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The function of prehistoric lithic tools: A combined study of use-wear analysis and FTIR microspectroscopy
Spectrochimica Acta Part A 86 (2012) 299–304
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
The function of prehistoric lithic tools: A combined study of use-wear analysis and FTIR microspectroscopy Stella Nunziante Cesaro a,∗ , Cristina Lemorini b a b
Istituto per lo Studio dei Materiali Nanostrutturati (ISMN-CNR) c/o Chemistry Department, University of Rome “Sapienza”, P.le A. Moro 5, 00185 Rome, Italy Dipartimento di Scienze dell’Antichità, University of Rome “Sapienza”, P.le A. Moro 5, 00185 Rome, Italy
a r t i c l e
i n f o
Article history: Received 3 December 2010 Received in revised form 13 June 2011 Accepted 14 October 2011 Keywords: FT-IR Microspectroscopy Use-wear Prehistory Lithic tools
a b s t r a c t The application of combined use-wear analysis and FTIR micro spectroscopy for the investigation of the flint and obsidian tools from the archaeological sites of Masseria Candelaro (Foggia, Italy) and Sant’Anna di Oria (Brindisi, Italy) aiming to clarify their functional use is described. The tools excavated in the former site showed in a very high percentage spectroscopically detectable residues on their working edges. The identification of micro deposits is based on comparison with a great number of replicas studied in the same experimental conditions. FTIR data confirmed in almost all cases the use-wear analysis suggestions and added details about the material processed and about the working procedures. © 2011 Elsevier B.V. All rights reserved.
1. Introduction The study of prehistoric stone tools aiming to infer their use gives an important contribution to the knowledge of economic, social and symbolic aspects of ancient communities life. The interest towards prehistoric activities induced archaeologists, at the end of the 19th century, to analyze the polishes induced by the worked material on prehistoric stone tools and compare them to traces observed on replicas [1,2] or on ethnographic items whose function was known [2]. The interest engendered by the translation of the Semenov’s book “Prehistoric Technology” [3] encouraged many western scholars to deal with use-wear analysis. Lithic tools were usually analyzed by means of low powered microscopes in reflected light looking principally at the micro-fractures developed on the working edge-profiles [4–6]. The use of high powered microscopes was introduced by Keeley [7] and allowed to gain information on polishes defined as visible alteration of the stone tool surface influencing its reflectivity when viewed through the microscope. The capability of the low or high powered microscopic analysis was controversial until the methodological settlement reached only in 1989 at the Conference “The interpretative possibilities of micro-wear studies” held in Uppsala (Sweden) where the validity and complementarity of both methods was recognized [8].
∗ Corresponding author. Tel.: +39 0649913962; fax: +39 0649913951. E-mail addresses: [email protected] (S. Nunziante Cesaro), [email protected] (C. Lemorini). 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.10.040
Nowadays, the microscopic observation of a variety of traces, hereafter referred as use-wear analysis, based on the evidence that each worked material induces distinctive alteration on lithic artefacts, is a well established method. The presence of microscopic amounts of the worked material entrapped in the micro-cavities of the irregular surface of lithic tools edges was ascertained in the late 70s and reported in a number of papers sometimes aiming to understand the formation process of use-wear whose genesis is still an open problem [9 and refs. therein]. In this view the pioneer morphological and/or chemical analysis of residues [10,11] of the material worked opened new perspectives of research alongside the more traditional use-wear analysis. Although residues can suffer morphological and chemical degradation in the archaeological deposits still the detection of surviving residues with a variety of experimental procedures gave encouraging results in the last decades [9,12]. Scanning electron microscopy (SEM), electron dispersive X-ray (EDX) and ion beam analysis (IBA) techniques, for example, were extensively applied to determine the elemental composition of residues and allowed to distinguish between bone or wood deposits from the relative abundance of calcium and phosphor [13–15]. In addition, it was possible to estimate for many residues a surface density of few g/cm2 and a thickness ranging from few g/cm2 up to 1 mg/cm2 . This means that thick deposits are not simple overlayers but diffuse into the stone and this fact explains their survival since prehistoric periods [15]. More recently, organic residues of animal and vegetable origin were identified by means of gas chromatography–mass spectrometry (GC–MS) after extraction via Fatty Acid methyl Ester (FAME)
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technique [16, 17 and refs. therein] or studied adopting the crossover immune electrophoresis (CIEF) method [18]. Up till now FTIR micro-spectroscopy was never adopted for noninvasive identification of residues on archaeological lithic tools although this technique does not require chemical or mechanical pre-treatment of the sample investigated and can distinguish between organic and inorganic samples. In order to test the advantages and the limits of this technique and to combine two independent methods we carried out a systematic use-wear analysis of lithic assemblages from well preserved prehistoric sites. All items showing micro-traces were therefore spectroscopically analyzed to ascertain the presence of residues. These were identified by comparison with a reference collection of replicas that worked a wide selection of animal, plants and mineral materials. The procedure here proposed can introduce a new perspective in the functional study of lithic industries. Since stone tools were used for a variety of activities including butchering, hide, bone and wood-working, harvesting, etc., we are providing a database where inferences drawn by the mentioned approaches are reported and critically compared. In this paper results related to the activities involving contact with animal materials are presented.
Table 1 List of the lithic replicas and material worked.
2. Experimental
Use-wear analysis was performed with both low and highpower approach using respectively a stereomicroscope SMZ (Nikon) with objective 0.5×, oculars 10× and magnification range 0.75×–7.5× and a metallographic microscope Eclypse (Nikon) with oculars 10× and objectives 10× and 20×. Both microscopes were used in reflected light.
