Macroscopic XRF imaging in unravelling polychromy on Mycenaean wall-paintings from the Palace of Nestor at Pylos

Journal of Archaeological Science: Reports 29 (2020) 102079

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Macroscopic XRF imaging in unravelling polychromy on Mycenaean wallpaintings from the Palace of Nestor at Pylos

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Eleni Kokiasmenoua,b, Claudia Caliric, Vasiliki Kantareloua, Andreas Germanos Karydasa, , Francesco Paolo Romanod, Hariclia Brecoulakie Institute of Nuclear and Particle Physics, NCSR “Demokritos”, 153 41 Agia Paraskevi, Athens, Greece Aristotle University of Thessaloniki, University Campus, 54124, Greece c INFN-LNS, Via Santa Sofia 62, 95123 Catania, Italy d IBAM-CNR, Via Biblioteca 4, 95124 Catania, Italy e Institute of Historical Research, The National Hellenic Research Foundation, 11635 Athens, Greece a

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A R T I C LE I N FO

A B S T R A C T

Keywords: Macroscopic XRF imaging Ancient polychromy Mycenaean wall-paintings Palace of Nestor at Pylos Late Bronze Age

The wall painting fragments from the Mycenaean “Palace of Nestor” at Pylos, are characterized by their high artistic quality, their unusual iconographic variety and the use of tempera and secco painting techniques. Systematic in-situ XRF analyses combined with the results of other portable and laboratory analytical techniques have already revealed a rich gamut of inorganic pigments with respect to the common Aegean “palette”, including different white and black pigments, iron based ochres ranging from dark brown to orange and pinkish hues, manganese based umbers, natural copper based greens, goethite, Egyptian blue and organic purple dyes. Macroscopic X-ray Fluorescence (MA-XRF) imaging, although well-established for non-invasive analysis of historical or contemporary painted artworks has hitherto been applied in a few cases only regarding the study of ancient polychromy. The purpose of applying in-situ MA-XRF imaging on selected wall painting fragments from the Palace of Pylos was to evaluate the capabilities of this technique in identifying the composition of pigments and their spatial distribution within heavily deteriorated pictorial layers, and in revealing iconographic information invisible to the naked eye. The results of MA-XRF imaging allowed us to critically re-consider previous artistic reconstructions, providing significant evidence on the painting techniques and materials used by Late Bronze Age painters.

1. Introduction 1.1. The Palace of Nestor at Pylos The Palace of Nestor at Pylos, discovered by Carl Blegen and his colleagues in 1939 is located on the Ano Englianos Ridge in Western Messenia and is one of the most important and best-preserved Mycenaean palaces. (Blegen et al., 2001; Davis, 2010) The palace is dated to the LH (Late Hellenic) IIIB period (c. 1200 BCE) and consists of four main buildings and some smaller ones. The wall-paintings from the interior and exterior of the palatial complex represent a unique corpus of the Late Bronze Age painting. (Brecoulaki et al., 2012) For the first time, “a secco” techniques (egg, tragacanth gum) have been identified for such an early period in the history of ancient Greek painting. (Brecoulaki et al., 2012) A few wall-painting fragments from the Palace are exhibited at the Archaeological Museum of Chora, however, approximately 15.000 fragments are located at the storage room of the

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museum. Since 2002, a project on the study and publication of this important pictorial corpus by a multidisciplinary working group has been supported by the Hora Apotheke Reorganization Project (HARP). Ever since, a systematic documentation, conservation and scientific examination of the wall painting corpus has allowed an enhanced understanding of the making of the paintings, their materials and techniques, the artistic workshops and the iconographic programs of the various rooms, revealing unpublished scenes and producing new revised graphic reconstructions of already known compositions. The obtained results have, therefore, significantly enhanced our perception and appreciation of the Palace’s painting narrative. Since the middle ‘70s the scientific examination of Aegean Bronze Age wall paintings by means of analytical laboratory and portable nondestructive techniques, has produced a series of publications regarding the reconstruction of Aegean painters’ “palette”. (Jones and PhotosJones, 2005) A variety of inorganic and organic pigments has been identified, including iron-based ochres, (Brecoulaki et al., 2008;

Corresponding author.

https://doi.org/10.1016/j.jasrep.2019.102079 Received 24 July 2019; Received in revised form 31 October 2019; Accepted 6 November 2019 2352-409X/ © 2019 Elsevier Ltd. All rights reserved.

