{"word_count": 8144, "character_count": 64868}
1. Introduction        At the beginning of the first millenium AD, the        Indian Ocean became a region of long-distance trade between the Middle        East, China, India, South Asia and Africa. Over the centuries, mostly        thanks to monsoons, it was organized into a space around which the        first World Trade system was built (Beaujard, 2009; Beaujard, 2012).        Indeed, by its geographical situation, the Indian Ocean is subject to        the phenomenon of monsoon winds whose seasonal fluctuation determined        navigation and commerce in the area (Nativel &#38; Rajaonah, 2007). At        the time, it was possible to travel from Asia-to-Africa and up to the        entrance of the Mozambique Channel in a single season; on the other        side, trade to ports located more to the South needed a waiting period        for the next cycle. Livestock, raw or processed materials like ivory,        pearls, wood, metals, pottery and glass beads have travelled over the        Indian Ocean trade routes. Glass beads, which were used as a currency,        attest to international trade by their presence. They are among the        most abundant objects found at excavations due to their very good        preservation, even in the humid tropics.        Identifying the source of excavated beads is useful        to understand the history of exchanges and the building of trade        routes. Beads are present from the 7th and the        20th century and over this period morphological        and compositional changes take place. These modifications can be        associated to the onset of specific periods of production or to some        geographical area (Dussubieux et al., 2008;        Prinsloo &#38; Colomban, 2008; Robertshaw et        al., 2006; Robertshaw et al., 2009;        Robertshaw et al., 2010; Tournié et al., 2011; Wood, 2005; Wood, 2011; Wood et al., 2009; Denbow et al.,        2015). International trade to South/East Africa through the Indian        Ocean during the Iron Age (~ 600-1750 AD.) received considerable        attention (Beaujard, 2009; Beaujard, 2012). The first study of glass        beads discovered in South Africa followed the excavation in 1930 of        two large sites in the Limpopo valley, namely Mapungubwe and K2. The        chronology of these sites has long been debated; the abundance and the        variety of beads found there naturally led to use them as markers. To        this end, numerous studies attempted to classify beads according to        morphological criteria (Beck, 1937; Van Riet Low, 1955; Schofield        1958; Gardner, 1963), elemental composition or traces of rare earths        (REE) (Davidson, 1972; Davidson, 1974). Recently, Wood proposed a        classification system for southern African beads from the precolonial        period (700-1600 AD.) (Wood, 2005; Wood, 2011; Wood et al., 2009). This classification, based on        morphological and technological characteristics – which implies        subjectivity – defines seven different sets of beads, each of them        being related to a particular period determined by radiocarbon dating        (RC) of the site from which they were excavated. By definition, this        classification requires reliable radiocarbon dating of the associated        sites. However, the 1970s’ RC dating of Mapungubwe and K2 sites was        heavily influenced by the ideological context of the time, and        questioned by the recent identification of chrono-technological        markers (Tournié et al., 2011), which were more        in line with the early work by Gardner (1963). To improve this ranking        system, elemental analyzes were conducted by LA-ICP-MS (Robertshaw et al., 2006; Robertshaw et        al., 2009; Robertshaw et al., 2010) so to        provide information on glass production techniques and origins,        including colouring elements (Robertshaw et        al., 2010). Additionally, trace elements usually found in African        glass beads compared to those found in India, Sri Lanka and East/South        African Coast ones have enabled more accurate time correlations        (Chaisuwan, 2011; Dussubieux et al., 2008;        Dussubieux et al., 2010; Robertshaw et al., 2006; Robertshaw et al.        2009).        Meanwhile, Raman spectroscopy has emerged as the        most effective non-invasive method to identify chromophores, pigments        and opacifiers in glasses and enamels (Bonneau et        al., 2013; Colomban et al., 2001; Colomban        &#38; Treppoz, 2001; Colomban et al., 2003;        Ricciardi et al., 2009a; Ricciardi et al., 2009b; Prinsloo &#38; Colomban, 2008;        Prinsloo et al., 2011; Tournié et al., 2010, Tournié et        al., 2011; Welter et al., 2007) as well as        the types of glass matrix (Colomban et al.,        2006a; Colomban et al., 2006b). This approach        is widely used now (Baert et al., 2011;        Caggiani et al., 2014;        de Ferri et al., 2012; Gedzevičiūtė et al., 2009; Koleini et        al., 2016a; Prinsloo et al., 2011;        Prinsloo et al., 2012). Some pigments and        chromophores are unique technological chrono-markers. In addition to        confirming the first chronology of the site established by Gardner,        Raman analysis of Mapungubwe and K2’s beads also confirmed the links        that Africa had with the outside world thanks to the finding of:        Indo-Asian black beads with Fe-S chromophore (Prinsloo &#38; Colomban,        2008); Lapis Lazuli colored blue beads typical of Islamic glasses        between the 13th and 15th        century (Caggiani et al., 2014; Prinsloo et al., 2011). These studies concern the major        sites of the upper valley of the Limpopo River (Mapungubwe / K2) but        other sites were studied: such as further along the Limpopo in South        Africa (Koleini et al., 2016c), Botswana        (Koleini et al., 2016a), and Zimbabwe sites,        rivals of Mapungubwe and K2 ones in a later date (Koleini et al., 2016b) and on the material collected in the        early 20th century at Vohemar, a harbor occupied        by Malagasy Islamized and in close relationship with the Swahili world        in northeastern Madagascar (Colomban &#38; Simsek, 2014).        This work concerns a selection of beads from the        necropolis of Antsiraka Boira, Mayotte, one of the four islands in the        Comoros Archipelago in the Indian Ocean. Mayotte is located at the        northern entrance of the Mozambique Channel between the island of        Madagascar and East Africa, and because of its position at the end of        the road of Monsoon (going south imposes waiting for the next cycle of        Monsoon) an important step in trade with southern Africa. Commercial        networks with the other islands of the channel, Madagascar and Africa,        are attested from the 8th to the 13th century (Beaujard, 2009; Beaujard, 2012; Pauly,        2014). Because of its position at the entrance of the Mozambique        Channel, many Islamic traders chose to establish trading posts in the        island of Mayotte ever since the 9th century,        which led to the introduction of the Swahili culture and the Muslim        religion into the Island. The spread of Islam across the Indian Ocean        is closely related to commercial networks linking Africa to the Middle        East (Pauly, 2014). Recent excavations (2012-2014) have uncovered a        medieval necropolis dated to around 1100-1250 with a well-defined        stratigraphy (Pauly, 2014). Nearly two thirds of the excavated tombs        contained glass beads, for a total of about ten thousand. These        burials revealed a phase of synergy between Muslim funeral rituals and        pre-Islamic rituals. With the exception of the Islamic Necropolis of        Vohemar (13th-17th centuries),        northeast of Madagascar, Antsiraka Boira is the sole provider of bead        adornments found in funerary context (Table 1, the concordance between        the labels used in this work and those of the funerary excavation).        