The Investigation of the Medieval Russian Bronze Reliquary Cross Pendant Using a Complex of Nondestructive Methods

The medieval Russian bronze reliquary cross pendant was investigated using a complex of nonde-structive methods in order to determine the degree its integrity and identify the material filling its internal cavity. The metal composition is
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  841 ISSN 1063-7745, Crystallography Reports, 2019, Vol. 64, No. 5, pp. 841–846. © Pleiades Publishing, Inc., 2019.Russian Text © The Author(s), 2019, published in Kristallografiya, 2019, Vol. 64, No. 5, pp. 826–831. The Investigation of the Medieval Russian Bronze Reliquary Cross Pendant Using a Complex of Nondestructive Methods E. S. Kovalenko a , K. M. Podurets a , *, E. A. Greshnikov  a , I. Y. Zaytseva b , S. S. Agafonov  a , V. A. Somenkov  a † , N. N. Kolobylina a , A. A. Kaloyan a , L. I. Govor a , V. A. Kurkin a , and Y. B. Yatsishina a a National Research Centre “Kurchatov Institute,” Moscow, 123182 Russia b Institute of Archaeology, Russian Academy of Sciences, Moscow, 117036 Russia * e-mail: Podurets_KM@nrcki.ru Received April 23, 2018; revised January 15, 2019; accepted January 15, 2019  Abstract —The medieval Russian bronze reliquary cross pendant was investigated using a complex of nonde-structive methods in order to determine the degree its integrity and identify the material filling its internalcavity. The metal composition is established. It is found that the cross material was subjected to spatially inho-mogeneous corrosion and that the cavity is filled with soil. It is shown that application of complementary nondestructive methods provides the most reliable information on historical heritage objects. DOI: 10.1134/S1063774519050110 STATEMENT OF THE PROBLEM A reliquary cross pendant is a small cross-shapedreliquary, aimed at being worn on breast, which con-sists of two connected valves. Reliquary cross pen-dants are used to store and wear religious relics. Thepossible relics inserted in reliquary cross pendants,related to different historical periods, were describedin [1].The object of our study was the bronze reliquary cross pendant (Fig. 1) that was found in a mixed arableland in the ancient settlement Soroguzhino 2 inSuzdal’skoe Opol’e (Vladimir oblast, Yur’ev-Pol’skiidistrict) during the Suzdal archaeological expeditionof the Institute of Archaeology of the Russian Acad-emy of Sciences in 2015, headed by AcademicianN.A.Makarov). The sizes of the cross with a headingare 54 × 25× 5 mm. The cross valves have semicircu-lar branch endings with bead protrusions aside. Thereare a convex relief Crucifix image in the center of theface valve, which has one loop in the top and one loopin the bottom (Fig. 1a), and a convex relief image of the Mother of God with palms open before the breastin the center of the rear shutter, which has two loops inthe top and two loops in the bottom (Fig. 1b, type III.3.1according to oldthe classification of A.A. Peskova [2]).The valves were cast from an impression of ready products, the figures of saints are presented schemati-cally, and the details are not elaborated. There are76findings of crosses of this type in the list of reliquary cross pendants [2]; the finding sites are known for 52of them. Most of these crosses originate from theSouthern Rus monuments; however, products of thistype were also found on the northern Russian terri-tory: in Novgorod (two) in the layers dated back to theperiods from the end of the XI century to the begin-ning of the XII century and from the XII century to thefirst half of the XIII century, in Tver, in Beloozero(two) in a layer dated back to the XII century, in theancient settlements Vorkop’ and Poteryaevo on theSheksna river, and in Kostroma mounds. By analo-gies, the type of the reliquary cross pendant investi-gated in this study is dated back to the XII century (maybe, to the end of the XI century) [2].The reliquary cross pendant has retained entirely. Itconsists of two closed valves, connected by a pin pass-ing through a loop in the upper part of the cross (thelower locker pin is absent) and a heading. When thecross was found, its valves were closed, so that one would expect the insertion to retain. Both adherentsoil and oxidized portions were observed on the cross valves. Our purpose was to investigate the specific fea-tures of the cross structure; analyze the degree of itsintegrity; and, if possible, identify its content. It wasimportant to preserve the cross integrity by applyingonly nondestructive methods.EXPERIMENTAL The study was performed using the experimentalresources of the National Research Centre “Kurcha-tov Institute.” Methods of neutron and synchrotrontomography were applied for imaging the cross inter-nal structure. A neutron tomography experiment wascarried out on an instrument [3] at the IR-8 reac- † Deceased. CRYSTALLOGRAPHIC