Raman spectroscopy of ancient beads from Devin Castle near Bratislava and of four intaglios from other archaeological finds in Slovakia.
The use of Raman spectroscopy to study archaeological materials has a long tradition, mainly because it is a non-destructive technique and does not require removal of samples from their mountings. Various materials have been analysed, including gems, pigments, glass and ceramics (e.g. Hanni et al., 1998; Smith and Clark, 2004; Zoppi et al., 2005; Vandenabeele et al., 2007; Colomban, 2012; Katsaros and Ganetsos, 2012). The aim of the present research is to identify the minerals in selected archaeological items from Slovak National Museum collections (beads from the Bratislava City Museum and intaglios from the Archaeological Museum in Bratislava) that had been previously described only on the basis of their macro-appearance. Preliminary results of our analyses were published by Gregor et al. (2013).
Necklace and Bracelet from Devin Castle Beads were studied from a necklace and a bracelet that were found in graves from the 11th and 12th centuries at Devin Castle near Bratislava (Placha and Divilekova, 2012). The necklace, consisting of 23 beads (Figure 1), was found in tomb 12/1980, which contained an incomplete skeleton of a woman. The skull, shoulder blades and lower limbs were preserved in good condition. This grave hosted a rich inventory of artefacts: a silver earring on the left side of the skull, necklace beads between the shoulder blades and a ring at the position expected for the right hand. The bracelet, consisting of six beads (Figure 2), was found in grave 145/1985, in which another woman's skeleton was discovered. The beads were found below the mandible. All the beads are drilled through axially. Selected properties of the beads are summarized in Table I.
Beads from the necklace can be divided into three categories. The first contains only one bead, which is the shell of Cypraea moneta (or 'money cowrie', named after the use of this shell as money since ancient times). It was probably positioned as a pendant in the necklace. The second category includes six ball-shaped beads (probably glass) coated with gold foil and typically showing a weathered surface; these beads were studied only macroscopically as they do not correspond to natural gem material. In the third category were 16 roughly faceted oval beads with dull lustre and showing various colours (mostly colourless to dark violet). One of these beads with a dark red colour (no. 13) was previously identified as amber by its macroscopic properties (lustre, colour, inferred hardness and specific gravity; see Placha and Divilekova, 2012). This amber bead, as well as the shell bead, were not examined for this report.
The bracelet consisted of three colourless-to-light-violet and three red-to-orange beads. The violet beads were similar in shape to the oval beads in the necklace described above, while the red-to-orange ones consisted of a seed-style bead and two roughly faceted bicone beads.
Other Ancient Gems from Slovakia
These samples consisted of three gems set in rings and one unmounted stone. Figure 3a shows a gold ring (AP 44 419) dating to the second half of the 3rd century ad from Castle Hill in Bratislava, above the Church of St Nicholas. It contains a light red oval intaglio that is engraved with a nude human figure holding a helmet in the right hand and another object (perhaps a mace) in the left hand. The metal part of the ring is undecorated. Figure 3b shows an unmounted orangey red intaglio (AP 44 749) with an image of the goddess Fortuna holding a steer in her left hand and a horn-of-plenty in her right hand. This intaglio is also from Castle Hill (above the Church of St Nicholas), and dates from the middle of the 2nd century ad; it is part of a collection of artefacts from the La Tene culture. Figure 3c shows a ring (AP 17 343) from a tomb at Sered (located approximately 50 km northeast of Bratislava) that is dated to the 2nd century ad. This ring features a red intaglio that is set in silvery white metal. The opaque stone is decorated by the bust of a woman, viewed from the left profile, holding a round object (probably an apple). Figure 3d shows a bronze ring (AP 51 487) containing a translucent dark red intaglio engraved with a parrot sitting on a sprig. This ring comes from Rusovce (just south of Bratislava) and is dated to the first half of the 2nd century AD.
The colourless-to-violet and red-to-orange beads from Devin Castle, and all four intaglios from the other archaeological finds in Slovakia, were examined with a binocular visor magnifier and an optical microscope, and their colour, transparency, lustre and UV fluorescence were determined.