About a hundred beads of the necropolis of Antsiraka Boira,        representative of 331 beads chosen on morphological criteria (shape,        color, size and type of apparent production technology) were first        Raman analyzed with a portable 532 nm set-up that can be used on site        (Colomban, 2013). Twenty-two of them (figure 1) were selected based on        their Raman signature representative of the different groups for        further analysis with a laboratory instrument. Indeed, this work also        aims at establishing an appropriate on site selection methodology, in        order to limit the number of objects requiring additional laboratory        analysis.        Table 1: Correspondence between archaeological        labels (sepulture number (SP), bead number (P) color (red, R; …), loin        cloth (p), necklace © / Tableau 1: Correspondance        entre les numéros d’inventaire archéologiques (numéro de sépulture        (SP), de perle (P) ; symboles : couleur (rouge, R; …), pagne (p),        collier (c)                      2. Materials and methods                  Beads          Figure 1 shows the 22 selected beads and the          first classification according to the morphological criteria defined          by Wood (Wood, 2005, Wood, 2011, Wood, 2012). The beads used in the          discriminating criteria can be linked to a series associated with a          chronological period. According to visual criteria, almost all beads          belong to the Indo-Pacific category, divided into three series:          K2-IP, East Coast (EC-IP), and Khami-IP (Figure 1 and Table 2). All          the beads are monochrome, but of different colors: black (n), blue /          turquoise (b), yellow (y), and red-brown (r). Most of the selected          beads were made by drawing a glass gob and have a cylindrical shape.          Two beads were made by winding in a more or less spherical fashion          (10-n and 22-r). Beads 18-y and 17-b do not exhibit morphological          criteria suitable to assign them to a particular series and bead #11          is not made of glass.          Figure 1: Representative glass beads of          Antsiraka Boira site (Mayotte Island), selection based on their          color (blue, red, yellow and black), their method of manufacture          (drawn, wound) and their state of transparency (translucent,          translucent-opaque, opaque) / Figure 1 : Sélection          de perles de verres représentatives de la nécropole d’Antsiraka          Boira (île de Mayotte), en fonction de la couleur (bleu, rouge,          jaune ou noir), la méthode de fabrication manufacture (étirage ou          enroulage) et du degré de transparence (translucide, opaque ou          intermédiaire)                    The classification series (Khami-IP-; EC-IP;          K2-IP) according to the morphological criteria defined by M. Wood is          indicated. / La classification morphologique selon          Wood est aussi donnée (IP-Khami; EC-IP; K2).          Table 2: Classification of Mayotte beads,          according to the morphological criteria presented by (Wood, 2005,          2009, 2011), correspondence with archaeological names are specified          in Table 1 / Tableau 2: Classification des perles          de Mayotte selon les critères morphologiques de Wood (Wood, 2005,          2009, 2011), voire Table 1 pour les symboles                                    Analyses          A small spot on the bead surface was cleaned with          a fine dry abrasive paper in order to remove surface residues and          any loose layers of corrosion products, to obtain the best Raman          signature on the uncorroded matrix. Micro-Raman analyzes were          performed with 4 spectrometers: a portable HE 532 (HORIBA Jobin Yvon          Scientific), a fixed HR 800 (HORIBA Jobin Yvon Scientific), a          transportable Infinity (Dilor-HORIBA Scientific) and a transportable          SENTERRA Scope III (Bruker Optics). All are coupled with long          working distance microscope objectives, magnification of x10, x50          and x100 that lead to 100, 500 and 1000 magnifications. The use of          different optics allows controlling the glass heterogeneity. For          each record, Raman spectrometers were used with an acquisition time          of 30 to 450 seconds, and if needed, several accumulations to          improve the signal / noise ratio and clear the cosmic photons. The          hundred beads were analyzed with the portable spectrometer (under          excitation of ~ 2-5 mW for black beads because of the high          absorption, and ~ 10-20 mW for colored beads). Those whose spectrum          recorded with HE532 portable instrument was of low quality (yellow          and blue) were also measured with the HR 800 spectrometer under          laser excitation of 458 nm, blue excitation being well suited for          the analysis of glasses. Infinity (633 nm, 35 mW) and SENTERRA (785          nm, 10-50 mW) spectrometers were used on black beads to evaluate and          / or to overcome the resonance effect of the Fe-S chromophore.          Despite the lower spectral resolution of the          portable instrument and the limited access to low wavenumber range          (&#60;100 cm-1), most Raman spectra obtained with          the portable apparatus are significant and exploitable (Figure 2a)          and rather similar in quality to those obtained with the laboratory          instruments (Figure 2b). On a single bead, depending on the analyzed          spot, the results can differ (e.g. Figure 3c) due to the glass          heterogeneity among beads.          Figure 2: Examples of Raman spectra recorded          using different spectrometers: a) portable (532 nm). b) fixed          (HR800, 458 nm; Infinity 532/633, and Senterra, 785 nm) / Figure 2 : Exemples de spectres Raman obtenus avec          différent spectromètres: a) portable (532 nm) - b) fixe (HR800 458          nm ; Infinity, 532/633 ; Senterra, 785 nm)                    Bead labels are given according to Fig. 1          (Colours; n: black, r: red, y: yellow and b: blue/turquoise. / Les symboles de la Fig. 1 sont utilisés (Couleur: n:          noir, r: rouge, y: jaune &#38; b; bleu/turquoise.          Archaeological materials generally exhibit strong          fluorescence due to organic residues on the surface or in the pores          and cracks of the material. These residues are removed under          energetic radiation (a few mW blue laser or tens of mW green laser,          typically with x50 objective) or by examination of a fresh fracture.          Thus, a bead of each colour (1-r, 15-b, 18-y, 21-n and 22-r) was cut          parallel to the perforation by performing a cut with a diamond saw          Minitom (Struers) and then mechanical fracturing to rate the          heterogeneity of the matrix with fixed Raman spectrometers by          performing five records in the section along a diagonal.          Subtracting the background of the Raman spectra          was conducted using the multi-segment procedure validated in other          glass studies (Colomban, 2008; Tournié, 2009) with the Labspec          software to compare the spectra obtained on various instruments.          The Raman spectra recorded with fixed instruments          and different wavelengths have a resolution twice as good and in          some cases a lower background than those recorded with the portable          set-up. For crystalline compounds, pigments or secondary phases, the          characteristic Raman bands are narrow, intense and thus easily          detectable (Figure 3). In case of (pre)resonance, change of the          excitation wavelength significantly modifies the respective          intensities of the chromophore and its matrix allowing a better          observation of one or the other (Faurel et          al., 2003).          