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Archaeology
Conservation

Now that the Hamilton and Scourge have been found and investigated, they may need to be conserved, especially if they are ever raised.   Click on a topic below to learn about various issues in conservation (including information provided by Cliff Cook of the Canadian Conservation Institute).

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Conservation and Protection - An example from the Vasa

Now that more and more underwater sites are being discovered the question of what to do with the vessels and the artifacts found must be answered. Each government has its own answers but the debate rages as to who actually owns the wrecks and what measures must be put in place to conserve and protect the sites from destruction.

The recovery of the Vasa from Stockholm harbour in 1961 marked a revolutionary event in underwater archaeology. This 17th century war ship was raised in successive stages by passing heavy steel cables in tunnels dug below the hull. The raising of the ship to the surface represented an extraordinary technical feat.

The work did not end here though. Conservation of the metal and wooden artifacts associated with the ship was an enormous problem to the technical teams charged with preserving the remains once exposed to air.

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Conservation of Wood: the Vasa

Wooden artifacts from the Vasa was preserved by impregnating the water-logged wood cells with a water soluble wax-like chemical called PEG (polyethylene glycol).  When the Vasa was raised in 1961, the 700 cubic metres of wood from the hull and artifacts (mostly oak) in need of conservation presented an opportune test case. For the artifacts. experimentation demonstrated that PEG was most effective after being diluted and heated to 65 degrees Celsius. After 17 months of soaking in a tank each piece of wood was dried for six months. At the end of this period PEG accounted for 40% of the weight of the wood. Conservation of all wooden artifacts took almost 20 years.  The ship's hull was kept intact and sprayed with a PEG solution for 206 months and then was slowly air dried for many years (source: Brigitta Hafors, "The Drying pattern of the Outer Planking of the Wasa hull" in Waterlogged Wood Study and Conservation, Proceedings of the 2nd ICOM Waterlogged Wood Working Group Conference, 28-31 August 1980, ed. Regis Ramiere and Michel Colardelle, pp. 313-326).

In view of the cost and time involved for PEG treatment, alternatives are now being sought by conservators. A treatment for artifacts that has been extensively researched in Canada involves freeze-drying wood under reduced pressure. This technique was derived directly from industrial and medical research. Vacuum freeze-drying will vaporize the ice in the artifact without melting it, thus limiting the drying stresses within the structure of the degraded wood. Impregnation of the wood with PEG is still an essential step in the freeze-drying process.

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Preserving Iron Artifacts

Metals brought up from a salt-water environment are threatened as soon as they are exposed to air. The main cause of deterioration occurs when salt (sodium chloride) combines with the metal which then crystallizes upon exposure to air. Conservation techniques such as electrolysis (see the next paragraph for details) are aimed at eliminating salt crystallization in a gradual but effective manner.

The metals found on the wrecks of the Hamilton and Scourge will not require extensive chloride removal when compared to those recovered from salt water sites.  The most common metal will be iron, but there will also be copper alloys (i.e.: brass) and probably lead.  In all cases, the objects will have to be kept wet after excavation until they can be cleaned and stabilized.   It is much easier to remove sediment or encrustations that have not dried out.   To aid in cleaning, and to remove any soluble salts that might be present, electrolysis might be used.  Electrolysis is especially effective at cleaning and stabilizing cast iron - the material that most of the cannon on the ships are made from.   After cleaning, metal artifacts are usually washed with distilled water to remove residues of soluble salts and other chemicals.  The metal can then be dried.   The final step is almost always the application of a protective surface coating (source: Katherine Singley, The Conservation of Archaeological Artifacts from Freshwater Environments, 1988).

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In-Situ Preservation

A new concept in the conservation of underwater sites has recently emerged. Underwater objects may be kept in situ, which means in place, to alleviate the problem of conserving large-scale metallic or wooden artifacts. Wrecks left in place on the ocean floor or lake beds can be stabilized underwater and converted into a monument which can be visited by the diving public. This approach has been used with 22 wrecks found in Fathom Five National Marine Park at the mouth of Georgian Bay.  These wrecks are preserved in the water and are visited by thousands of divers each year.

Similarly, the wreck of the Célèbre, a warship built in 1755 and sunk during the siege of Louisbourg in 1758, has been left intact for divers to visit. Divers are presented with a map of the wreck site to guide their visit. This type of approach represents an original solution to the problem of conserving or excavating wrecks in their entirety.

Another type of in-situ preservation is the burial or re-burial of historical material after excavation and study.  Between 1980 and 1984 the wreck of the San Juan, a 16th century whaling ship sunk in Red Bay, Labrador, was excavated and dismantled piece by piece for study by Parks Canada marine archaeologists.  The complications and costs that would be result from extensive conservation of the remains were avoided by reburial on the bottom of the harbour of most of the wreck.  The individual components were placed in three layers surrounded with sand and the entire mound was covered with a geotextile to keep the wreck protected (source: John Stewart and Lorne Murdock, "Reburial of the Red Bay Wreck as a form of Preservation and Protection of the Historic Resource," in Material Issues in Archaeology IV: Symposium held May 16-21, 1994, Cancun, Mexico.  pp. 791-805).

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Conservation Issues for the Hamilton & Scourge

The question of conserving the hulls and the artifacts from the Hamilton and Scourge is a complicated and controversial one. It is worth noting that the environment surrounding the vessel is probably the most amenable one possible for preserving cultural resources in an underwater archaeological context. The depth of the water and the resulting low temperatures and low light penetration, combined with the lack of salinity, has most likely reduced the rate of deterioration of the ships and associated material.

If the hulls or associated artifacts were excavated, the freshwater nature of the environment would greatly shorten the time required for cleaning and conservation when compared to cultural material from salt water environments.  However, the massive long-term problem of  hull conservation remains the most important project consideration.  If the ships are ever raised, some of the conservation techniques outlined on this page will likely be employed.

 

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