Introduction

« Under Bellini’s brush the Transfiguration is realized as an event in which Christ literally mediates between the subtle air and dense matter, between the radiant heaven and the rock strata beneath the earth. (…) A sign of heavenly grace is the preeminent quality of colour in Bellini’s autograph works.» [1]

How does Bellini achieve such an effect, translating a divine event—“There he was transfigured before them. His face shone like the sun, and his clothes became as white as the light. (Matthew 17: 2, Bible, new international version)”- into the materiality of his painting? To answer this question, a technical investigation of Giovanni Bellini’s transcendental masterpiece, The Transfiguration, was carried out in the Capodimonte museum (Fig. 1). The Transfiguration is part of the cycle of the Glorification of Christ, together with the Resurrection and the Ascension, and represents not only the recognition of Jesus as Son of God, but also the continuity of the New Testament with the Old: the figure of Moses (to the left of Christ) stands for the Hebrew Law, and Elijah (to the right) for the Prophets. The figure of Christ, enveloped in the white draperies required by tradition, is presented in the posa orante—the pose characteristic of the Byzantine tradition—his arms outstretched, praying and receiving God’s grace [2]. The painting was under restoration, being cleaned of its old oxidised varnishes, and retouching removed [3, 4]. We were thus asked to answer specific questions linked to the restoration process in addition to furthering our understanding of Bellini’s materials and technique.Footnote 1

Fig. 1
figure 1

The Transfiguration by Giovanni Bellini, 1478–1479, 115 × 152 cm2, after its restoration in 2021, Capodimonte museum (Naples)

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Point XRF measurements as well as XRF and hyperspectral imaging techniques (which benefited particularly from the absence of reflectant varnish on the paint surface) were employed to this end. Although Bellini’s technique has been studied in depth over the years [5,6,7,8,9,10,11], chemical imaging is a recent addition to the field [7] which enriches our understanding of Bellini’s handling of the materials at his disposal. Comparative material—both published and unpublished—was provided by examinations of the works and scientific documentation at the National Gallery, London,Footnote 2 as well as articles in scientific publications and catalogues addressing the subject of Bellini’s technique. We highlight here a number of points focusing on the head and draped figure of Christ which we investigated in greater detail.

Historical elements and provenance

The precise original location and commission of the work are not known, although likely hypotheses have been put forward ([3], p. 350). What is known with a degree of certainty are the dates of execution, thanks to the interpretation of the Hebrew inscriptions on the scrolls held by Moses and Elijah, who stand by the sides of the Transfigured Christ: the Transfiguration was painted after the year 5239 of the Hebrew calendar (September/October 1478 and October 1479). In those years, Giovanni Bellini (c. 1430–1516) was fully developing what would become the core characteristics of the Venetian style. The founding element was the unity of the figures with the landscape enveloped in light, which here plays a key role, at the same time natural and symbolic. The use of oil as a binder, the knowledge of Flemish works and the assimilation of the Byzantine iconographic tradition are combined with a 'modern' approach, in full awareness of the achievements of Italian Renaissance art.

We find Bellini’s Transfiguration already referred to in 1644 and 1653 in the inventories of the Farnese palace in Rome. The work was subsequently moved to Parma, where—in about 1680—it appears in the Palazzo del Giardino, before being selected as one of the three hundred works to be exhibited in the new gallery in the Palazzo della Pilotta. It appears continuously in the Parma inventories until its transfer to Naples with Charles of Bourbon, Elisabetta Farnese’s heir in 1734, together with the rest of the Farnese collection exhibited now in the Museo di Capodimonte.

Methods

The painting was investigated with VNIR hyperspectral imaging [12,13,14,15] combined to MA-XRF [16, 17], which combination have proven to be efficient tool to characterize most pigments and provide information about paint techniques [18,19,20,21].

A VNIR hyperspectral camera made by Specim (Oulu, Finland) was mounted on a rotation stage to acquire the images in push broom technique. The painting was lit with halogen lamps during the period of acquisition. The spectral range was 350 nm to 1000 nm with 212 wavelength channels (rebinned from 1200) with a spectral sampling of 2.8 nm and 1600 spatial pixels. The scan was acquired with an OL50 objective from Specim (focal length 50 mm) and with 100 ms integration time, 5 fps (frames per second) and 0.03°/s rotation speed. The dedicated ENVI software (Harris Corporation, Melbourne, Florida, USA) was used for data treatment. The data was normalized with dark and bright field images using the Specim plug-in in ENVI. The spectral angle mapper (SAM) algorithm of ENVI was used to obtain reflectance maps.