METHODSIN HUMANITARIAN SCIENCES  842 CRYSTALLOGRAPHY REPORTS Vol. 64 No. 5 2019 KOVALENKO et al. tor [4]. A monochromatic neutron beam (with a main wavelength of 1.526 Å) was formed by a reflection by Cu(111) monochromator crystal. The object wasrotated relative to the vertical axis with a step of 0.5 ° .The object projections were recorded using a position-sensitive detector, consisting of a ZnS(Ag) + 6 LiFscintillator, objective lens, and a charge-coupleddevice (CCD) array. The exposure time of one projec-tion at a reactor power of 5.8 MW was 480 s. The spa-tial resolution in neutron tomography was 160 µm.The synchrotron tomography experiment was per-formed on the LIGA station of the Kurchatov syn-chrotron radiation source “KSRS-Kurchatov” [4].The spectrum of the synchrotron radiation (SR) beamfrom the bending magnet was formed using a 7.5-mm-thick copper filter; the spectral maximum corre-sponded to an energy of ~83 keV. The object wasrotated with respect to the vertical axis with a step of 0.5 ° . The object projections were recorded using aposition-sensitive detector, consisting of a Gd 2 O 2 S(Tb)scintillation screen, an objective lens, and a CCDarray. The exposure time per image was 100 s. Sincethe SR beam cross section has a small height, the pro- jections were composed of several images, shifted over height with a step of 2 mm. The spatial resolution of synchrotron tomography was 130 µm. Since the beamabsorption in the sample was close to 100% in sometransmission directions, the reconstructed projectionsare fairly noisy. A local study of the composition of the cross sur-face material was performed by scanning electronmicroscopy (SEM) and energy-dispersive X-ray microanalysis in a scanning electron-ion microscopeat a maximum accelerating voltage of 30 kV. The ele-mental composition of the cross throughout the entire volume was determined using fast-neutron radiationanalysis [5, 6] in the horizontal expreimental channelof the IR-8 reactor (by detecting the characteristicgamma lines of elements). Note that this method doesnot make it possible to detect hydrogen and boron, because they enter the composition of biologicalshielding materials, and the gamma-spectrum back-ground contains strong characteristic lines of theseelements. To study the metal structure and detecthydrogen, we applied methods of diffraction and inco-herent neutron scattering on the DISK diffractometer [7], installed at the horizontal expreimental channel of the IR-8 reactor, at a wavelength of 1.668 Å.The methods applied in this study are complemen-tary. The main difference between the X-ray and neu-tron tomographies is the different mechanisms of interaction between radiation and material. The mate-rials indistinguishable for X rays can be detected usingneutrons and vice versa [8]. Neutron radiography andtomography are often applied to detect corrosion of metals [9, 10], because the total interaction cross sec-tion between thermal neutrons and hydrogen isapproximately an order of magnitude larger than theinteraction cross section with most of elements. Theefficiency of this complex approach to the study of cultural heritage objects was demonstrated in [11, 12].RESULTS AND DISCUSSIONThe elemental composition of the cross was studiedusing energy-dispersive analysis (EDA) at severalcharacteristic points on the face valve in the regionsthat were rubbed (to make the metal surface bare), onoxide layers of different colors, and on surface con-taminations. Table 1 contains the measurementresults, which demonstrate a large inhomogeneity of  both metal and surface contaminations. The contentsof the elements found by neutron radiation analysisare listed in Table 2. It follows from Tables 1 and 2 thatthe cross is made of lead tin bronze.The thermal-neutron diffraction pattern from thetop part of the cross, which did not contain a cavity, was obtained for a rotating sample; the neutron beamcross section was 7 × 10 mm 2 . Previously [13] neutrondiffraction was applied to study the composition of cast bronze, in particular, as a material of cultural her-itage objects. The diffraction pattern (Fig. 2) containsmainly strong peaks, corresponding to a solid solutionof tin in copper (having an fcc lattice with a period of  а  = 3.665 Å) and weak peaks of intermetallic cop-per‒tin compound ( δ  phase), lead, copper oxide, andquartz. The absence of broadening for the strongestpeaks indicates that the tin content is the same in thecomposition of all cross details (two valves and head- Fig. 1. External appearance of the reliquary cross pendant:images of (a) the Crucifix on the face valve and (b) theMother of God on the rear valve. 