Adornment and garb objects (bronze bracelets, bronze or silver pendants, fibulas, red ... In the cremation and inhumation graves from the Dacian. â Carpathian ...
The Study of Textile Impressions from Corossions Products of Some Old Iron Artefacts by Means of the Complementary Analytical Techniques OTILIA MIRCEA1, IOAN SÂRGHIE2, ION SANDU3*, MARTA QUARANTA3, ANDREI VICTOR SANDU4 Roman Museum of History, 19 Cuza-Vodã Str, 611009, Roman, Romania 2 „Gh. Asachi” Technical University, Faculty of Industrial Chemistry and Environment Protection, 71 Mangeron Blvd., 700050, Iasi, Romania 3 „Al. I. Cuza” University, Arheoinvest Platform,22 Carol I Blvd., 700506, Iasi, Romania 4 Romanian Inventors Forum, 3, L11, III/3, Sf. Petru Movila Str., 700089, Iasi, Romania
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The paper presents the experimental results obtained by applying some non-invasive methods such as the optical microscopy (OM), the Scanning Electron Microscopy coupled with the EDX Spectrometry for determining the surface and the internal microstructures, respectively, together with the X-rays fluorescence (XRF) for the elements arranged within the corrosion crust on the metallic fragments with textile impressions discovered in cremation and inhumation graves from the 2-nd and 3-rd centuries A.D. Keywords: iron archaeological artefacts, textile impressions, OM, SEM-EDX, XRF
The excavation from the archaeological site of the completely mineralized artefacts, most frequently made of iron, without a certain form, transmits most often only the evidence of time corresponding to some productions and materials, a time interposed between civilizations by centuries or even millenniums. As the result of archaeological diggings or agricultural works there have been discovered in pottery vessels charred seeds or objects (whole or fragmentary) such as monetary treasures [1]. Adornment and garb objects (bronze bracelets, bronze or silver pendants, fibulas, red or white glass beads, etc.) have also been found besides charred bones in the urns from the cremation graves [2, 3]. In such cases one speaks about micro-archaeological discoveries which can offer precious testimonies about the social, economic and religious life of that particular time and space. Whole or fragmentary vestiges discovered in the cremation urns represent a special category of objects, i. e. those resulted from burial rituals. Site impressions such as fragments of glass, bone, textile fibres or wood resulted from the pedological monolitization and embedding processes in the bulk of the degradation products have been found on these types of objects. Their conservation as impressions is determined not only by the nature of the interaction with the lying medium and by the aggressiveness and complexity of the adjacent elements from the site, respectively, but also by the presence of some chemical species resulted from the base metals during the corrosion processes.
The paper presents the study, by multi-analytical methods implying the optical microscopy, the SEM – EDX Scanning Electron Microscopy and X-rays Fluorescence, of some iron objects discovered in a Dacian – Carpathian necropolis, objects which conserve well the form and structure of a textile material monolitized and mineralized in bulk. Experimental Part Description of the Pieces In the cremation and inhumation graves from the Dacian – Carpathian necropolis found on Gabãra Hill, Moldoveni, Neamþ, Romania, studied between 1957 -1959, there have been found, besides whole adornment and garb objects, small completely mineralized metallic fragments. These fragments have a special archaeological interest because the textile support impressions render evident the structural-functional elements (filling, warp, etc.). The first object is a fragment from a fibula pin, broken into two parts, inventory number 12836 (fig. 1). It has been discovered in a cremation grave (M 8) together with charred bones. The urn from this cremation grave, found in one piece but slightly cracked, has been made from grey paste; the lid has the common form of a bowl [2 ]. The second object is a fragment from an iron pin, inventory number 12868 (fig. 2), discovered in 1958 in an inhumation grave (M 208). The pin is broken at both ends and shows the brittleness of the metallic core. Fig 1. Fragments of pin, inventory number 12836
Fig. 2. Fragment of pin, inventory number 12868
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Fig. 5. Products of iron corrosion and soil sediments on the pin with the inventory number 12868
Fig. 3. Textile fibres impressions on the pin with the inventory number 12836 (the two fragments a, b)
Fig. 4. Textile fibres impressions on the pin with the inventory number 12868
The Conservation State of the Artefacts During the lying period the degradation of the pieces produced by the complex action of the chemical, electrochemical and microbiological processes cumulated with the thermal ones before the abandonment (e. g. the cremation in the case of the pin with the inventory number 12836) has been amplified by the physical deterioration processes. When extracted from the archaeological site the two artefacts have presented finely divided or brittle ends produced by the corrosion and erosion processes. Material traces such as mineralized textile fibres impressions have been conserved on both objects (fig. 3a, b, and fig. 4). Within the corrosion crusts there appear products resulted from the iron degradation as well as elements produced by physical deteriorations such as crevices, cavities by solvolysis and small dimensions cracks (fig. 5). The inclusion of some microstructures from the lying medium (silica, caolin, etc.) has determined the formation by monolitization of a crust with an ununiform aspect, coarse at the fragment with the inventory number 12868, and which presents colour variations of red – brick red, yellow – orange as well as whitish sediments.