Figure 3: Raman spectra of the chromophore          Cr-Sn / sphene recorded by a) the fixed HR800 instrument (458nm) and          b) the portable HE532, (532nm); c) comparison of representative          spectra recorded with 532 (not labelled) or 458 nm (labelled)          excitation (LB: the baseline has been subtracted) / Figure 3 : Spectres Raman du chromophore Cr-Sn sphène          obtenus avec a) le spectromètre fixe HR800 (458nm) et b) le          spectromètre portable HE532, (532 nm). c) Comparaison de spectres          typiques obtenus avec les excitations à 532 or 458 nm (LB: une ligne          de base a été soustraite).                                    Scanning electron microscopy (SEM-EDS)          Elemental analyzes (by oxide weight %, Table 3)          of Boira Antsiraka beads were performed with a SEM (JEOL JSM-5510LV)          equipped with an EDS detector (Energy Dispersive Scattering). A 30kV          acceleration voltage was used with a working distance of 20 mm.          Fixed to a metal support with carbon adhesive recoveries to best          remove the charges created by electron irradiation, beads were          examined without preparation. The validity of the measurements was          monitored by applying the same procedure to certified          glass-reference samples “Corning Museum B, C and D” and American          “National Bureau of Standard (NBS 620)”, as usual (Vicenzi et al., 2002; Henderson et          al., 2016). The error is below 1% for SiO2,          Na2O and CaO, and below 5% for the other oxides.          For each bead, several qualitative and quantitative measurements          were performed, first at low magnification (100x, overall analysis),          then at high magnification (up to 3000 x) to assess the material          heterogeneity.          Table 3: SEM-EDX oxide compositions of beads          (wt%) measued using 100x magnification on the surface. Only major          oxides are considered. Σ Flux = CaO + Na2O +          K2O / Tableau 3: Compositions          de surface (% pondéral en oxyde) des perles mesurées par MEB-EDX          pour un grossissement de 100. Seuls les éléments majeurs sont pris          en compte. Fondants : Σ Flux = CaO + Na2O + K2O                                    Label              % SiO2              %Al2O3              %              CaO              % Na2O              % K2O              Σ              Flux              Total                            %              CaO              % Na2O              % K2O              Total                                      1              71.3              6.6              2.1              17.9              2.1              22.1              100.0                            9.5              81.0              9.5              100.0                                      2              71.4              8.25              1.4              17.3              1.6              20.3              100.0                            6.9              85.2              7.9              100.0                                      3              71.6              9.5              3.0              13.7              2.1              18.8              99.9                            15.8              73.0              11.2              100.0                                      4              73              7.4              2.5              15.5              1.6              19.6              100.0                            12.8              79.1              8.2              100.0                                      5              70.8              7.8              2.4              16.5              2.4              21.3              99.9                            11.3              77.5              11.3              100.0                                      6              70.9              7.6              2.3              16.7              2.5              21.5              100.0                            10.7              77.7              11.6              100.0                                      7              74.5              10.7              1.5              11.8              1.4              14.7              99.9                            10.2              80.3              9.5              100.0                                      8              76.5              5.3              1.3              14.9              2              18.2              100.0                            7.1              81.9              11.0              100.0                                      9              77.2              8.8              2.2              9.8              2.0              14.0              100.0                            15.8              70.2              14.0              100.0                                      10              70.1              8.3              2.4              18              1.2              21.6              100.0                            11.1              83.3              5.6              100.0                                      12              71.9              8.2              1.9              15.8              2.2              19.9              100.0                            9.5              79.4              11.1              100.0                                      13              69.7              6.9              3.1              17.4              2.8              23.3              99.9                            13.3              74.7              12.0              100.0                                      14              72.1              8.2              2              16              1.6              19.6              99.9                            10.2              81.6              8.2              100.0                                      15              70.5              6.1              2.1              19.3              2.1              23.5              100.1                            8.9              82.1              8.9              100.0                                      16              73.9              8.6              1.8              13.4              2.3              17.5              100.0                            10.3              76.6              13.1              100.0                                      17              67.4              13.3              3.1              14.1              2.0              19.2              99.9                            16.2              73.6              10.2              100.0                                      18              72.5              6.4              2.5              16.7              1.8              21.0              99.9                            11.9              79.5              8.6              100.0                                      19              72.5              8.8              1.6              15              2.1              18.7              100.0                            8.6              80.2              11.2              100.0                                      20              70.9              7.9              1.4              18.3              1.5              21.2              100.0                            6.6              86.3              7.1              100.0                                      21              75.6              7.9              1.6              13.7              1.2              16.5              100.0                            9.7              83.0              7.3              100.0                                      22              73.1              5.9              2.2              17.2              1.6              21.0              100.0                            10.5              81.9              7.6              100.0                                            3. Results                  Identification of the chromophores          Raman spectroscopy has proven to be particularly          effective in identifying colouring matters, except for the          chromophore ions (Cu2 +, Fe2          +, Fe3 +, Co2 +, Mnn+, etc.) that are "simply" dissolved in the glass          matrix, as their presence do not have a strong influence on the          matrix spectrum (Colomban et al., 2001). The          Raman signature of well crystallized compounds usually consists of          narrow peaks that are easy to detect. This is the case of most          pigments and opacifiers: highly crystalline compounds that are          stable in the molten glass or have precipitated on cooling.          