2.1. Samples 699 archaeological flint tools and 53 obsidian tools were selected for use-wear analysis. They represent the knapped lithic assemblage of two Neolithic sites from Southern Italy dating from VII to VI millennium BP. 628 flint tools come from the three layers of the Middle Neolithic deposit of Masseria Candelaro (Foggia), one of the few entrenched villages characterizing the Neolithic period of the wide plain bordering eastwards the Adriatic Sea called “Tavoliere” [19]. 267 lithic tools had use-wear; out of them 72 showed traces attributable to animal materials processing [20]. 71 flint tools and 53 obsidian tools come from the Neolithic settlement of Sant’Anna di Oria (Brindisi) consisting of two huts, the more recent built over the remains of the previous one [21]. According to use-wear analysis, 8 flint tools and 13 obsidian tools were used to process animal tissues [22]. The reference collection for FTIR analysis consists of 64 flint and 22 obsidian tools (Table 1) that were used to reproduce prehistoric activities as hunting, butchering, hide processing and production of hard animal material implements and ornaments. 2.2. Cleaning procedures Following the most diffused protocol carried out by use-wear analysts, the archaeological tools were washed with water to remove the soil deposit from the surface. A further washing with de-ionised water in ultrasonic tank for 5–10 concluded the procedure. Before FTIR analysis, the second step of the washing procedure was repeated in order to eliminate all the residues not firmly entrapped in the micro-cavities of the surface. Replicas expressly made for infrared observation were not washed at all. Conversely, experimental samples to be submitted to use-wear study only, were washed in threes steps: water and soap, chemical washing with a diluted acid followed by diluted base and finally with de-mineralized water in ultrasonic tank, in order to maximize the removal of residues while preserving the traces.
Replicas
Raw material
Material worked
2 3 2 7 6 1 1 7 11 1
Obsidian Flint Obsidian Flint Obsidian Flint Obsidian Flint Flint arrowhead Flint
9 20 6 1 1 4 2 1 1
Obsidian Flint Flint Flint Flint Flint Obsidian Flint Flint
Antler Antler Bone Bone Fleshy tissues Fleshy tissues Fleshy tissues + bone Fleshy tissues + bone Fleshy tissues + bone Fleshy tissues + bone boiled + marrow Hide Hide Hide + brain Hide + salt + brain Hide + fleshy tissues Tendons Shell Shell Teeth
Replicas with detectable residues 2 1 0 6 5 1 0 4 6 1 3 18 4 1 1 4 0 1 1
2.3. Optical analysis of archaeological use-wear
2.4. FTIR spectroscopy Reflectance spectra were obtained using the last generation infrared microscope Hyperion (Bruker) in the frequency range 4000–600 cm−1 at a resolution of 2 cm−1 or better cumulating at least 200 scans to achieve an optimal signal-to-noise ratio. Spots of 100 × 100 were normally selected. All archaeological and experimental items were analyzed both on regions not showing use-wear, in order to have a suitable reference (‘blank’ spectra) and on many points of the used edges in order to individuate the micro-residues and check the reproducibility of their spectral patterns. The samples housing was kept under continuous flow of dry nitrogen to eliminate atmospheric water and carbon dioxide. 3. Results and discussion FTIR analysis singled out detectable residues on 49 flint replicas out of 64 (77%) and 10 obsidian replicas out of 22 (45%) (Table 1). Among the artefacts showing use-wear attributed to animal material contact, the presence of residues was spectroscopically ascertained on 52 archaeological flint implements out of 79 (66%) and on 3 archaeological obsidian implements out of 13 (23%). This are collected in Table 2 where use-wear analysis suggestions are compared to the proposed nature of micro-residues spectroscopically individuated. In the same table, 9 flint tools from Masseria Candelaro showing use-wear interpreted as stone, minerals, abrasive and not defined medium hard material are also reported since FTIR analysis detected residues of animal tissues in contrast with use-wear suggestions. The higher percentage of residues observed on both prehistoric and experimental flint tools with respect to obsidian ones seems compatible with the greater roughness of the former material. The stones, in fact, have identical chemical composition (mainly silicon oxide) but flint is microcrystalline while obsidian is a volcanic glass
S. Nunziante Cesaro, C. Lemorini / Spectrochimica Acta Part A 86 (2012) 299–304 Table 2 List of archaeological tools from Masseria Candelaro and Sant’Anna di Oria with related use-wear interpretation and proposed attribution of micro-residues. Archaeological site Masseria Candelaro
Use-wear analysis
Micro-residues
Fleshy tissues Fleshy tissues Fleshy tissues
Adipocere Adipocere, calcite Adipocere, bone, proteins, calcite Adipocere, bone, proteins Adipocere, proteins, calcite Adipocere, lipids, proteins, calcite Bone, calcite Proteins Calcite Adipocere, bone, calcite Adipocere Adipocere, calcite Adipocere, proteins, calcite Proteins, calcite Calcite Adipocere, calcite
3 4 1
Adipocere, bone, lipids, calcite Adipocere, proteins, calcite Calcite
1
Fleshy tissues Fleshy tissues Fleshy tissues Fleshy tissues Fleshy tissues Fleshy tissues Hide Hide Hide Hide Hide Hide Hide and fleshy tissues Hide and fleshy tissues Hide and fleshy tissues Hide and fleshy tissues Hide, fleshy tissues and bone Medium hard material Medium hard material Medium hard material Hard animal material Hard animal material Hard animal material Hard animal material Abrasive Abrasive Stone Minerals Sant’Anna di Oria
Hide Hide Hide Hide Hide Hide Fleshy tissues Fleshy tissues
Adipocere, bone, lipids, calcite Adipocere, bone, lipids, proteins, calcite Bone, calcite
Items
1 1 1 1 1 1 2 3 7 2 1 4 2
1 2 1 2
2
Bone, proteins, calcite Adipocere, bone, proteins, calcite Bone, calcite
1
Bone, proteins, calcite Calcite
1
Adipocere, bone, lipids, calcite Lipids, proteins Bone, calcite Proteins, calcite
1
Adipocere Adipocere, bone, calcite Bone, proteins Lipids Lipids, calcite Ipids, proteins, calcite Bone, calcite Lipids
1 1
3
1 1 1 1 1 1 2 1 1 1 1
which presents a smoother surface. The lack of micro-cavities suitable for long-lasting trapping of residues should also explain the lower amount of worked material found on prehistoric obsidian tools with respect to the experimental ones. All archaeological and experimental tools were firstly analyzed in unused parts. As expected, flint and obsidian showed two vibrations: an intense band around 1200 cm−1 and a medium
