Page 186 - Manual for Activities directed at the Underwater Cultural Heritage

 © G. Adams. Soft Coral on Rio de Janeiro Maru, Chuuk Lagoon, Federated Sates of Micronesia. Seawater is a highly complex environment composed of
water, mineral salts, dissolved gases, bacteria, a whole food chain of micro-organisms and macro-organisms, suspended organic matter and sediments. For archaeologists, its aggressive nature lies in the chemical and electrochemical reactions of
the various types of seawater with immersed objects, the mechanical actions of waves and sediments, and the effects of biological – especially bacterial
– colonization (microscopic and macroscopic living organisms). The factor to consider from the point of view of deterioration
is the amount of dissolved
oxygen in the environment both during an object’s burial and
after its excavation. Amounts
can vary from one geographical site to another. On a single
site, the quantity of dissolved oxygen decreases with depth, temperature (according to the seasons) and the nature of the sediment (sand, mud or rock). The deeper under water the wreck, the better preserved it will be. In addition, the more deeply buried it is and the denser the
silt, the better preserved the
state of the artefacts.After a few years, equilibrium is achieved between the surrounding
water and the artefacts leading
to a relative stabilisation of degradation processes. In terms of preservation time, greater exposure to ambient dissolved oxygen increases the degradation of the artefacts (weakening
of artefacts’ structure and development of concretions).This is due to the combined effects of water and erosion by sand carried by the waves. Finally, the greater the depth of salt penetration into the objects, the longer it will take to treat them.
as possible, every picture or drawing should be linked to the file and all this information should be retrievable for future research.
Minimalist interventions: The conservator should first establish the necessity of each in- tervention and measure the degree of intervention necessary to minimize impact on the artefact also in the long-term, and to intervene to the least possible degree.
Reversibility of the interventions: As far as po- ssible, every intervention should be reversible, i.e. any modification made to an artefact should be able to be undone or removed without adverse affect.
Visibility of the interventions: The goal of the interventions is not to create a “new” artefact but to reveal its shape and the archaeological information without losing the history en- graved on it by the degradation process. All the interventions undertaken on the artefact must seek to restore the original surface of the object, so that at a glance, the public can easily understand its function.
Fundamental to the notion of archaeological study,
the original surface of the artefact corresponds to
the surface of the object at the time of its immersion.
This surface is not only the area carrying all the ornamentation, manufacturing marks and traces of 185
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Conservation and site management