Additionally, when the excitation wavelength (almost) corresponds to          the coloration, the (pre-)resonance character of the spectrum          improves its detectivity and small amounts of chromophores (&#60;%          wt) give intense spectra.                      Yellow beads            For yellow beads 3-y and 4-y (Figures 2, 3            &#38; 4) the Raman spectrum is characteristic of a pyrochlore            pigment, a complex solid solution PbSb2-xSnxZyO7-δ, also called Naples Yellow. The spectrum of this            pigment is characterized by bands at about 135, 330 and 453 cm-1 (Kirmizi et al., 2010;            Rosi et al., 2009; Sakellariou et al., 2004). The exact position of these            bands and the relative intensities vary according to both the            composition (including the Sn / Sb ratio and the non-stoichiometry            in oxygen resulting from oxidation state of the metal elements)            and heat treatments, thus modifying the non-stoichiometry and            order (Pereira et al., 2009). It is often            difficult for determining the non-stoichiometry (Naples Yellow            Type I [Sb-rich, usually recognized from its 510 cm-1 band] or II [Sn-rich with characteristic 450            cm-1 component]) only on the basis of the            Raman spectrum. The yellow bead 18-y, does not exhibit the            pyrochlore signature. The absence of lead is confirmed by SEM-EDS            analysis, and high iron content (1.9 wt oxide %) rather indicates            a colour due to Fe3+ ions, a known technique            for enamels but rare for glass objects. A resonant spectrum            (761-775 cm-1 and 942-963 cm-1 peaks followed by harmonics / combinations,            Figure 4) characteristic of a sphene (malayite) containing tin            doped with chromium and used for the pink to brown porcelain            enamel since the 19th century (Faurel et al., 2003), is obtained at points of the            beads 18 and 4-y. The SEM-EDS analysis confirms the presence of            chromium (0.02-0.04 wt%) and tin (0.2-0.3 wt%). The ratio between            the two elements is consistent with this type of pigment. When            this sphene pigment is combined with other chromophores, such as            Naples yellow (bead 4-y) or the yellow iron (bead 18-y), it could            only change the hue, not the colour. This very specific Raman            signature can be used as a marker of bead production.            Figure 4: Representative Raman spectra of            a) red (532 and 633 nm laser lines) and b) yellow (458 nm) glass            beads / Figure 4 : Spectres Raman représentatifs            obtenus a) pour les perles rouges sous différentes excitations            (532 et 633 nm), et b) avec l’excitation 458 nm pour les perles            jaunes                                            Red beads            Raman signatures vary according to the beads            and the analysed spot (Figure 4a, spectrum 22-r and 1-r).            Elemental analyses were able to detect the presence of copper            (0.04 - 0.2 wt%) and iron (0.4 - 0.8 wt%) in all the red beads, in            accordance with a red colouring obtained by dispersing Cu0 metallic copper nanoparticles in the glass            matrix (Colomban, 2009; Colomban et al.,            2009). This is consistent with the complexity of Raman signatures            (Colomban &#38; Schreiber, 2005). The above mentioned Raman            signature of the Cr-Sn chromophore was also identified for three            beads, 2-r, 20-r and 22-r, with some variations as a function of            the analysed spot (Figure 4a). Elemental analyses confirm the            presence of tin (0.1-0.2 wt%) and chromium traces (0.01-0.1            wt%).                                Turquoise Beads            No specific Raman signature was observed for            turquoise beads (15-b, 17-b, 19-b) of Antsiraka Boira (e.g. Figure            2, the spectrum 17-b), in agreement with a dispersion of Cu2+ ion in an alkaline glass matrix (Eppler &#38;            Eppler, 2000; Colomban et al., 2001). The            SEM-EDS elemental analysis confirmed the presence of copper (0.1 -            0.3% by weight of oxide), and iron (0.3-0.8% by weight of oxide).            The Fe2+ ion gives a light blue colour whereas            the Cu2+ ion is the classic turquoise            chromophore of alkaline glasses and enamels (Colomban &#38;            Schreiber, 2005). The Cr-Sn chromophore is detected in bead 19-b            (Figure 3).                                Black Beads            Representative Raman spectra of black beads are            given in Figure 5. For almost all of the analyzed beads, the            identified black pigment corresponds to the amber chromophore            “Fe-S” used to produce amber glass (Schreurs and Brill, 1984;            Prinsloo &#38; Colomban, 2008). The resonant Raman spectrum of            this pigment is characterized by a broad band around 415 cm-1, which is superimposed on the spectrum of the            glass. The position of this band and its components depends on the            glass matrix, i.e. the direct environment of the Fe-S chromophore            (Figure 5a) and of the laser line used (Figure 5b). In Figure 5b,            examples of the Raman signatures of bead 21-n obtained with            different excitation wavelengths are given. Depending on the            wavelength of the laser, the intensity and position of the main            Raman band of the chromophore Fe-S vary (Prinsloo &#38; Colomban,            2008): the main peak at 413 cm-1 under green            excitation (532nm) moves to ~ 390 cm-1 under            red excitation (633 and 785 nm), and loses intensity (Prinsloo and            Colomban, 2008; Prinsloo et al., 2011). The            spectrum recorded with the 785 nm laser line allows access to the            Raman signature of the bead’s vitreous matrix (SiO4 νmax = 1071 cm-1, SiO4 δmax = 482 cm-1, Fig 5b,            spectrum 21-n at 785 nm).            Figure 5: Representative Raman spectra of            the black beads a) with 532nm excitation and according to the            excitation wavelength for the black bead 21-n / Figure 5 : Spectres Raman représentatifs obtenus a)            pour différentes perles noires sous 532 nm et b) pour la perles            noire 21-n sous différentes excitations laser                        Another black pigment has been detected in bead            13-n (Figure 5a), which corresponds to a manganese oxide            characterized by the bands at 297, 480 and 633 cm-1 (Julien et al., 2004)            and confirmed by SEM-EDS analysis (1.8 wt% of MnO2). A similar spectrum and a high Mn content was            observed in Magoro black beads (Koleini et            al., 2014; Koleini et al., 2016c).            Precise identification of the oxide remains difficult, because of            the high sensitivity of these (black) oxides to laser heating, as            heating changing the degree of oxidation and allotrope. As with            some yellow and red beads, the spectrum of Cr-Sn chromophore was            identified in some spots of the black beads 13-n and 21-n.            Analyses by SEM-EDS clearly illustrate chromium (0.02-0.2 wt%) and            tin (0.09-0.1 wt%).                                White beads            The Raman spectra of white beads (e.g. Figure            6a) are typical of aragonite, an allotrope of calcium carbonate            (CaCO3) occurring in living matter, which            exhibit characteristic peaks at 153, 208, 709 and 1084 cm-1 (White, 2008).            