5 mm(а)(b)  CRYSTALLOGRAPHY REPORTS Vol. 64 No. 5 2019 THE INVESTIGATION OF THE MEDIEVAL RUSSIAN BRONZE843 ing); therefore, it is highly probable that they were castfrom the same metal.Thus, the material of reliquary cross pendant is atin bronze, consisting of copper, tin (10 wt %), andlead (less than 1 wt %). The diffraction and neutronactivation data are consistent, and the compositiondetermined using EDA is characterized by a largespread, because depends strongly on the compositionof contaminations and corrosion products. Compari-son of the results of the local and integral elementalanalysis did not reveal the presence of any insertion.Lead in low concentrations could enter the alloy com-position not intentionally but as an impurity in cop-per [14]. Phosphorus is apparently an impurity pres-ent in bronze. The presence of copper oxide suggests bronze oxidation. Silicon, iron, magnesium, and alu-minum likely enter the composition of the soil on thecross surface.Three-dimensional images of the cross internalstructure were obtained by tomographic methods.Figures 3 and 4 show some characteristic neutron andsynchrotron tomographic cross sections of the objectof study. The neutron tomographic images demon-strate that the internal cavity of the reliquary crosspendant is filled with a solid material by approximately 50%. It is mainly distributed over the cavity walls;however, there are fragments in the cross center thatare not fixed on the walls. The material yields analmost uniform contrast with small variations over theentire cavity, as well as the soil adherent to the crossexternal surface (Fig. 5а). The cross sections show thatthe material filling the cavity is adjacent to the gaps between the valves (Fig. 5b) and that it is transparentfor X-rays of 80 keV energy (Fig. 5c). All these datasuggest that the cross cavity is filled with soil. Individ-ual inclusions are found in the material filling the cav-ity; they significantly attenuate the neutron beam. The Table1. Elemental composition of the cross according to the energy-dispersive microanalysis dataContent, at %elementmetal (rubbed surface)metal (rubbed surface)emerald green patinapale green patinasurface contaminationsCu65.3138.0737.6559.8610.07Sn15.7212.50Pb02.2600.64Si07.4914.3734.9410.0762.67 Al08.6709.7424.3619.05Fe06.2802.9202.5505.45K02.0804.89Mg02.53P07.6611.4503.88Ca03.8106.3906.6301.1902.22Ti01.9700.73Cl01.52 Table2. Elemental composition of the cross according to the neutron-activation data Standard deviations are given in parentheses. ElementCuSnPbSiAlFeMgPKCContent, at %89.2(3)5.8(5)0.35(6)2.8(5)0.84(12)0.25(3)0.23(5)0.49(9)less than 1less than 3 Fig. 2. Thermal neutron diffraction pattern of ( 1 ) Cu–Snsolid solution, ( 2  ) SiO 2 , ( 3  ) Cu 41 Sn 11 , ( 4  ) Cu 2 O, and( 5  )Pb. Intensity, rel. units510152002255111114334 406080100202 θ , deg  844 CRYSTALLOGRAPHY REPORTS Vol. 64 No. 5 2019 KOVALENKO et al. size of these inclusions is comparable with the spatialresolution, and so they cannot be identified. Thematerial filling the cross cavity forms locally roundedpores about 1mm in size. A clear boundary betweenthe cross material and the material filling the cavity isabsent in some regions in neutron images. The cavity  boundary can be revealed using synchrotron tomogra-phy. Thus, the cross cavity does not contain in signifi-cant amounts either metal objects, or bone fragments,or organic residues; hence, it is filled with soil.The tomographic images reveal inhomogeneity of the bronze. In the neutron images, it manifests itself inthe form of regions significantly attenuating the neu-tron beam. The image in Fig. 6a is a 3-D rendering, which shows the distribution of attenuating regionsover the metal volume. One can see that these regionsare 1–5 mm in size; they barely emerge on the surfaceof the cross and are distributed more or less uniformly over its volume (except for the ends of the cross beam). A comparison of the neutron and X-ray images showsthat these regions have an opposite contrast: they aremore transparent for X rays than the metal (Figs. 6b–6d).One would suggest these inhomogeneities to becorrosion regions. Corrosion products, which containhydroxyl group, are characterized by elevated hydro-gen concentration and, therefore, attenuate signifi-cantly a neutron beam. However, the density of corro-sion products is lower than the metal density; there-fore, the X-ray attenuation is smaller in them. Basedon the contrast value in the X-ray and neutron images,one can roughly estimate the copper-to-hydrogenratio as 4 : 1. A neutron beam could be significantly attenuated by materials characterized by large neutronabsorption cross sections (B, Li, Cd, etc.); however,elemental analysis did not reveal such materials.The experiment on local neutron diffraction con-firms that the inhomogeneities observed in the metalare corrosion regions. A tomographic image was usedto fabricate a mask with holes 3 mm in diameter, coin-ciding with the regions of high and low neutron trans-mission. The corresponding diffraction pattern isshown in Fig. 7. One can see a significant excess of the background incoherent scattering intensity