Beyond Photography. An interdisciplinary, exploratory case study in the recording and examination of Roman silver coins
Anna Bentkowska-Kafel, Vera Moitinho de Almeida, Lindsay MacDonald, Julio M. del Hoyo-Meléndez and Aurore Mathys
A study was undertaken by an interdisciplinary group of COSCH researchers between 2014‒16, to record and examine silver coins believed to be ancient Roman in origin. The aim was to evaluate the suitability of various advanced, non-invasive optical and spectrometric techniques for analyzing the physical characteristics and elemental composition of numismatic objects. In order to compare results, the same two silver coins were used throughout the study: two denarii portraying Empress Faustina I, wife of Antoninus Pius, believed to be posthumous deification issues of 141 A.D. The questions addressed included the characterization and authentication of test coins, as well as technical issues in the multimodal recording of material cultural heritage with meta- and paradata. The team investigated whether the methods chosen for this case study responded to the needs of numismatists, and whether they can feasibly be applied in museum practice, to support research and conservation of historic coins, and to enhance the documentation and dissemination of numismatic objects through heritage science.
A more comprehensive account and discussion of this study with additional visual material and multimodal data sets, can be found on the dedicated website, COSCH Roman Coins.
Keywords: Numismatic studies, Roman silver coins, examination, optical techniques, multimodal recording, COSCH
Figure 1. The COSCH “Day of the Denarius” held at University College London, 22 June 2016. Photos: A. Bentkowska-Kafel.
Figure 2. Numismatic display with a denarius of Faustina the Elder. J. Paul Getty Museum, Santa Monica, CA. Photo: A. Bentkowska-Kafel, 2016
Figure 3. The denarii of Faustina the Elder used in the COSCH study. Left: coin A (Aeternitas). Right: coin B (Vesta). The images were derived by image processing from sets of 64 images taken by a Nikon D200 camera with directional flash illumination. The effect simulates images of coins obtained by a photographic studio setup with axial illumination. © Lindsay MacDonald, 2017.
Figure 4. Proposed methodological framework for the 3D digital data acquisition, processing and analysis of historical silver coins © Vera Moitinho de Almeida, 2016
Table 2. Equipment and parameters of capture of the domes. (*) RTI builder cannot process images so large, so they have to be scaled down. Participating institutions: CyI ‒ The Cyprus Institute; RBINS ‒ Royal Belgian Museum of Natural Sciences, Brussels, Belgium; UCL ‒ University College London, UK; US ‒ University of Southampton, UK © Aurore Mathys, 2016
Figure 5. Appearance of coin A obverse, detail: (a) RTI from dome 1;
(b) RTI from dome 2; (c) RTI from dome 3, albedo mode; (d) RTI from dome 3,
ambient mode; (e) RTI from dome 4; (f ) focus stacked picture.
© Aurore Mathys, 2016.
Figure 6a. 3D topography based on photometric stereo technique and laser 3D triangulation © Jaroslav Valach, 2015.
Figure 6b. 3D reconstructed surface based on photometric stereo.
Horizontal section with elevation showing (a) laser scanner height
and (b) reconstruction. © Lindsay MacDonald et al., 2017.
Table 7.Quantitative XRF analysis of the evaluated coins by two instruments. For the Artax 200, concentrations are reported as the average of 6 and 12 measurements for coins B and A respectively. © Julio M. del Hoyo- Meléndez and CyI, 2015.
Figure 8. Cross-section of coin A showing deviation in height between (SLS)
Smartscan (red line) and (PS) LS-PTM (colour deviation map, from red to dark blue). Inset 1 shows an enlarged detail of the profile of the hair, whereas inset 2 shows an enlarged detail of the profile of one of the letters. © Lindsay MacDonald et al., 2017.
Figure 9. Micro-XRF spectrum of the point shown in the inset for the
obverse of coin B. Unidentified peaks are likely due to three factors, namely
interactions in the detector, X-rays contributed by the analysis system, and
X-ray interactions in the sample. © Julio M. del Hoyo-Meléndez, 2015.
Figure 10. Elemental maps obtained by the Artax 800 instrument for the obverse of coin A showing Ag Ka (top) and Ag La lines (bottom). Although the map obtained for the Ka line shows that the coin is rather homogeneous, the less penetrating La line shows an uneven surface most likely associated with surface corrosion effects. © Julio M. del Hoyo-Meléndez, 2015.
Figure 11. Crack inside coin B visualized by microCT method (three perpendicular
microCT sections and rendered 3D model). © Miroslav Hain, 2014.
Figure 12. Multimedia displays provide a vehicle for dissemination, in situ and
online, of rich information about the object, its scholarship, and heritage science.
Numismatic galleries of the Museum of Fine Arts, Boston, MA (left) and the Hutten-
Czapski Collection, National Museum in Kraków, Poland (right). Screenshot of
http://www.mfa.org, accessed 13 October 2015. Photo: A. Bentkowska-Kafel, 2016.