Page 189 - Manual for Activities directed at the Underwater Cultural Heritage

of its parameters (type of substrate, seawater parameters, hydrodynamic currents, tides, etc). This data will allow them to prepare the excavation project under the best conditions and fully aware of all the likely circumstances.
(b) Preparative work: Documentation at the preliminary stage will allow conservators to organize the adequate material needed to take care of the artefacts that are expected to be excavated (including materials for marking, recovering, conditioning, transporting and storing the artefacts). Usually, conservators will propose an on-site intervention kit and a list of materials that underwater archaeologists might need during their work.
These two preparative steps are important in regard to the security of artefacts and those working on the site. They also provide information that is valuable for accurate budgeting of the excavation. Conservation can be time consuming and costly, and must be properly considered prior to the excavation and recovery of archaeological material from a site.
The conservation programme should be integrated into the budget and the costs related to the preventive
 © Archivo IAPH – CAS. Removal of concretions in situ, Cádiz, Spain.
Most objects, after long years
of being buried in a marine environment, emerge covered in calcium concretions. Concretions are stone-like encrusted conglomerates created by grains of sand, shell particles, coral and sea plants around an artefact. These natural elements begin
to build up on objects beneath the sea as they start to rust and corrode. After a while concretion covers the object, preserving it
in a hard protective shell.The hardness, thickness and porosity of the concretions will depend on the burial environment (location and duration of exposure). Following analysis, minor concretions can be carefully removed in situ in order to allow for the identification of the artefacts and if this is necessary for a scientific purpose.
However, solid concretions should never be removed or cracked
in situ, just documented because without the protective concretion, the exposed artefact is exposed to further erosion or rusting.
If a decision is made to recover the object and to remove the concretions, post-excavation conservation is very important. The 5 major stages of the post-excavation conservation- restoration procedure are 1) preventive conservation, 2) diagnosis, 3) cleaning concretions, 4) extracting salts or chlorides and 5) finishing.
Before cleaning concretions, conservators shall first X-ray the artefact in order to determine
the exact shape and the fragility of the object underneath the tough outer casing. Using special mechanical tools to free the artefact from the concretion the artefact shall be quickly treated for corrosion, pending further investigation. 
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Conservation and site management