Journal of Archaeological Science: Reports 29 (2020) 102079

E. Kokiasmenou, et al.

height of ca. 0.65 m. Given the fragmentary state of the Naval Scene and the frequent absence of critical details, the proposed reconstruction (Fig. 1) partly relied on better preserved Mycenaean ship images coming from either wall-paintings or other artistic media, such as seals and pottery. (Brecoulaki et al., 2015). All of the preserved elements of the ships in the Naval Scene are rendered in lighter and darker tones of brown and yellow ochre, however we may not fully appreciate the chromatic range employed in the composition because the surface of the plaster has been severely damaged by fire. The lines that define the sheer of the hull and keel are dark brown, outlining the mass of the hull which itself is a lighter yellowish brown. The only other color employed in the composition, besides carbon black and calcium carbonate white, is the light purple used to indicate the sea, deriving from Murex seashells. Physicochemical analyses have already confirmed that pigments were applied with the “a secco” and not the “buon fresco” technique, using both egg and vegetable gums as binders. (Brecoulaki et al., 2012) Mechanical damage and chemical alteration of the original colors due to environmental factors and high temperature, can be observed on the actual surface of the examined fragments (labelled as I, II, III in Fig. 2). The plaster, composed of a homogenous white calcium-based layer, is visible in different areas where paint has fallen. Due to the total or partial loss of the paint layer, the identification of a number of iconographic details is seriously obstructed. The Battle Scene wall-painting (Fig. 3) reconstructed by Piet de Jong decorated the wall to the right of the doorway between Hall 64 and lobby 66. (Brecoulaki, 2014; Lang, 1969) Hall 64 is part of the Southwestern Building, located southeast of the Main Building of the palatial complex, played a central role in the circulation patterns, leading through a central door in its southwest wall into the Megaron, and through a wide-open entrance with two columns to the large Court 63, which spread southeast and beyond. (Shaw, 2001). The fragment (Lang, 1969) from the Battle scene of Hall 64 has total dimensions 21 cm height and 16 cm width and is the best preserved from the examined wall-painting fragments (Fig. 4). It shows a more varied range of colors, including red, purple, blue, black, white and from light brown to dark brown hues. The iconography is easily comprehensible, even in detail. The figure of a warrior is represented in the active time of a hand-to-hand battle. The dark brown almost red colored body of the warrior emerges from a violet background. His garment has a white color with a black pattern on top of it. The white color has been also employed in the weapon holding in his right hand and in his helmet, which are both decorated with black repeated motives. The figure of the opposite warrior is partly saved. His clothing and weapon differentiate from the other’s. The hands of the two warriors holding the weapons are crossed, capturing a concomitant scathe. The background of the Battle Scene wall-painting has mainly a uniform purple color, which in certain areas presents a darker hue or a bright

Brysbaert, 2008; Brysbaert et al., 2006; Brysbaert and Vandenabeele, 2004; Coleman et al., 1973; Dandrau, 1999; Profi et al., 1974, 1976, 1977; Sotiropoulou et al., 2012; Brecoulaki et al., xxxx; Brysbaert and Perdikatsis, 2008; Pantazis et al., 2003; Perdikatsis et al., 2000; Perdikatsis, 1998) carbon and mineral based blacks, (Brecoulaki et al., 2008; Brysbaert, 2008; Brysbaert et al., 2006; Cameron et al., 1977; Coleman et al., 1973; Profi et al., 1974, 1976, 1977; Brecoulaki et al., xxxx; Perdikatsis, 1998) and Egyptian blue. (Brecoulaki, 2018; Brysbaert, 2008; Brysbaert et al., 2006; Cameron et al., 1977; Coleman et al., 1973; Dandrau, 1999; Filippakis et al., 1976; Profi et al., 1974, 1976, 1977; Brecoulaki et al., xxxx; Brysbaert and Perdikatsis, 2008; Pantazis et al., 2003; Perdikatsis et al., 2000; Perdikatsis, 1998; Vlachopoulos and Sotiropoulou, 2012) Minerals of the amphibole group (riebeckite and glaucophane) have also been attested on wall paintings from Knossos, Thera, Ayia Irini, Ayia Triada and Amnissos, to produce grey-blue hues often in mixtures with Egyptian blue. (Cameron et al., 1977; Filippakis et al., 1976; Profi et al., 1977; Sotiropoulou et al., 2012; Perdikatsis et al., 2000; Perdikatsis, 1998; Vlachopoulos and Sotiropoulou, 2012) The use of manganese based umbers has been attested in Pylos for the production of dark brown hues. (Brecoulaki, 2018; Brecoulaki et al., xxxx) Although the use of natural green pigments is relatively rare, malachite and other copper based greens (chrysocolla, atacamite/paratacamite) have been identified in Tiryns and Pylos. (Brecoulaki, 2018; Brecoulaki et al., xxxx; Heaton, 1912) Most frequently green hues are produced through the blending of Egyptian blue or of an amphibole mineral with yellow ochre, a practice that has been encountered in several sites and particularly in Tiryns, Knossos and Akrotiri. (Brysbaert et al., 2006; Brysbaert and Vandenabeele, 2004; Cameron et al., 1977; Brysbaert and Perdikatsis, 2008; Pantazis et al., 2003; Perdikatsis et al., 2000) Calcite has been identified as the main painting material for the white color (Brysbaert, 2008; Cameron et al., 1977; Coleman et al., 1973; Dandrau, 1999; Profi et al., 1976; Brecoulaki et al., xxxx) with seldom use of kaolinite, identified in Knossos and Pylos. (Cameron et al., 1977; Dandrau, 1999; Brecoulaki et al., xxxx) A parsimonious use of Murex purple has been attested in the wall-paintings of Akrotiri; Thera and Pylos. (Brecoulaki, 2014, 2018; Doumas, 1992; Sotiropoulou et al., 2012; Brecoulaki et al., xxxx; Chrysicopoulou and Sotiropoulou, 2003; Sotiropoulou and Karapanagiotis, 2006). 1.2. Description of the wall-paintings fragments The examined fragments are part of two major compositions, a Naval Scene (Figs. 1, 2) and a Battle Scene (Figs. 3 and 4), which originally adorned the northeastern and northwestern walls of Hall 64. The Naval Scene depicts three seagoing ships sailing from left to right across a light purple background, prows and sterns overlapping slightly. The hulls of the ships vary from 0.70 to 0.90 m, allowing us to reconstruct the total length of the frieze at approximately 2.50 m, with a

