Proceedings of the 39th International Symposium for Archaeometry, Leuven (2012) 193-197
X-ray tomographic examinations of Teleac, Cic!u and Apulum rattles C. Pavel1, F. Constantin1, C. I. Suciu2 and R. Bugoi1 1.
‘‘Horia Hulubei’’ National Institute for Physics and Nuclear Engineering, 30 Reactorului street, P.O. BOX MG-6, M!gurele 077125, Romania,
[email protected],
[email protected],
[email protected] 2. ‘‘Lucian Blaga’’ University of Sibiu, 5-7 Victoriei street, Sibiu 550024, Romania,
[email protected]
ABSTRACT
Such imaging techniques can reveal details that cannot otherwise be obtained through ordinary visual examination. CT provides information about the structure of the objects that cannot be disclosed in any other way but through destructive investigations or sampling. Once the internal structure is determined, further hypotheses about the possible uses and roles played by the objects can be inferred.
The examination and characterization of cultural heritage artefacts involves the employment of a wide palette of analytical techniques. Preferably, the examination of art and archaeological objects should be conducted in a nondestructive or at least minimally invasive manner. Computed Tomography (CT) is a powerful, non-destructive technique useful for the visualization of the inner structure of complex objects, providing information on their threedimensional geometry.
CT examinations can be also meaningful for the restoration and conservation planners, supporting them in deciphering ancient manufacturing techniques. Additionally, tomographic studies can reveal previous interventions on the artefacts or might even reveal forgeries (Lehmann et al. 2010, Schreiner et al. 2004).
In recent years, an X-ray tomographic device was developed in the Department for Applied Nuclear Physics from “Horia Hulubei” National Institute for Physics and Nuclear Engineering, M!gurele, Romania. This device and the software implementing the appropriate reconstruction algorithms were specially designed to perform imaging investigations of cultural heritage artefacts made of low-Z materials - clay, wood, bone. Recently, a large number of archaeological ceramics objects from several Romanian museums were imaged using this home-made CT machine.
The most common way of performing X-ray tomography is in transmission mode. It consists in directing an X-ray beam towards an object and then measuring its attenuation from multiple directions. The X-ray beam attenuation depends on the X-ray energy, path length, and on the material from which the object is made (Ketcham et al. 2001). Specialized algorithms are subsequently used for the reconstruction of the imaged object, usually implemented by a computer programme (Kak et al. 2001).
This paper presents the results of the tomographic investigations of three rattles from the Romanian cultural heritage. The objects belong to Alba Iulia National Museum of Union and Aiud Municipal Museum and they were dated to the Iron Age, Bronze Age and Roman periods, respectively. The obtained tomographic images led to the identification of the precise number and shape of bodies contained in their inner structure. The CT scans helped in the determination of the internal dimensions of the artefacts.
Tomography is widely employed in industry, medicine and material research (Gomez-Morilla et al. 2009, Salvo et al. 2003). Generally, CT machines are purposely built for such applications. However, some tomographic devices have been specially developed for archaeological investigations (Haneca et al. 2012, Morigi et al. 2010, Van der Linden et al. 2010).
KEYWORDS
The X-ray tomographic machine used in this paper was designed for archaeometric studies, it is unique in Romania. The CT device and the software implementing the reconstruction algorithm were created in the Department for Applied Nuclear Physics from “Horia Hulubei” National Institute for Physics and Nuclear Engineering, M!gurele (Constantin et al. 2010). After the initial tests, the apparatus was employed for the tomographic screening of a large number of cultural heritage artefacts made of ceramics, in the frame of an on-going post-doctoral project.
Ceramics, Cultural Heritage, Rattle, X-ray Computed Tomography.
Introduction The examination and characterization methods based on Computed Tomography (CT) are more and more frequently employed in the field of cultural heritage (Applbaum et al. 2005, Casali 2006, Ghysels 2003, Haneca et al. 2012, Harvig et al. 2012, Lehmann et al. 2010, Morigi et al. 2007, Tuniz et al. 2012, Van der Linden et al. 2010, De Witte et al. 2008).
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This paper reports some illustrative results of this project, namely the tomographic studies of three ceramics rattles. The objects were dated to the Iron Age, Bronze Age and Roman periods, respectively; they belong to Alba Iulia National Museum of Union and Aiud Municipal Museum. 193
Materials and methods Archaeological objects All the ceramic artefacts reported in this work contain inner bodies whose presence can be detected by the noise they produce when the objects are shaken. Consequently, they were identified as rattles. Fig. 2. Rattle shaped as water bird from the Teleac settlement.
The aims of the CT investigations were to establish the precise number, shape and dimensions of these inner bodies and to eventually identify what kind of material was used for their manufacture.