301
Table 3 Infrared absorption frequencies (cm−1 ) of flint, obsidian and residues with the proposed assignment. Frequency (cm−1 ) 2913 2845 1735 1647 1523 1573 1537 1392 1158 790 1412 877 912
Proposed assignment C–H of proteins C–H of proteins C O of lipids C O of proteins (amide I) ␦N–H and C–N of proteins (amide II) C–O of fatty acid calcium salt carboxylate (adipocere) C–O of fatty acid calcium salt carboxylate (adipocere) ␦CH2 of proteins Si–O (flint) ␦O–Si–O (flint) as CO3 stretching of calcite ␦as CO3 deformation of calcite P–O (hydroxiapatite)
intensity peak approximately at 780 cm−1 readily assigned to the Si–O stretching and to O–Si–O bending modes respectively [23–25]. The presence of the fundamental modes of SiO2 is an obvious constraint to the detection of residues vibrations. However, ‘blank’ spectra of both materials did not present other features apart the mentioned ones even at high magnification. In addition, they were absolutely reproducible and, as a consequence, the spectral changes observed were confidently attributed to the presence of different material. Table 3 summarizes the infrared vibrations assigned to residues and detected, separately or in different combination, both in archaeological and experimental samples. As no diagnostic bands were detected in the 4000–3000 cm−1 range, the stack plots of the 3000–600 cm−1 interval only are reported in the following. The spectra of unused portions and ‘polished’ areas of flint replicas which worked hard tissues such as bone or teeth or antler showed, in a high percentage of cases, appreciable differences with respect to the blank. Analogous changes were observed in the spectra of several experimental flint tools used for hide processing. Experimental obsidian tools appeared affected by the contact with antler only. The slope of the intense silicate stretching band, in fact, appeared less steep towards the low frequency side and a shoulder was detected at 912 cm−1 . A few samples showed additional peaks: weak broad features at 1633, 1533, 1392 cm−1 and sharper peaks of low intensity at 2913 and 2845 cm−1 . It is known that hard animal tissues (teeth, bone, antler and tusks) are a complex mixture of a phosphatic mineral phase (carbonated hydroxiapatite) and an organic matrix, mainly constituted of a flexible protein (collagen). The vibrational behaviour of recent and ancient samples of human or animal origin has been extensively investigated in the past. Literature data agree in assigning the most intense IR absorption lying in the 1170–900 cm−1 interval to the asymmetric stretching mode (3 ) of the PO4 3− of hydroxiapatite [26–29] and the peaks around 1630, 1540 and 1390 to the amide I (C O ) and amide II (␦N–H and C–N ) modes and CH2 deformation of the proteinaceous component (mainly collagen) respectively [30–32]. Amide III absorption, normally weak and expected around 1240 cm−1 was never detected because of its closeness to the SiO2 stretching intense mode. Bands appearing in the 2800–3000 were assigned to C–H stretching cm−1 . In recent samples the organic matrix/mineral phase ratio is about 0.5 [27,29] but it can decrease in fossil samples since collagen can survive for millennia but it is very affected by the burial conditions [33,34]. In this work a few samples of ancient and recent bones, teeth and antler were examined in the same experimental conditions of stone items. In all cases an excellent agreement with literature data was found. In Fig. 1 an archaeological bone is compared to a bovine
S. Nunziante Cesaro, C. Lemorini / Spectrochimica Acta Part A 86 (2012) 299–304
3000
2500
2000
1500
cm-1
1000
Fig. 1. Micro FTIR spectra of fossil (a) and recent (b) bone.
912 1392
1533
1633
2845
2913
0.4
0.5
0.6
0.7
fresh sample showing the expected lowering of intensity of peaks attributed to collagen. In Fig. 2 the spectra of flint replicas that worked bone and fleshy tissues are compared to archaeological tools of different provenance: flint artefact n. 1066, 3105 and 3388 from Masseria Candelaro showing traces attributed to stone, hard material of unknown nature and bone respectively and n. 222 and 1092 from Sant’Anna di Oria with polishes interpreted as hide and fleshy tissues contact. Unfortunately the strong SiO2 stretching mode of flint and obsidian partially hides the PO4 3− stretching mode. However, it seems reasonable to attribute the spectral changes observed to the overlapping of the mentioned bands. The concurrent detection of absorption peaks attributable to the amide I, amide II and CH2 bending bands of the organic component, in the proper intensity ratio, supports the hypothesis of hard animal material micro residues entrapped in micro cavities of the edges of the archaeological artefact. As predicted, the intensity of peaks assigned to proteins vs the silica and apatite overlapped stretching modes appear less prominent in archaeological than in experimental tools. The identification of hard animal tissues residues in ancient artefacts showing traces of bone contact, e.g. the flint tool n. 3388 from Masseria Candelaro (Fig. 2h) and in the correspondent experimental implements seems quite straightforward. More surprising, however, the presence of hard animal material residues on ancient artefacts with polishes suggesting only soft animal tissues contact. As an example, the flint item n. 1092 from Sant’Anna di Oria (Fig. 2e) shows use-wear of meat while spectroscopic data reveals the presence of hard animal tissues residues.
h g f
0.3
Reflectance
0.0
0.1
0.2
e
3000
d c b a
2500
2000
1500
cm-1
1000
Fig. 2. Micro FTIR spectra of: unused portion of flint tool (a), flint replica that worked skin (b), flint replica that worked bone (c), working edge of flint tools n. 222 and n. 1092 from Sant’Anna di Oria (d and e), working edge of flint tools n. 1066, 3105 and 3388 from Masseria Candelaro (f–h).
912
3000
1574 1540
1736
2913 2845
Reflectance 0.20 0.25
0.0
a
0.00 0.05
0.10
0.15
1392
1633 1533
0.6 0.4
b
0.2
Reflectance
0.30
0.8
0.35 0.40
1.0
302
d
c b a
2500
2000
1500
cm-1 1000
Fig. 3. Micro FTIR spectra of: unused portion of flint tool (a), flint replica that worked hide (b), working edge of flint tools n. 3405 and n. 2920 from Masseria Candelaro (c and d).