Figure 6: Raman spectrum (HE 532) of            mineral phases present in a) shell bead (11-w) and b) glass            matrices; 1-r: sodium-rich feldspar; 4-y: zircon / Figure 6 : Spectres Raman représentatifs obtenus            avec le spectromètre HE 532 des phases minérales : a) perle            blanche (11-w, coquillage) et b) perles de verre, 1-r: feldspath            sodique; 4-y: zircon                                            Other Phases            Figure 6b presents the characteristic spectra            of secondary crystalline phases encountered in glass matrices. The            Raman spectrum 4-y, with peaks at 357, 440 and 1008 cm-1 is characteristic of zircon, ZrSiO4 (Raskovska et al., 2010).            This mineral, a very stable nesosilicate, detected in the beads            4-y, 13-n and 21-n is present in many ancient rocks and products            of their degradation (clays).            The Raman spectrum 1-r (290, 478, 506, 760 and            812 cm-1) is characteristic of a sodium-rich            feldspar, albite NaAlSi3O8            (Freeman et al., 2008). It was identified            in the beads 1-r and 21-n. The feldspars are commonly used as            fluxes in the glass or ceramic production. All characteristic peak            wavenumbers are summarized in Table 4.                                    Glassy matrix          The micro-Raman spectrometry of amorphous          silicate phases has already been subjected of numerous studies for          non-destructive identification of glass or enamelled objects          (Colomban et al., 2003; Colomban et al., 2006a; Colomban &#38; Treppoz, 2001;          McMillan &#38; Piriou, 1982 and references herein). The glass is a          more or less polymerized SiO4 network, with each          tetrahedron sharing or not their oxygen ion. Ions lowering the          melting point (mainly Na+, K+, Pb2+ and Ca2+) and the colouring ions are housed in the void          spaces of the polymer network.          The Raman spectrum of an amorphous silicate is          composed of two wide bands resulting from vibrations of the SiO4 tetrahedron, a strong covalent entity and          vibrationally well defined: in the middle frequencies the band          centred around 500 cm-1 corresponds to the          symmetrical deformation vibrations (δ SiO4); the          second band around 1000 cm-1 corresponds to the          symmetric stretching vibrations of the tetrahedron (ν SiO4). Actually, the contribution of asymmetric          stretching and bending modes can be neglected (Colomban &#38;          Prinsloo, 2009). The graphical representation of ν SiO4 vs. δ SiO4 maximum wavenumber          distinguishes types of glass (Figure 7) (Caggiani et al., 2014; Colomban et          al., 2005b; Colomban et al., 2006a). It          is noted that an increase in alumina (i.e. the network ionicity) or          lead (i.e. the depolymerization) in the glass composition causes          major wavenumber shift (Colomban et al.,          2006b; Tournié et al., 2008). Corrosion          phenomenon with the protonation/leaching may also be responsible for          lowering the bending and stretching mode wavenumber (Tournié et al., 2008).          Figure 7: a) representative Raman spectra of          the main glass matrix: 18-y) depolymerized glass; 17-b) soda glass          with a high alumina content (Al2O3 Na2O); 10-n) soda glass; 20-r)          soda corroded glass. b) Classification of glassy matrices of the          beads according to the maximum position of the Raman stretching          (νmax Si-O4) as a function          of the maximum deformation position (δmax          Si-O4) / Figure 7 : a)          Spectres Raman représentatifs des matrices vitreuses: 18-y) verre          dépolymérisé; 17-b) verre sodique riche en alumine (noté Al2O3 Na2O); 10-n) verre sodique;          20-r) verre sodique corrodé. b) Classification des matrices          vitreuses à partir des positions des maxima du massif Raman des          modes d’élongation (νmax Si-O4) et de déformation (δmax Si-O4)                    The areas delineated as typical of eras and          backgrounds glass (see Figure 8). The colour of the beads and the          specificities of each field are indicated. Symbols markers          correspond to the classification of Wood. / Les          zones des principaux types de verre sont indiquées (cf. Figure 8).          Les couleurs et les principales caractéristiques sont notées. Les          symboles correspondent à la classification morphologique de          Wood.          Consistent with the results of the elemental          analysis (Figure 7, Table 3), almost all beads are made of soda          glass. Na2O content ranges between 12% and 18%,          except for beads #7 (11.8%) and #9 (9.8%). K2O          content ranges between 1.5% and 2.8%, except for black beads #7, 10          and 21 exhibiting lower values (1.2%-1.4%). Only a spectrum          corresponds to a more highly depolymerized glass (18-y, corrosion          pits are visible in Figure 1) and a bead belongs to the          soda-lime-type (13-n, stained with manganese oxide). The wound bead          10-n is located outside the dispersing zone of other soda beads in          accordance with its particular process. The deformation band maximum          (δmax SiO4 at 470-500 cm-1) and the elongation band maximum (νmax SiO4, around 1080 to 1090          cm-1) are typical of a sodium silicate glass          rather rich in Al2O3. The          17-b spectrum (Figure 7a) is typical of a highly polymerized soda          glass, with three bands at 335, 495 and 576 cm-1          and two very intense stretching components in 1090 cm-1 and another of medium intensity at 990 cm-1. The spectrum 13-n of soda-lime type is          characterized by a band at 554 cm-1, and three          stretching components at 945, 992 and 1082 cm-1.          The data is somewhat scattered but it is possible to identify          subgroups. The dispersion of structural changes is due to          compositional variations, linked to variable raw materials used, or          to the implementation of technology (purification / selection of raw          materials). The beads “specificity” in terms of composition of the          glass matrix is also found in terms of chromophore (13-n and 18-y)          or manufacturing technique (10-n).          The examination of the Raman profiles brings a          number of additional information. In Figure 7a, the representative          Raman signatures of the main glass matrices, demonstrate that in          spite of their belonging to the same group (17-b, 10-n and 20-r)          differences are visible. The 20-r spectrum is characteristic of a          corroded glass. This alteration is attributed to a chemical reaction          between the glass surface and an acidic aqueous solution causing the          exchange of K+ and Na+ /          Mg2+ ions by protonic species: moving the νmax SiO4, to a lower wave number          (1072 cm-1) corresponds to an elongation of the          Si-O bond due to the interaction of oxygen atoms with the protonic          species (Tournié et al., 2008).          The analysis by SEM-EDS was performed to complete          the classification obtained by Raman spectroscopy, and identify          chromophores which do not give specific Raman signatures. Most beads          have a relatively high content of Al2O3 (6 to 9.5 wt%, Table 3, in agreement with the          original Indo-Pacific beads (Dussubieux et          al, 2010; Robertshaw et al, 2010),          reflecting the use of a flux of mineral type. These compositions are          shown graphically in ternary diagrams (Figure 8). The ternary          diagram (SiO2 - Al2O3 - Σ fluxes) in the Figure 8a &#38; a’, is          sensitive to both raw materials but also to technology because of          the direct correlation between the amount of fluxes and of the          operation temperature. This is to distinguish four sub-groups:                      A large majority of beads from Antsirak            Boira consists of a flux-rich glass (~ 20 wt%).            