Imaging Analysis and Digital Restoration of the Holy Face of Manoppello—Part I
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heritage Article Imaging Analysis and Digital Restoration of the Holy Face of Manoppello—Part I Liberato De Caro 1,* , Emilio Matricciani 2 and Giulio Fanti 3 1 Istituto di Cristallografia, Consiglio Nazionale delle Ricerche (IC-CNR), via Amendola 122/O, 70126 Bari, Italy 2 Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milano, Italy; [email protected] 3 Dipartimento di Ingegneria Industriale, Via Gradenigo 6/a, Università di Padova, 35131 Padova, Italy; [email protected] * Correspondence: [email protected] Received: 28 September 2018; Accepted: 21 October 2018; Published: 25 October 2018 Abstract: The Veil of Manoppello is an icon of the face of Christ (Holy Face). Its particular characteristic is being semitransparent. The face is visible on both sides (front–back) and, depending on the lighting and observation conditions, shows some differences in the anatomical details. An analysis of this icon has allowed us to clarify some aspects of the possible physical mechanism underlying its unusual optical behavior. It is a linen fiber fabric consisting of very thin threads with a thickness of about 0.1 mm, separated by distances even double the thickness of the threads, so that about 42% of the Veil is empty space. The fibers constituting the linen threads may have been cemented by an organic substance of chemical composition similar to cellulose, presumably starch, eliminating the air between them. Such a structure causes the optical behavior of the medium to be intermediate between those of a translucent medium (thin cemented linen threads) and a transparent one (empty space between the threads). The problem of digital image restoration in spatial terms has also been tackled, since the Holy Face is deformed due to distortions of the meshes of the Veil, caused by the yielding of the very fine structure of the fabric. Keywords: artwork; optical characterization; Veil of Manoppello 1. Introduction The Veil of Manoppello is a small rectangular canvas of dimensions 240 × 175 mm2 characterized by a very thin, semitransparent fabric, on which is depicted the image of a male face with long hair and a divided beard. The represented face is associated in Christian iconography with Jesus Christ and, for this reason, it is called the Holy Face. It is kept in the Sanctuary of Manoppello (PE), Italy. This is a very special icon because the image is visible on both sides, as shown in Figure1 which shows the reliquary containing the Veil of Manoppello photographed front and back. The cheeks are markedly unequal because one of the two is particularly swollen. At first glance the chin does not seem to be in line with the rest of the face, and the eyes do not seem to be at the same distance from the nose. All these characteristics give an evident asymmetry to the face. The image has been studied by many scholars because it is not clear how it was created [1–10]. Its peculiarity is due to the fact that, observing the face in reflected light, it is visible from both sides. When the observer and the light source are on the same side and look at the front side of the Veil, the image that emerges is that shown in Figure1a; if, instead, the observer looks at the back side, the image represented in Figure1b emerges. The image is as if it were two-faced, although it shows some small differences such as, for example, the direction of the gaze. Heritage 2018, 1, 289–305; doi:10.3390/heritage1020019 www.mdpi.com/journal/heritage Heritage 2018, 1 290 Heritage 2018, 2, x FOR PEER REVIEW 2 of 17 Moreover, the face is visible even if it is observed by back-illuminating it with grazing light and observingHeritage 2018 the, 2 Holy, x FORFace PEER transmittedREVIEW by the Veil, as schematically shown in Figure2. 2 of 17 Figure 1. Face of the Veil of Manoppello seen from the front (a) and back (b), illuminated frontally and seen in reflection. Figure 1. Face of the Veil of Manoppello seen from the front (a) and back (b), illuminated frontally Figure 1. Face of the Veil of Manoppello seen from the front (a) and back (b), illuminated frontally and Moreover,and seen in reflection.the face is visible even if it is observed by back-illuminating it with grazing light and seen in reflection. observing the Holy Face transmitted by the Veil, as schematically shown in Figure 2. Moreover, the face is visible even if it is observed by back-illuminating it with grazing light and observing the Holy Face transmitted by the Veil, as schematically shown in Figure 2. Figure 2. Images of the Holy Face visible on the Veil of Manoppello depending on the conditions