Fig. 1. Reconstruction of the Naval Scene from Hall 64, by R. Robertson. The corresponding wall-painting fragments composing the Naval Scene are marked in the reconstruction as I, II and III. The different areas of the fragments scanned by MA-XRF imaging are also outlined in the reconstruction and are depicted with small letters. (Copyright. Department of Classics, University of Cincinnati.) 2

Journal of Archaeological Science: Reports 29 (2020) 102079

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Fig. 2. Wall-painting fragments (I, II and III) composing the Naval Scene from Hall 64. The different areas of the fragments scanned by MA-XRF imaging are also outlined with small letters. The two ‘spot-like’ areas I-c, I-d in the fragment I correspond to the selected subareas of interest of the scan (I-a). (Copyright. Department of Classics, University of Cincinnati.)

focusing elements, along with real-time scanning possibilities have driven the establishment of Macroscopic XRF (MA-XRF) imaging analysis as a key methodology for the examination of multicolored surfaces (Romano et al., 2017) MA-XRF analysis can visualize the spatial distribution of detected elements on the decimetre scale at sub-millimetre resolution creating individual elemental maps and thus providing a more comprehensive basis even for non-experts to get insights into the painting’s creation process. Moreover, MA-XRF imaging has succeeded in many cases to revisualize an overpainted image or to reveal iconographic elements that are either invisible to the naked eye or illegible due to their bad state of conservation. The continuous optimization of MA-XRF spectrometers has allowed the creation of elemental images over extended areas of painted artworks (Romano et al., 2017; Trentelman, 2017; Križnar et al., 2018), whereas most recently been applied for the investigation of ancient painting and polychromy. (Alfeld et al., 2017, 2018b; Kantarelou et al., 2016; Alfeld et al., 2018a) Macro-XRF imaging and mobile hyperspectral reflectance were applied on the marble frieze of the Siphnian Treasury in the Sanctuary of Delphi (Greece), allowing the detection of traces of pigments invisible to the naked eye and therefore never previously recorded. The benefits of performing MA-XRF on painted stationary objects with a mobile instrumentation have also been made evident in the investigation of the Etruscan wall-paintings of the Banditaccia Necropolis, near Cerveteri

blue color. This diversity could be due to chemical alteration or the mixing of pigments. Although in the suggested reconstruction of the Naval scene (Fig. 1) and the Battle Scene (Fig. 3) a significant number of pictorial elements has been revealed by means of optical pictorial elements has been revealed by means of optical microscopy and technical photography (raking light, UV and VIL), (Accorsi et al., 2009; Verri, 2009a,b) certain details remained uncertain and their reconstructions hypothetical. It was, therefore, a challenging perspective to examine the aforementioned fragments of the Naval Scene and the Battle Scene with MA-XRF imaging and figure out whether additional pictorial elements could eventually be traced, likely to enhance our understanding of the original compositions and their iconography. 2. Experimental 2.1. MA-XRF imaging on ancient polychromy X-ray fluorescence analysis is a well-established technique, due to its non-invasive character, the possibility of an in-situ and fast examination of a large variety of artefacts and its analytical capability of simultaneous multi-elemental analysis of inorganic materials. The continuous development of the analytical features of different X-ray instrumentation components, in particular of X-ray detectors and X-ray

Fig. 3. Reconstruction of the Battle Scene from Hall 64, by Piet de Jong. The area outlined on the reconstruction corresponds to the wall-painting fragment examined by MA-XRF imaging. (Copyright. Department of Classics, University of Cincinnati.) 3

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Fig. 4. The Battle Scene fragment (IV) from Hall 64, Palace of Nestor at Pylos. Cumulative MA-XRF spectra were generated from few characteristic tiny areas (6–18 mm2) depicted with small letters (a-g). (Copyright. Department of Classics, University of Cincinnati.)

(Alfeld et al., 2018a) and on the Archaic statue of Phrasikleia, (Kantarelou et al., 2016) while a first impressive application of a multimodal chemical imaging, including MA-XRF analysis was presented for the characterization of painting materials on a Greco-Roman portrait from Fayum, Egypt. (Delaney et al., 2017)

2.2. The Macro-XRF spectrometer (Landis X-scanner) LANDIS-X is a novel mobile MA-XRF scanner developed at the LANDIS laboratory of INFN-LNS and IBAM-CNR in Catania (Italy). (Romano et al., 2017) It is based on a microfocus 30 W Rh-target X-ray tube coupled to a polycapillary with a nominal spot diameter of 26 μm at the energy of the Rh Kα-line and at about 1 cm focus distance. The emitted X-ray fluorescence is detected by means of two 50 mm (Davis, 2010) active area SDD detectors with an energy resolution of 133 eV at 5.9 keV. X-ray spectra are acquired in a time-list mode (TLIST) by using two Digital X-ray Processors (DXPs) with 40 ns time resolution. The detectors are installed on a compact 3-axis platform, which permits the alignment of the detector with the primary beam in a manual way. Furthermore, it is possible to mechanically adjust and find the proper position of the detector when samples with irregular surfaces are analyzed. The X-ray source and detectors operate in a 45–90-45 geometry (Fig. 5). When scanning is performed with samples at the focus position of

Fig. 5. Portable ΜΑ-XRF spectrometer (Landis X-scanner) developed at the LANDIS laboratory of INFN-LNS and IBAM-CNR in Catania during in-situ measurements of wall-painting fragments at the Archaeological museum of Chora Messenia’s. (1) Rh-target X-ray tube (2) SDD X-ray detectors (3) Polycapillary X-ray lens.