When publishing it, Vasiliev described this object as: “a goose or a bird with a pebble inside it; it belongs to the first level of inhabitation; its use might be related to the worship of Sun” (English translation from Vasiliev 1985-1986). The bird’s dimensions are: length 92.81mm, wingspan 44.32mm and height 40.39mm.
This kind of information has a certain relevance for archaeologists and historians. It might help them understand the structure of these complex artefacts and the way they were manufactured, as well as providing hints about the roles these objects once played. CT images might support the already existing ideas about the techniques employed in the manufacture of these artefacts. Or, they might provide new explanations regarding the way they were constructed.
The first level of habitation from the Teleac settlement can be dated to the first Iron Age - more specifically to the end of the Hallstatt A2 period - beginning of the Hallstatt B1 period. This interval corresponds to the end of the first stage of the Gáva culture (Ciugudean 2009).
The objects reported in this paper are the following: (1) A rattle shaped as a water bird dated to the Iron Age, found in the archaeological excavations from Teleac; (2) A Bronze Age rattle shaped as a sceptre head found in the settlement from Cic!u-Sali"te; (3) A rattle shaped as a child bust dated to the 2nd or 3rd century A.D., found in the Roman settlement from Apulum.
(2) Bronze Age rattle shaped as a sceptre from Cic!u-Sali"te This sceptre-shaped rattle (Inventory Number 9948) nowadays belongs to the collections of the Aiud Municipal Museum - photo shown in figure 3. It was discovered in the Cic!u-S!li"te settlement, Alba County, in the archaeological excavations made by Winkler and Tákacs between 1969 and 1973 - point 2, figure 1.
Fig. 1. Maps showing the location of the settlements where the objects reported in this study were discovered: 1 - Teleac, 2 - Cic!u-S!li"te, 3 - Apulum.
Fig. 3. Rattle shaped as a sceptre from the Cic!u-S!liste settlement.
(1) Iron Age rattle shaped as a water bird from Teleac The rattle shaped as a water bird (Inventory Number P6512) is a ceramic object belonging to National Museum of Union from Alba Iulia, Romania - see figure 2. The object was found through archaeological excavation in the Teleac settlement, Alba County - number 1 in figure 1.
At its publication, the object was described as: “a clay globe made from sandy paste that turned dark grey from the secondary combustion; its dimensions are the following: 3.2cm globe diameter, 1.2cm handle diameter and 3.7cm height; the handle is broken; it contains several pebbles that are enclosed at the maximum diameter. It is incised with white linear motifs and it has two equidistant cufflinks” (English translation from Winkler et al. 1979, 1980). This object sparked a vivid debate regarding its temporal attribution and about its functions. Thus, Winkler (Winker 1979, 1980) considered the sceptre to be an object typical to
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the Wittenberg culture. As a consequence this rattle cannot be considered as a toy, but rather a ritual object with magic powers.
It contains a compact X-ray source from Spellman High Voltage Electronics Corporation (160kV maximum X-ray tube voltage, 3mA maximum current intensity), a homemade positioning system, capable of rotation and translation movements and a Varian PaxScan flat panel detector with large dimensions (40!30cm2). The detector is made from amorphous silicon (127mm pixel pitch), that was engineered for high-speed radiographic imaging. The spatial resolution that can be acquired using this CT machine is around 300µm. The tomograph can be used to investigate small objects with a maximum volume of 20!20!20cm3 (Constantin et al. 2010).
Another author who investigated this object - Ciugudean made another chronological attribution, assigning it to the Co!ofeni horizon and considering it a combination of a rattle with an anthropomorphic object (Ciugudean 2000).
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(3) Roman rattle shaped as a child bust from Apulum The rattle shaped as a child bust (Inventory Number 539) belongs to the old collections of the Aiud Municipal Museum. Initially, the artefact belonged to the Alba Iulia National Museum of Union.
To achieve the image reconstruction, a home-made software based on a modified Filtered Back Projection algorithm was also written (Constantin et al. 2010). The tomographic measuring procedure involves several steps. The proper placement of the object with respect to the incoming X-ray beam is achieved using the positioning system of the device, a system that allows performing transversal movements under computer-control. After switching on the X-ray tube, the working parameters are adjusted. In the case of ceramic objects, the experiments showed that the most appropriate values for the X-ray tube voltage is roughly 70kV, while the X-ray tube current should be set to around 700"A. The whole object volume is then scanned in 120 steps, representing a 360° rotation of the object around its central axis. The resulting partial images are then summed up to obtain the final projection.
Fig. 4. Rattle shaped as a child bust discovered in the Roman settlement from Apulum. The description from the Aiud Municipal Museum inventory indicates that the place of discovery for this object was the Roman settlement from Apulum - point (3) from figure 1. Taking into account the unclear circumstances of its finding, the artefact can be roughly dated to the 2nd or the 3rd century A.D.
