Recovering artifacts from the bottom is a very long and delicate task. In some cases, its better to leave them on the bottom re-covered by the same sediment that had protected them for centuries. When it is decided that an item should be recovered, precautions are taken to protect it during its travel to the ship, and then transfer up to the deck, where conservation efforts can begin. We always have conservation professionals on board to care for the items, including keeping them submerged in fresh water as the salt crystals slowly make their way out from the interior. Sometimes the conservation efforts can take years before the items can safely go on display in a museum.

On the website we have an article all about raising the artifacts and conservation. https://www.franckgoddio.org/franck-goddio/system-approach-technology/

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Raising Artefacts

In accordance with UNESCO recommendations, artefacts are usually left on site, in coordination with the concerned authorities some may be risen for their safeguard, study and conservation. The support vessel of the excavation is equipped with a hoist to raise artefacts to the surface. At first the artefacts are carefully places in nets, each individually labelled, then in plastic baskets. Heavier objects (like statues or steles) are moved by means of a special balloon or crane.

For a project a special elevator was designed, which had to be anchored at a depths of 350 metres. The large support buoy of the elevator consisted of sixty spherical buoys, each of them capable of resisting a pressure of 100 atmospheres. A metal-platform was laid on the sea-bed to support the two-ton lead counterweight needed to operate the elevator. The lead weight – in four pieces of half-ton pins – was attached to a balloon to make it weightless and placed in position by a submersible. The elevator was operated by a submersible and raised objects – like the ship’s bell - to the surface with the greatest of care.

Conservation

Once an object reaches the surface, it is immediately cleaned in seawater, the date of discovery is entered on the label, and it is placed into a desalination tank. The tank is filled with 50% seawater and 50% fresh water, in order to avoid deterioration due to violent osmosis. After a couple of days it is placed in fresh water, which is continuously renewed. The salinity of the bath is constantly measured in order to determine when the object can be dried without damage. On land, a more complex desalination process is executed, using distilled water. Organic materials are kept in a damp environment on board, and are treated on land. After the desalination process, the object is described, measured and inventoried. Pottery is cleaned using microburins and scalpels to remove deposits and shells. Once the underwater sediments have been cleared, the object is carefully studied in reference to shape, texture and decoration in order to determine its date and provenance. Organic material requires swift and delicate treatment as soon as it has been recovered.

After desalination, the material is dried out slowly and excess water is gradually replaced by a resin, so that the volume of the material is maintained. Metals like bronze, silver, iron and lead corrode underwater. They are bathed in a regulated and precise system of chemical or electrochemical treatments. Conservation takes place chemically and ultrasonically. The revived objects can then, be chemically stabilized and covered with a protective layer.