This evidence suggests a butchering activity with a consequent contact with bones. In this case, the FTIR investigation details traces analysis. Spectroscopic data add information also in case of the flint tools 3105 and 1066 from Masseria Candelaro (Fig. 2f and g). In the former case, polish is interpreted as generic hard material contact while the residues analysis evidences the presence of hard animal material remains. In the latter case, the spectrum suggests the existence of an analogous residue in contrast with the traces interpretation. The spectroscopic investigation is therefore particularly valuable in detailing not well developed polishes due to stone or bone or teeth which can appear quite similar. It is worth adding that hide worked with replicas (Fig. 2b) was contemporary processed with osseous tools. Evidently, during the experiment bits of bone from osseous tools scattered on the worked surface of hide and migrated on the edge of the stone tool. A similar procedure could be hypothesized in order to justify the presence of hard animal tissues on the archaeological stone tools showing usewear of hide processing such as the artefact n. 222 from Sant’Anna di Oria (Fig. 2d). The stack-plots reported in Fig. 3 compares the spectrum of a flint replica used for hide processing to those of archaeological flint items n. 2920 (Masseria Candelaro) with traces interpreted as hide working and n. 3405 (Masseria Candelaro) with polishes interpreted as contact with fleshy tissues, hide and bone. In the spectra of all specimens, excluding the artefact n. 2920 (Fig. 3d), the mentioned bands in the 1650–1400 cm−1 range are still detectable and assigned to amide I and II modes of proteins present in the biological tissues. An additional peak is observed at 1736 cm−1 and attributed, for its spectral position, to the carbonyl CO band of unsaturated triacylglycerols constituting the subcutaneous fatty layer of the skin [35–38]. Some dissimilarities between recent and archaeological artefacts must be evidenced. In the spectra of the ancient tool n. 3405 from Masseria Candelaro (Fig. 3c), e.g., the bands attributed to proteinaceous tissues, that is the amide bands and CH stretching modes, loosen intensity with respect to the peak assigned to fat tissue. Amide bands show also some coalescence indicating same degradation of the remain [39]. The tool n. 3405 from Masseria Candelaro shows also the shoulder at 912 cm−1 , discussed above and confidently attributed to hard animal material working in agreement with use-wear analysis. In addition, a doublet starts to appear at 1574/1540 cm−1 definitely indicating the presence of calcium palmitate which is an important constituent of adipocere [35–37]. The formation of adipocere or grave wax is the result of a microbial activity converting body fat
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4. Conclusions
Fig. 4. Micro FTIR spectra of a flint tools that worked calcite: unused portion of flint tool n. 169 from Masseria Candelaro (a), working edge of flint tool n. 169 from Masseria Candelaro (b), flint replica that worked calcite (c).
into a mixture of fatty acids palmitic, stearic and myristic, and/or in their calcium salts [38]. The conversion is a long-lasting process which requires the proper conditions of humidity. In the spectrum of sample n. 2920 from Masseria Candelaro (Fig. 3d), only the adipocere fingerprint is present suggesting that residues of different nature were too scarce to be spectroscopically observed. Alternatively, a complete conversion of fatty micro residues can be considered due to a particularly favorable archaeological context at least for some lapses of time. The latter hypothesis seems quite probable since the doublet at 1574/1540 cm−1 was detected in a great number of specimens coming from Masseria Candelaro excavation (Table 2). As a further proof, several replicas used for process the inner part of hide were spectroscopically analyzed just after the contact and showed the band at 1736 cm−1 . This lost intensity after few month and the doublet started at 1574/1540 cm−1 to appear reproducing the transformation hypothesized for archaeological items. A broad absorption band centered about 1412 cm−1 was observed in many prehistoric stone tools and when intense it was paralleled by a weaker feature at 877 cm−1 . On grounds of comparison to experimental tools that worked calcareous stones, the bands are assigned to 3 and 2 modes respectively of calcite residue [40]. For sake of example, the spectra of a flint replica which worked calcite and the flint item n. 169 from Masseria Candelaro, with traces suggesting a contact with hide, are compared in Fig. 4. The presence of calcite traces on ancient tools deserves some discussion. The mineral can be present as a more or less abundant impurity of flint and obsidian. In this case, however, it should have been detected both in the used and unused portions of the tools while, in this investigation, it was observed in the spectra of working edges only. In case of tools showing polishes and spectroscopic evidence of hard animal materials working (see above), the presence of the mentioned features should be coherent with remains of carbonated hydroxiapatite [28,41]. The explanation, however, is not completely satisfactory since both bands attributed to carbonate radical are lacking in the spectrum of the experimental tool that worked bone while detected in the spectra of replicas that worked soft animal tissues on a calcareous slab. In conclusion, it seems quite probable that the most of calcite residues observed on archaeological samples is due to their employment on a calcareous slab. This hypothesis seems supported by the finding of many dolomite or limestone slabs [42] in the archaeological site of Masseria Candelaro.
This work emphasises the usefulness of combined use-wear and residues analyses to interpret the function of prehistoric stone tools. Flint or obsidian assemblages from the Masseria Candelaro and Sant’Anna di Oria archaeological sites showing use-wear of animal tissues processing have been investigated. For the first time FTIR micro spectroscopy has been extensively employed for the non destructive individuation of deposits without pre treatment or manipulation of samples. The identification of the remains has been based on comparison with residues present on a suitable number of replicas. In almost all cases spectroscopic data supported the use-wear analyses adding some explicative details. Organic and inorganic remains have been confidently individuated indicating the presence of hard and soft animal tissues and/or calcite. Moreover, the simultaneous presence of residues of different nature detailed the work processing adopted in the prehistoric times. The percentage of residues on archaeological items itself indicates the existence of more or less favorable conditions to their survival through centuries which can be schematized in three factors: implements raw material, working time-span and postdepositional processes. A very high percentage of implements with micro remains on the working edges has been observed in the assemblage of Masseria Candelaro. The industry of Masseria Candelaro consists only of flint implements which, for their coarse surface, traps the worked material more efficiently than obsidian. All tools present very well developed traces attributed to a very long lasting employment of the tool itself. Moreover, the archaeological site suffered, after is genesis, a desertification process which probably ensured the best conditions for the survival of the resides. Acknowledgments The authors acknowledge the Wenner Gren Foundation (NY) that supported this research with an International collaborative Research Grant. The authors acknowledge Prof. A. Manfredini (University of Rome “Sapienza”) and Prof. E. Ingravallo (University of Lecce) who gave the permission to analyze, respectively, Masseria Candelaro and Sant’Anna di Oria lithic assemblages. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
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The function of prehistoric lithic tools: A combined study of use-wear analysis and FTIR microspectroscopy Stella Nunziante Cesaro a,∗ , Cristina Lemorini b a b
Istituto per lo Studio dei Materiali Nanostrutturati (ISMN-CNR) c/o Chemistry Department, University of Rome “Sapienza”, P.le A. Moro 5, 00185 Rome, Italy Dipartimento di Scienze dell’Antichità, University of Rome “Sapienza”, P.le A. Moro 5, 00185 Rome, Italy
a r t i c l e
i n f o
Article history: Received 3 December 2010 Received in revised form 13 June 2011 Accepted 14 October 2011 Keywords: FT-IR Microspectroscopy Use-wear Prehistory Lithic tools
a b s t r a c t The application of combined use-wear analysis and FTIR micro spectroscopy for the investigation of the flint and obsidian tools from the archaeological sites of Masseria Candelaro (Foggia, Italy) and Sant’Anna di Oria (Brindisi, Italy) aiming to clarify their functional use is described. The tools excavated in the former site showed in a very high percentage spectroscopically detectable residues on their working edges. The identification of micro deposits is based on comparison with a great number of replicas studied in the same experimental conditions. FTIR data confirmed in almost all cases the use-wear analysis suggestions and added details about the material processed and about the working procedures. © 2011 Elsevier B.V. All rights reserved.