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Optical Microscopy The microscopical researches have been carried out on an Olympus SZ60 stereomicroscope at various magnifying powers up to the maximum 60 X allowed by the apparatus. The SEM-EDX Electron-scan Microscopy The researches have been carried out with a SEM VEGA II LSH scanning electronic microscope manufactured by the TESCAN Co., the Czech Republic, coupled with an EDX QUANTAX QX2 detector manufactured by the BRUKER / ROENTEC Co., Germany. The microscope, entirely computer operated, contains an electron gun with tungsten filament that may achieve a 3nm resolution at 30kV, with a magnifying power between 13 and 1,000,000 X in the “resolution” mode, a gun potential between 200 V and 30 kV, a scanning speed between 200 ns and 10 ms per pixel. The working pressure is lower than 1 . 10-2 Pa. The obtained image can be constituted by the secondary electrons (SE) or by the backscattered ones (BSE), respectively. Quantax QX2 is an EDX detector used for qualitative and quantitative micro-analysis. Quantax QX2 is a 3-rd generation Xflash detector which does not require liquid nitrogen cooling and is about 10 times faster than the conventional Si(Li) detectors. This technique, together with the microphotogram vizualization, allows the rendering of the image with the mapping (arrangement) of the atoms on the studied surface, and, on the basis of the X-rays spectrum, the determination of the elementar y composition (in gravimetric or molar rates) of a microstructure or of a chosen area as well as the estimation of the composition variation along a vector set in the analysed area or section. X-rays fluorescence. The analyses with the X-rays fluorescence have been carried out with an INNOV-X SYSTEM portable apparatus with tungsten anti-cathode tube, 35 kV, 40μA, 30 s exposure time; the data processing has been done with a specialized software. Results and discussions Archaeological textiles are rather rarely found within sites; that is why the metallic objects with impressions are interesting artefacts both for the authentication and for REV. CHIM. (Bucureºti) ♦ 60♦ Nr.2 ♦ 2009
the estimation of the degradation state of the organic and inorganic materials from the structure of the piece under the influence of the pedological factors and of the reciprocal interactions. Immaterial of the conservation state of these textile fibres fragments under the form of impressions embedded by monolitization, as a result of the interactions with various materials from the soil as well as with the base material of the piece, they are reciprocally influenced in the contact area. For instance, the Fe2+ ions in the presence of certain simple ligands or natural keratizants from the soil, can be solubilized or precipitated, thus giving rise to some penetration processes of the cellulosic or colagenic fibre, and to form some protecting films, respectively, thus conserving the fibre and creating on the surface a series of adducts with passivant activity for the metal and protective for the fibre. This aspect generates the following question: what effect stands at the basis of the interaction between the organic material and the metal in the contact area, be it passivant or activating for the degradation processes. Another question is whether the passivant effect is a reciprocal one and what mechanism intervenes in the monolitization and mineralization of the organic products. These two questions have been into the continuous attention of our team when interpreting the experimental data. The textile materials obtained by interlacing or twisting by using either proteinic fibres (for instance, wool) or cellulosic ones (cotton, hemp, linen) in the archaeological sites become brittle as a result of the microbiological, chemical, hydrical processes and under the action of the pedological factors. From the beginning of the usage period up to the abandonment time one can speak about the natural ageing of fibres to which cooperate three groups of external factors, namely, the physical, chemical and biological agents. When irreversible processes appear at the abandonment time, the activity of these three agents is ver y much accelerated, thus leading to their disappearance as material traces within the archaeological site. However, there are cases when the textile fibres are partially conserved. The problem which arises in this case is connected with the making clear of the mechanisms of the processes which are at the basis of these complex cumulative effects. Some researchers [4] consider that two processes are at the basis of the fibres ageing, namely, the physical ageing which takes place depending on the temperature even in non-aggressive chemical mediums and which has as a result the increase of the fibres rigidity and brittleness, and the chemical ageing which is produced as a result of some reactions such as