This section provides an overview of the most essential literature in the field, comparing global trends in mixed-methods NDE with those applied within the South African context. The section aims to highlight the uses and applications of complementary technologies, rather than provide comparative examples through case studies (which is the aim of §3.5).
Festa, G., et al. 2013. “Simultaneous and Integrated Neutron-based Techniques for Material Analysis of a Metallic Ancient Flute.” Measurement Science and Technology 24: 1-9.
The research highlights the value of a mixed-method approach, as the application of ND, neutron relative capture analysis and neutron radiography delivered complementary data on a 19th century metallic flute. It was found that the mouth piece and body of the flute consists of different metallic components; lead for the mouth piece and zinc for the body (2013, 6). While the body can be traced to the Frenchman, Charles Mathieu (a 19th century flute maker), not enough data is available to validate the mouth piece as an original part of the flute (2013, 8). However, the re-soldering of the mouthpiece, along with its differential composition to the body, clearly suggests that it was replaced at a later stage. In short, although only one object was analysed, the research highlights the possibilities of using multiple and integrated NDE techniques in the assessment and authentication of composite artefacts, with the strengths and weaknesses of each technique directly related to the material composition (lead and zinc) of each component.
Jacobson, L., et al. R. 2011. “Tomography Imaging of South African Archaeological and Heritage Stone and Pottery Objects.” Nuclear Instruments and Methods in Physics Research
A 651: 240-423.
In this locally (South African) conducted research, the focus falls on the analysis of a tempered ceramic sherd and alleged ―engravings‖ on rock slabs. Although the findings do not bear direct relevance to our investigation of metal artefacts, the study highlights the potential value of applying a mixed method approach, in which MXCT and NT provide comparative data. While neutrons resulted in lower contrast images, X-rays produced images of a higher resolution and displayed better contrast between the matrix and inclusions. It was found that dark spots (radiotransparent) represent voids, lighter areas (radiopaque) represent quartz and
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grit inclusions, while grey and dark grey parts represent the clay matrix (2011, 241). This information is important to keep in mind when dealing with Egyptian bronze figurines that could potentially feature in-tact clay cores, or even remnants thereof.
Enguita, O., et al. 2002. “Characterization of Metal Threads using Differential PIXE Analysis.”
Nuclear Instruments and Methods in Physics Research B 189: 328-333.
This study employed the Proton Induced X-ray Emission (PIXE) technique to characterise the structure of selected ancient gold and silver threads that were wrapped around silk and cotton cores. The technique provided insight into the homogenous nature of the alloys used to make the threads and also determined the presence, or absence, of certain archaeological trace elements, including lead (Pb) and Mercury (Hg). The research focused on objects belonging to the textile collection of La Alhambra (19th century) and the textile collection of the National Archaeological Museum of Spain.
The study also suggests that the thickness of metal alloy threads can be used as chronological markers (2002, 328) when authenticating artefacts and identifying forgeries. This type of information can prove of great value when analysing the silver threads encountered on the Arabian dagger in this thesis.
Goffer, Z. 1980. “Archaeological Chemistry: A Sourcebook on the Application of Chemistry to Archaeology.” Chemical Analysis: A Series of Monographs on Analytical
Chemistry and its Applications (vol. 55). New York: John Wiley.
The article provides a review of the work done on a bronze statuette of a horse, which is credited as being an authentic example of ancient Greek bronze work, housed by the Metropolitan Museum of Art. During previous research (conducted in 1967), magnetic surveys suggested the presence of iron while visual inspection revealed what appeared to be a casting fin (1980, 359–360). X-rays also exposed the use of iron wires (armature) in the internal cavity of the statuette, leading researchers to brand the item as a modern forgery. However, doubts among the academic community prompted later researchers to perform more detailed studies on Roman bronzes. The 1969 study of Blumel (in Goffer 1980) revealed that iron armatures were indeed used in ancient Greek statuary. The composition of the metal, its structure and levels of corrosion were also seen as indicative of authenticity. Further research, which incorporated thermoluminescence dating of the core material, proved that the item was indeed ancient, with an estimated age of 2000-3500 years.
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Bettuzzi, M., et al 2015. “Computed Tomography of a Medium Sized Roman Bronze Statue of Cupid.” Applied Physics A: Materials Science & Processing 118: 1161-1169.
In their investigation of a 1st century C.E. bronze statue of Cupid from the J. Paul Getty Museum, the authors included endoscopy, cross-sectional microscopy, X-ray fluorescence (XRF) and X-ray diffraction as part of their preliminary examinations. Through these preliminary investigations, the researchers were able to identify chemical compounds within the patina, measure wall thickness and record casting features such as joints, chaplet holes, casting flaws, air bubbles and minor repairs. Although the introductory information focused on a mixed-method approach, the article‘s main focus was the showcase how X-ray computed tomography revealed ancient casting and construction techniques.
Most importantly, CT scans revealed that the figure was cast in several parts using the lost wax method, with components being joined at a later stage using either wax-to-wax or metallurgical joins. Lead and iron corrosion deposits on the body also suggest that the item once featured additional attachments (possibly wings) (2015, 1163).
It was noted that metal sheet or wall thickness could also be considered diagnostic when dealing with bronze statuettes, as the methods and techniques of artisans developed over time, thus providing us with chronological markers. According to tomographic examinations, Roman statuettes boast much thinner walls compared to their Renaissance counterparts (2015, 1161). Wall thickness across the entire object may also be used as a diagnostic feature, as thickness variability and consistency represent different production processes. While variable thickness suggests direct work, the consistent tracking of inner and outer contours suggests indirect wax application to the mould (2015, 1166). In the past, researchers relied mainly on ultrasonic measurements to determine wall thickness, but these can now be measured using CT-derived cross-sections.
Lehman, E.H. et al., 2010. “Investigation of the Content of Ancient Tibetan Metallic Buddha Statues by Means of Neutron Imaging Methods.” Archaeometry 52(3): 416-428.
In this study of ancient metallic Buddha statues from Tibet, neutron imaging revealed that material homogeneity indicates the use of similar metals for different components. Organic glue, wax or lacquer was used to secure decorations imitating gemstones on various positions on the statues, especially the eyes. Interestingly, some statues contained wooden sticks (tsog-
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sin) rolled in textile. Some statues contain flowers in the lower parts of the figure, while
others contained ceramic residues that were particularly noticeable along the internal surfaces.
Kockelmann, W., et al. 2006. “Applications of TOF Neutron Diffraction in Archaeometry.”
Applied Physics A: Materials Science & Processing 83: 175-182.
Microstructural analyses conducted by means of Time-of-Flight Neutron Diffraction (TOF- ND)32 revealed microstructural evidence of production methods among a selection of synthetic samples (bronze). Texture maps revealed that certain specimens showed signs of working strength and working direction, while the hammered specimens were associated with the alignment of poles in relation to the specimen surface. The results hold relevance in establishing links between texture strength and hardening range (2006, 179). The purpose of using a synthetic collection was to establish as many behavioural patterns (of different alloys compositions) as possible for comparison with ancient counterparts (2006, 179). In their analysis of 16th century silver Taler coins, it was also affirmed that grain orientation can be used to distinguish between minted originals and cast copies (2006, 179), as irregular grain distributions are usually associated with forgeries (2006, 181).