1. Introduction The study of prehistoric stone tools aiming to infer their use gives an important contribution to the knowledge of economic, social and symbolic aspects of ancient communities life. The interest towards prehistoric activities induced archaeologists, at the end of the 19th century, to analyze the polishes induced by the worked material on prehistoric stone tools and compare them to traces observed on replicas [1,2] or on ethnographic items whose function was known [2]. The interest engendered by the translation of the Semenov’s book “Prehistoric Technology” [3] encouraged many western scholars to deal with use-wear analysis. Lithic tools were usually analyzed by means of low powered microscopes in reflected light looking principally at the micro-fractures developed on the working edge-profiles [4–6]. The use of high powered microscopes was introduced by Keeley [7] and allowed to gain information on polishes defined as visible alteration of the stone tool surface influencing its reflectivity when viewed through the microscope. The capability of the low or high powered microscopic analysis was controversial until the methodological settlement reached only in 1989 at the Conference “The interpretative possibilities of micro-wear studies” held in Uppsala (Sweden) where the validity and complementarity of both methods was recognized [8].
∗ Corresponding author. Tel.: +39 0649913962; fax: +39 0649913951. E-mail addresses: [email protected] (S. Nunziante Cesaro), [email protected] (C. Lemorini). 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.10.040
Nowadays, the microscopic observation of a variety of traces, hereafter referred as use-wear analysis, based on the evidence that each worked material induces distinctive alteration on lithic artefacts, is a well established method. The presence of microscopic amounts of the worked material entrapped in the micro-cavities of the irregular surface of lithic tools edges was ascertained in the late 70s and reported in a number of papers sometimes aiming to understand the formation process of use-wear whose genesis is still an open problem [9 and refs. therein]. In this view the pioneer morphological and/or chemical analysis of residues [10,11] of the material worked opened new perspectives of research alongside the more traditional use-wear analysis. Although residues can suffer morphological and chemical degradation in the archaeological deposits still the detection of surviving residues with a variety of experimental procedures gave encouraging results in the last decades [9,12]. Scanning electron microscopy (SEM), electron dispersive X-ray (EDX) and ion beam analysis (IBA) techniques, for example, were extensively applied to determine the elemental composition of residues and allowed to distinguish between bone or wood deposits from the relative abundance of calcium and phosphor [13–15]. In addition, it was possible to estimate for many residues a surface density of few g/cm2 and a thickness ranging from few g/cm2 up to 1 mg/cm2 . This means that thick deposits are not simple overlayers but diffuse into the stone and this fact explains their survival since prehistoric periods [15]. More recently, organic residues of animal and vegetable origin were identified by means of gas chromatography–mass spectrometry (GC–MS) after extraction via Fatty Acid methyl Ester (FAME)
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technique [16, 17 and refs. therein] or studied adopting the crossover immune electrophoresis (CIEF) method [18]. Up till now FTIR micro-spectroscopy was never adopted for noninvasive identification of residues on archaeological lithic tools although this technique does not require chemical or mechanical pre-treatment of the sample investigated and can distinguish between organic and inorganic samples. In order to test the advantages and the limits of this technique and to combine two independent methods we carried out a systematic use-wear analysis of lithic assemblages from well preserved prehistoric sites. All items showing micro-traces were therefore spectroscopically analyzed to ascertain the presence of residues. These were identified by comparison with a reference collection of replicas that worked a wide selection of animal, plants and mineral materials. The procedure here proposed can introduce a new perspective in the functional study of lithic industries. Since stone tools were used for a variety of activities including butchering, hide, bone and wood-working, harvesting, etc., we are providing a database where inferences drawn by the mentioned approaches are reported and critically compared. In this paper results related to the activities involving contact with animal materials are presented.
Table 1 List of the lithic replicas and material worked.
2. Experimental
Use-wear analysis was performed with both low and highpower approach using respectively a stereomicroscope SMZ (Nikon) with objective 0.5×, oculars 10× and magnification range 0.75×–7.5× and a metallographic microscope Eclypse (Nikon) with oculars 10× and objectives 10× and 20×. Both microscopes were used in reflected light.