An in-house-built XRF instrument was used, featuring a Pd anode end window X-ray tube (Moxtek MAGNUM, Orem, UT) operated at 30 kV and 50 μA and a silicon drift detector (X-123FAST SDD, Amptek, Bedford, MA) with an active area of 25 mm2 collimated to 17 mm2 and a nominal thickness of 500 μm. The X-ray tube was connected to the detector via a holder produced by 3D printing (fixing the angle between both to 45° for single point analysis, or 32° for imaging). As a collimator primary optic, a Pd tube of 800 μm inner diameter was used, yielding a beam size of approximately 1.2 mm. The typical working distance is 1 cm. A digital microscope (Dino-lite, AnMo Electronics Corporation, New Taipei City, Taiwan) and a laser distance measurement device (OADM20, Baumer, Frauenfeld, Switzerland) allow for measuring the position of the primary beam on the surface of the object. The system was used with manual translation stages for single-point analysis with acquisition time of 300 s. For XRF imaging the measurement head was mounted on a motorized XY stage with 20 cm travel range in both directions (M-403.8PD, PhysikInstrumente (PI) GmbH & Co. KG, Karlsruhe, Germany) with an additional manual Z translation. The motorized stage was fixed to a 3-axis manual rotation stage mounted on a photographic tripod. The instrument has been previously described elsewhere [22]. The central area was investigated using a step size of 1 mm and a dwell time per pixel 0.2 s. For the evaluation of the raw, full spectral XRF data, the PyMCA software was used [23].

Macrophotographs (Olympus OM-D E-M5 Mark II with Olympus 60 mm macro lens) of the analysed areas were also taken.

Results and discussion

The discussion will focus on Bellini's account of the manifestation of the divine on Earth, hence on the head and torso of the transfigured Christ and the surrounding area of the sky, and details related to the event. The figure of Christ is central to the meaning of the painting and our results for this area are therefore emblematic of Bellini’s entire approach to the depiction of the Transfiguration.

The sky

Two different blue pigments have been identified in the sky (Fig. 2 and XRF spectra in Additional file 1: Fig. S1 and Table S1). In the azure sky against which we see Christ’s head with rays of Divine light, the main chemical elements identified by XRF analyses were silicon and potassium (no cobalt) indicating the presence of lapis-lazuli (confirmed by the reflectance spectrum [24, 25] extracted from this area, Fig. 2f). In the sky beyond the clouds, which is of a darker hue, the main chemical element identified by XRF analyses was copper indicating the probable use of the blue pigment azurite, in accordance with its visible spectrum (Fig. 2f). The use of both lapis-lazuli and azurite has been found in other works by Bellini [3] but more traditionally either with underlayer of azurite followed by surface layer of lapis or at times in mixtures which is a less common occurrence [5]. The use of lapis in this particular painting may be linked to a symbolic value of these two pigments: lapis-lazuli, the most precious pigment, stands for divine. At the time lapis-lazuli originated in what is now Afghanistan, and was identified with the Garden of Eden, so that it may also have a symbolic value as well as being prized in terms of monetary worth [26, 27]. This blue area painted with lapis-lazuli is correlated with the overpowering radiance of the transfigured Christ. Azurite is used for the dark cloud that appears to envelop the onlookers and conceal the sight of God the father speaking from above, while the clear, limpid sky is painted using lapis-lazuli. It is interesting to note that in the landscape, while copper-based pigments are present elsewhere (mountains, river…), lapis-lazuli is also present in tiny blue flowers near what can be interpreted as the cross of Christ (Fig. 3).

Fig. 2
figure 2

a Detail of the Transfiguration; MA-XRF elemental distribution images of b Cu and c K, in the corresponding zone; d infrared false colour image obtained from VNIR hyperspectral data (Red 900 nm, Green 628 nm, Blue 542 nm) of a detail of the painting; e azurite and lapis map obtained after SAM treatment (Spectral Angle Mapper) of the VNIR hyperspectral data, from pre-defined end members shown in f (dark blue stands for lapis, light blue for azurite).

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Fig. 3
figure 3

Detail of the landscape, with the pre-figuration of the Cross, and the tiny blue flowers painted with ‘celestial’ lapis-lazuli

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The figure of Christ

Specific composition of the halo

The rays in the halo around the head of Christ were represented with gold whereas lead tin yellow has been used for the rays of the sun in the sky (Fig. 4). The difference in the nature of the rays is thus reflected in the materials used to represent them: both are manifestations of ‘light’, but the rays emitted by the figure of Christ are of a divine nature, as symbolized by the gold. The light emitted by the sun is, in contrast, of a terrestrial nature.

