Working methods and techniques
In order to correctly intervene, archaeologists must well-define project objectives and then use appropriate methods and working techniques. Research is integral to any intervention though there is no single recipe, but it is up to the archaeologist to identify and use the best methodology available. The scientific method, as implied by its etymology, is a means of arriving at reliable knowledge. Irrespective of the concrete methodology chosen, it will have to meet some minimum conditions if it is to respond effectively to the challenges that working under water presents.
The working method will have to be:
- Clearly explained. It will need to be understood by the team working under water, often taking turns, which will have to take individual decisions.
- Rapid to implement. There is a limit to the time that can be spent under water.
- Straightforward to implement. Working under water is hard enough without the addition of further complications.
A basic rule is that not everything that can be done on land ought to be done on the working platform, and things that can be done on the surface ought not to be done under water. Furthermore every contingency will need to be exhaustively planned for, so that problems can be resolved under the best possible conditions. If there is anything besides discipline and orderliness that ought to characterize the operations of an underwater archaeological excavation, it is planning for possible incidents that might affect the safety of individuals and the site itself.
The Method of Research
- Research is integral to any intervention.
- There is no recipe for dealing with the underwater cultural heritage. Only a properly trained, qualified and competent archaeologist following a scientific methodology can ensure that society is provided with reliable knowledge.
- The working method must be clear, rapid and straightforward.
- More technical resources do not necessarily mean better scientific results.
- Before starting to excavate, the archaeologist must have adequate knowledge of the culture of the human group concerned by the site.
The purpose of the methodology is not to recover objects but to obtain knowledge
Suitability of the method
To be effective, the methodology and techniques used must be appropriate for the scientific objective being pursued. This means that the archaeologist needs to have the requisite intellectual training, first to establish the scientific objectives, and then to design and apply the methodology and techniques best suited to the project’s goals . A successful excavation is of no avail in the absence of the capabilities and knowledge required to draw scientifically reliable conclusions that can be communicated to society.
The next step in developing the methodology is thus to identify the appropriate techniques that are available and practicable in the context of the project. Whatever research question is being studied, each site requires consideration about which technologies are most appropriate for answering that question. If the question is about the age of the site, then dendro-chronology, radio-carbon dating, thermo-luminescence or sedimentology studies may be considered, but not all may be appropriate. Dendro-chronology, for example, is only appropriate if certain wood species are present and if enough samples can be taken.
On the other hand, it then also produces information on the provenance of that wood. If the question is about construction techniques, (e.g., a shipwreck lost at a known time in history), then the techniques may focus on three-dimensional recording of the structure of the site. More often than not, a chosen approach can contribute to several aims at once, thus adding to the efficiency of the drafted project.
The Project Design needs to clearly advise the competent authority about the technical equipment that will be used, how it will be used and the extent of site disturbance. This will enable the authority to assess the relevance of the project in relation to its long term impact on the site.
Unfortunately, some television documentaries have given the false impression that greater technical resources mean better scientific results, so that underwater archaeology has come to be seen as something hugely complex and expensive. What is overlooked is that in a difficult environment like the marine environment, an excess of equipment is not only a drain on financial resources, but actually tends to create problems which then have to be solved, leaving less time for investigating the site.
Types of research methodology
Site survey, investigation (including, if appropriate, excavation) and analysis describe the main steps of archaeological research.
The underwater archaeological survey comprises the process of locating, exploring and recording a site. Its aims and objectives are determined in the project design, thus the survey is an end point in itself.
Two main types of survey can be distinguished:
- pre-disturbance survey and
- site monitoring survey.
Surveys are conducted to obtain an accurate representation of the site and in view of recreating it on paper and digitally. They facilitate the understanding of the relationship between the archaeological material, the site and the people who are connected to the site.
The following area search and survey methods are available for locating, exploring and recording a site:
- the accumulated knowledge of local people, especially scuba divers and fishers; survey and excavation work should be taken as an opportunity to involve them in the conservation effort;
- information in archives and libraries;
- toponymy, palaeotopography and ethnography;
- data from archaeology on land;
- historical cartography and aerial photography;
- topography and climatology;
- findings of visual prospecting;
- findings of marine geophysical prospecting;
- findings of position fixing methods;
- 2-dimensional and 3-dimensional survey methods
Survey tools are used to sketch the site, to record the position of features (detail points on artefacts and structure in relation to known fixed control points), thus determining distances and bearings. Control points should be permanent, stable, uniquely identified, located around the exterior of the site and at different heights. At least four measurements should be taken from such control points to each detail point, always recording the depth.
With this range of methods, informed predictions can be made. Unfortunately, the current limitations of geophysics as applied to underwater archaeology mean that a negative result from this method of prospection does not necessarily rule out the presence of archaeological sites in the area prospected. In addition, the archaeologist will always need to carry out soundings. Moreover, the depth of sedimentation needs to be assessed for its potential of containing archaeological traces.
The preparation of underwater archaeological surveys is a basic management tool and needs to be a priority objective of the authorities responsible for conserving the underwater cultural heritage. If it is to be successful, the underwater archaeological survey must conclude by specifying the location of the artefacts, their state of conservation, their scientific interest, the risk of alteration and the corrective measures envisaged.