the breaking of the main chain (by successive depolymerization or statistical splitting), with the dereticulation and the chemical losing or modification of the lateral groups of the macromolecular structure. These researchers are referring only to the usage / displaying period up to the abandonment time when the artefact gets to the “pre-collapse” or “collapse” stages and not to the period from the archaeological site from after the abandonment time. The exception from this case is represented by the “hidden and forgotten” goods and by those affected by calamities or disasters whose “life” is interrupted in spite of the fact that they possess a good conservation state. Their burial in the archaeological site does not allow the usage of the natural ageing term. Here there are taken into account the pedological processes which lead to the two deterioration and evolutive degradation effects which bring the artefact in a certain state of conservation discovered during the excavation / extraction processes. REV. CHIM. (Bucureºti) ♦ 60♦ Nr. 2 ♦ 2009
In the archaeological site a special influence is that of the elements connected with the nature and structure of these materials (the content in cellulose, lignine), of the working technology associated with the aggressiveness of the microclimate from the soil. For instance, the linen and the cotton under humidity conditions are sensible to the attack of bacteria and very seldom survive to the lying conditions [5]. There has been noted that the textile materials from the graves can be conserved when they are in contact with certain metals whose ions have an antibiotic, antimycotic and / or antifungic activity, respectively. Responsible for the monolitization, mineralization and fossilization effects of the fibres are both the primary corrosion products as well as the secondary and tertiary ones, the main role being that of the compounds with an amphoteric character, capable of interactions for ionic exchange as well as of complexing and hydrical interactions. These effects are being based on the complex processes of diagenesis and metasomatosis, especially in the anaerobic medium and in the absence of high temperatures. Such impressions are often used as elements or attributes in the authentication studies. Within the corrosion crust they are easily identified and rendered evident by optical and electronic microscopies both on surface by non-destructive techniques and in the volume phase by the cross sections involving the “cross-section” method coupled with the “staining test”. Corrosion of the Iron Artefacts The corrosion of the metals in atmosphere, water or soil has been much studied by the specialists from various domains (metallurgy, machine manufacturing industry, civil and industrial engineering, environmental engineering and the scientific conservation of the works from the cultural inheritance) [6 – 12]. Among these the open air monuments and the artefacts which have been lying for a long time in water or soil constitute very interesting subjects as far as the making clear of the degradation mechanism is being concerned [13 – 15]. The degradation of the iron archaeological pieces is produced by the chemical, electrochemical or microbiological corrosion processes [16, 17]. At the chemical corrosion the reactions for the electrical charge transfer between the metal and the corrosive gases take place in a dry medium. The electrochemical corrosion appears at the contact of the metal with the electrolyte solutions or at the contact with another metal with various electrochemical activity in wet media. The microbiological corrosion is a process which assists the two types of corrosions which, under the influence of micro-organisms (bacteria, algae and fungi), leads to complex cumulative effects by the consumption of metallic ions, on one hand, and by the degradation under the action of the metabolism products (e. g., the humic acids), on the other hand [16]. Superimposed layers of iron oxides in various stages of oxidation, interpenetrated or diffused with oxyhydroxides, oxysalts, acido-complexes, crystal-hydrates, etc., are formed on the iron alloys. The composition of the rust is modified in time, depending on the alloy composition. The reaction which takes place in the atmospheric environment is the following 2Fe + H2O + 3/2O2 → 2FeOOH In exchange, in saline aerosol media, the primary reaction is: 203
