X-ray tomography of a soil block: a useful tool for the restoration of archaeological finds
© Re et al.; licensee Springer. 2015
Received: 9 June 2014
Accepted: 9 January 2015
Published: 3 February 2015
X-ray imaging is a very powerful tool which can be exploited in several fields. In the last few years, its use in archaeology has grown consistently. One of the most recent and interesting applications of computed X-ray tomography (CT) is the analysis of soil blocks, coming from excavations, in order to seek for finds of different kinds and materials possibly contained therein. For this purpose, both medical and industrial CT scanners have been employed. In this paper, the application of a CT instrument specifically designed and developed for the analysis of Cultural Heritage materials is presented. We analysed a soil block extracted from a necropolis in the Italian region of Abruzzo and probably dating back to the VI-IV century B.C., which was found to contain a bronze belt.
Thanks to the versatility of the CT equipment we designed, a complete scan has been obtained in less than four hours and has delivered extremely useful information in a completely non-invasive way. The CT dataset and images allowed a virtual extraction of the find to be performed before the actual stratigraphic recovery that, in this case, was simplified thanks to the merging of the archaeological evidences and with information coming from scientific analyses. The information provided by the tomography consisted in: the distribution, shape and dimensions of fragments composing the artefact; indications about its general conditions; the recognition of repairs done in the past and the presence of different materials (although not precisely identified).
The use of CT has great potential for the work of both archaeologists and restorers. The indirect extraction of an artefact from an archaeological excavation, which entailed moving a soil block to the laboratory, allowed one to reconstruct almost all its parts and to collect information about materials. CT analysis has been particularly useful for determining both its conditions and its repairs before the actual recovery, thereby facilitating the restoration process.
The recovery and conservation of an historical piece like the one presented here can help archaeological and conservation studies, enrich a museum collection and contribute to the dissemination of acquired cultural information.
KeywordsComputed tomography (CT) Cultural heritage Archaeology Soil block Restoration
X-ray imaging provided important contributions to archaeology, especially in the recent years, both through radiography [1-4] and tomography . X-ray computed tomography (CT) has been used in many cases because of its potential to visualise inner and invisible parts of an object, providing information in a completely non-invasive way. Thanks to their availability medical CT scanners have often been used in the archaeological field: to investigate mummies and related materials [6-8], to discover the content of a pot before opening it [9,10] or simply to study the inner and outer of an object in high detail . CT proved to be a very powerful tool even in the related field of anthropology [12,13]. Synchrotron radiation can also be used for some special cases ; an example was presented of a dedicated transportable instrument developed specifically to analyse fossils .
The analysis of soil blocks from excavations is one of the most recent applications of CT in the field of archaeology. Medical  and industrial [17,18] scanners have been employed so far to scan the blocks in the search for artefacts of different nature. In this paper we would like to present the application of a CT instrument  specifically designed for the analysis of Cultural Heritage materials. This instrument has been developed within the neu_ART project  and installed in the Centre for Conservation and Restoration “La Venaria Reale”: although it has already demonstrated its reliability and usefulness for the analysis of large artworks , however, thanks to its versatility both in energies and geometry, it proved suitable for the analysis of artefacts from an archaeological excavation too.
The archaeological recovery and restoration
The soil block we analysed was extracted in the necropolis of Villalfonsina, discovered in the province of Chieti (Abruzzo, Italy) and probably dating back to the VI-IV century B.C. . It is one among several other blocks excavated in the same and surrounding areas and containing artefacts of very different use (weapons, finely decorated objects, clothing accessories). This block contained a decorative, elegant and wide bronze belt for men, worn by the deceased. It is composed of two engraved buckles and a continuous metal belt strap, perforated on both upper and lower edges to fasten a leather strip.
The tomographic system used for this measurement is described in detail in Ref. : it is composed of an X-ray tube, a rotating platform and a linear X-ray detector which scans the projection plane thanks to a high precision mechanical system. The equipment is installed in a shielded area and it operates remotely through a fully automated acquisition procedure. For this measurement 540 projections have been acquired: each one has been obtained by means of a horizontal translation of the detector of 26 cm (at a speed of 2 m/min) and a following rotation of the object (up to a final rotation of 270°, with one image acquired each 0.5°). The X-ray source has been used at its maximum tube voltage and power, 200 kV and 900 W respectively, and, to limit the beam-hardening effects , a 2 mm thick aluminium slab has been introduced to absorb the softer X-rays. The air-cooled tube has been used with cycles of 40 minutes of irradiation and 20 minutes of cooling to avoid overheating.
Soil block dimensions
40 × 15 × 10 cm3
Source-Detector Distance (SDD)
Source-Object Distance (SOD)
Object-Detector Distance (ODD)
Detector pixel size
Reconstructed voxel size
Focal spot size
Detector scan speed
Number of projections
26 × 51.2 cm2
1300 × 2560 pixel2
3 h 40 min
To minimize the penumbra effect due to the focal spot size, the object-detector distance was chosen as the minimum achievable, while the source-detector distance was set large enough to obtain good resolution while keeping a reasonable signal intensity.
Results and discussion
As already discussed, a preliminary radiograph obtained with the same CT equipment indicated the complexity of the recovery, but only the CT rendering delivered a detailed overview of the content of the soil block. In fact it shows the exact position of the various elements and their fragmentation, as well as the stratification of materials. The CT dataset and images allowed a virtual recovery of the find to be performed before the actual stratigraphic recovery. Below some of the main results obtained by the CT are listed, highlighting how they have been used by the restorers for the extraction and final display of the find.
This paper has confirmed the high potential of tomography for both archaeologists and restorers. The removal of a soil block from the archaeological excavation and the indirect extraction of the artefact performed later in a controlled environment allowed to recover information about the material contained therein and to replace correctly almost all the fragments. The use of CT for the analysis of this artefact has been particularly useful for determining its conservation conditions before the actual recovery, thereby facilitating the restoration process. The presence of a custom-made instrument in a Centre for Conservation and Restoration avoids risky transports of delicate materials to other labs to perform CT scan.
The information provided by the tomography consisted in: the distribution, shape and dimensions of the fragments composing the artefact; indications about the state of conservation; the presence of repairs done in the past and the presence of different materials (although not precisely identified).
The recovery and conservation of an historical object like the one presented here can help archaeological and conservation studies, enrich a museum collection and contribute to the dissemination of acquired cultural information.
This study was carried out in the framework of the neu_ART research project funded by Regione Piemonte. All the neu_ART collaboration is warmly acknowledged for the development of the CT instrument and for the support to this work. We express our gratitude to the Superintendence for Archaeological Heritage of Abruzzo, particularly to Dr. Annamaria Faustoferri and Dr. Isabella Pierigé. We also thank the student Chiara Armigliato, who performed an exemplary restoration of the belt during the course of the Conservation and Restoration of Cultural Heritage at the University of Turin, and Dr. Stefano Argirò, for his help in the English revision of this paper.
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