2.1. Samples 699 archaeological flint tools and 53 obsidian tools were selected for use-wear analysis. They represent the knapped lithic assemblage of two Neolithic sites from Southern Italy dating from VII to VI millennium BP. 628 flint tools come from the three layers of the Middle Neolithic deposit of Masseria Candelaro (Foggia), one of the few entrenched villages characterizing the Neolithic period of the wide plain bordering eastwards the Adriatic Sea called “Tavoliere” [19]. 267 lithic tools had use-wear; out of them 72 showed traces attributable to animal materials processing [20]. 71 flint tools and 53 obsidian tools come from the Neolithic settlement of Sant’Anna di Oria (Brindisi) consisting of two huts, the more recent built over the remains of the previous one [21]. According to use-wear analysis, 8 flint tools and 13 obsidian tools were used to process animal tissues [22]. The reference collection for FTIR analysis consists of 64 flint and 22 obsidian tools (Table 1) that were used to reproduce prehistoric activities as hunting, butchering, hide processing and production of hard animal material implements and ornaments. 2.2. Cleaning procedures Following the most diffused protocol carried out by use-wear analysts, the archaeological tools were washed with water to remove the soil deposit from the surface. A further washing with de-ionised water in ultrasonic tank for 5–10 concluded the procedure. Before FTIR analysis, the second step of the washing procedure was repeated in order to eliminate all the residues not firmly entrapped in the micro-cavities of the surface. Replicas expressly made for infrared observation were not washed at all. Conversely, experimental samples to be submitted to use-wear study only, were washed in threes steps: water and soap, chemical washing with a diluted acid followed by diluted base and finally with de-mineralized water in ultrasonic tank, in order to maximize the removal of residues while preserving the traces.
Replicas
Raw material
Material worked
2 3 2 7 6 1 1 7 11 1
Obsidian Flint Obsidian Flint Obsidian Flint Obsidian Flint Flint arrowhead Flint
9 20 6 1 1 4 2 1 1
Obsidian Flint Flint Flint Flint Flint Obsidian Flint Flint
Antler Antler Bone Bone Fleshy tissues Fleshy tissues Fleshy tissues + bone Fleshy tissues + bone Fleshy tissues + bone Fleshy tissues + bone boiled + marrow Hide Hide Hide + brain Hide + salt + brain Hide + fleshy tissues Tendons Shell Shell Teeth
Replicas with detectable residues 2 1 0 6 5 1 0 4 6 1 3 18 4 1 1 4 0 1 1
2.3. Optical analysis of archaeological use-wear
2.4. FTIR spectroscopy Reflectance spectra were obtained using the last generation infrared microscope Hyperion (Bruker) in the frequency range 4000–600 cm−1 at a resolution of 2 cm−1 or better cumulating at least 200 scans to achieve an optimal signal-to-noise ratio. Spots of 100 × 100 were normally selected. All archaeological and experimental items were analyzed both on regions not showing use-wear, in order to have a suitable reference (‘blank’ spectra) and on many points of the used edges in order to individuate the micro-residues and check the reproducibility of their spectral patterns. The samples housing was kept under continuous flow of dry nitrogen to eliminate atmospheric water and carbon dioxide. 3. Results and discussion FTIR analysis singled out detectable residues on 49 flint replicas out of 64 (77%) and 10 obsidian replicas out of 22 (45%) (Table 1). Among the artefacts showing use-wear attributed to animal material contact, the presence of residues was spectroscopically ascertained on 52 archaeological flint implements out of 79 (66%) and on 3 archaeological obsidian implements out of 13 (23%). This are collected in Table 2 where use-wear analysis suggestions are compared to the proposed nature of micro-residues spectroscopically individuated. In the same table, 9 flint tools from Masseria Candelaro showing use-wear interpreted as stone, minerals, abrasive and not defined medium hard material are also reported since FTIR analysis detected residues of animal tissues in contrast with use-wear suggestions. The higher percentage of residues observed on both prehistoric and experimental flint tools with respect to obsidian ones seems compatible with the greater roughness of the former material. The stones, in fact, have identical chemical composition (mainly silicon oxide) but flint is microcrystalline while obsidian is a volcanic glass
S. Nunziante Cesaro, C. Lemorini / Spectrochimica Acta Part A 86 (2012) 299–304 Table 2 List of archaeological tools from Masseria Candelaro and Sant’Anna di Oria with related use-wear interpretation and proposed attribution of micro-residues. Archaeological site Masseria Candelaro
Use-wear analysis
Micro-residues
Fleshy tissues Fleshy tissues Fleshy tissues
Adipocere Adipocere, calcite Adipocere, bone, proteins, calcite Adipocere, bone, proteins Adipocere, proteins, calcite Adipocere, lipids, proteins, calcite Bone, calcite Proteins Calcite Adipocere, bone, calcite Adipocere Adipocere, calcite Adipocere, proteins, calcite Proteins, calcite Calcite Adipocere, calcite
3 4 1
Adipocere, bone, lipids, calcite Adipocere, proteins, calcite Calcite
1
Fleshy tissues Fleshy tissues Fleshy tissues Fleshy tissues Fleshy tissues Fleshy tissues Hide Hide Hide Hide Hide Hide Hide and fleshy tissues Hide and fleshy tissues Hide and fleshy tissues Hide and fleshy tissues Hide, fleshy tissues and bone Medium hard material Medium hard material Medium hard material Hard animal material Hard animal material Hard animal material Hard animal material Abrasive Abrasive Stone Minerals Sant’Anna di Oria
Hide Hide Hide Hide Hide Hide Fleshy tissues Fleshy tissues
Adipocere, bone, lipids, calcite Adipocere, bone, lipids, proteins, calcite Bone, calcite
Items
1 1 1 1 1 1 2 3 7 2 1 4 2
1 2 1 2
2
Bone, proteins, calcite Adipocere, bone, proteins, calcite Bone, calcite
1
Bone, proteins, calcite Calcite
1
Adipocere, bone, lipids, calcite Lipids, proteins Bone, calcite Proteins, calcite
1
Adipocere Adipocere, bone, calcite Bone, proteins Lipids Lipids, calcite Ipids, proteins, calcite Bone, calcite Lipids
1 1
3
1 1 1 1 1 1 2 1 1 1 1
which presents a smoother surface. The lack of micro-cavities suitable for long-lasting trapping of residues should also explain the lower amount of worked material found on prehistoric obsidian tools with respect to the experimental ones. All archaeological and experimental tools were firstly analyzed in unused parts. As expected, flint and obsidian showed two vibrations: an intense band around 1200 cm−1 and a medium