of Figure 2. Images of the Holy Face visible on the Veil of Manoppello depending on the conditions of lighting and observation. lighting and observation. Figure 2. Images of the Holy Face visible on the Veil of Manoppello depending on the conditions of lighting and observation. Heritage 2018, 1 291 Heritage 2018, 2, x FOR PEER REVIEW 3 of 17 ThatThat is, is, it isit visibleis visible even even when when the the observer observer and an thed the light light source source are are not not on on the the same same side. side. When When the observerthe observer and the and light the source light source are on are the on same theside same and side look and at look the frontat the side front of side the Veil,of the the Veil, reflection the imagereflection that canimage be that seen can is representedbe seen is represented by the green by the box green in Figurebox in 2Figure, which 2, which reproduces reproduces the image the ofimage Figure of1a; Figure if, instead, 1a; if, instead, the observer the observer and the and source the source are not are bothnot both on theon the same same side side and and the the VeilVeil is illuminatedis illuminated with with grazing grazing light, light, the imagethe image is transmitted is transmitted by by the the Veil Veil and and is thatis that visible visible in in the the yellow yellow box of Figurebox of 2Figure. Analogous 2. Analogous behavior behavi canor be can obtained be obtained if the iconif the is icon rotated is rotated by 180 by degrees. 180 degrees. In other In other words, twowords, very similartwo very images similar are images visible are and visible are and of the are type of the indicated type indicated in the greenin the boxgreen of box Figure of Figure2—one visible2—one from visible the front from side, the thefront other side, from the theother back from side. the Moreover, back side. it Moreover, is possible it to is view possible another to view couple ofanother images, couple also very of images, similar also to each very other—onesimilar to ea visiblech other—one from the visible front from side, the the front other side, from the the other back sidefrom of thethe icon—ofback side theof the type icon—of indicated the intype the indicate yellowd boxin the of Figureyellow 2box. However, of Figure they 2. However, differ in they some anatomicaldiffer in some details anatomical from the firstdetails couple from (those the first of thecouple green (those box). of We the pass green from box). the We images pass from of the the type representedimages of the in thetype green represented box to thosein the green of the box yellow to those box of by the changing yellow box the by conditions changing the of visualization conditions of visualization and illumination of the icon, i.e., passing from direct to grazing light and from and illumination of the icon, i.e., passing from direct to grazing light and from observer and source observer and source placed on the same side to observer and source placed on opposite sides of the placed on the same side to observer and source placed on opposite sides of the Veil. Veil. Finally, the direct light backlighting does not immediately make the face visible, because the Veil Finally, the direct light backlighting does not immediately make the face visible, because the Veil is so thin that the amount of light that reaches the observer would be excessive. Instead, by placing an is so thin that the amount of light that reaches the observer would be excessive. Instead, by placing obstaclean obstacle between between observer observer and and source source to shield to shield the the excess excess of light,of light, like like the the hand hand shown shown in in Figure Figure3 a, it is3a, possible it is possible to see to the see part the ofpart the of face the face that that falls falls in the in the shielded shielded area. area. Figure 3. Veil of Manoppello deformation: (a) detail of the Veil of Manoppello visible when light Figure 3. Veil of Manoppello deformation: (a) detail of the Veil of Manoppello visible when light source source and observer are perpendicular to the Veil but are on opposite sides, and the direct beam is and observer are perpendicular to the Veil but are on opposite sides, and the direct beam is partially partially shielded. The thin weave of the fabric is visible. The distortion of the threads which, shielded. The thin weave of the fabric is visible. The distortion of the threads which, obviously, deforms obviously, deforms the image has been highlighted; (b) face always seen in backlighting but with the image has been highlighted; (b) face always seen in backlighting but with grazing light coming grazing light coming from a lateral source.