The gems selected for analysis by Raman spectroscopy included two violet faceted beads (no. 2 from tomb 12/1980 and no. 3 from grave 145/1985), all three red-to-orange beads (nos. 4-6 from tomb 145/1985) and all four intaglios from the other archaeological finds in Slovakia. The samples were analysed at room temperature without any preparation. Raman spectra were collected with a Dilor-Jobin Yvon-Spex LabRam spectrometer. The samples were placed on the micrometric manipulator of a confocal microscope (Olympus BX-40) and visualized in a video monitor. The excitation source was an He-Ne laser (632.8 nm, 15 mW). The scattered radiation was focused onto the entrance slit of a grid monochromator (1,800 grooves/mm), and the spectral range was up to 4000 [cm.sup.-1]. The spectrometer was equipped with a multichannel CCD detector with a resolution of 1.3 [cm.sup.-1]; it was calibrated to the 520.7 [cm.sup.-1] band of monocrystalline silicon. The focused beam was approximately 2 pm in diameter, and the time of data collection ranged from 20 to 200 seconds depending on the intensity of Raman scattering and fluorescence.
The Raman spectra were processed using the LabSpec software package, and the results were compared to Raman spectral databases (e.g. rruff.info) and with the literature (Loudon, 1964; Ganetsos et al., 2013). The signal-to-noise ratio was sufficient for identifying the Raman bands.
Results and Discussion
Beads from Devin Castle
The colourless-to-violet beads from both the necklace and bracelet were 11-16 mm long and showed roughly faceted oval shapes with rounded edges. They varied from colourless (sometimes with a violet or green tint) to light violet to dark violet. The colourless and light violet beads were translucent, and some of the latter showed colour zoning. The dark violet beads were opaque, and all showed a dull lustre. Most of the beads fluoresced blue to long-wave UV radiation, with two of the dark violet beads being inert. Some of the beads were broken (e.g. no. 9) and they showed perfect cubic cleavage. No inclusions could be observed through the poorly polished surfaces.
Selected Raman spectra of the violet beads are shown in Figure 4. Both spectra correspond to fluorite. The Raman [T.sub.2g] band at 322 [cm.sup.-1] is a triple-degenerated vibration of the F- anion sub-lattice with respect to stationary [Ca.sup.2-] cations (Loudon, 1964). Previously, violet or dark violet roughly faceted oval beads from early Medieval cemeteries were commonly believed to be amethyst (e.g. Rejholcova, 1974). However, our visual observations of the beads were not consistent with amethyst, and Raman spectroscopy clearly confirmed that they were fluorite.
The red and orange beads from the bracelet were translucent to opaque and showed a vitreous lustre. They were inert to UV radiation. Raman spectroscopy (Figure 5) identified them as quartz ([alpha]-quartz, trigonal Si[O.sub.2]), confirming that they are carnelian (a variety of chalcedony composed of orange-to-red fibrous microcrystalline quartz). Red bead no. 4 also showed Raman bands for moganite, a monoclinic quartz polymorph. The Raman features corresponding to [alpha]-quartz are [A.sub.1] bands at 207, 355 and 465 [cm.sup.-1] and E bands at 264, 394 and 401 [cm.sup.-1]. The band at 503 [cm.sup.-1] with E symmetry indicates the presence of moganite and corresponds to Si-O-Si vibrations (Kingma and Hemley, 1994).
Other Ancient Gems from Slovakia
All four intaglios were previously described in museum records as carnelian. Intaglio AP 44 419 was translucent and without any observable inclusions. Its Raman spectrum (Figure 6, top) shows a dominant vibrational band centred at 463 [cm.sup.-1] and additional bands at 128, 207, 264, 353 and 393 [cm.sup.-1] that identify it as [alpha]-quartz. In addition, a band at 502 [cm.sup.-1] corresponds to moganite. The presence of quartz could be reliably established not only through the dominant band at 463 [cm.sup.-1] but also by the band at 353 [cm.sup.-1] (Kingma and Hemley, 1994). Our visual observations of this intaglio (i.e. red colour and its inferred hardness) corresponded to carnelian. Gem AP 44 749 had similar macroscopic characteristics, and its Raman spectrum (Figure 6, bottom) also identified it [alpha]-quartz and moganite (i.e. carnelian).
