(Top) Experimental set-up; (bottom) direct two-photon fluorescent imaging of the painted area.
Previous experiments on amphora fragments found in the same archaeological site allowed us to test our system and determine the photodamage threshold, optimal focusing and scanning parameters. These preliminary experiments also showed that the measured fluorescence was generated only from painted areas. After these experiments, we scanned the painted area of the amphora. In order to adapt to the amphora’s curvature and maximize the excitation of fluorescence, we divided the painted area into three regions, and scanned each region at three different focusing positions. The scanning of one zone was performed in 100 min in complete darkness.
The fluorescence image is shown in the inset image of the figure below. At first glance, the fragment may seem to show little evidence of any writing. However, as we previously mentioned, two vital pieces of information had to be considered. First, the generated fluorescence corresponded to regions where agglutinant was present, and, second, regions that contain pigment in fact inhibit the fluorescence. In our scanned image, this resulted in large dark areas.
To fully recover the information on the amphora, we then performed a processing imaging technique based on histogram equalization that took these features into account. Histogram equalization adjusts for the total distribution of the signal, modifying the scale to better determine regions with similar intensity level. Moreover, we applied it on small zones corresponding to the position where presumably each of the letters for the second consul was.
Equalization histogram image processing technique: (a) Recovered information from using an equalization histogram image processing technique; (b) result after Gaussian blurring and binarization; and (c) the two options for the Roman consul written using Capitalis Rustica calligraphy.
The area corresponding to the first name initial was affected by a crack and therefore impossible to analyze. The resulting images for the remaining letters (the surname) are shown in part (a) of the figure on the right, where some dark and brighter areas can be observed. To help the eye, we performed some additional basic image processing techniques (Gaussian blurring and binarization), which enabled us to obtain a clear image of the areas where the paint was (part b of the figure). This result, by itself, was not conclusive enough to determine the missing letters. As a consequence, we needed to delve deeper by making use of historical information.
Solution to the puzzle
As we mentioned earlier, there were two possible occasions in which a consul could have been named Quintus Fabius. In the year 121 B.C.E., the consul Quintus Fabius Maximus Allobrogicus was ruling together with the consul Lucius Opimius. Later, in the year 116 B.C.E., Quintus Fabius Maximus Eburnus was the consul in conjuction with Caius Licinius Geta. Therefore, one of the possibilities for the lost writing corresponded to the surname “OPI” (for Opimus) and the other one to “LIC” (for Licinius).
To make the final analysis, we proceeded to compare our results with the two possible consul names using the Roman calligraphy Capitalis Rustica; see part (c) of the figure on the right. This calligraphy was the informal cursive capital letterform used in that time for painted inscriptions. Examining the two options, it is clear that the first letter could be an “O” and the last can be an “I.” In addition, there is a certain resemblance between the top part of the letter “P” in Capitalis Rustica and the central panel in (b).
We therefore could confidently conclude that the missing name was Lucius Opimius, and the wine contained in the amphora was from the 121 B.C.E. harvest. This result provides what in archaeology is named a “terminus post quem” for the foundation of Iesso—in other words, the earliest point in time when the city could have been founded. Now, archaeologists must deduce the wine’s age to provide a more precise foundation date of Iesso.
The authors want to thank Professors Josep Guitart and Josep Ros from the ICAC-Institut Català d’Arqueologia Clàssica in Tarragona, the Potronat d’Arqueologia de Gissona for their contribution to the archaeological aspects of the work, and Emilià Pola from the Generalitat of Catalunya, who initially encouraged the collaboration between the two research institutions.
David Artigas, Iain G. Cormack and Pablo Loza-Alvarez are with the ICFO-Institut de Ciències Fotòniques and the department of signal theory and communications, Universitat Politècnica de Catalunya, Mediterranean Technological Park, Castelldefels, Spain.
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