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the poly-capillary lens, an optimum lateral resolution down to 26 μm can be achieved. However, all present measurements were carried out with a sub-millimeter spatial resolution (0.5–1 mm) by properly adjusting the analyzed surface closer to the lens. To ensure that the measurement head remains at focus during the scanning, a triangulation laser proximity sensor with a 750 Hz read-out rate is used offering a distance precision of about 4 μm and spot size equal to 210 μm. During the scanning, a stop signal triggered by the laser proximity sensor is produced to ensure a safety pre-defined distance between the measurement head and the object analyzed. The sample is placed perpendicularly to the exciting beam. The movement of the measurement head during scanning is carried out by means of a three-axis system, that allows a travel range of 110 cm, 70 cm and 20 cm along the X, Y, Z directions respectively. In order to determine the exact position of the measurement head, wire sensors are integrated into each of the axes. In this way, if the measurement is interrupted for any reason, it can be restarted at a subsequent time, as the absolute position of the measurement head in XYZ coordinates is known. The maximum continuous speed of the scanning is 100 mm/s. (Romano et al., 2017) LANDIS-X scanner is equipped with a custom-developed central unit (CU) including a graphical user interface (GUI) programmed in Labview that allows the real-time control of the scanner. During the measurement, the CU controls all sensors installed in the scanner in a deterministic mode and it provides deconvoluted elemental distribution images on the fly. The pixel size is initially selected by users, though there is the possibility to redefine it in case that the forming images are not satisfactory in terms of counting statistics. Once pixel spectra are elaborated, they are processed in real-time by the least square fast fitting procedure developed in PyMca (Solé et al., 2007) and integrated in the system. Many analytical tools (e.g. scatter plot, PCA and ICA analysis, ROI Imaging and pixel spectra analysis, RGB correlation plots etc.) can be applied during scanning to the forming elemental images. (Romano et al., 2017; Solé et al., 2007) The experimental conditions used for each MA-XRF scan of the examined wall-painting fragments are presented in Table 1. The parameters step size and time/pixel were being adjusted according to the dimensions of the scanned area. Generally, no filter was used in the exciting X-ray path, except for the detailed scans, performed on the purple (II-c) and substrate (II-d) areas of the fragments. In this case, a combined filter material composed by the following elements: Ni (24 μm) / Fe (6 μm) / Ti (25 μm) was interposed between the X-ray tube and the sample to improve effectively the peak – to background ratio and thus optimizing the

detection of certain trace elements like bromine (Br). 2.3. Objectives of the present work A representative number of wall-painting fragments from the Palace of Nestor at Pylos have already been examined by complementary nondestructive and destructive laboratory techniques (XRD, SEM-EDS, HPLC-UV–Vis, GC–MS, PY-GC–MS, DE-MS, PIXE-alpha, FTIR and μRAMAN spectrometry), in order to identify the painters’ materials and techniques (This work is expected to be published in the book “Technologies of Representations in the Aegean Bronze Age”, with the title “Representing in Colours at the ‘Palace of Nestor’. An Evaluation of the Original Polychromy, The Painting Materials and their Meaning”). (Brecoulaki et al., 0000) A total number of about 400 single spots were analyzed by means of portable XRF on fragments from different rooms of the Palace, providing qualitative information and identification of a large variety of inorganic pigments. (Brecoulaki et al., 2008; Brecoulaki et al., 0000) The present work constitutes a first very promising application of the MA-XRF imaging for the study of Late Bronze Age wallpaintings, aiming at characterizing the chemical composition of the painting materials, as well as revealing technical and iconographic information non-visible to the naked eye. 3. Results and discussion 3.1. The fragments from the Naval Scene The pigments identified on the Naval scene fragments are rather restricted, composed mainly of Fe and Cu depicted in GB correlation with green (Fe) and blue color (Cu), respectively (Fig. 6). In Fig. 6, the generated iron and copper MA-XRF distribution images are presented alone (left part) and superimposed to the analysed fragments (middle part), while on the right part the existing reconstructions, prior to the updated MA-XRF results regarding the iconography are shown. In the iron distribution image of all the three fragments the brushstrokes and lines defining the different elements of the depicted ships are revealed (Fig. 6). It is, therefore, possible to conclude that ironbased ochres were used to render the general shape of the hulls, the oars and superstructures, as well as other details related to their decoration. The copper distribution images have accrued by spreading Egyptian blue grains on the background, except for the reserved areas of the ships

Table 1 List of all wall-painting fragments and MA-XRF scans performed with information on the experimental conditions used. The specific scans (I-c), (I-d) and (IV-b) to (IVg) refer to selected subareas extracted from the large scans (I-a) and (IV-a) respectively. Wall-painting

Fragment

MA-XRFScan

Scanned area(pixel × pixel)

Step size (μm)

Time/pixel (ms)

Tube voltage (kV)

Tube current (μA)

Filter

Naval Naval Naval Naval Naval Naval Naval Naval Naval Naval Battle Battle Battle Battle Battle Battle Battle

