Large‐Area Elemental Imaging Reveals Van Eyck's Original Paint Layers on the Ghent Altarpiece (1432), Rescoping Its Conservation Treatment

Abstract

A combination of large-scale and micro-scale elemental imaging, yielding elemental distribution maps obtained by, respectively non-invasive macroscopic X-ray fluorescence (MA-XRF) and by secondary electron microscopy/energy dispersive X-ray analysis (SEM-EDX) and synchrotron radiation-based micro-XRF (SR m-XRF) imaging was employed to reorient and optimize the conservation strategy of van Eycks renowned Ghent Altarpiece. By exploiting the penetrative properties of X-rays together with the elemental specificity offered by XRF, it was possible to visualize the original paint layers by van Eyck hidden below the overpainted surface and to simultaneously assess their condition. The distribution of the high-energy Pb-L and Hg-L emission lines revealed the exact location of hidden paint losses, while Fe-K maps demonstrated how and where these lacunae were filled-up using an iron-containing material. The chemical maps nourished the scholarly debate on the overpaint removal with objective, chemical arguments, leading to the decision to remove all skillfully applied overpaints, hitherto interpreted as work by van Eyck. MA-XRF was also employed for monitoring the removal of the overpaint during the treatment phase. To gather complementary information on the in-depth layer build-up, SEM-EDX and SR m-XRF imaging was used on paint cross sections to record microscale elemental maps.Several methods for obtaining information about the distribution of pigments and other chemical constituents of artworks have been developed; [1] such methods are necessarily non-invasive and employ radiation in the infrared, visible, ultraviolet or X-ray range. Traditionally, the spectroscopic characterization of artworks was done on a point-by-point basis, an approach that has inherent limitations with respect to representativeness. The recent transformation of spectroscopic instrumentation into mobile scanning systems [2][3][4][5] that allow the examination of all locations on the surface of (flat) artworks, proved to have a significant added-value for the study of cultural heritage objects. These forms of (spectro)-chemical imaging allow the consideration of large and complex spectroscopic datasets as (hyperspectral) image stacks that are (more) easily understandable by non-chemists such as art conservators and art historians than extensive series of spectral data derived from individual points. Whereas subtle point-to-point variations in the spectral response may be hard to notice and even more difficult to interpret correctly, gradual compositional variations that become apparent in large-scale chemical or elemental maps are usually much easier to link to (in)visible features of the paint surface and/or its conservation state.Since its introduction by Alfeld et al., [2] mobile MA-XRF scanning has met with considerable attention and success, for example, by supplying new and pivotal arguments for authentication of high-profile works of art in cases in which more conventional analytical and/or imaging techniques led only to ambiguous in...

Reviving degraded colors of yellow flowers in 17th century still life paintings with macro- and microscale chemical imaging

“…Although MA-XRF scanning is less sensitive to elements with a low atomic number (29), the elemental distribution of sulfur is consistent with the above-mentioned MA-XRPD results, in particular, showing less S to be present in area II, rich in schultenite, than in the orpiment-rich border of the flower (area I), while the arsenic distribution map shows a comparable arsenic content in areas I and II.…”

More than XRF Mapping: STEAM (Statistically Tailored Elemental Angle Mapper) a Pioneering Analysis Protocol for Pigment Studies

“…Furthermore, detectors with a larger detection area (or more than one detector in combination) highly increase the detected signal, speeding the measurement time up. Moreover, the size and the portability of these system allows to analyze samples with different dimensions, from manuscripts to large paintings [32][33][34][35][36], not only in museums or archives but also in archaeological sites [37], extending in this way the advantages of this kind of analysis to all the possible objects of the CH world. Besides, the higher spatial resolution has opened new possibilities for this technique, which allows not only to analyze the composition of the artist palette, or the presence of underdrawings, but that is also capable of recovering degraded and illegible daguerreotypes [38].…”

Dual mode standoff imaging spectroscopy documents the painting process of the Lamb of God in theGhent Altarpieceby J. and H. Van Eyck

“…This combined analysis contributed objective chemical evidence to the scholarly debate on conservation treatment decisions. With a much more complete understanding of the extent of overpaints and the state of preservation of the original paint below, it was decided to fully remove these 16th century nonoriginal layers, bringing to light the exquisite quality of the original Eyckian paint surface (20).…”