Some black beads have clear inclusions            and / or corrosion of red dots (9-n, 7-n, 21 n), and the blue bead            16-b contains less flux (~ 15 wt%).             Bead 17-b appears isolated, with a very            alumina-rich glass (Al2O3            ~ 13 wt%).            Beads 13-n and 15-b are richer in fluxes            than all the other beads (~ 23 wt%). The main difference of this            black bead with those recovered from South-African Magoro Hill            site is its higher Al and less Mn content.                     The ternary diagram of fluxes (Na2O - CaO - K2O, Figure 8b &#38;          b’) refines the visualization of differences. The homogeneity of a          glass notably depends on the temperature and heating time, the          agitat ion of the melt, etc. Although all of the beads seem to be          composed of a soda glass (Figure 7b), two sub-groups are          emerging:                      The first consists of a glass matrix rich            in sodium, which brings together the red beads (1-r, 2 r, 14 r,            20-r and 22-r) and a large majority of black beads (5-n, 6-n, 7-n,            8-n, 10-n, 12-n, 21-n).            The second group consists of beads made            of a glass richer in calcium (3-y, 9-n, 13-n, 17-b).                    The comparison with literature data, presented in          the ternary diagram of “Flux” (Figure 8 a’ &#38; b’), confirms the          beads of this assemblage belonging to the group of “Indo-Pacific”          soda glass beads.          Figure 8: Ternary composition diagrams for          glass beads (SiO2 - Al2O3 - Σ fluxes) and (Na2O - CaO -          K2O), normalized to 100 (see Table 2) - a) and          b) are related to the composition of Mayotte beads. The colour of          markers depends on the beads: a’) and b’) illustrate the literature          data (Denbow et al, 2015; Dussubieux et al.,          2008; Prinsloo and Colomban, 2008; Robertshaw et          al., 2009, 2010; Welter et al., 2007) /          Figure 8 : Diagrammes en composition oxyde          normalisée des perles pour les éléments majeurs (SiO2 - Al2O3 - Σ fondants) et les          fondants (Na2O -          CaO - K2O, cf.          Table 2) : a) &#38; b) perles de Mayotte (les couleurs des symboles          correspondent aux couleurs des perles) ; a’) &#38; b’) données          représentatives de la littérature (Denbow et al., 2015; Dussubieux          et al., 2008; Prinsloo and Colomban, 2008; Robertshaw et al., 2009,          2010; Welter et al., 2007).                                4. Discussion        We will highlight the identified characteristics of        each family of bead, those features that are useful in the discussion        of origins and dating. Table 4 lists the elements identified, pigments        or dyes, and highlights the specific characteristics.        Table 4: Raman fingerprints of pigments,        chromophores and crystalline phases were in Mayotte beads. (IP:        Indo-Pacific. MO: Middle East) / Tableau 4:        Principaux pics Raman des pigments ou chromophores et des phases        cristallines. (IP: Indo-Pacific. MO: Middle East)                              Pigments / Coloring            agents / Phases crystalline            Bead color            Phases            Raman peak cm-1            Chromo-phore             PeriodOrigin            Reference                                PyrochloreSolidsolution            Yellow            Pb2Sb2-x SnxO            137-144            Pb            1293-1570 av. J.-C.MO / IP             Kirmizi et al.,            2009                                Amber            Black            Chromophore Fe-S            415-420            Fe. S            I-P            Prinsloo et Colomban, 2008                                Albite            (Na-feldspar)            BlackRed-brun            NaAlSi3O8            290. 478. 506                                    Freeman et al.,            2008                                Copper            BlueRed            Cu2+Cu0            no            Cu            Europe. MOIP            Colomban et Schreiber,            2005                                Pyrolusite            RedBlack            β-MnO2            280. 490. 630            Mn                        Julien et al.,            2004                                Iron            ions            BlueYellow            Fe2+Fe3+            no            Fe            IP            Colomban, 2004                                Sphene(+anastase)            BlackRedYellow            Chromophore Sphène Sn(+TiO2)            147. 780            Ti. Sn(&#60; 0.2%)                        Faurel et al.,            2003                                Calcium phosphate                        BlackRedYellow            P-O            950-960            /            MO            Ricciardi et al.,            2009b                                Zircon            BlackYellow            ZrSiO4            358. 440. 1008            Zr (21-n)                        Tournié et al.,            2009                                Aragonite            shell            CaCO3            155. 207. 704. 1085                                    White S.C., 2008                                    Yellow beads          Raman spectroscopy demonstrates for yellow beads          3-y and 4-y (Figure 3c) the use of a pyrochlore solid solution based          on Pb2Sb2-xSnxZyO7-δ solid solution, also called Naples Yellow          (Colomban et al., 2001, Kirmizi et al., 2010, Perreira et          al., 2009; Rosi et al., 2009). The          presence of lead is confirmed by elemental analysis (0.1 to 0.2% by          weight) with the exception of the 18-y bead which is colored by an          iron yellow (~ 1.8 wt%) whose orange tone is due to the presence of          the chromophore Cr-Sn, identified by Raman scattering. The elemental          analysis showed the presence of tin traces (Sn 0.05 wt%). Naples          Yellow solid solutions have been used in the Mediterranean area and          Mesopotamia since Antiquity (Colomban, 2013) but the presence of          Cr-Sn chromophore was not reported in the previous Raman          studies.                          Red beads          The element identified in red-brown beads is the          metallic copper nanoparticles. The Cu content varies from 0.05 to          0.2 wt%. In agreement with this type of coloring agent, Raman          spectra of the glass matrix are very variable and difficult to          obtain, as expected for glasses containing metallic nanoparticles          (Colomban &#38; Schreiber, 2005). Since the Neolithic, the red color          of the lead-based glasses is achieved in Europe by the dispersion of          copper nanoparticles (Cu0) in the glass matrix          (Colomban et al., 2009) in a reducing          environment. This practice has been widely used in the Roman period          (Ricciardi et al., 2009a) and in some Islamic          productions. Production in China was also suspected (Beaujard,          2012). The joint observation of Cr-Sn chromophore is also a very          special feature of the studied glass.                          Blue and turquoise beads          No blue pigment (Co2SiO4, CoAl2O4,          Lapis lazuli) was detected with Raman spectroscopy . The lack of the          above mentioned signature is consistent with the color obtains by a          small amount of cobalt dissolved in its ionic form in the glass.          Elemental analyzes by SEM-EDS show a very low cobalt content, ~ 0.01          wt% for the bead 16-b, in agreement with the light blue colour of          the bead (less than 0.5 wt% of cobalt is sufficient to give an          intense blue colour). The turquoise color (beads 15-b, 17-b &#38;          19-b) is the classical result of the dissolution of Cu2+ ions in an alkaline silicate glass matrix          (Colomban &#38; Schreiber, 2005). Elemental analyses indicate Cu          content between 0.1 and 0.3 wt%. Iron detected by elemental          analysis, is probably an impurity with no significant role in the          color of matrix. So no specific markers for these beads were found,          except the Cr-Sn chromophore present in the bead 19-b.                          