Fe + Cl-(aq)+ H2O + 1/2O2 → [Fe2+ + 2HO- + Cl-](aq), because the presence of the chloride anion allows the catalyzing of the oxidation process and the formation of the Fe2+ slightly hydrated basic oxide. Subsequently, the processes take place according to the diagram suggested by Hache [18] with the following formation order of the components from the structure of the rust layer: the α-Fe 2O 3 hematite, the α-FeO(OH) goethite, the γFeO(OH) lepidocrocite and the Fe3O4 (inert) loadstone. The changing of the goethite into lepidocrocite takes place by crystalline reforming processes while the changing of the lepidocrocite into loadstone takes place by a slow ageing process [17]. Monolitization and Mineralization of the Textile Fibres on Iron Artefacts The fragment of the pin with the inventory number 12836 In the lying microclimate the products resulted by the iron corrosion migrate on the organic support when the iron pieces are in contact with organic materials such as for instance textile fibres, wood, bone or nummulitic structures. In the case of textiles the mineralization process of the fibres takes place by the migration of the iron products while the form of the braiding, embroidery, etc., is conserved on the metallic object. Thus the corrosion products are found again in the structure of the impressed textile fibres. In the SEM images (figs. 6 – 8) one can notice the presence of some impressions of textile fibres on the fragment of the pin with the inventory number 12836. These are strongly deteriorated and degraded having in composition besides the chemical elements from textiles the ones resulted from the degradation of the metal as a result of the contamination within the archaeological site. Table 1 presents their composition which has been determined by EDX on the basis of the spectrum shown in figure 9. At the X-rays fluorescence analyses carried out on one of the two fragments of the pin with the inventory number 12836 there has been determined the following elementary
Fig. 6. SEM 180x image, Textile fibres
Fig. 7. Arrangement of the atoms on the textile fibres from the SEM image
Fig. 8. SEM 400x image, Textile fibres
Fig. 9. EDX spectrum for the textile impressions from the sample with the inventory number 12836 204
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Table 1 COMPOSITION ON THE TEXTILE FIBRES FROM THE PIN WITH THE INVENTORY NUMBER 12836 Element
AN
[norm. wt.-%]
[norm. at.-%]
Error in %
Fig. 10. X-rays fluorescence spectrum obtained for the fragment of the pin with the inventory number 12836
surface composition: 93.35% Fe, 5. 11% Pb, 1.54% Cu, on the bassis of the spectrum presented in figure 10. The Cu percentages are considered to be the result of the contact of the piece with other objects made of copper alloys from the archaeological site. The fragment of the pin with the inventory number 12836 The chemical composition of the alloy and the manufacturing technology of the piece are two very important characteristics which are taken into account when the degradation processes are estimated. The nonuniformity of the corrosion crusts is explained as being the result of the manufacturing faults, breakings, cracks etc. The corrosion processes are also contributing to the formation of some compounds which can be “transfered” and to the materials from the archaeological site when these are conserved as impressions in the metallic bulk. Similarly, in the process of the mineralization of the textile fibres there are formed iron hydrated compounds such as the iron nestoequiometrical oxyhydroxides. Such microstructures (figs. 11 – 12) appear among the textile fibres impressed on the fragment of the pin with the inventory number 12868. These microspheric formation, empty inside, could be the result of microbiological activity in situ, as it has been presented by some authors [19-21] who considers the action of chemoautotrophic iron bacterium Ferrobacillus ferrooxidans which transform hydrogels into Fe(II, II) oxyhydroxides. The chemical composition in the area of these microstructures is presented in table 2 on the basis of the spectrum shown in figure 13. Components of the soil such as the silica and the caolin are also presented among the textile fibres in the chemical composition Si, Al being beside Fe, Ca, Na, Pb, K, Mg, O (table 2). The textile fibres are deteriorated (fig. 14), the form of the braiding being maintained by the iron corrosion REV. CHIM. (Bucureºti) ♦ 60♦ Nr. 2 ♦ 2009
Fig. 11. SEM 300X image (pin with the inventory number 12868) of the microstructures of oxyhydroxides from the textile fibres under the form of dew pearls or dots
Fig. 12. SEM 298X image of the textile impressions (pin with the inventory number 12868)
products. The elements which have been determined by EDX are Fe, C, Si, Ca, Al, Mg, P, K, Pb, the chemical
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Fig. 14. SEM 123X image of the textile impressions (pin with the inventory number 12868)
Fig. 13. EDX spectrum obtained in the area of microstructures from the pin with the inventory number 12868
Table 2 CHEMICAL COMPOSITION IN THE AREA OF THE MICROSTRUCTURES FROM THE FRAGMENT OF THE PIN WITH THE INVENTORY NUMBER 12868 Element
AN
[norm. wt.-%]
[norm. at.-%]
Error in %
Fig. 15. EDX spectrum obtained for the mineralized textile fibres from the pin with the inventory number 12868 206
