The coin hoard has been revealed while excavating the shipwreck located in Syrna island. The hoard contains approximately 35000 roman coins and dates to the second half of 3rd century A.D. The coins are made of bronze covered by a thin silver plating. Yet in only some coins the silver layer is preserved partially; in most cases it has been either disappeared due to corrosion or has been detached due to the bronze products of the underlying layer. In the period between 2012 and 2013 1350 coins out of 11175 have been conserved. The conservation process took place in the laboratory of the Ephorate of Underwater Antiquities.
Considering the applied conservation method of the coins the main issue has been the preservation of their initial surface and of the silver layer, wherever it was possible. Therefore we tried to: 1. preserve and highlight the initial layer (including the corroded products) 2. preserve the metal surface with the better preserved details and 3. stabilize this latter layer in order to avoid further corrosion.
Thus the applied conservation method combined chemical and mechanical cleaning of the coins. The main concern has been twofold; 1. the removal of the corroded products, which were thicker than the metal 2. the appearance of the preserved details of the depiction without jeopardizing the metal (e.g etched marks, removal of the material at the surface).
The applied solutions were chosen according to the corrosion products; a formic acid 20% by volume in water for dissolving the hard green encrustations and the white salt. Solution of ammonium thiosulfate 15% by weight in water has been used for the case of silver cloride whereas a silver dip has been used against the purple crystal silver bromide and silver iodite. The chemical solutions were applied either individually or in combination using compresses. The conservation procedure included also the mechanical cleaning of the coins using needles, scalpels, etc, followed by washing them in purified water and drying them in acetone. The coins were stabilized -in case of active corrosion- using solution of benzotriazole 3% by weight in ethanol. Paraloid B72 8% has been used for further protection.
Details on the surface of the coins were revealed by the end of the conservation process enabling the scholars to read and study the depictions.
The coin hoard found in the shipwreck of Syrna island is important and one of the most abundant in the Mediterranean. The conserved coins depict 13 different emperors often by different issues. The surface of the coins is not preserved always. Porosity in various small cavities is present. Where the silver is preserved the surface of the coins is smooth. Cracks appeared at the surface of the coins. The mechanical durability of the coins consider to be medium due to concretion on and around the coins. Also the level of preservation is medium.
By the end of the conservation process the details of the reliefs appeared whereas the surface of the coins is stable. As a conclusion, the scholars have a basis to study the coins due to the great number of the conserved coins.


Funding: Ministry of Culture and Sports