The Raman spectrum of gem AP 17 343 (Figure 7) confirmed the presence of hematite, with vibrational bands centred at 228 ([A.sub.1g]), 248 ([E.sub.g]), 294 ([E.sub.g]), 413 ([E.sub.g]), 501 ([A.sub.1g]), 614 ([E.sub.g]) and 1322 [cm.sup.-1] (cf. Porto and Krishnan, 1967). The Raman spectrum also contains weak vibrational bands centred at approximately 130 and 466 [cm.sup.-1] that reflect the presence of quartz. The band at 466 [cm.sup.-1] is not expected in hematite using the group theory (de Faria et al., 1997). On the basis of its Raman spectrum and visual macroscopic characteristics (deep red colour, opaqueness, fracture pattern and lustre), we concluded that this gem is jasper.
Gem AP 51 487 in the bronze ring has a distinctly dark red colour and was transparent with a vitreous lustre. Its Raman spectrum (Figure 8) shows bands centred at 171, 217, 347 (subdominant band), 374, 500, 557, 633, 861, 918 (dominant band) and 1028 [cm.sup.-1], clearly placing it in the garnet structural group. A shift of the band positions can occur as atoms with different masses occupy the cationic sites. Based on data provided by Pinet and Smith (1993), the calcic series uvarovite-grossularandradite is not a possibility because of differing Raman bands. However, spectra from the aluminian series pyrope-almandine-spessartine fit well with our measured Raman spectrum (cf. Pinet and Smith, 1994). As indicated by the data in Table II, the stone consists of almandine with a spessartine component rather than a pyrope component. Further support for the almandine-dominant composition was obtained by comparing its Raman spectrum with various spectra for almandine (rruff.info/almandine-R040076), spessartine (rruff.info/spessartine-R050063) and pyrope (rruff.info/pyrope-R040159), as well as with the spectra for almandine from Tyrol in Austria and from the historical site of Alabanda in Turkey (Ganetsos et al., 2013).
Raman spectroscopy was used to analyse selected beads from a necklace and a bracelet dating from 11th- and 12th-century burials at Devin Castle in Slovakia. The violet beads were previously believed to be amethyst, but our investigations confirmed they are fluorite. In addition, red-to-orange beads from the bracelet were identified as carnelian (confirming their previous identification from visual observations). One of the carnelian beads also showed the presence of moganite (monoclinic Si[O.sup.2]) in its Raman spectrum. The intergrowth of quartz and moganite polymorphs of Si[O.sub.2] is typical for agate structures (Heaney and Davis, 1995).
In addition, four ancient gems (intaglios) from elsewhere in Slovakia were analysed. Two of them were identified as carnelian, showing Raman bands for quartz and moganite. Another intaglio had Raman bands corresponding to hematite and subordinate quartz, suggesting it was jasper. The fourth gem corresponded to almandine with some vibrational bands for spessartine.
Carnelian and jasper are relatively common gems that are known from numerous sources, so the provenance of those ancient beads/intaglios is unknown. The provenance of the almandine-dominant intaglio also is not clear. Garnet with this composition is known from various localities in Zillertal in the Austrian Alps (Grundmann, 1988). Also the classical locality of Alabanda in Turkey should not be excluded (e.g. Rapp, 2002; Ganetsos et al., 2013), as it was known in the Roman age. Clearly, the geographical origin of the ancient almandine-dominant intaglio documented in this article cannot be identified only on the basis of its mineralogical composition.
