Conservation and restoration work on the stock of a roman anchor
As an indispensable part of a ship's equipment, anchors are a very frequent find at underwater archaeological sites. Besides on sunken vessels, they are also found in places where there are no traces of a shipwreck, as a chance find that came to the seabed in various ways. A basic anchor consisted of a lead stock, wooden shank and arms with metal hoops and lead anchor ring. Given that the wooden parts of an anchor are by their nature subject to decomposition and are rarely preserved to the present day, the most frequent evidence of the existence of an anchor are its leaden parts.
The first phase of the work consisted of the measurement of the stock's dimensions, photographing the condition it was received in and preliminary investigation. A microscope-assisted visual investigation shows that this Roman period anchor was manufactured with an iron core wrapped in lead. The iron core is severely corroded, preserved only in fragments and is present in a somewhat better preserved state only at the ends of the stock. The iron ring at the middle of the stock is also completely corroded, separated from the core itself and structurally very unstable. Visible on the actual surface of the stock, along with corrosion deposits of lead oxides, carbonates and chlorides, are shells, pebbles and various other calcareous growths. Most of the lead surface is very well preserved, while iron corrosion has only "penetrated" the lead in a few places, causing it to decay and disappear.
The next phase of the intervention began with the cleaning of the stock and removal of corrosion deposits. Because of the exceeding softness of lead this procedure required particular care. A combination of mechanical and chemical cleansing was applied. Most of the larger incrustations were softened with heated water and successfully removed mechanically using scalpels of various sizes. The calcareous growths that could not be cleaned off mechanically were carefully removed with a diluted 5% chloride acid solution. Using the acid, applied to the surface with a brush, all of the incrustation was removed, leaving only the remaining deposits of lead oxides and carbonates. These were softened with a hot water solution of Kompleksal III (Ethylenediaminetetraacetic acid disodium salt dihydrate) and removed by gentle use of a wire brush. Residual traces of chemicals were removed following this treatment by boiling in distilled water. The fully mineralised fragments of the iron core and the iron ring at the middle of the stock do not have a preserved metal core. Any further treatment could result in the destruction of their structure and they have as a result been subject to only partial cleaning and stabilised with a 2% solution of tannin in alcohol and consolidated to preserve their form.
A mixture of 2% Paraloid B72 and 5% Cosmolloid H80 microcrystalline wax in toluene solutions was used for the final protection and consolidation of the lead and iron anchor stock. The procedure was carried out by surface coating. Lead objects such as this stock are best kept in rooms in which the relative humidity of the air does not exceed 40%, while the temperature in an ideal situation is under 15°C.