I I, Figure detail I, faded purple area I, substrate area II II, Fish detail II, purple area II, substrate area III, part III, part IV Brown area Black area White area Purple area Blue on purple area Brown/blue/purple area

I-a I-b I-c I-d II-a II-b II-c II-d III-a III-b IV-a IV-b IV-c IV-d IV-e IV-f IV-g

256 × 189 80 × 90 40 × 10 40 × 10 260 × 167 53 × 66 10 × 10 10 x10 171 × 129 109 × 98 153 × 121 6×2 4×3 4×5 6×6 6×4 4×3

1000 500 1000 1000 1000 1000 100 100 1000 1000 1000 1000 1000 1000 1000 1000 1000

150 400 150 150 150 500 3000 3000 150 150 200 200 200 200 200 200 200

40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40

200 250 200 200 250 250 500 500 200 200 300 300 300 300 300 300 300

Unfiltered Unfiltered Unfiltered Unfiltered Unfiltered Unfiltered Filtered Filtered Unfiltered Unfiltered Unfiltered Unfiltered Unfiltered Unfiltered Unfiltered Unfiltered Unfiltered

scene scene scene scene scene scene scene scene scene scene scene scene scene scene scene scene scene

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Fig. 6. . MA-XRF images in Green-Blue (GB) correlation showing the spatial variation of the Fe-Kα and Cu- Kα intensities with green and blue colors, respectively, alone and superimposed to the analyzed fragments. The reconstructions on the right were made by R. Robertson. (Copyright. Department of Classics, University of Cincinnati.) (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

been used together with the organic pigment Murex purple (Brecoulaki, 2014, 2018; Brecoulaki et al., xxxx), in order to produce a specific hue for the depiction of the sea. Iron MA-XRF distribution images of the ships allowed not only to

(the identification of Egyptian blue was confirmed by means of VIL (Verri, 2009a,b). The use of Murex purple has been already attested on the background of the Naval Scene (Brecoulaki, 2018) and based on the copper distribution image it can be concluded that Egyptian blue has

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better visualize details that were already incorporated into the graphic reconstruction, but also to recover new elements that had not been tracked previously. The shape of the hull and the deck of the first ship to the left (Fig. 6, scan (I-a)) are clearly indicated in the iron distribution image, in full accordance with the reconstruction. Part of the depicted fish in the left edge below the ship and the shape of a figure inside the ship’s cabin are also distinct. However, the exact position of the oars cannot be verified with certainty, since the iron distribution image does not provide any evidence for their presence. The only indirect indication for their presence is provided by the copper distribution image, where at specific positions that correspond to the oars the copper is absent. In the iron MA-XRF distribution image of the middle ship (Fig. 6, scan (II-a)) the parts of two oars and two rudders are visible, allowing for a better understanding of their original shape and exact position. In particular, the second oar to the right on the hull of the ship revealed by the scanning, was not included in the original reconstruction (Fig. 6, scan (II-a)) due to the poor state of the paint layer and the difficulty to visualize it with the naked eye or with other imaging techniques. On the hull of the leading ship, the iron distribution enhanced the exact form of the geometric decorative pattern (Fig. 6, scan (III-a)) and of the two rudders, confirming the existing reconstruction. Furthermore, the iron distribution in the area depicting the crossing of the hulls of the leading and the middle ship (Fig. 6, scan (III-b)) emphasized the different pictorial levels that the painter had wished to evoke, in order to produce a certain impression of depth in his composition. However, in the Cu MA-XRF distribution image, it was possible to recover traces of a copper-based pigment within the areas of the hull’s decorative pattern that had not been previously considered, as can be seen in the existing reconstruction where those areas have been left white. It is therefore suggested by the MA-XRF images that the original polychromy of the hull would have originally been more varied than it had been suspected, with a chromatic alternation of the zig-zag lines in yellowish-brown and a cooler hue of blue. As a general remark from the MA-XRF elemental maps obtained from the three fragments it could be suggested that iron-based ochres were used for the ships and the figures of the composition, directly applied on the white plaster, whereas the layer of the purplish color, produced with a mixture of Murex purple and Egyptian blue, was applied at a second pictorial stage to define the sea background.

3.1.2. The purple background of the Naval Scene A more thorough analysis was performed on selected areas of the background of the second fragment, where traces of purple are better preserved. Three areas were scanned to achieve good statistics, also using an appropriate filter in the excitation path to further improve the peak to background ratio. The acquired spectra were summed, while a blank area on the substrate was also analyzed for comparison purposes (Fig. 8a). In the examined areas, relatively elevated traces of bromine (Br) were detected, with respect to the substrate, suggesting the use of the organic colorant Murex purple (Fig. 8a and b), a hypothesis which is in accordance with the results of HPLC analysis on purple colored samples from Hall 64. (Alfeld et al., 2017) The spectra in Fig. 8a and b were acquired by using the Ni/Fe/Ti combined filter in the exciting X-ray beam path, which improved considerably the peak – to background ratio in the energy region that the Br-Kα peak is expected to be recorded. By observing the XRF spectrum of Fig. 8a, more chemical elements were identified, suggesting the use of additional pigments. The combined detection of copper and silicon in the MA-XRF sum spectrum collected from the purple area without the use of filter in the excitation path indicate the presence of Egyptian blue pigment (Fig. 8c). This pigment was used in mixture with Murex purple, in order to produce the purple color of the background, as was observed with the macroscopic examination of its top surface (Fig. 9). (Brecoulaki et al., 2015). The identification of iron in the same paint layer may also be related to an intentional addition of yellow ochre in the purplish layer of the background, in order to obtain a specific hue. Alternatively, the presence of iron could be related to a contamination of the background from the yellowish paint layers, depicting the ships. Murex purple was a precious material in antiquity and its use was therefore restricted to selected rooms of the Palace with a special function, as were for example the Throne Room and Hall 64. (Brecoulaki et al., 0000; Brecoulaki, 2014) In general, wherever Murex purple has been identified in Aegean wall-paintings, (Doumas, 1992) its use has always been parsimonious. The use of purple color permeates the Naval Scene with a distinct sense, reflecting the artist’s intentions and his cultural and historical background. “May the purple background have evoked a departure ceremony during sunset? Or perhaps Murex purple, in this context, was a visual marker of the Pylian power?”. (Brecoulaki, 2014).