Fig. 4
figure 4

Study of the halo a Detail of the Transfiguration centered on the face of Christ; b UV fluorescence photographof the corresponding zone; MA-XRF elemental distribution images of: c Au (L lines) and d Sn (L lines), in the corresponding zone; e macro-photograph of a ray of the halo showing the shell-gold; f macrophotograph of the halo and g reflectance spectra of the two points indicated in f)

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It is also particularly interesting to note the presence of a broad, dark golden yellow halo (particularly visible in the UV photograph, Fig. 4b below) surrounding Christ’s head, beneath the golden rays. We then compared the reflectance spectrum of this yellow halo to the one of the surrounding sky (Fig. 4f, g below). The halo induces a significant absorption in the blue part of the reflectance spectrum leaving the rest of the spectrum unchanged. In the same way as an old discoloured varnish, it acts as a yellow filter [28]. This suggests, as does observation of the paint surface, that this halo is an organic layer painted over the sky. However, the warm hue of this layer is not simply due to ageing, but deliberate, in that both particles of Fe and Hg (that is an earth pigment and vermilion) have been added (visible in macrophotographs and confirmed by XRF). A similar technique was used by Bellini in the early Blood of the Redeemer in the National Gallery (London) [6, 7] (p. 39) in conjunction again with shell-gold, in the latter painting used in the chalice as well as the halo.Footnote 3

Modelling of flesh tones and hair

When we compare the X-radiograph and the complementary Pb XRF map of Christ’s head with what we see in the painting (Fig. 5), it becomes clear that the current outline gives Christ a broader head compared to the original more elongated one. This broader shape is more in keeping with a powerful figure of Christ resurrected and transfigured, rather than the Christ of Sorrows. The image also suggests a change in the position of the Christ’s eyes and/or of head. Christ may originally have had his eyes turned towards the heavens or towards Moses, as in the early Bellini’s Correr Transfiguration (Fig. 6a), rather than fixed outside of the picture plane towards the onlooker.Footnote 4 This is a theologically significant change: in the later Capodimonte Transfiguration, Christ is looking towards us. We have observed above how Christ’s pose is that found in the Byzantine tradition, but it is possible to be more precise. Christ is depicted as the shepherd of his flock, symbolized also by the presence of the sheep in the landscape on the left, on the hill. On the other side, to the right of the figure of Christ, we see the tower of St Apollinare in Classe in Ravenna in which church is found one of the most magnificent and beautiful mosaic symbolic representations of the Transfiguration of Christ (Fig. 6b). In the mosaic Christ is represented by the Cross, the three apostles by three sheeps, while the figure of St Apollinaris is depicted as the good shepherd, in an orating pose, with the flock of sheep on his right and left. Comparing these different images (Fig. 5) suggests that the figure of the transfigured Christ at first was perhaps closer to the Christ painted by Bellini in the Correr Transfiguration before becoming closer to that of the orating St Apollinaris in the Ravenna mosaic.

Fig. 5
figure 5

a Detail of the Transfiguration centered on the face of Christ; b X-radiograph and c MA-XRF elemental distribution image of Pb (L lines).

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Fig. 6
figure 6

a Detail of the early Transfiguration (1454–1460) Museo Correr, Venice (Wiki commons); b Transfiguration mosaic in Sant’Apollinare in Classe, Ravenna; c Giovanni Bellini Resurrection (1475–1479), Gemäldegalerie, Berlin (Wiki commons).

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As is customary, both vermilion (characterized by the presence of Hg) and an earth pigment have been both used for faces and hands (Fig. 7 and Additional file 1: Fig. S2). Calcium is also present in greater quantities in areas of shadow, in such cases it is usually linked to the presence of earth pigments or bone black; however here, it does not follow the same variations as iron, and there is no phosphorus. The same kind of calcium variations seems to be present in Christ’s tunic. These variations might be due to the absorption of lead white: thick layers of lead white in the lights will absorb the calcium signal from the gesso ground, in contrast to the nearly lead-free layers of the shadows.

