A survey of stabilization and storage techniques to protect iron encrustations and artifacts recovered from salt-water marine archaeology sites

Artifacts removed from maritime conditions are usually found encrusted together and can enclose items of disparate materials in one mass. To prevent further decay of these artifacts the conservator must keep the objects wet throughout the processes of recovery, cataloguing, and treatment To maintain the integrity of each artifact in conservation after recovery from an archaeological site requires appropriate solutions for immediate and long-term treatment. Iron is the most common material found in encrustations, so the most common conservation solutions chosen are those that will render passive chemical reactions of iron, and yet keep other possible associated materials safe. Unlike iron excavated from terrestrial sites, iron excavated from a maritime environment poses unique conservation requirements. It is essential to stabilize iron immediately upon removal from the archaeological site; even objects assumed to be hollow encrustations should be treated as though they contain an artifact until further study using X-rays or by other examinations. Chloride levels present a singular threat to maritime iron artifacts. The most popular form of iron stabilization is wet storage, but due to the higher chloride levels more intensive measures must be taken than those used traditionally for terrestrial objects. Although it may seem contradictory, a strong oxidizing solution will inhibit iron deterioration since a resistant oxide film will form and turn the iron passive. Alkaline potassium dichromate has been used in the past years successfully in this context, but unfortunately this chemical has high chromate ion levels, which are highly toxic and hazardous to the conservator. A successful and less-toxic method of initial stabilization is use of highly-alkaline inhibiting solutions with a pH 10-13. Subsequently, long-term storage tends to be more effective using chromate solutions, but care must be taken in the use and disposal of the chemicals.