Laser and Structured Light 3-Dimensional Imaging of Stone Shot
One of the most interesting set of artefacts recovered from the wreck site were the large igneous stone shot that were all identically marked with the same two characters ‘VS’. These large cannonballs, average diameter 220mm and weight 16 kgs, were probably made for a mortar type or siege gun, which the Portuguese called a bombardas grossas. This type of muzzle-loading artillery would have been mainly used for bombarding fortifications on land. Although all the large guns were salvaged by the surviving Captain Pêro d’Ataíde and by Malik Ayaz in 1508, we know from the historical accounts that the Portuguese did bombard Calicut and thus had this type of gun on ships within the fleet.
In order to better visualize and precisely measure the ‘VS’ mark one of the shot was scanned by both laser and structured-light 3D scanners. The images produced by these different techniques clearly show that the ‘VS’ mark was purposefully carved into the surface of the shot. Whether the stonecutter’s purpose was to mark these particular shot for use with a specific gun or to be delivered to a specific Captain or ship is unknown. All we do know is that instances where stone shot have been similarly marked are a very rare occurrence. The nearest comparable we could find were the cast iron shot recovered from the Mary Rose marked with an ‘H’ for King Henry VIII as owner of the ship. One theory to be explored in future studies is whether the ‘VS’ are the initials for Vicente Sodré and that these shot were specifically made for a gun on board the Esmeralda.
Stone Shot Provenancing
In an effort to match the source of rock used in making the igneous stone shot to known lithologies in Portugal, two of the smaller shot were subjected to separate geochemical and geochronological analyses. The initial assessments made by Dr. Luisa Ribeiro at the Instituto Geológico Miniero in Lisbon (reformed as the National Laboratory of Energy and Geology of Portugal) and by Dr. Ana P. Jesus of GUTech in Oman based on whole rock and trace element analysis ruled out two possible locations in Portugal: the Massif of Sines and the Beja Layered Gabbroic Sequence, respectively.
It was then decided to try and determine the geochronological age of the rock by the dating of detrital zircons entrained within the rock. This analysis was performed by Dr. Andrew Carter at the London Geochronology Centre using laser ablation (193 nm) quadrupole-based ICP-MS. The dating results showed a Neo-Archean to Paleo-Proterozoic source that was overprinted by a Cadomian event circa 550 + 51 Ma. No zircons younger than 500 Ma were found, thus ruling out the Beja LGS or as any other igneous rocks from the South Ossa Morena Zone where magmatic events are dated from 350 Ma onwards. The combination of Cadomian age and apparent lithological variability seen in the two samples suggest that the rocks came from the Sardoal-Mouriscas Complexes, a geologically complex area found in the Abrantes region roughly 150 km north-east of Lisbon along the route of the Tagus River as there are no equivalent rocks with such characteristics in Portugal. Because there is limited available data on the major and trace element geochemistry of the Sardoal-Mouriscas Complexes this suggestion cannot be proved without additional testing, which we hope to conduct in a future study.
CT Scanning of Silver Coin Clump
All the silver coins recovered from the site were found within a small, concreted mass that also included five gold Portuguese cruzados. As silver coins from this period are better tools for dating than corresponding gold coins, the mass was brought to the UK to be conserved and for detailed examination. Initial X-ray scans of the mass showed numerous silver coins arranged in three discreet coin blocks adhered to a row of five cruzados. The three blocks were mechanically separated from the cruzados following the application of 10% formic acid. Overlying corrosion was removed by scalpel under magnification to fully reveal the surfaces of two silver coins welded together in one of the blocks, enabling their identification by visual means alone.
The two silver coins that could be identified by visual examination were the Manuel índio minted in 1499, and the real grosso minted in the reign (1438-1481) of Dom Afonso V sometime between 1475 and 1479. The índio is an especially important and exciting discovery as it is a legendary coin ordered by Dom Manuel to be struck after the return of da Gama’s first voyage to India. According to the chronicler Damião de Góis, in 1499 Dom Manuel ordered two new coins specifically for trade with India; a large gold coin equivalent to 10 cruzados called the português and a silver coin of the same weight of the Italian coins that were being used in the Indian trade, which was named índio: “The Indian”. The índio and the português are distinctive, almost unmistakable coins as they share virtually the same reverse engraving which for the first time with any Portuguese coin included the cross of the Military Order of Christ and the legend IИ HOC SIGИO VIИCES: “in this sign you will conquer”. As Dom Manuel was already Grand Master of the Order of Christ before becoming king he adopted the cross as his personal insignia, thus endowing the índio and português with even greater significance and status.
There is only one other known example of índio coin in the world, which is held within the numismatic collection of the National Historical Museum of Brazil (MHN) in Rio de Janeiro. Despite the existence of the MHN specimen, the índio, because of its extreme rarity, has assumed legendary status within the numismatic community of Portugal as the ‘lost’ or ‘ghost’ coin of Dom Manuel I. To ensure correct identification of the índio recovered from the site, the block within which it was contained was CT scanned at WMG, University of Warwick using the 225kV head of the Nikon CT scanner, which provides 16-micron resolution. Even with such relatively poorly preserved coins the resulting scans clearly revealed the same coat of arms and legend on the obverse matching the MHN specimen as well as the detailed description of the same coin that featured in a 1910 auction catalogue from Amsterdam. This same CT scan was also used to confirm identification of the Dom Afonso V real grosso partially visible on the opposite side of this block.
The extent of overlying corrosion of the other two coin blocks (containing three and seventeen individual coins, respectively) was such that no coin surfaces could be seen visually. An attempt to separate the coins in the largest of the two blocks was terminated when it was clear that any further mechanical cleaning or chemical treatment could damage the coins causing information to be irretrievably lost. The only method for investigating the coins encapsulated within the blocks, therefore, was by the CT scanning described above. João Pedro Vieira, Curator of Coins and Paper Money with the Bank of Portugal, assisted the analysis, which included the precise measurement of individual coin diameters. Although visualization of the coin surfaces in the CT scans was difficult all the coins in these two blocks were identified as either meios vinténs or vinténs from the reigns of Manuel I or João II.