3.1.1. Details of the Naval Scene composition Detailed analyses with increased dwell time were performed in selective areas of the larger fragments I and II, in order to obtain more information on the original iconography of the depicted scenes. The generated iron and copper distribution image on fragment I (Fig. 7, scan (I-b)) revealed the approximate outlines and certain facial features (shape of an eye) of a male head with neck, located inside the ship’s cabin. Iron based ochre was used for the depiction of the figure, while the presence of copper corresponds to the tiny areas of purple visible in the reconstruction, remnants of the background’s original paint layer. From the elemental distribution maps it seems that the figure was painted with iron-based ochre on top of the purple background. The addition of such an iconographic element to the reconstruction of the Naval Scene is highly significant for it provides us a confirmation for the presence of human figures inside the ship’s cabins, an important narrative element that until now have been only hypothetical. Another detailed scan taken at the lower part fragment II, highlighted the outlines of a form that has been reconstructed as a fish in the area of the sea (Fig. 7, scan (II-b)). The presence of iron all over the body of the fish suggests the use of ochres as well. The detection of Cu on the area surrounding the fish is related to the creation of the background, composed of a mixture of Egyptian blue and Murex purple.

3.2. The Battle Scene of Hall 64 The main pigments identified on the Battle Scene fragment are composed of iron (Fe), copper (Cu) and manganese (Mn), with green, blue, red color respectively (Fig. 10a–c), as well as in RGB correlation (Fig. 10d). The iron distribution image (Fig. 10a) corresponds to the reddish-brown color of the bodies of the warriors, suggesting that they were painted with an iron-based ochre. The iron detected in some parts of the warriors’ garments may be attributed to the iron signal coming from the layer underneath or to contamination. Based on the manganese distribution image (Fig. 10c), it is possible to deduce that a manganese-based pigment (most likely the mineral pyrolusite, since sources of the minerals pyrolusite and todorokite have been identified in southeast Peloponnese) (Perdikatsis, 0000) was used for the black color of the warrior’s skirt, as well as for other minor details. However, after analyzing selected areas from the body and the garment of the warrior respectively (Fig. 11), it was possible to observe that Fe was also present in the black paint layer, consisting mainly of a manganese-based mineral pigment. The scatter plot of Fe-Kα versus Mn-Kα pixel intensities reveals a clear linear Fe-Mn association (Section A in the scatter plot of Fig. 12a). Using the XRF Imaging tool of LANDIS Laboratory (Romano et al., 2017) it is possible to visualize the pixels exhibiting the Fe-Mn linear association and to confirm that it originates from the area where the 7

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Fig. 7. . MA-XRF images in Green-Blue (GB) correlation showing the spatial variation of the Fe-Kα and Cu-Kα intensities with green and blue colors, respectively, alone and superimposed to the analyzed fragments. At the iron and copper distribution image of fragment I (I-b), the outline of the resulting male head has been marked with red color in order to be more comprehensible. The reconstructions on the right were made by R. Robertson. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) (Copyright. Department of Classics, University of Cincinnati.)

Fig. 8. XRF sum spectra of selected purple and substrate areas: (a) From the purple area (II-c) vs substrate area (II-d) of the Naval Scene, using a filtered exciting beam, (b) Spectrum similar to (a) but expanded at the energy region from 10 to 14 keV, (c) From the faded purple area (I-c) in comparison with the substrate area (Id). The escape peak (EP) and the pile-up peak originate both from the Ca-Kα line. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

purple colored substrate (Fig. 12e), showing the presence of Mn in trace-minor amounts. Finally, the minor amounts of sulfur detected in both brown and black subareas (Fig. 11) can be due to the environmental contamination and calcite deterioration, which yields gypsum as corrosion product. Copper distribution within the image corresponds to the Egyptian blue layer of the background (Fig. 10b), applied around the outlines of the figures’ bodies. The elemental mapping, in addition to the identification of the inorganic pigments, also provided information on the

manganese-based pigment was used (see Fig. 12b and 12c for the Fe-Kα and Mn- Kα X-ray intensities, respectively). Further on, based on this spatial Mn-Fe association, the relative abundance of Fe within the manganese-based pigment (Fig. 12c) was estimated to be ~7.5%. The high intensity Fe data that correspond also to negligible amounts of Mn (B section in the scatter plot of Fig. 12a) correspond to the area where the iron-ochre has been used, namely the figure of the warrior body (Fig. 12d), while the area which presents low Fe-Kα and Mn-Kα pixel intensities (C section in the scatter plot of Fig. 12a) corresponds to the 8

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Fig. 9. . Top surface of the sea depicted on the Naval Scene, composed of Murex purple and occasional grains of Egyptian blue (photo by H. Brecoulaki). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) (Copyright. Department of Classics, University of Cincinnati.)