The work was supported by grant VEGA 1/0601/13 of the Ministry of Education of the Slovak Republic. We are grateful to specialists at the Bratislava City Museum for their help, and to V. Placha, D. Divilekova, M. Danova, R. Cambal, V. Turcan, T. Stefanovicova and A. Ruttkay for the use of their information.
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Magdalena Kadlecikova, Juraj Breza and Lubomir Vanco
Slovak University of Technology
Ilkovicova 3, 812 19 Bratislava, Slovakia
Milos Gregor and Igor Bazovsky
Slovak National Museum, Vajanskeho
Nabrezie 2, 810 06 Bratislava, Slovakia
Table I: Properties of the beads recovered from Devin Castle, Bratislava, Slovakia. Bead Item number Colour Transparency Necklace 1 Dark violet Opaque beads from grave 2 Light violet Translucent 12/1980 3 Light violet Translucent 4 Dark violet Opaque 5 Colourless Translucent 6 Colourless Translucent 7 Colourless with green tint Translucent 8 Colourless with green tint Translucent 9 Colourless Translucent 10 Colourless with green tint Translucent 11 Colourless Translucent 12 Light violet Translucent 13 Dark red Opaque 14 Light violet Translucent 15 Light violet Translucent 16 Dark violet Opaque Bracelet 1 Colourless with violet tint Translucent beads from grave 2 Colourless with violet tint Translucent 145/1985 3 Light violet Translucent 4 Red Translucent 5 Orange Translucent 6 Orange Opaque Bead Long-wave UV Item number Lustre Material fluorescence Necklace 1 Dull Fluorite - beads from grave 2 Dull Fluorite Blue 12/1980 3 Dull Fluorite Blue 4 Dull Fluorite Blue 5 Dull Fluorite Blue 6 Dull Fluorite Blue 7 Dull Fluorite Blue 8 Dull Fluorite Blue 9 Dull Fluorite Blue 10 Dull Fluorite Blue 11 Dull Fluorite Blue 12 Dull Fluorite Blue 13 Waxy Amber - 14 Dull Fluorite Blue 15 Dull Fluorite Blue 16 Dull Fluorite - Bracelet 1 Dull Fluorite Blue beads from grave 2 Dull Fluorite Blue 145/1985 3 Dull Fluorite Blue 4 Vitreous Carnelian - 5 Vitreous Carnelian - 6 Vitreous Carnelian - Bead Drill hole Item number Size (mm) diameter (mm) Necklace 1 16x11x10 3 beads from grave 2 16x11x10 3 12/1980 3 15x13x8 3 4 13x10x8 3 5 12x12x9 3 6 13x12x9 3 7 13x12x7 3 8 12x11x7 3 9 11x10x6 3 10 14x12x8 3 11 12x11x8 3 12 14x12x7 3 13 11x8x7 3 14 15x10x7 3 15 16x14x8 3 16 16x12x9 3 Bracelet 1 15x12x9 3 beads from grave 2 14x12x6 3 145/1985 3 11x8x7 3 4 7x7x7 1.5 5 19x8x8 1.5 6 22x9x9 1 Table II: Raman bands ([cm.sup.-1]) useful for the identification of garnet intaglio AP 51 487. Aluminian-series garnets (Pinet and Smith, 1994) Spectral This Band range Spessartine Almandine Pyrope work symmetry 1100-750 1030 1038 1062 1028 [T.sub.2g] 906 915 924 918 [T.sub.2g] 850 862 867 861 [T.sub.2g] 750-450 632 630 648 633 [T.sub.2g] 553 557 561 557 [A.sub.1g] 503 499 511 500 [T.sub.2g] 450-120 375 370 380 374 [T.sub.2g] 352 345 364 347 [A.sub.1g] 224 216 208 217 [T.sub.2g] 175 168 174 171 [T.sub.2g]
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|Title Annotation:||Feature Article|
|Author:||Kadlecikova, Magdalena; Breza, Juraj; Vanco, Lubomir; Gregor, Milos; Bazovsky, Igor|
|Publication:||The Journal of Gemmology|
|Date:||Jun 1, 2015|
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