel resolution and over areas of 15 centimeters by 20): in order to document everything with the utmost precision, the photographers built a special dolly on which the camera was slid. The files in raw format were then processed with special software, called Phocus 2.9, which allowed the individual areas to be merged to have photographs of the work as a whole. The algorithm developed to merge the portions also automatically corrected for slight differences in light between areas-the end result was photographs...giant, 18 gigabytes each.

Macrophotograph of a detail of a city view

Infrared macrophotograph of the detail of the lamb’s snout (note how well the image shows the design of the eyes as van Eyck had conceived it: here it is compared with the sixteenth-century repainting)

KIK-IRPA technicians take macrophotographs of the polyptych with the machine mounted on the carriage

Infrared reflectography (supervised by Christina Currie and Sophie De Potter of KIK-IRPA) enabled further and even more in-depth analysis of the preparatory drawing. For example, it turns out that Jan van Eyck, in drawing the setting of theAnnunciation scene, did not initially plan to include the wood-beamed ceiling that we now appreciate in the finished painting: on the contrary, the initial idea was to include above the archangel Gabriel and the Virgin trilobed arches like those that surmount the characters in the lower register (a very interesting piece of information because it allowed us to know that the van Eyck brothers had worked on all the panels at the same time, and this allowed us to solve a problem on which art historians had previously debated but failed to reach a conclusion). Reflectography is conducted with digital cameras equipped with special sensors that subject the painting to infrared radiation: since carbon (a chemical element found in the charcoal or pencils with which the painters used to trace preparatory drawings) absorbs radiation (as opposed to the white parts, which instead repel it), the results in the variations in the ways in which the materials react to infrared rays make it possible to trace a kind of mapping of the image (reflectogram) that reveals the underlying drawing. The Polyptych of the Mystic Lamb was examined with a special camera developed by KIK-IRPA, operated by remote control on an additional trolley specially made for the occasion: the device documented individual portions of the painting (5 x 4 cm), which were then assembled using Adobe Photoshop.

As a final step, theradiographic survey (carried out by Christina Currie, Catherine Fondaire, and Guido van de Voorde of KIK-IRPA) was carried out, repeating an operation that had already been conducted in 1986: in this way, it was possible to make a comparison between the new radiographs and those from twenty-four years earlier. Radiography serves two main reasons: to analyze the different layers of paint and to investigate the structural aspects of the boards (with radiographs, it is therefore possible to examine the wood grain, knots, joints, and fractures, so as to understand what state the support is in, which are its weakest points and those that hold up best, and thus have a complete overview of the tightness of the boards). The radiographic analysis did not reveal any major changes from its previous condition, confirming the fact that the Polyptych of the Mystic Lamb has a support that is in substantially good health.

Reflectography comparing with the painting (see how above the angel the preparatory drawing called for a trefoil arch, later replaced by the beamed ceiling)

Sophie De Potter deals with infrared reflectography

Radiography on St. John the Baptist

X-rays are taken on the polyptych in the KIK-IRPA laboratory

Claudia Dafarra of INOA performs multispectral infrared reflectographic scanning on a panel of the polyptych

Finally, some notes on the latest analysis. The multispectral infrared reflectographic scan was was conducted by Italian researcher Claudia Dafarra of the National Institute of Applied Optics (INOA) in Florence, Italy, and allowed the team working on the Polyptych of the Mystic Lamb to obtain an important “map” of the retouches that Jan and Hubert van Eyck made to the painting, while ultraviolet fluorescence, X-ray fluorescence and combined XRD/XRF analysis were used to examine the composition of the materials and verify their presence in the different layers of the painting. In fact, fluorescence lamps make it possible to record a lot of useful information (old cleaning, repainting, retouching) by exploiting the reactions to the brightness of the different materials (pigments, varnishes, materials that have been deposited on the surface).

All the results of the investigations were finally made available to the public and scholars on a special website, Closer to van Eyck, where it is possible to view both high-resolution photographs of the painting before and after restoration and images of the examinations conducted on the work (also before and after restoration). The site, the realization of which was also coordinated by Ron Spronk and was been taken care of by Frederik Temmermans and Iris Vanhamel of the company Universum Digitalis, involved several professionals (including technicians, photographers, programmers, content editors) and was financially supported by the Getty Foundation in Los Angeles and the Gieskes Strijbis Foundation in Wassenaar (Netherlands) for the web part, while the processing of the images for online publication was financially supported by the government of Flanders. The site also received technical support from KIK-IRPA, the University of Antwerp, Ghent University, Queen’s University in Kingston, Radboud University in Nijmegen, and the Free University of Brussels. And, of course, the entire material resulting from the survey campaign provided the basis for the long and delicate restoration: we will deal with this in the next in-depth discussions.

Focus restoration of the Polyptych of the Mystic Lamb. Second installment: investigations into the work

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