Fig. 11. . XRF sum spectra of the selected subareas with brown and black color (b, c from Fig. 4) applied directly on the plaster, located on the Battle Scene fragment. Measurement time 2.4 s. The escape peak (EP) and the pile-up peak are originated from the Ca-Kα line.

technique of their application. For instance, it might be observed that the artist painted the figure of the warrior directly on the background, since copper, which is the key element of the colored background, is completely absent from this area. Subsequently, the color of the background was carefully applied surrounding the warrior’s figure, while all the minor details were painted in subsequent superimposed stages.

The technique of mixing an organic colorant of purple hue with Egyptian blue in order to obtain a cooler hue, was also attested in the Naval Scene. Their difference relies on the technique of application: while in the Naval Scene grains of Egyptian blue (and possibly of an iron-based ochre) were mixed with Murex purple within the same layer, in the Battle Scene, the mixture of purple and Egyptian blue was achieved through a more sophisticated system of superimposition of pictorial layers. (Brecoulaki, 2014, 2018; Brecoulaki et al., xxxx) The MA-XRF analysis of selected areas of the background, showing lighter hues of blue and darker hues of purple (Fig. 4f and e), allowed for a more thorough understanding of the composition and application of the paint layers. A bottom layer consisting of an organic Murex purple mixed with grains of a manganese based black pigment and a thin layer of finely grinded Egyptian blue, applied on top. (Brecoulaki, 2014, 2018; Brecoulaki et al., xxxx) While the higher intensity of copper and silicon peaks in area (IV-f) (Fig. 14) is clearly related to the preserved top layer of Egyptian blue, the presence of both elements even in the areas where no blue pigment may be observed today with the naked eye (Fig. 14, area (IV-e)) suggests that originally a thin layer of Egyptian blue was applied all over the background. Variations in the hue of the background color seem to be related with the preserved amount of Egyptian blue on the painting’s top

3.2.1. The purple background of the Battle Scene The examination under reflected light of a sample cross-section taken from the background (Fig. 13), has enlighten aspects of the applied painting technique. Although the Egyptian Blue particles (their presence was confirmed by SEM-EDS) are seen in the cross section diffused within the purple layer, macroscopically, it has been observed with precision, that a thin layer of Egyptian Blue is preserved on several background areas. Similarly, the rather large black grains of a manganese-based pigment that must have been mixed with the purple pigment are visible in the cross section scattered and diffused towards the bottom interface of the purple layer. The stratigraphy, except the plaster layer (bottom) and an alteration layer composed most likely by salts (top), seems to include just above the purple pigment a yellow layer thicker on the left and very thin on the right, most likely related with the presence of an iron-based pigment.

Fig. 10. . MA-XRF images of Fe-Kα (Fe-ochre), Cu- Kα (Egyptian Blue) and Mn-Ka (Mn-based) intensities depicted with green, blue and red colors, respectively, produced by the MA-XRF analysis of the examined area (IV-a) of the Battle Scene. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) 9

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Fig. 12. . Scatter plot of Fe-Kα with Mn-Kα net area from the total spectrum of the analyzed fragment of the Battle scene, b) Iron and c) Manganese distribution images related to the linear under examination area of the scatter plot, d) Iron distribution image related to the figure of the warrior, e) Manganese distribution image related to the substrate.

Fig. 13. . Cross section under reflected light. Sample taken on the purple background. The paint layer is composed of two distinct layers: a lower layer of Murex purple with black grains of a manganese-based pigment and a blue layer of Egyptian blue (photo by H. Brecoulaki). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) (Copyright. Department of Classics, University of Cincinnati.)

Fig. 14. . XRF sum spectra of selected background purple and blue colored areas (f, e subareas are shown in Fig. 4) from the Battle Scene fragment. Measurement time 2.4 s. The escape (EP-Ca) and pile-up peaks are originated from the Ca-Kα line. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

surface. The detection of manganese in both areas further confirms the addition into the purple layer of a manganese-based pigment. Due to the restrictions in the availability of the Battle scene fragment during the in-situ measurements, the filtered mode of the MA-XRF imaging could not be applied to detect traces of bromine on a purple background area. As H. Brecoulaki has stressed: “the layer of blue did not entirely overlap with the purple underneath, creating an optical mixture between blue and purple” (Brecoulaki, 2018), whereas the additional use of a manganese-based black pigment in the purple layer served to create darker mauve hues. The presence of Μurex purple was not verified by the XRF data, since bromine was not detected in any of the two examined areas. In addition to the two areas of the background, selected areas on the

figure of the warrior were also analyzed (Fig. 15, areas (IV-d), (IV-g)), in order to investigate the composition of the paint layers that were applied on top of the background. The exclusive abundance of calcium in the spectrum from a white area on the warrior’s sword (Fig. 15, area (IV-d)) confirms the use of calcite. Iron is the major element detected in the brown area (Fig. 15, area (IV-g)), suggesting the use of ochre for the brown coloration of the warrior’s skin. The detection of copper in the examined brown and white areas may be explained by the fact that the layers of red ochre and calcite were applied over the background’s top layer of Egyptian blue, conforming to the principles of a multi-layer technique. The multiple stages of such a technique may be described as follows: 10