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Table 3 COMPOSITION OF THE MINERALIZED TEXTILE FIBRES FROM THE PIN WITH THE INVENTORY NUMBER 12868 Element
AN
[norm. wt.-%]
composition being presented in table 5 on the basis of the spectrum shown in figure 15. Conclusions The analysis of the whole or fragmentary objects discovered in clods, pottery vessels or cremating urns by means of the micro-archaeology allows the rendering evident of some very important elements used as attributes for authentication or as effects in making clear the forming mechamism of the bulk. A special place is occupied by the archaeological artefacts subjected to the cremation processes before burial as part of some burial ceremonies, processes which are very difficult to notice. The obtained experimental results lead to the following conclusions: - the surfaces of the iron alloys are changed into crusts with variable thicknesses under the form of bulk with strong brittle metallic core, depending on the degree of transformation of the iron as a result of the pedological processes; -the corrosion crusts are composed both of the products obtained as a result of the redox chemical or electrochemical processes, of the acid-basic, complexation, hydrical and thermal processes and from the contamination with microstructural components from the soil embedded by monolitization; -the contamination components usually occupy free spaces, for instance holes, craters or cracks, thus determining the formation of some coarse and non-uniform crusts which have a determining role upon the mineralization of the organic products in contact with the piece at the time of burial; -the presence of some crystalline reforming structures such as for instance hydrated nestoequiometrical oxychlorides and phosphorus demonstrates the involvement of some cremation thermal processes before the burial; -textile materials impressions, very important elements in the authentication process, have been found well monolitized and mineralized embedded in these structures at the studied pieces; -the structure and the composition of these impressions demonstrate that in the mineralization process an important role is played both by the primary compounds and by the secondary ones for the iron corrosion, on the basis of the diagenesis and metasomatosis processes in a semi-anaerobic medium and in the absesnce of high temperatures which allow the partial preservation of the form and the texture of the textile material; REV. CHIM. (Bucureºti) ♦ 60♦ Nr. 2 ♦ 2009
[norm. at.-%]
Error in %
-the presence of the lead in the structure of the impressions is considered the result of the fact that the textile materials have been dyed with lead-based dyes, another element useful for the authentication process. References 1. URSACHI, V., Carpica XXVI/1, Bacãu, 1997, p. 123 2. ANTONESCU, I., Materiale ºi Cercetãri Arheologice, VI, 1959, p. 473 3. IONIÞÃ, I., URSACHI, V., Vãleni, o mare necropolã a dacilor liberi, Editura Junimea, Iaºi, 1988 4. MARIAN, C., Repere ale restaurãrii textilelor arheologice din mãtase naturalã, Editura Tehnopress, 2001 5. CYBULSKA, M., MAIK J., Fibres & Textiles in Eastern Europe, 15, 56 (64-65), p. 185 6. ROBBIOLA, L., PORTIER, R., Journal of Cultural Heritage, 7, 2006, p. 1 7. ROBBIOLA, L., BLENGINO J. M., FIAUD C., Corrosion Science, 40, 12, 1998, p. 2083 8. ROBBIOLA, L., HURTEL, L.P., Metal 95, James and James Ltd, 1997, p. 109 9. SANDU, I., URSULESCU, N., SANDU, I.G., BOUNEGRU, O., SANDU, I.C.A., ALEXANDRU, A., Corrosion Engineering Science and Technology, 43, 3, 2008, p. 256 10. SANDU, I., QUARANTA, M., BEJINARIU, C., SANDU, I.G., LUCA, D., SANDU, A.V., “Study on the specific effects of corrosion processes on ancient bronze artefacts”, The Annals of “Dunãrea de Jos” University of Galaþi (ISSN 1453-083X), Fasc. IX Metalurgy and Materials Science, 1, 2007, p. 64 11. STAMBOLOV, T., The Corrosion and Conservation of Metallic Antiquities and Works of Art”, CL Publication, Amsterdam, 1985, p. 95 12. MOUREY, W., Conservarea antichitãþilor metalice - de la sãpãturã la muzeu, Ed. Tehnicã, Bucureºti, 1998 13. MAZZEO, R., Patine su manufatti metallici, în Le Patine. Genesi, Significato, conservazione - Kermesquaderni, Ed. Nardini, Firenze, 2005 p.29 14. SANDU, I.G., STOLERIU, S., SANDU, I., BREBU M., SANDU A.V., Rev. Chim. (Bucureºti), 56, nr. 10, 2005, p. 981 15. SANDU, I. G., SANDU, I. C. A., DIMA, A., SANDU, I., NEACªU, I., Bulletin of the Polytechnic Institute of Iaºi, ªtiinþa ºi Ingineria Materialelor, Tom XLXI (LV), Fasc. 2, 2005, p.167 16. SANDU, I., DIMA, A., SANDU, I.G., Restaurarea ºi conservarea obiectelor metalice, Ed. Corson, Iaºi, 2002 17. SANDU, I., Deteriorarea ºi degradarea bunurilor de patrimoniu cultural - bunuri din materiale anorganice, Editura Universitãþii “Alexandru Ioan Cuza”, I, 2008 18. HACHE, A., La corosion des metaux, Ed. Que-Sais-Je, Paris, 1996 Manuscript received: 25.11.2008 207