See also under “Excursion: Inventory”
Investigation and analysis
With proper scientific and technical training, the archaeologist will be able to use the minimum of technical resources needed to obtain the best possible scientific results at the lowest cost and with a methodology that is simple to execute. Essential stages of investigation and analysis, planned in accordance with the data obtained from the archaeological survey, should be:
(a) Removal of sediment. The low- and high-pressure compressors used to charge the compressed air tanks and operate the suction tubes will need to be mounted on a working platform. It is sometimes possible to use the shore itself for this purpose.
(b) On site documentation. This is the phase of the excavation that will justify all the work done and it thus needs to be taken extremely seriously, since the quality of the results will largely determine the reliability of the conclusions reached. Excavation involves the destruction of the site, so the objective is attained when enough information is produced for the site to be subsequently reconstructed. It is essentially this phase that distinguishes an archaeological excavation from the pure underwater recovery of ancient artefacts. See Rules 26 and 27.
(c) Site stabilisation / in situ preservation. After having evaluated the stock of archaeologically interesting sites, the state or condition of selected sites may need to be preserved. Unless effectively safeguarded, many good examples of maritime heritage will be lost forever. In stabilizing a site under water, the idea is to create an archive under water that is accessible and to make sure that the heritage is kept until this archive is opened. It is important to have an idea how long the protection has to be effective: for 5 years, 20 years or a hundred years. The protective measures have to be selected in a way that deterioration of the site can be reduced to a minimum and that it is still possible to access the site in the future for archaeological research. See Rule 24.
(d) Extraction. Objects should not be removed if there is no valid objective and until secure arrangements have been made to conserve them properly out of the water. An underwater conservator needs to be on hand to ensure adequate safeguards are in place when an extraction is carried out.
(e) Preventive conservation. As soon as an archaeological object is removed from the water, it begins to undergo physical and chemical processes that may result in major alteration and even destruction. It is thus essential for a conservation specialist to be on hand to see that the object is transported to the conservation laboratory under the best possible conditions. See Rule 24.
(f) Documentation and analysis. Every object extracted needs to be inventoried, documented and studied. The information thus obtained, in conjunction with what has been learned during the excavation, will then allow conclusions to be drawn. The number and variety of the artefacts yielded by an underwater investigation mean that a large team of specialists usually needs to be involved. Thanks to technical advances in archaeometry, key objective data can be obtained by laboratory analysis. See Rules 26 and 27.
(g) Conservation and restoration. Proper restoration using secure, tried and tested methods ensures that pieces are better conserved, restored and can be exhibited to the public. See Rule 24.
(h) Scientific reporting. Scientific publication is the only way of advancing knowledge and obtaining conclusions that can then be presented to society. See Rule 30 and 31.
(i) Dissemination All the hard work done and the money spent would be of no avail if we failed to provide society with clear, accessible and reliable information on its past. It is the effort of dissemination that engages society with the work to protect this heritage, and public commitment depends upon a sense of ownership. See Rules 35 and 36.
Techniques for in situ preservation
In deploying a policy for the protection of underwater cultural heritage, it is sometimes useful to temporarily consolidate an important site. A lot can be achieved with very simple techniques, but more extensive measures may be necessary if the aim is to consolidate a site for longer periods or to make sure that public access is compatible with protection and management. Examples of techniques used for site stabilization and in situ protection are sandbags, polypropylene debris netting, specific hands-on solutions, sand deposition, road barriers, artificial sea grass and the covering with geo-textiles. Artificial metal cathodes have been tested to stop metal corrosion. It is also possible to establish under water depots in proximity to the endangered sites, in order to stock timbers while avoiding their extraction from under water.
All of these techniques have their advantages, but also their limitations. Sandbags may change currents, textiles may block biological gas and thought should be given to these issues beforehand. Changes should be monitored that might occur in the condition of the site, in order to measure the effectiveness of the chosen in situ protection strategy and to be able to act upon any possible detrimental changes. The methodology for management projects should be well-chosen and should be as non-intrusive as possible.
Considerations on excavation
Excavation may produce important scientific results, but only if significant and up-to-date research questions have been formulated in advance. As excavation means destruction, it is irresponsible to excavate without knowing what research questions are asked: once a site is excavated, it has lost its most valuable and vulnerable information. Before taking such a drastic step, one needs to tread carefully and after much consideration. Is excavation indeed the correct choice? What are the questions that need answering? Would it be wise to test the questions elsewhere and then reconsider them for this particular site? What other purposes can this site serve? How can it best be enjoyed? Which techniques can or should be employed in this specific case? Can this site provide the answers we seek? Has an assessment been made of all other similar sites? Is it justifiable to partially or wholly sacrifice the site for answering the research question?
The research questions will determine how much of a site needs to be disturbed and the type of excavation techniques that will be employed. Investigation of a 19th century ship’s galleys may for instance only require that the area around the galley needs to be disturbed, although at the cost of the general integrity of the site. A general principle is that site disturbance should be kept to the minimum required to answer the identified research questions. This allows the value of a site to be retained for future research or for exhibition for tourism purposes.
Given the need to conserve underwater cultural heritage for future generations, and the limited resources available for this purpose, the archaeological survey will reveal which archaeological sites should be a priority for excavation in view of the risk of destruction and their scientific interest.
Archaeology is not synonymous with excavation. Excavation is a small part of a process that begins with the archaeological survey and culminates when society is given access to a body of knowledge which is part of its cultural inheritance and for which the objects recovered are the evidence. One of the differences between archaeology and treasure-hunting is that the ultimate goal of the former is to acquire knowledge, while for the latter the aim is to acquire objects.