Black Beads          The main identified coloring agent by Raman          scattering in black beads, is the “Fe-S” amber chromophore. In          parallel with the morphological and chemical classifications, the          presence of “Fe-S” chromophore is in agreement with black          “Indo-Pacific” beads, which are supposed to originate from the south          of India, Sri Lanka or South-East Asia (Dussubieux et al., 2008; Prinsloo &#38; Colomban, 2008;          Prinsloo et al., 2011). Accordingly, beads          with variations in the position and intensity of the main Raman          bands (Figure 5a) may indicate various origins or periods /          production qualities.          The 13-n seems morphologically consistent with          Indo-Pacific series. Nevertheless, and contrary to the morphological          criteria, the lack of “Fe-S” chromophore shows another technology in          production of this bead . It is possible these beads are related to          a specific Indo-Pacific sub-group. A manganese oxide pigment is also          observed in red, yellow and black beads (Figures 4a and 4b, Table          4). Cr-Sn sphene is also observed.                          White beads          The white beads are made of aragonite, the          allotrope of most limestone shells or corals. Visually similar beads          were found on the African coastal sites, Tanzania (the ruins of          Kaole) (Wood, 2012) and at Chibuene, south of the Mozambique Channel          (Wood, 2012). Other aragonite beads were also identified at Mahilaka          and Sandrakatsy, Madagascar, two sites dated between the 9th and 15th century AD          (Robertshaw et al., 2006). Shells of Tridacna maxima were found as offerings in          burials on Antsiraka Boira. The inorganic compound of this shell is          aragonite (Romaneck et al., 1987). Since it          is the most abundant species found in the archaeological levels          around Acoua, these beads may well be locally manufactured, although          no contemporary Mayotte site show traces of this production. In          contrast, bead polishers were found on the Lamu Archipelago’s Kenyan          sites (Horton, 1996; Pauly, 2014) demonstrating this type of local          production. These beads could thus be of African origin.                          Glass matrices          Subgroups that were identified by Raman analysis          coincide well with those identified by the ternary composition          diagrams (Figure 8a &#38; b), but dispersions within each groups is          different. Indeed, the structure of the network of SiO4 tetrahedron forming the glass skeleton is not only          a function of composition, but also depends on other factors          (temperature, manufacturing process etc.). Therefore, the same          material composition may not have the same structure and vice versa.          Furthermore, the SEM-EDS analysis made with different magnifications          shows a significant differences in the local composition.          Soda glass is the constituent of all Indo-Pacific          beads (type K2, East-Coast or Khami) dated according to Wood between          the 10th and the 17th          century (Robertshaw et al., 2010; Wood, 2005;          Wood, 2011; Wood et al., 2009). The          dispersion within the Na2O group may result in          variations between compositions K2 groups, EC-IP and Khami due to          the variability of raw materials but also of the surface alterations          of some beads. So the red beads (1-r, 2-r, 14-r, 20-r and 22-r)          belong to the soda group but the majority of Raman spectra are          typical of a slightly corroded glass (whatever the elimination of          surface film by grinding). The easy oxidation of metallic copper          used for colouring (Colomban &#38; Schreiber, 2005; Ricciardi et al., 2009a) may be the source of significant          corrosion for these red beads. The bead 17-b, outside of the main          soda group presents a characteristic Raman signature similar to that          of the K2 series (Prinsloo et al., 2011;          Koleini et al., 2016a; Koleini et al., 2016c). The use of soda glasses is common          in Southeast Asia/China (16th century enamels),          Venice and Holland (16th and 17th century AD) (Ricciardi et          al., 2009b; Robertshaw et al., 2010;          Dussubieux et al., 2010; Kirmizi et al., 2010; Colomban et          al., 2006; Tournié, 2009; Prinsloo et          al., 2011; Tournié et al., 2011) and          this criterion alone does not qualify objects.          The presence of albite is consistent with a poor          refining of molten glass (albite, chalk and silicates form liquid          phase below 900°C), and zircon a geological marker of raw materials.          These minerals were detected in opaque beads, red-brown or black,          which could then be categorized as very heterogeneous beads, closer          to a molten ceramic. The same result was also obtained for some          reddish beads of the Vohemar necropolis dated from 12th-17th century, north of          Madagascar (Colomban &#38; Simsek, 2014). SEM imaging supports this          hypothesis for the red and black cut beads, also revealing a highly          porous matrix typical of unrefined molten material (Fischbach,          2015).                          Origin / production time          Table 5 and Figure 9 summarize the          characteristics of the different Antsiraka Boira beads according to          Raman signature. The first observation compared to the results for          the South African sites is the homogeneity of the corpus from the          Antsiraka Boira necropolis.          Table 5: A summary on the classification and          analysing results of Antsiraka Boira beads. Colouring agents and          types of glass matrices are given. Possible origins of pearls on the          basis of the identified colorants are indicated / Tableau 5: Résumé des caractéristiques des perles          d’Antsiraka Boira, en particulier les agents colorants et les types          de matrice vitreuse. Les origines supposées sont indiquées                                    Similar Raman              spectra(89)              Selected              beads(22)              Pigment /              Chromophore/Phase              Glass matrix              Origin / Period                                                    Na2O              Na2O / CaO              PbO              Corroded                                      5              1a              Fe3+ ion yellow /              corrosion                                          x              x              ?                                      6              2b              Pyrochlore              x                                                        Middle East / Indo-Pacific /              Europe                                      13              5c              Cu0              nanoparticles              x                                          x              Indo-Pacific / Islamic                                      26              4d              Turquoise (Cu2+              ion)              x                                                        Indo-Pacific                                      32              8e              Black/ « Fe-S »              x                                                        I Indo-Pacific                                      3              1              Black / Mn oxyde                             x                                          Mapungubwe / Europe?                                      