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Table 3 Infrared absorption frequencies (cm−1 ) of flint, obsidian and residues with the proposed assignment. Frequency (cm−1 ) 2913 2845 1735 1647 1523 1573 1537 1392 1158 790 1412 877 912
Proposed assignment C–H of proteins C–H of proteins C O of lipids C O of proteins (amide I) ␦N–H and C–N of proteins (amide II) C–O of fatty acid calcium salt carboxylate (adipocere) C–O of fatty acid calcium salt carboxylate (adipocere) ␦CH2 of proteins Si–O (flint) ␦O–Si–O (flint) as CO3 stretching of calcite ␦as CO3 deformation of calcite P–O (hydroxiapatite)
intensity peak approximately at 780 cm−1 readily assigned to the Si–O stretching and to O–Si–O bending modes respectively [23–25]. The presence of the fundamental modes of SiO2 is an obvious constraint to the detection of residues vibrations. However, ‘blank’ spectra of both materials did not present other features apart the mentioned ones even at high magnification. In addition, they were absolutely reproducible and, as a consequence, the spectral changes observed were confidently attributed to the presence of different material. Table 3 summarizes the infrared vibrations assigned to residues and detected, separately or in different combination, both in archaeological and experimental samples. As no diagnostic bands were detected in the 4000–3000 cm−1 range, the stack plots of the 3000–600 cm−1 interval only are reported in the following. The spectra of unused portions and ‘polished’ areas of flint replicas which worked hard tissues such as bone or teeth or antler showed, in a high percentage of cases, appreciable differences with respect to the blank. Analogous changes were observed in the spectra of several experimental flint tools used for hide processing. Experimental obsidian tools appeared affected by the contact with antler only. The slope of the intense silicate stretching band, in fact, appeared less steep towards the low frequency side and a shoulder was detected at 912 cm−1 . A few samples showed additional peaks: weak broad features at 1633, 1533, 1392 cm−1 and sharper peaks of low intensity at 2913 and 2845 cm−1 . It is known that hard animal tissues (teeth, bone, antler and tusks) are a complex mixture of a phosphatic mineral phase (carbonated hydroxiapatite) and an organic matrix, mainly constituted of a flexible protein (collagen). The vibrational behaviour of recent and ancient samples of human or animal origin has been extensively investigated in the past. Literature data agree in assigning the most intense IR absorption lying in the 1170–900 cm−1 interval to the asymmetric stretching mode (3 ) of the PO4 3− of hydroxiapatite [26–29] and the peaks around 1630, 1540 and 1390 to the amide I (C O ) and amide II (␦N–H and C–N ) modes and CH2 deformation of the proteinaceous component (mainly collagen) respectively [30–32]. Amide III absorption, normally weak and expected around 1240 cm−1 was never detected because of its closeness to the SiO2 stretching intense mode. Bands appearing in the 2800–3000 were assigned to C–H stretching cm−1 . In recent samples the organic matrix/mineral phase ratio is about 0.5 [27,29] but it can decrease in fossil samples since collagen can survive for millennia but it is very affected by the burial conditions [33,34]. In this work a few samples of ancient and recent bones, teeth and antler were examined in the same experimental conditions of stone items. In all cases an excellent agreement with literature data was found. In Fig. 1 an archaeological bone is compared to a bovine
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3000
2500
2000
1500
cm-1
1000
Fig. 1. Micro FTIR spectra of fossil (a) and recent (b) bone.
912 1392
1533
1633
2845
2913
0.4
0.5
0.6
0.7
fresh sample showing the expected lowering of intensity of peaks attributed to collagen. In Fig. 2 the spectra of flint replicas that worked bone and fleshy tissues are compared to archaeological tools of different provenance: flint artefact n. 1066, 3105 and 3388 from Masseria Candelaro showing traces attributed to stone, hard material of unknown nature and bone respectively and n. 222 and 1092 from Sant’Anna di Oria with polishes interpreted as hide and fleshy tissues contact. Unfortunately the strong SiO2 stretching mode of flint and obsidian partially hides the PO4 3− stretching mode. However, it seems reasonable to attribute the spectral changes observed to the overlapping of the mentioned bands. The concurrent detection of absorption peaks attributable to the amide I, amide II and CH2 bending bands of the organic component, in the proper intensity ratio, supports the hypothesis of hard animal material micro residues entrapped in micro cavities of the edges of the archaeological artefact. As predicted, the intensity of peaks assigned to proteins vs the silica and apatite overlapped stretching modes appear less prominent in archaeological than in experimental tools. The identification of hard animal tissues residues in ancient artefacts showing traces of bone contact, e.g. the flint tool n. 3388 from Masseria Candelaro (Fig. 2h) and in the correspondent experimental implements seems quite straightforward. More surprising, however, the presence of hard animal material residues on ancient artefacts with polishes suggesting only soft animal tissues contact. As an example, the flint item n. 1092 from Sant’Anna di Oria (Fig. 2e) shows use-wear of meat while spectroscopic data reveals the presence of hard animal tissues residues.
h g f
0.3
Reflectance
0.0
0.1
0.2
e
3000
d c b a
2500
2000
1500
cm-1
1000
Fig. 2. Micro FTIR spectra of: unused portion of flint tool (a), flint replica that worked skin (b), flint replica that worked bone (c), working edge of flint tools n. 222 and n. 1092 from Sant’Anna di Oria (d and e), working edge of flint tools n. 1066, 3105 and 3388 from Masseria Candelaro (f–h).
912
3000
1574 1540
1736
2913 2845
Reflectance 0.20 0.25
0.0
a
0.00 0.05
0.10
0.15
1392
1633 1533
0.6 0.4
b
0.2
Reflectance
0.30
0.8
0.35 0.40
1.0
302
d
c b a
2500
2000
1500
cm-1 1000
Fig. 3. Micro FTIR spectra of: unused portion of flint tool (a), flint replica that worked hide (b), working edge of flint tools n. 3405 and n. 2920 from Masseria Candelaro (c and d).