for theregion of low transmission in comparison with thehigh-transmission region. Incoherent scattering is adirect indicator of the presence of hydrogen in mate-rial [15]. However, corrosion products could not beidentified from diffraction data, maybe, as a result of their amorphization. The intensity ratios for the mainreflections in Fig. 7 differ from those shown in Fig. 2 because of the coarse-grained bronze structure. Todetermine the corrosion products, one could also usethe data on the chemical composition of the soil in which the cross was found [16]; however, its composi-tion has been changed for a long time. Fig. 3. Neutron tomographic cross sections of the cross:(a, b) face and rear valves near their interface and(c,d)vertical and horizontal cross sections of the crossnear its center. (а)(b)(c)(d) Fig. 4. Synchrotron tomographic cross sections of thecross: (a) face and (b) rear valves near their interface. (а)(b) Fig. 5. Fragments of tomographic cross sections of thecross: (a) comparison of neutron images of the soiladherent to the surface and the internal content and(b,c) images of the slit between the valves, obtained using(b) neutron and (c) SR beams. (а)(b)(c)  CRYSTALLOGRAPHY REPORTS Vol. 64 No. 5 2019 THE INVESTIGATION OF THE MEDIEVAL RUSSIAN BRONZE845 The tomographic study revealed some specific fea-tures of casting. They are pronounced on the inner surface of the valves. First, in the rear valve, there is barely any cavity in the right arm of the cross beam(Fig. 4). Second, bronze protrusions are observed insome regions on the inner surface (for example, in thetop part of the cross in Fig. 4b). It is unclear if they aregate traces or are caused by casting form wear. Theexternal cross surface has no casting defects; they could be removed when processing the product. The valves are characterized by different casting quality.Casting defects (protrusions, nonuniform cavity shape) and the largest scale corrosion damage, up tothe through corrosion of wall, are observed in the rear  valve. There are no any significant casting defects onthe face valve; however, there are many pores ~250–550 µm in diameter in the bulk of metal walls, whichcan be seen well on the cross sections obtained by syn-chrotron tomography. The more porous valve turnedout to be more stable against corrosion.CONCLUSIONS A complex study of the medieval Russian bronzeclosed reliquary cross pendant was performed usingneutron and synchrotron tomography, methods of elemental analysis, and neutron diffraction. The com-position of the cross metal was determined, and theresults obtained by different methods were compared.Corrosion-induced inhomogeneities were found, thepattern of distribution of corroded portions in themetal bulk was obtained, and some specific features of casting were revealed. Images were obtained, whichdemonstrated the presence of both internal cross cav-ity and its filling. The cross was likely filled mainly  with soil, and neither tomography nor elemental anal- ysis made it possible to identify possible embedding.The results of our study demonstrated the efficiency of complex approach to the analysis of complex objects(to which cultural-historical heritage objects generally  belong), in which the potential of different versions of tomography using radiations of different types is com- bined with the data obtained by elemental analysis anddiffraction. FUNDINGThis study was supported in part by the Russian Foun-dation for Basic Research, project OFI-m no.17-29-04129,and in part by the Ministry of Science and Higher Educa-tion of the Russian Federation within the Federal TargetProgram “Investigation and Engineering in High-Priority Lines of Development of Science and Technology in Russiafor 2014‒2020” (state contract no. 14.619.21.0007, projectRFMEFI61917X0007). ACKNOWLEDGMENTSThis study was performed using the unique researchfacility Kurchatov Synchrotron Radiation Source at theNational Research Centre “Kurchatov Institute.” REFERENCES 1.A. A. Lipatov, E. Yu. Mednikova, A. E. Musin, and A.A. Peskova, Christian Iconography of East and West inthe Monuments of Material Culture of Medieval Rus and Byzantine Empire: In Memory of T. Chukova  (Peterburg-skoe Vostokovedenie, St. Petersburg, 2006) [in Rus-sian], p. 291. Fig. 6. (a) 3-D rendering of the cross, based on neutrondata with contrasted attenuating regions; (b, c) images of across portion with such a region, obtained using (b) syn-chrotron radiation and (c) neutrons; and (d) image pro-files along the white line: ( 1 ) synchrotron and ( 2  ) neutrondata. The arrows indicate the attenuating region. (а)(b)(c)(d)037101417 12 Coordinate, mm Attenuation, rel. units Fig. 7. Local diffraction patterns of neutron scattering for regions with ( 1 ) high and ( 2  ) low transmission. 51015200204060801001202 θ , degIntensity, rel. units 112 2 
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