4              1              White / Aragonite                                                                      East Africa                                a : 18-j. corrosion (HR 532 et 458 nm) +          chromophore Cr-Sn (458 nm) – b : including 4-j Cr-Sn (458 nm) +          zircon (HR 532) – c : including Cr-Sn in 2-r et 22-r (HR 532) and          feldspar in 1-r (HR 532) – d : including 19-b Cr-Sn (HR 532) – e :          including zircon &#38;t Cr-Sn in 21-n &#38; 13-n (HR 532). feldspar          in 21-n (458 nm).          Figure 9: Comparison of the distribution of          the glass types for beads from Antsiraka Boira necropolis with those          of Mapungubwe and K2 sites, depending on the maximum position          wavenumber of the Raman stretching band (νmax          Si-O4) vs. the maximum position of the          deformation band (δmax Si-O4) (Mapungubwe Hill &#38; K2 data according Tournié          et al., 2012) / Figure 9 :          Comparaison de la distribution des types de matrices vitreuses pour          les perles de la nécropole d’Antsiraka Boira avec celles des sites          de Mapungubwe Hill et de K2 (Tournié et al., 2012) dans le diagramme          établi à partir des maxima des modes Raman d’élongation (νmax Si-O4) et de déformation          (δmax Si-O4)                    The beads’ compositional data for different sites          in South Africa shows a good correlation between Raman signatures          and compositions (Figure 8a’ &#38; b’). The classification of          Antsiraka Boira beads on the basis of Wood morphological          classification system appears almost correct. The beads of          Indo-Pacific series (East Coast-IP, K2- IP, Khami-IP), Mapungubwe          Oblate and Islamic (South Africa), have a composition richer in          Al2O3 than beads of Zhizo          series. The series of Islamic, Mapungubwe Oblate and Zhizo have a          high CaO content in comparison with Indo-Pacific beads. Dispersal          areas of South Africa beads on the diagrams of Figures 7 and 8          belonging to the Indo-Pacific and Khami series match those beads of          Antsiraka Boira, supporting the first conclusion of the Wood’s          morphological classification (Figure 1). However, there are          compositional variations within the series (Figure 8, compatible          with an inherent inhomogeneous quality of a non-industrial          production), and allocating a bead to a specific series on the basis          of its morphological features or its composition alone is not always          clear cut, especially for Indo-Pacific series. The Cr-Sn sphene          Raman signature (Table 6) in many beads offers a tool to identify          this subgroup of Indo-Pacific production.          Table 6: Beads selection having a sphene type          phase related to a Cr-Sn chromophore (colour: b. blue or turquoise;          n. black; r. red; y. yellow) / Tableau 6: Perles          où le chromophore Cr-Sn sphène a été observé (couleur: b. bleu ou          turquoise; n. noir; r. rouge; y. jaune)                          A comparison with the beads of Mapungubwe and          K2 sites          Figure 9 compares the distribution of many beads’          glass matrices from the Mapungubwe and K2 sites – two twin sites in          the upper valley of the Limpopo River near the present meeting point          of South Africa, Botswana and Zimbabwe (Prinsloo et al., 2011). The diagram constructed on the          Raman parameters in analysing the structure of the polymeric network          of SiO4 tetrahedron. Almost all of the beads          from the Antsiraka Boira and K2 sites are soda (Na2O), while a significant portion of Mapungubwe beads          belong to soda-lime group (Na2O/CaO).          A wider dispersion was recorded between Na2O and Na2O/CaO groups for          Mapungubwe beads, while most of K2 beads belong to the Na2O group. The variety in glass structure can be          explained by a much longer occupation of Mapungubwe (11th-19th century), which could be          in accordance with many supplies origins and multiple technologies          used, compared to K2 site and its shorter period of occupation (9th-13th century). Mayotte is          much comparable to the contemporary K2 site for both short period of          occupation and a more uniform glass structure. Mapungubwe Na2O/CaO glass bead also have less consistency in          composition than Na2O group which is in          accordance with the various sources and technologies used. K2 and          Antsiraka Boira beads also have not much variety in pigments than          those reported for Mapungubwe beads (Prinsloo et          al., 2011; Tournié et al., 2011).                      5. Conclusion        The use of parameters extracted from the Raman        signature of matrices, allowed classifying Antsiraka Boira glass        artefacts into a main group of Indo-Pacific soda glass, similar to        that of the contemporary site of K2 in South Africa. Elemental        analyses with SEM EDS certified the Raman results. Differences in the        morphology of the beads are however clear. The peculiarity lies in red        and some of the black beads, which seem to be closer to a molten        ceramic than to a glass, akin to some beads from the Vohemar        necropolis in the north of Madagascar (14th to        16th century necropolis). The used coloring agents        are generally conventional: copper red, “Naples Yellow” – a pyrochlore        solid solution –, the amber/black Fe-S chromophore, and Cu2+ ions in the turquoise color. Unexpectedly in the        study of these beads, resonance Raman spectroscopy has identified the        presence of a Cr-Sn sphene chromophore. This pigment has been detected        in several different beads: yellow, black, red, and turquoise; the        presence of chromium and tin elements being confirmed by SEM-EDS        analysis. This Raman signature is a marker of the origin of these        glasses. The chromophore was not used as a colouring agent.        The Indo-Pacific beads of the Antsiraka Boira        necropolis open a long period of overlap with other sites to determine        the location of production facilities. A comparative study is        necessary, especially to investigate whether the Cr-Sn sphene        chromophore is present.        Despite the lower spectral resolution of the        portable device, and its strong complex background, most of the        measurements performed with the portable Raman spectrometer led to        significant and usable Raman spectra (Table 4). For crystalline        compounds such as pigments, the characteristic Raman bands are narrow,        often intense, and easily detectable on the Raman spectrum (Figure 2,        3-y). Therefore, the spectra obtained with the portable device allow        easy identification of almost all crystal phases. Regarding the glass        matrices, portable Raman analysis of yellow and turquoise beads is        more difficult but sufficient in numerous measures. However, for red        and black beads the useful signal can be very small compared to the        background, especially if fluorescence is superimposed. The latter is        very common for porous archaeological samples due to the biological        film’s degradation at the oxide surface. In this case, laboratory        fixed instruments are better suited because of their better accuracy        and overall performance. Blue, violet or UV energy excitement        eliminates the biofilm causing fluorescence very easily and in a few        minutes of irradiation.        The use of mobile equipment that can be implemented        on-site overcomes the technical and ethical constraints related to the        subject, offering the possibility of direct and rapid, in situ identification, without having to move /        export objects. Thus, expanding the areas of intervention and the        amount of accessible objects, and resulting in the acquisition of        richer and more representative data. However, these portable devices        are less efficient due to the devices’ miniaturization which leads to        low resolution, continuous background ... and may – by degrading the        quality of data – cause inappropriate conclusions.