This evidence suggests a butchering activity with a consequent contact with bones. In this case, the FTIR investigation details traces analysis. Spectroscopic data add information also in case of the flint tools 3105 and 1066 from Masseria Candelaro (Fig. 2f and g). In the former case, polish is interpreted as generic hard material contact while the residues analysis evidences the presence of hard animal material remains. In the latter case, the spectrum suggests the existence of an analogous residue in contrast with the traces interpretation. The spectroscopic investigation is therefore particularly valuable in detailing not well developed polishes due to stone or bone or teeth which can appear quite similar. It is worth adding that hide worked with replicas (Fig. 2b) was contemporary processed with osseous tools. Evidently, during the experiment bits of bone from osseous tools scattered on the worked surface of hide and migrated on the edge of the stone tool. A similar procedure could be hypothesized in order to justify the presence of hard animal tissues on the archaeological stone tools showing usewear of hide processing such as the artefact n. 222 from Sant’Anna di Oria (Fig. 2d). The stack-plots reported in Fig. 3 compares the spectrum of a flint replica used for hide processing to those of archaeological flint items n. 2920 (Masseria Candelaro) with traces interpreted as hide working and n. 3405 (Masseria Candelaro) with polishes interpreted as contact with fleshy tissues, hide and bone. In the spectra of all specimens, excluding the artefact n. 2920 (Fig. 3d), the mentioned bands in the 1650–1400 cm−1 range are still detectable and assigned to amide I and II modes of proteins present in the biological tissues. An additional peak is observed at 1736 cm−1 and attributed, for its spectral position, to the carbonyl CO band of unsaturated triacylglycerols constituting the subcutaneous fatty layer of the skin [35–38]. Some dissimilarities between recent and archaeological artefacts must be evidenced. In the spectra of the ancient tool n. 3405 from Masseria Candelaro (Fig. 3c), e.g., the bands attributed to proteinaceous tissues, that is the amide bands and CH stretching modes, loosen intensity with respect to the peak assigned to fat tissue. Amide bands show also some coalescence indicating same degradation of the remain [39]. The tool n. 3405 from Masseria Candelaro shows also the shoulder at 912 cm−1 , discussed above and confidently attributed to hard animal material working in agreement with use-wear analysis. In addition, a doublet starts to appear at 1574/1540 cm−1 definitely indicating the presence of calcium palmitate which is an important constituent of adipocere [35–37]. The formation of adipocere or grave wax is the result of a microbial activity converting body fat
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4. Conclusions
Fig. 4. Micro FTIR spectra of a flint tools that worked calcite: unused portion of flint tool n. 169 from Masseria Candelaro (a), working edge of flint tool n. 169 from Masseria Candelaro (b), flint replica that worked calcite (c).
into a mixture of fatty acids palmitic, stearic and myristic, and/or in their calcium salts [38]. The conversion is a long-lasting process which requires the proper conditions of humidity. In the spectrum of sample n. 2920 from Masseria Candelaro (Fig. 3d), only the adipocere fingerprint is present suggesting that residues of different nature were too scarce to be spectroscopically observed. Alternatively, a complete conversion of fatty micro residues can be considered due to a particularly favorable archaeological context at least for some lapses of time. The latter hypothesis seems quite probable since the doublet at 1574/1540 cm−1 was detected in a great number of specimens coming from Masseria Candelaro excavation (Table 2). As a further proof, several replicas used for process the inner part of hide were spectroscopically analyzed just after the contact and showed the band at 1736 cm−1 . This lost intensity after few month and the doublet started at 1574/1540 cm−1 to appear reproducing the transformation hypothesized for archaeological items. A broad absorption band centered about 1412 cm−1 was observed in many prehistoric stone tools and when intense it was paralleled by a weaker feature at 877 cm−1 . On grounds of comparison to experimental tools that worked calcareous stones, the bands are assigned to 3 and 2 modes respectively of calcite residue [40]. For sake of example, the spectra of a flint replica which worked calcite and the flint item n. 169 from Masseria Candelaro, with traces suggesting a contact with hide, are compared in Fig. 4. The presence of calcite traces on ancient tools deserves some discussion. The mineral can be present as a more or less abundant impurity of flint and obsidian. In this case, however, it should have been detected both in the used and unused portions of the tools while, in this investigation, it was observed in the spectra of working edges only. In case of tools showing polishes and spectroscopic evidence of hard animal materials working (see above), the presence of the mentioned features should be coherent with remains of carbonated hydroxiapatite [28,41]. The explanation, however, is not completely satisfactory since both bands attributed to carbonate radical are lacking in the spectrum of the experimental tool that worked bone while detected in the spectra of replicas that worked soft animal tissues on a calcareous slab. In conclusion, it seems quite probable that the most of calcite residues observed on archaeological samples is due to their employment on a calcareous slab. This hypothesis seems supported by the finding of many dolomite or limestone slabs [42] in the archaeological site of Masseria Candelaro.
This work emphasises the usefulness of combined use-wear and residues analyses to interpret the function of prehistoric stone tools. Flint or obsidian assemblages from the Masseria Candelaro and Sant’Anna di Oria archaeological sites showing use-wear of animal tissues processing have been investigated. For the first time FTIR micro spectroscopy has been extensively employed for the non destructive individuation of deposits without pre treatment or manipulation of samples. The identification of the remains has been based on comparison with residues present on a suitable number of replicas. In almost all cases spectroscopic data supported the use-wear analyses adding some explicative details. Organic and inorganic remains have been confidently individuated indicating the presence of hard and soft animal tissues and/or calcite. Moreover, the simultaneous presence of residues of different nature detailed the work processing adopted in the prehistoric times. The percentage of residues on archaeological items itself indicates the existence of more or less favorable conditions to their survival through centuries which can be schematized in three factors: implements raw material, working time-span and postdepositional processes. A very high percentage of implements with micro remains on the working edges has been observed in the assemblage of Masseria Candelaro. The industry of Masseria Candelaro consists only of flint implements which, for their coarse surface, traps the worked material more efficiently than obsidian. All tools present very well developed traces attributed to a very long lasting employment of the tool itself. Moreover, the archaeological site suffered, after is genesis, a desertification process which probably ensured the best conditions for the survival of the resides. Acknowledgments The authors acknowledge the Wenner Gren Foundation (NY) that supported this research with an International collaborative Research Grant. The authors acknowledge Prof. A. Manfredini (University of Rome “Sapienza”) and Prof. E. Ingravallo (University of Lecce) who gave the permission to analyze, respectively, Masseria Candelaro and Sant’Anna di Oria lithic assemblages. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
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