The acquisition time necessary for a full tomographic scan is roughly 5 minutes, while the image reconstruction lasts no longer than 4 minutes. These relatively short times needed for a complete tomographic examination allowed the screening of a large number of ceramic objects belonging to different Romanian museums (# hundreds of items scanned in 2012 only), from which, in this paper, only some of the most significant results are described.
The rattle - see figure 4 - is made from reddish, fine sandy clay. Its dimensions are: height 13.5cm, width 6.5cm maximum (the distance between shoulders) and thickness 4.6cm. The figurine represents a child bust with a round face and an oversized head. The eyes are roundly-shaped, being very well emphasized - at least compared to other Roman statuettes found in Apulum. In the frontal part of the bust, the folds of a draped tunic can be seen. The boy holds in its right arm a dove (height 2.4cm ! width 1.8cm). In the lower part of the statuette there is a small hole, presumably made to evaporate the water (Anghel 2009).
Results and discussions (1) Iron Age rattle shaped as a water bird from Teleac Figure 5 shows the projections of the rattle shaped as a water bird viewed from two different angles.
On the lateral sides of the object, some connection marks can be noticed. These marks indicate that the statuette was made by sticking two pieces together that were shaped using moulds.
Tomographic device and experimental procedures The tomographic device employed in these studies was specially designed for studies of cultural heritage artefacts made out of low-Z materials - e.g. clay, bone, wood.
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Fig. 5. Projections of the rattle shaped as a water bird. 195
From the obtained images one can see the cavity of the rattle and the inner bodies contained in it - namely four clay balls. The tomographic examinations contradicted the hypothesis of the archaeologist who published the object, who speculated that this rattle has a pebble inside it. The CT measurements showed in an unambiguous manner that the internal cavity of this object contains four spheres (4mm diameter) produced from the same material as the one used to shape the body of the rattle, i.e. clay. The walls of this rattle are quite thick. The internal dimensions of the internal cavity provided by the CT scans are the following: length 45mm, width 20mm and height 29mm – compare this with the external dimensions of the bird: length 92.81mm, wingspan 44.32mm and height 40.39mm.
Fig. 7. Projection and reconstructed slice image of the child bust. Slice coordinates: != 38; "=263°; #=187°.
(2) Bronze Age rattle shaped as a sceptre from Cic!u-S!li"te
The tomographic images showed the thickness of the ceramic walls and revealed the entire internal structure of the object. In some cases, small stones used as temper for the ceramic paste were noticed inside the walls. In any case, the quality of the clay from which this object was manufactured is clearly superior to the ones from which the other two objects presented in this paper were made.
Conclusions The tomographic examination of three ceramic rattles belonging to some Romanian museums and dated to the Bronze Age, Iron Age and Roman periods unveiled some details about their internal structure. The CT investigations showed that all the investigated objects contained enclosed clay balls, findings in contradiction with the initial beliefs of the archaeologists who published the objects, who speculated that these rattles have pebbles inside them. The CT scans helped in the determination of the precise number, shape and size of these tiny inner clay balls and allowed the precise measuring of the dimensions of the internal cavities. This thus improved the knowledge and understanding of these archaeological artefacts.
Fig. 6. Projection and reconstructed slice image of the sceptre. Slice coordinates != 42; "=91°; #=204°. The tomographic analysis of this artefact confirmed the idea that this object is a fragment from a larger object - most likely the upper part of an anthropomorphic statuette or, more likely, the superior end (the handle) of a sceptre. The external surface of this object is decorated with motifs incised with a white paste from a different material - details that are also visible in the CT images. The CT scans showed that the bulge from its top is not perfectly spherical, its dimensions being more precisely measured using the recently acquired images: 25.0mm ! 12.4mm.
Acknowledgements Work performed in the frame of the postdoctoral project “X-ray Tomography for Romanian cultural heritage” (PN II RU-PD-20113-0100-49) financed by Romanian Ministry of Education, Research, Youth and Sport - The Executive Agency for Higher Education, Research, Development and Innovation.
The sound produced by shaking this rattle is rather faint, a fact that suggested the idea that the inner bodies - no matter the raw material from which they were made - are small sized objects. The tomographic investigations proved that the sceptre head does not contain pebbles, but four tiny clay spheres with 4.5mm diameter.
Mr. Paul Scrobot$ from Aiud Municipal Museum and dr. Horia Ciugudean from Alba Iulia National Museum of Union are gratefully thanked for granting access to the rattles subjected to the CT investigations.
References
(3) Roman rattle shaped as a child bust from Apulum
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As it is can be seen from figure 7, the interior of the bust contains three clay balls with 8mm diameter.
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