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Therefore, through the obtained elemental distribution images, an immediate visual impression is produced on how the different elements are distributed in close conjunction with the iconographic elements unravelling their possible associations. In this way, more comprehensive interpretation can be achieved regarding the nature of pigments employed and of their application techniques. Moreover, particularly for heavily deteriorated pictorial layers such as the wall-paintings of the Nestor’s Palace, uncovered hidden iconographic elements and polychromy were revealed, thus allowing to integrate the iconography and perform an objective, scientifically based re-assessment of the accuracy of previously executed wall-painting reconstructions. The gamut of pigments identified by MA-XRF imaging in both compositions includes iron-based ochres for the red, yellow and brown hues, a manganese-based pigment for the black color, while calcite is the major material used for the white coloration. The Egyptian blue has been identified for the background coloration using different application techniques. The MA-XRF analysis was even able to detect bromine in remnants of purple color in one fragment from the Naval Scene in accordance with the detection by specialized laboratory techniques of the use of the organic pigment Murex purple for the background coloration. Purple was used as a background color to indicate the sea in the Naval Scene and to produce an abstract field on the Battle scene. The technique applied for the production of the purple color is different in the two compositions, as it has been attested by the MA-XRF results, and further supported by the foregoing microscopic examination of purple samples. The Μurex purple probably mixed with Egyptian blue has been applied in the Naval Scene. An iron based ochre pigment was also identified by means of the MA-XRF analysis contained within the Naval Scene background, suggesting the additional use of this pigment for the creation of a particular hue, although further examination is required. A technique of superimposed layers has been applied in the Battle Scene background. A layer of Egyptian blue was superimposed to a layer composed of Murex purple mixed with grains of a manganesebased pigment. The addition of a manganese-based pigment served to create darker hues, while the superimposition of a blue colored paint layer created an optical mixture between blue and purple. This complex painted stratigraphy is not aiming only to a particular aesthetic result, but it seems to participate in the artist’s narrative intentions. Moreover, the MA-XRF results have further provided insights into the applied painting techniques by evaluating the complementarity of the acquired elemental images. The artist would prepare a preliminary drawing including the outlines of the main figures which were painted directly on the plaster, defining the base on which his synthesis was further developed. Subsequently, the color of the background was carefully applied surrounding the preserved parts of the main pre-drawn figures. At the final stage, all the secondary details and possible drawing adjustments were superimposed to the colored background, providing a fully configured composition.

Fig. 15. . XRF sum spectra of selected brown and white colored areas (d, g subareas are shown in Fig. 4) from the warrior figure on the Battle scene fragment. Both brown and white colored areas are superimposed on the purple colored background. Measurement time 2.4 s. The escape peak (EP) and the pile-up peak are originated from the Ca-Kα line. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

the background’s first layer (purple) was applied following the predefined contours of the figures, reserved very schematically on the white plaster before the application of any other color; red-brown ochre was subsequently used to fill the bodies of the figures, inside the reserved parts; garments and other details were then superimposed on top of the red-brown ochre of the warriors’ bodies. A thin layer of Egyptian blue, corresponding to the second layer of the background (from bottom to top) was painted at a final stage, following the basic forms of the compositions’ figured elements. However, the painter revised some details of his figures after the background was over, as for example in the aforementioned brown area IV-g (Fig. 15, spectrum (IV-g)), where the co-existence of copper and silicon clearly suggests that this area was painted on top of the Egyptian blue layer. In fact, by comparing the XRF spectra of the two brown areas analyzed (Fig. 11, spectrum (IV-b) and Fig. 15, spectrum (IV-g)), basically composed of iron corresponding to the skin color of the warriors, it was observed that only in one case copper was also detected (Fig. 15, spectrum (IV-g)). The presence of copper allowed us to conclude that this brown area was painted on top of the Egyptian blue layer of the background, a detail that was not visible with the naked eye. On the contrary, in the brown area painted directly on the white plaster no copper was found (Fig. 11, spectrum (IV-b)). 4. Conclusions

Declaration of Competing Interest X-ray fluorescence (XRF) is recognized as a safe technique for analyzing in-situ and non-invasively artworks of historical and archaeological interest/value. The wall-paintings of the Nestor’s Palace have been affected by severe deterioration first from the fire and next by the burial environment for almost four millennia. Thus, the wall paintings are particularly characterized by a complex multi-layered and heterogeneous composition of the pictorial surface. The present work, as an unprecedented application of MA-XRF imaging in the study of Late Bronze Age wall-paintings, has demonstrated the superior and advanced capabilities of the portable MA-XRF scanning technique compared to the conventional single spot XRF analysis. At first, the MA-XRF scanning technique allows simultaneous mapping of different chemical elements on a large dimensioned pictorial surface that may include complete iconographic elements.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements All authors gratefully acknowledge Dr. Sharon Stocker for continuous encouragement and support of the “Palace of Nestor” wallpainting project and the Department of Classics, University of Cincinati for financial support. All the authors would like to thank both the anonymous reviewers for their fruitful comments.

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