Fig. 7
figure 7

Selection of MA-XRF elemental distribution images

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The brown colour of the hair is obtained using a mixture of pigments, rather than a single pigment—earth, vermilion and probably lead tin yellow (the presence of tin being difficult to assess in low concentrations, given the calcium content). This use of a mixed brown for hair—the tonalities of which can be manipulated in accordance with the fall of light and shadow by varying the proportions of individual pigments—is also found in the works of Raphael’s father, Giovanni Santi [29] and the early Raphael,Footnote 5 for example [30], as well as being a technique used by Bellini from his earliest works.Footnote 6

Modelling light and shadow/warm and cool tonalities in the draperies

In Christ’s pale blue/grey cloak, the XRF spectra (Additional file 1: Fig. S3) indicated the presence of antimony (Sb), characteristic element of the dark grey pigment stibnite (Sb2S3), a pigment which has been found in other works painted in this period [31, 32]. This would appear to be the earliest work in which the pigment has been to date identified. Marika Spring ([19], p. 209) rightly observes that although these metallic pigments have luster when seen under the microscope, this is not the case when observed on the picture surface. For comparison with Bellini, she observes "In the Virgin and Child with four Saints (NG 3091) by Bonsignori stibnite was used for the grey shadows of the white drapery of the saint on the right and for the dark grey beard of the elderly saint" ([32], p. 102]). In Bellini’s Transfiguration stibnite produces the cold metallic grey tones that we see in the shadows of Christ’s cloak.

In contrast to the cloak with its cool tonalities, the warm white of the tunic—under magnification—shows not only the presence of red lake particles imparting the rosiness, but also a few blue particles, thus bridging and unifying the two draperies. Paul Hills, examining Bellini’s Resurrection (thought to have been painted in these same years, Fig. 6c) from the Gemäldegalerie, Berlin during the exhibition at the Quirinale in 2008, also noted the difference in the whites between the loin cloth and the winding sheet (the shroud), the former a bluer tonality, and the other pinkerFootnote 7 [33]. Other works by Bellini show his interest in capturing exactly the desired tonality of white, either to be true to the light, or to the symbolic message of the painting. In the Madonna of the Meadow in the National Gallery for instance the white of the Virgin’s veil—both in lights and shadows—is tinged with green, particles of verdigris are visible under magnification.Footnote 8 It is again Paul Hills, who makes the following observations which, although directed to the role of white in a later altarpiece by Bellini, are equally valid for his Capodimonte Transfiguration: « In this spatial play of colour the orchestration of whites plays a crucial part: even if subtleties have been lost due to changes over time, we can still appreciate Bellini’s strategy in deploying a range of near-whites shifting between warm and cool. (….) what is most distant—the luminosity of the sky with its modulation of blue, warm grey, and palest apricot—is associated with what is most near. So the light of heaven is admitted through the intercessory saints, and through the almost secret, luminous presence of the pale flesh of Christ, into the very space of the church, San Giovanni Crisostomo» ([1] p. 194). The artist achieves with his handling of pigments the radiance of the gold of mosaics and the luminosity, so central to the depiction of the divine scene—“His face shone like the sun, and his clothes became as white as the light” (Matthew 17: 2, Bible, new international version).

From evidence in the painting it is possible to go further in the comparison with the mosaic representation in Ravenna: in the mosaic, Christ is represented as a jewelled, metallic cross. Bellini in his painting has not only indicated the church, but has included the flock of sheep (Christ is the living—human—shepherd) and the modelling of Christ’s cloak with this unusual metallic pigment can be interpreted as a material allusion to his Divine as well as human nature (as in the mosaic). Such a symbolic interpretation can also be extended, as we have observed above, to the tree stump with its three ‘nails’ in the bottom left of the painting, alluding to the Cross. Such symbolic pictorial language was an integral part of the medieval tradition of representation, which continued and fed the arts well into the Renaissance period and beyond.

Conclusion

Giovanni Bellini’s Capodimonte Transfiguration stands at the crossroads between the Byzantine and medieval traditions and the modern age: the results show both continuity with the Flemish technique (in particular in the rendering of the natural light over the figures and, moreover, the landscape) and with that already described in works by Bellini that precede this work (shell gold and tinted organic layers already found in early work). On the contrary, innovative features can be highlighted such as the earliest example to date of the use of stibnite. The choice of different pigments (gold vs lead tin yellow, lapis vs azurite) appears to be linked to their symbolic value in order to represent the divine event but also to modulate colour as in nature. Bellini takes from tradition the hieratic pose of the praying Christ, the fixity of his gaze, the very distribution of the figures in space, but everything is set in nature, everything is rendered with verisimilitude. The description of the light in this work by art historians is confirmed by material analysis, in particular thanks to chemical imaging that allows the handling of the material to be visualized. The artist achieves with his handling of pigments the radiance of the gold of mosaics and gold-backgrounds transmuted into modulations of light belonging to the natural world.